LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 Class 
 
THE CHEMISTRY OF PIGMENTS 
 
THE 
 
 CHEMISTRY OF PIGMENTS 
 
 BY 
 
 EENEST J. PAEEY, B.Sc. (LoND.), E.I.C., F.C.S. 
 
 AUTHOR OF " THE CHEMISTRY OF ESSENTIAL OILS AND ARTIFICIAL 
 PERFUMES," ETC. 
 
 JOHN H. COSTE, F.I.C., F.C.S. 
 
 WITH FIVE ILLUSTRATIONS 
 
 LONDON 
 SCOTT, GEEENWOOD & CO. 
 
 19 LUDGATE HILL, E.G. 
 1902 
 
 [All rights reserved] 
 
t> 
 .; -^C^ 
 
 
 
 GENERM- 
 
PREFACE. 
 
 THE authors have in the following pages endeavoured 
 to indicate the chemical relationships, composition 
 and properties of most of the better -known pigments. 
 During recent years they have given a great deal 
 of attention to the examination of painters' colours, 
 and have from time to time found some difficulty 
 in obtaining reliable information on the subject. 
 This led to a considerable amount of work in 
 obtaining and examining specimens of pigments, 
 and it was felt that the information thus gained 
 might usefully be published. 
 
 Speaking generally, the plan of the authors has 
 been to treat the various pigments in groups, allied 
 chemically rather than chromatically. Motives of 
 convenience have in some cases led to a modifica- 
 tion of this scheme. The methods of manufacture 
 of colours have been considered rather from the 
 chemical than the technical point of view ; it is 
 not suggested by the authors that the present work 
 is in any sense a manual of colour-making. 
 
 Analytical processes which, in most cases, the 
 authors have by experience found suitable are 
 described, and the nature of probable impurities, 
 
 104628 
 
VI PREFACE. 
 
 adulterations and other causes of inferiority pointed 
 out, and numerous analyses of genuine and sophisti- 
 cated pigments, for the most part by the authors, 
 are given as illustrating the composition of these 
 bodies. Preliminary chapters on colour and on the 
 application of pigments have been added. 
 
 It is the hope of the authors that this work 
 may be found of use by those who are called 
 upon to use or examine pigments as a guide to 
 the selection of those which are suitable, and the 
 rejection of those which as a class or through 
 individual inferiority are unsuitable for the class 
 of work to be undertaken. 
 
 E. J. P. 
 J. H. C. 
 
 LONDON, October, 1901. 
 

 CONTENTS. 
 
 CHAPTER I. 
 
 INTRODUCTORY. 
 
 Light White Light The Spectrum The Invisible Spectrum- 
 Normal Spectrum Simple Nature of Pure Spectral Colour 
 The Kecomposition of White Light Primary and Comple- 
 mentary Colours Coloured Bodies Absorption Spectra 
 
 pages 1 to 17 
 
 CHAPTER II. 
 
 THE APPLICATION OF PIGMENTS. 
 
 Uses of Pigments: Artistic, Decorative, Protective Methods of 
 Application of Pigments : Pastels and Crayons, Water Colour, 
 Tempera Painting, Fresco, Encaustic Painting, Oil-Colour 
 Painting, Keramic Art, Enamel, Stained and Painted Glass, 
 Mosaic pages 18 to 76 
 
 CHAPTER III. 
 
 INORGANIC PIGMENTS. 
 
 White Lead Zinc W T hite Enamel White Whitening Red Lead 
 Litharge Vermilion- -Royal Scarlet The Chromium Greens 
 Chromates of Lead, Zinc, Silver and Mercury Brunswick 
 Green The Ochres Indian Red Venetian Red Siennas and 
 Umbers Light Red Cappagh Brown Red Oxides Mars 
 Colours Terre Verte Prussian Brown Cobalt Colours 
 Cceruleum Smalt Copper Pigments Malachite Bremen 
 Green Scheele's Green Emerald Green Verdigris Bruns- 
 wick Green Non-arsenical Greens Copper Blues Ultramarine 
 Carbon Pigments Ivory Black Lamp Black Bistre -Naples 
 Yellow Arsenic Sulphides: Orpiment, Realgar Cadmium 
 Yellow Vandyck Brown pages 77 to 181 
 
Vlll CONTENTS. 
 
 CHAPTER IV. 
 
 ORGANIC PIGMENTS. 
 
 Prussian Blue Natural Lakes Cochineal Carmine Crimson 
 Lac Dye Scarlet Madder Alizarin Campeachy Quercitron 
 Bliamnus Brazil Wood Alkanet Santal Wood Archil 
 Coal-tar Lakes Red Lakes Alizarin Compounds Orange and 
 Yellow Lakes Green and Blue Lakes Indigo Dragon's 
 Blood Gamboge Sepia Indian Yellow, Purree Bitumen, 
 Asphaltum, Mummy pages 182 to 275 
 
 INDEX pages 277 to 280 
 
THE CHEMISTRY OF PIGMENTS. 
 
 CHAPTEE I. 
 
 INTRODUCTORY. 
 
 COLOUR phenomena may, broadly, be divided into two classes. 
 In the larger and more important group they are due to the 
 selective action of what we v know as coloured bodies upon 
 light, whilst in the smaller group they are dependent upon 
 quite other causes, which, from the point of view of the 
 present work, need not be touched upon. The colour effects 
 produced by pigments belong entirely to the former class, 
 and to intelligently understand the principles of colouring 
 materials, an elementary but exact knowledge of the theories 
 of light is necessary. In the present chapter the theoretical 
 aspect of the subject is briefly referred to from this point of 
 view, but no mathematical details are introduced, except 
 where absolutely necessary for the comprehension of the 
 point at issue. 
 
 Light. 
 
 Light is due to a series of intensely rapid vibrations of 
 a medium which is assumed to be imponderable, and to 
 pervade all space and matter. Such a medium is, of course, 
 physically quite incomprehensible, but its existence must be 
 assumed to satisfactorily explain the ordinary phenomena of 
 light. These vibrations are transverse, that is, in planes at 
 right angles to the direction of propagation of the beam. 
 
 The vibrations in sound waves are, on the other hand, 
 
 1 
 
2 CHEMISTEY OF PIGMENTS. 
 
 longitudinal, that is, in the direction of the propagation of 
 the wave. This hypothesis is known as the wave theory, or 
 the undulatory theory of light, the vibrations evidently par- 
 taking of the nature of waves. Indeed they may be well 
 illustrated by ordinary waves, and the distance between two 
 successive crests is termed the ivave length, whilst the distance 
 from crest to trough is the amplitude. The intensity of the 
 wave depends on the latter, whilst its specific character, as 
 will be seen later, depends essentially on the wave length. 
 
 White Light. 
 
 The ordinary light of the sun, which we recognise as 
 white light, is a mixture of innumerable vibrations of different 
 wave lengths, or, what amounts to the same thing, of different 
 colours. This is best illustrated by the classic experiment 
 of Newton, which was undertaken by him to prove the pro- 
 position that " the light of the sun consists of rays differently 
 refrangible" (Newton, Opticks, book i., prop. ii.. theorem 2). 
 This experiment may be briefly described as follows : Into 
 a perfectly dark room (see Fig. 1) a beam of light is ad- 
 mitted through a small round hole, 0, and in its path is 
 placed a triangular glass prism P. The light falling on the 
 prism is refracted or bent (as is always the case when light 
 passes from any medium to any other of different density), 
 and on being received on the screen Q it is seen that instead 
 of a white spot we have an elongated band of different 
 colours. This is the " spectrum " S. 
 
 The Spectrum, 
 
 This coloured band, which is called the prismatic spectrum, 
 in order to distinguish it from that produced in another man- 
 ner (vide infra), is composed of a series of colours, situated in 
 the same order as are those in the rainbow, which owes its 
 
INTRODUCTORY. 3 
 
 existence to an action of this kind. As a matter of fact, every 
 vibration of different wave length is refracted to a different 
 degree, the rays of shorter being more refracted than those of 
 longer wave length. Hence the fact that the colours in the 
 spectrum merge gradually into one another, and although 
 each separate position as we advance from one end to the 
 other is of a different colour absolutely, we cannot, with the 
 eye, enjoy such fine distinctions, so that we are compelled to 
 separate the spectrum into arbitrary divisions in which the 
 
 FIG. i. 
 
 main colour is represented in its various shades. For con- 
 venience Newton divided the spectrum into seven parts, 
 starting from the least refracted rays, as follows : Ked, 
 orange, yellow, green, blue, indigo and violet. Any other 
 similar division is quite legitimate such, for example, as 
 the more extended red, orange red, orange, orange yellow, 
 yellow, etc., etc. To exactly define the spectral colours, as 
 they are called, however, we need something more exact. 
 We have this in the Frauenhofer lines (so named from their 
 discoverer), a series of fine dark lines which break the con- 
 
4 CHEMISTEY OF PIGMENTS. 
 
 tinuity of the spectrum of sunlight. As these dark lines 
 depend on the existence of definite elements in the sun's 
 atmosphere their position is absolutely fixed, and their posi- 
 tions having been determined with accuracy, they can be 
 used as points of reference. The most prominent lines are 
 those named from A to H, starting from, the red end of the 
 spectrum. These lines are reproduced as bright lines in the 
 same position, when, for example, the element responsible 
 for the given line is volatilised in a colourless flame. The 
 D line (which is in reality two lines extremely close together), 
 for example, is characteristic of the element sodium. If the 
 visible portion of the prismatic spectrum, that is, from the 
 red to the violet, be divided into 1,000 parts, the positions of 
 these lines are as follows : 
 
 A . . E 363-11 
 
 B . . 74-02 F . . 493-22 
 
 C . . 112-71 G . . 753-58 
 
 D . . 220-31 H . . 1,000 
 
 The Invisible Spectrum. 
 
 Hitherto we have referred only to the visible spectrum, 
 that is, the coloured bands which are produced when white 
 light is decomposed by, for example, a glass prism. But it 
 has been shown beyond doubt that heat waves are subject to 
 many of the same laws as light waves, and it appears that 
 the same class of vibration is responsible for the phenomena 
 of heat and light. If a delicate thermometer be placed in the 
 various parts of the visible spectrum, it will be found that, if 
 we use a prism of, for example, rock salt, which absorbs 
 practically none of the vibrations, the temperature varies 
 with the portion of the spectrum in which the thermometer 
 is placed. The maximum is obtained in the extreme red of 
 the spectrum, and a gradual fall occurs till the extreme violet 
 is reached. But if the thermometer be moved out of the 
 
INTRODUCTORY. 5 
 
 spectrum past the red an increase of temperature is noticed, 
 a maximum being obtained just beyond the visible rays. 
 These invisible rays, which, are less refracted, and of greater 
 wave length than the visible rays, are the dark heat rays. 
 Beyond the violet is also another set of rays which are 
 very highly refracted and of very small wave length, which 
 are known as the ultra-violet or chemical rays. These 
 are closely connected with many chemical effects and with 
 fluorescence phenomena, and can, to a small extent, be ren- 
 dered visible by special appliances. The spectrum, including 
 the ultra-violet and ultra-red rays, may thus be divided into 
 chemical, light, and heat rays. 
 
 The phenomena observed in heating a piece of iron will 
 illustrate this matter. At comparatively low temperatures 
 the slow vibrations in the mass are responsible for the emis- 
 sion of the longer or dark heat waves. As the temperature 
 increases and the vibrations become more energetic, waves 
 of shorter period are emitted, and at length the red of the 
 spectrum appears and the iron mass assumes a dull red heat. 
 As the temperature becomes more and more elevated the 
 vibrations of shorter and shorter period appear and are added 
 to the red, and finally all the colours of the visible spectrum 
 are emitted, and the iron assumes a white heat. 
 
 The Normal Spectrum. 
 
 Usually, spectra produced by means of a glass prism suffer 
 from two defects. Firstly, they are not quite pure, that is, 
 the colours seen overlap to a small extent, and therefore the 
 continuity of the pure colours is destroyed. Secondly, the 
 position of each colour is not exactly in proportion to its 
 wave length, and there is what may be called " crowding " 
 in places. With very special appliances these defects may 
 be almost entirely rectified, however, but by means of a 
 diffraction grating we can produce a spectrum that is both 
 
6 CHEMISTRY OF PIGMENTS. 
 
 pure and normal. A diffraction grating is a system of very 
 narrow, equal and equidistant rectangular apertures, usually 
 employed in the form of a glass plate with an enormous 
 number of parallel fine lines traced on it at equal distances 
 with a diamond point, the two series being at right angles to 
 each other. When a luminous centre is viewed through this, 
 a central or direct image is seen, and on either side of it are 
 several spectral fringes richly coloured with all the rainbow 
 colours. For the theoretical considerations connected with 
 the production of these diffraction spectra, the reader is re- 
 ferred to advanced text-books on optics. It here suffices to 
 say that there is no overlapping of the colours, and whilst 
 the intensity of the spectrum is small, it has the advantage 
 of being quite pure ; and, further, if the diffracted light is at 
 right angles to the surface of the grating the spectrum is 
 normal, that is, the position of each ray is in exact proportion 
 to its wave length. The importance of this is seen by the fact, 
 that not only, as mentioned above, is there some overlapping 
 in ordinary prismatic spectra, but the irrationality of dispersion, 
 as it is called, is so great in some substances that the order 
 of the colours is actually reversed. The relative space oc- 
 cupied by the various colours in a prismatic spectrum depends 
 on the prism, but for ordinary glass prisms made of crown 
 glass the following may be taken as representing the relative 
 spaces. Those of the normal spectrum are given as well. 
 In each case the spectrum is assumed to be divided into 
 1,000 parts : 
 
 Prismatic Spectrum. Normal Spectrum. 
 
 Red .... 0- 160 0- 330 
 
 Orange-red ... 150 195 330 435 
 
 Orange .... 195 210 435 460 
 
 Orange-yellow . . 210 230 460 485 
 
 Yellow .... 230 240 485 500 
 
 Green-yellow . . . 240 345 500 575 
 
 Green . . . . 345450 575 690 
 
 Blue .... 450 805 690- 880 
 
 Violet . . . . 805 1,000 880 1,000 
 
INTRODUCTORY. 7 
 
 The Simple Nature of the Pure Spectral Colours. 
 
 The true spectral colours are of a simple nature, that is, 
 they cannot be further decomposed into other colours as 
 white light can. This can be shown with great ease in the 
 following manner. A narrow slit, A', is made in a shutter 
 parallel to an opening, A, in the screen, S, which can be 
 moved as desired. The beam of light passing through A is 
 allowed to pass through a lens to render the emergent rays 
 parallel, and to fall on a prism, P. The spectrum appears 
 on the screen, and any desired portion can be made to pass 
 through the slit, A, and to again fall on a prism, Q, and after 
 
 FIG. 2. 
 
 traversing this on to the screen, T. It will be seen that the 
 image on T is always identical with the light which is allowed 
 to pass through the slit A ; hence the light cannot be further 
 decomposed. 
 
 The Recomposition of White Light, 
 
 The above experiments are of an analytical nature, but 
 the reverse experiments are easy to perform, and white light 
 can thus be synthesised from its components. There are 
 several methods of effecting this synthesis, amongst which 
 the following may be mentioned. A beam of white light 
 
8 CHEMISTRY OF PIGMENTS. 
 
 may be passed through a prism and so decomposed into its 
 component coloured rays, which are then allowed to fall on 
 a prism of the same nature in the reverse position, when 
 the refraction in the reverse direction takes place, and the 
 emergent beam is white again. 
 
 A second, but rough-and-ready method of showing this 
 effect is to paint a circle of cardboard in sections with the 
 seven principal spectral colours, and rotate it rapidly round 
 an axis passing through its centre. Owing to the phenomenon 
 of the persistence of vision, the impressions of the colours are 
 more or less superimposed, and an approximation to white 
 is the actual colour observed. 
 
 Primary and Complementary Colours, 
 
 The popular idea that the colours red, yellow and blue 
 are " primary " colours on account of the fact that no human 
 eye has been able to detect in them two different colours, 
 whilst all other colours contain at least two primary colours, 
 is quite erroneous, and is based on visible results obtained 
 in the mixture of pigments and the transmission of light 
 through coloured glasses. The interpretation of these pheno- 
 mena is of a different nature, and it is more correct to regard 
 each of the spectral colours as primary and elementary. It 
 is true that the theory first propounded by Dr. Thomas 
 Young, that there are three primary colour sensations, has 
 received universal acceptation. This theory propounds that 
 there are three chief elements in colour sensations, that is, 
 three distinct physiological actions, which, by their various 
 combinations produce all our sensations of colour. Each of 
 these primary colour sensations is excited by wave lengths 
 covering a wide range, but possesses its maximum excita- 
 bility for rays of definite wave length. These points of 
 maximum sensibility are in the green near Frauenhofer's line 
 
INTEODUCTOEY. 9 
 
 b, in the extreme red, and in the extreme violet. The im- 
 pression of white light on the retina of the eye may be pro- 
 duced by various combinations ; the results are identical 
 to the eye, but the differences in the combinations are at 
 once perceived when the light is spectroscopically analysed. 
 Thus the following pairs of colours, when combined, give 
 white light : 
 
 Red Blue-green. 
 
 Orange ...... Blue. 
 
 Yellow Violet-blue. 
 
 Greenish-yellow .... Violet. 
 
 Green Pink (red- violet). 
 
 Each of the spectral colours which in combination with 
 another colour yields white light is said to be complementary 
 to that colour ; thus yellow and blue are complementary 
 colours, and green and red (within the limits as shown above) 
 also. The term secondary colour is applied to the colour 
 resulting from the mixture of two primary colours, such as 
 red and blue, which produce a violet or purple, and tertiary 
 colours are those which result from the mixture of two 
 secondary colours. These terms, however, are exceedingly 
 arbitrary and, consequently, not very scientific. 
 
 Coloured Bodies. 
 
 For convenience we may study the substances which we 
 know as " coloured bodies," under two headings (a) opaque 
 bodies, (/3) transparent bodies. The former owe their colour 
 to the phenomenon known as irregular reflection, and to the 
 fact that this irregular reflection is usually of a selective 
 nature. The ordinary phenomena of reflection which obey 
 the two well-known laws viz., (1) that the reflected ray lies 
 in the plane of incidence ; (2) that the angle of incidence 
 and the angle of reflection are equal are known as regular 
 reflection. These phenomena do not render objects visible 
 
10 CHEMISTRY OF PIGMENTS. 
 
 at all, but merely give images of surrounding objects. In- 
 deed, the reason that an ordinary mirror surface is visible 
 is that a small quantity of diffused or irregularly reflected 
 light is emitted. This diffused or irregularly reflected light 
 consists of rays reflected in all directions, which do not 
 apparently obey the two above-mentioned laws owing to at 
 least two reasons : (1) on account of the small irregularities 
 of surface, and (2) on account of partial absorption and 
 internal reflection ; and to these the visibility of the object is 
 due. Now, a body which (irregularly) reflects all the rays 
 of the spectrum in the same proportion as they are pres- 
 ent in the incident light will appear of the same colour as 
 that light. The majority of bodies, however, reflect some 
 rays in greater proportion than others, their colour being due 
 to the mixture of reflected rays. From these remarks it will- 
 be seen that the colour of a given body depends on two chief 
 circumstances, (a) the inherent selective action which a given 
 body has for definite rays, which is constant for a given body ; 
 (8) the composition of the light falling on the body. The 
 colours we assign to given bodies are always those which 
 they possess when the incident light is white. Thus a body 
 which absorbs the blue, green and yellow rays of the 
 spectrum and reflects the red rays presents the appearance 
 we know as red when the incident light is white. But 
 when the majority of red bodies are examined in, for 
 example, the yellow light of the sodium flame, their colour is 
 a dull brown, on acccount of the fact that the amount of red 
 rays falling on the body is so small that the reflected light 
 contains a correspondingly few red rays, and the observed 
 colour is made up of the small number of rays of different 
 colours which the body is able to reflect. The usual form, 
 from our point of view, of opaque-coloured objects with 
 which we have to deal is that of coloured powders. But to 
 discuss these it is necessary to understand the cause of colour 
 
INTKODUCTOEY. 11 
 
 in transparent bodies. A transparent body when examined 
 by transmitted light is coloured if it is more transparent to 
 some rays than to others, its- colour depending entirely on 
 the nature of the transmitted rays, or, in other words, is due 
 to the absorption of certain rays dependent on the nature of 
 the substance itself. Many transparent substances appear of 
 different colours when different thicknesses are examined. 
 For example, a solution of chromic chloride is green when 
 light is allowed to traverse a thin layer of the solution, but 
 when the thickness of this layer is increased the colour 
 observed is a reddish brown. Such substances are termed 
 dichroic. In such a case as this, certain rays are only partly 
 absorbed, and the substance must be of a certain thickness 
 before the absorption is complete, the colour, of course, being 
 due to the residual transmitted rays. When two pieces of 
 different coloured glass are examined together by transmitted 
 light, the colour observed is not by any means t'he mean of 
 the two, nor is it the sum of the two colours. As the colour 
 is due to the transmitted rays only, it is dependent on those 
 rays which both pieces of glass allow to pass. Thus a piece 
 of red glass allows light to pass through which consists 
 almost entirely of red rays. Green glass, on the other hand, 
 allows practically no red rays to pass through. Hence a 
 combination of red and green glass will be almost opaque to 
 the observer. Again, light transmitted through blue and 
 yellow glasses will in general be green not because blue and 
 yellow mixed form green, as is popularly said ; but because 
 most yellows and blues when spectroscopically analysed are 
 found to contain a large amount of green rays, and it is the 
 green rays which both these colours transmit to the almost 
 entire exclusion of the other rays. Very few transparent 
 bodies are perfectly opaque to any rays. These are usually 
 transparent to a very high degree for that one set of rays 
 which dominates the observed colour, and allow other rays 
 
12 CHEMISTRY OF PIGMENTS. 
 
 to pass in small amount. These other rays, of course, 
 modify the colour according to their nature and quantity. 
 We may now return to the subject of coloured powders, 
 which, of course, form the vast majority of pigments in 
 everyday use. In a coloured powder every small particle 
 must be regarded as a small transparent body capable of 
 rendering light coloured by selective absorption in the sense 
 we have just detailed. It is quite true that powdered pig- 
 ments when taken in bulk are very opaque indeed, but nearly 
 every substance when examined in extremely thin layers is 
 found to be fairly transparent, and uoon this transparency 
 their colour effects depend. When white light falls on such 
 a powder a small portion of it is reflected from the outside 
 surface of the particles ; the remainder penetrates the 
 particles and undergoes reflection at some of their surfaces 
 of separation. The small portion which is reflected from the 
 immediate outer surface is white, as no absorption has 
 occurred, but that which is reflected after absorption is that 
 which determines the colour ; and since given substances 
 possess definite selective ability, the reflected rays are fixed 
 for a given substance in a given physical condition. It now 
 becomes easy to understand the reason of the alteration in 
 the colour of mixed powders. A mixture of green and blue 
 powders does not appear green because green is the colour 
 situated between the blue and yellow in the spectrum, but 
 because the blue pigment absorbs the red, orange and yellow 
 rays and the yellow absorbs the violet and blue. Hence the 
 only colour which is reflected by both of them is the green, 
 which reaches the eye as such. Many common phenomena 
 of the painter's art are easily explained in the light of the 
 above statements. For example, we all know that a coarsely 
 ground powder is more deeply coloured than the same 
 powder very finely ground. The quantity of light returned 
 at each successive reflection depends on the number of 
 
INTEODUCTOEY. 13 
 
 reflections. If the particles are large the light has to pene- 
 trate so much the deeper in order to undergo a given number 
 of reflections, and more light *will therefore be absorbed, and 
 the resulting colour will appear deeper. The finer the 
 particles the more white light is there reflected at the surface 
 before any penetration occurs. A very good example of this 
 is the white froth of a deeply coloured liquid. Again, the 
 reflection at the surfaces of particles is much weakened by 
 interposing between them a fluid whose refractive index is 
 nearer to that of the particles themselves than that of air is. 
 Pigments are thus rendered darker by wetting them with 
 water, and still more so by using the highly refracting oils. 
 Much less white light is reflected, and the colour appears far 
 darker. This explains the characteristic differences between 
 crayon drawings, water colours, and oil paintings (vide infra). 
 We have said that the light reflected from the extreme 
 outside surfaces of particles is white, but there are certain 
 exceptions to this rule, and some bodies appear to reflect 
 certain rays by selection in preference to others. Such 
 bodies are said to possess surface colours. Many of the ani- 
 line dyes are of this nature, and appear of different colours 
 when examined by transmitted and by reflected light. The 
 colour when seen by reflected light is determined (1) by the 
 normal irregular reflection, (2) by the abnormal reflection of 
 the selected rays which have been entirely refused admission 
 into the particles. The colour examined by transmitted light 
 is determined (1) by the absence of the abnormally reflected 
 selected rays mentioned above, (2) by the rays which are 
 absorbed in the body of the particles. A very well marked 
 example of this is the aniline colour, fuchsine. This appears 
 of a metallic green colour by reflected and of a rose red 
 colour by transmitted light. Incidentally we may mention, 
 as illustrating the dependence of colour phenomena on 
 external circumstances, that the solution is peacock blue 
 
14 CHEMISTRY OF PIGMENTS. 
 
 when examined through a polarising prism, but the explana- 
 tion of this is outside the scope of the present work. 
 
 The proper study of colour effects and mixtures is de- 
 pendent on a knowledge of the exact selective power of 
 various substances. This property is only to be exactly 
 understood by the examination of the absorption spectra of the 
 bodies in question. When a pure solar spectrum is examined, 
 it is seen to be crossed by a number of dark lines, usually 
 known, as mentioned above, as Frauenhofer's lines. Each 
 wave produces its own image of the slit of the spectroscope 
 in its proper position, according to its refrangibility, and in 
 a spectrum of an ordinary incandescent body, which is not 
 traversed by any dark lines, the wave lengths differ in so 
 gradual a manner that the various images are extremely 
 close together and the spectrum appears continuous. We 
 must not assume, however, that light rays of every possible 
 refrangibility are present because a spectrum is continuous. 
 It is more correct to say that all wave lengths are present, 
 within the limits of the resolving pow r er of the best 
 instruments we possess ; and were it possible to construct 
 spectroscopes of infinitely greater resolving power than the 
 best we now possess many continuous spectra might become 
 discontinuous. The black lines observed in the solar spectrum 
 indicate the absence of the rays of refrangibilities corre- 
 sponding to the positions of those lines. To be correct, we 
 should not say that these rays are completely absent, but 
 they are so nearly so that they appear black by contrast with 
 the other brilliant illumination. These dark lines are found 
 to be in the exact positions of the brilliant bands emitted 
 by certain definite incandescent vapours. For example, the 
 well marked D line of the solar spectrum (or, more correctly, 
 D lines, as powerful spectroscopes will effect this resolution) 
 is identical in position with the brilliant yellow sodium line 
 seen when sodium vapour is incandescent. The explanation 
 
INTRODUCTORY. 15 
 
 of these dark lines is that the inner mass of the sun emits 
 the light which gives a continuous spectrum. This, however, 
 has to pass through certains-cooler vapours on the outer 
 surface, and these absorb each its own special rays almost 
 entirely, thus accounting for the absence of these rays in 
 the solar spectrum, as we see it. In this manner a very 
 large number of elements have been shown to be present 
 in the sun's vapour. 
 
 These continuous or discontinuous spectra are produced 
 by luminous bodies, but colouring matters are not in them- 
 selves luminous, and to produce their absorption spectra we 
 must allow light to traverse a glass vessel containing a 
 solution of the colouring matter, before reaching the slit 
 of the spectroscope. The spectrum now observed will be 
 found to be traversed by one or more dark bands of varying 
 width, the colour bands observed being constant for definite 
 bodies under given conditions. The absorption spectra of 
 bodies may be graphically represented either by shading 
 the dark bands according to the degree of absorption on a 
 continuous spectrum diagram, or, better, by indicating the 
 spectrum by a horizontal line (abscissa), and the intensity 
 of the absorption at each point by means of vertical dis- 
 tances from the abscissa (ordinates). The resulting curve 
 at once gives an extremely comprehensive grasp of the 
 properties, of the colour. It will now be convenient to give 
 an account of the absorption spectra of a number of bodies 
 of various colours, starting, say, from the red end of the 
 spectrum. 
 
 Azorubine. This body is one of the coal-tar dyes of the 
 diazo series, known chemically as sodium naphthalene sulphonate 
 azo-a-naphtol sodium sulphonate. It is a full crimson colour, sup- 
 pressing practically all rays except the extreme red (Fig. 3, 1). 
 
 Scarlet E belongs to the same group of compounds, and 
 is sodium xylene-azo-/3-naphtol sulphonate. It is a fine scarlet 
 
16 CHEMISTEY OF PIGMENTS. 
 
 colour, and its absorption spectrum shows that it allows prac- 
 tically nothing but the red and a portion of the yellow-orange 
 rays to pass (Fig. 3, 2). 
 
 Alizarin. This body is the essential colour-bearer of the 
 well-known madder plant, but is now practically entirely 
 produced synthetically from anthracene, one of the hydro- 
 carbons present in coal tar. It is a dioxyanthraquinone. This 
 fine red colour gives absorption spectra, which do not mate- 
 rially differ if the solvents are neutral, but which are by 
 no means identical when acids or alkalies are added. Several 
 of these are given here, from which it will be seen that all rays 
 as far as the D line are fairly freely transmitted in all cases 
 (Fig. 3, 3). 
 
 Eosin. Typically pure eosin of commerce, which is usually 
 sold as Eosin J, is the hydrated potassium salt of tetrabromo- 
 fluorescein, of the formula C 20 H 6 Br 4 5 K 2 + 6H 2 0. Mixtures 
 of -this body with the analogous dibromo-compounds are sold 
 as Eosin 5 G, and have a more orange shade, and various 
 closely related compounds of lighter or darker shades are 
 common articles of commerce. The appended spectrum is 
 that of the typical compound in (a) concentrated, (/3) dilute 
 alcoholic solutions (Fig. 3, 4). 
 
 Tartrazine. This well-known colour is the sodium salt 
 of disulpho-diphenylizine-dioxytartaric acid. It is an orange 
 yellow powder which produces a fine yellow colour with a 
 reddish tint. Picric Acid, or trinitrophenol, is a typical 
 colour yielding a much yellower spectrum than tartrazine. 
 The two are here illustrated (Fig. 3, 5). 
 
 Acid Green is the typical name of a number of coal-tar 
 greens, which are sulphonic acids of the various aldehyde 
 greens. Of these the ordinary Helvetia green is one of the 
 most common. The spectrum given shows that the whole 
 of the red and yellow and much of the violet is totally ex- 
 tinguished, with the result that a brilliant green (with blue 
 in it) results (Fig. 3, 6). 
 
INTRODUCTORY. 
 
 17 
 
 Indigo. The spectrum yielded by indigo extract varies 
 to a small extent according to the exact method of prepara- 
 tion of the extract. But these variations are only slight, and 
 the chief feature of a typical extract, which is shown helow, 
 is the almost complete extinction of the red-yellow rays and 
 the extreme violet (Fig. 3, 7). 
 
 Methyl Violet. The last spectrum we shall here consider 
 is that of methyl violet, one of the coal-tar violets, whose 
 chemical relationships are expressed by the name pentamethyl 
 pararosaniline hydrochloride. The total extinction of nearly 
 the whole of the red, all the yellow and all the green rays is. 
 the characteristic of this spectrum (Fig. 3, 8). 
 
 A BC D E F G H 
 
 FIG. 3. 
 
 3. a Alcoholic solution. 
 
 Alcoholic ammoniacal solution. 
 
 7 Aqueous ammoniacal solution. 
 
 5. a Tartrazine. 
 
 fl Picric acid. 
 
CHAPTEK II. 
 
 THE APPLICATION OF PIGMENTS. 
 
 Ix deciding the relative suitability of pigments for any parti- 
 cular case two sets of circumstances must be taken into 
 consideration : on the one hand, the purpose for which 
 the pigment or pigments may be required, whether purely 
 artistic, decorative or protective, and the conditions under 
 which this purpose must be fulfilled ; and, on the other, 
 the nature of the pigments and of the media and methods of 
 .application at the worker's disposal. These circumstances 
 having such an important bearing on the chemistry of pig- 
 ments, we have thought it advisable to consider them before 
 proceeding to the systematic description of the pigments 
 themselves. 
 
 I, USES OF PIGMENTS. 
 (A) Purely Artistic Uses. 
 
 These include all those various methods of depicting 
 objects and events in colours which have been recognised 
 as most suitable when accuracy of representation, whether 
 imitative or suggestive, has been the principal object sought 
 to be attained. It is obvious that this is the highest use to 
 which colours can be put, and in many respects the most 
 exacting in its requirements, the more general of which, as 
 applying equally to all branches of pictorial art, we will now 
 consider. 
 
THE APPLICATION OF PIGMENTS. 19 
 
 Whatever surface may be adopted for the reception of 
 the picture, and in whatever manner it may be decided to 
 apply and fix the colours on ttiat surface, it is evident, in the 
 first place, that the relations of surface and colour must be 
 such that the masses of colour applied may be distributed 
 in any form that is necessary for depictive purposes, and, 
 whether the work is in natural colours or monochrome, shall 
 be capable of all gradations of shade or intensity, from the 
 full density of the colour to the merest suggestion of the 
 same. 
 
 In order that this quality of "workability" may be 
 possessed in the highest degree, it is necessary that the 
 pigment be in a very fine state of division, and uniformly 
 diffused throughout the medium by means of which it is 
 applied, and that some means of dilution can be adopted, 
 either by the addition of a white pigment in the case of 
 "body colour," or by increasing the proportion of medium 
 or the application of the colour in very thin layers in those 
 cases in which the colour is used as a " stain" or " glaze ". 
 This fine state of division is obtained by various processes of 
 crushing, grinding, occasionally by roasting and washing or 
 levigation. The latter method is particularly valuable, as 
 particles which could not be separated by the finest sieve 
 can be suspended in water and the finer matter, after the 
 coarser particles have settled to the bottom of the vessel, 
 run off with the water and allowed to slowly deposit, the 
 coarse particles being again ground. All these processes of 
 preparation of powders are described in various technical 
 works, and need not be considered at length. It is not 
 now the general custom for artists to prepare their own 
 colours, though before the rise of a special industry this 
 was necessarily the case. In this respect, at any rate, 
 modern artists are more fortunate than their predecessors, 
 as doubtless specialised machinery is more effective than 
 
 
20 CHEMISTRY OF PIGMENTS. 
 
 the more primitive appliances of earlier ages, and time is 
 not wasted in purely mechanical operations. It is possible, 
 however, that in some other respects the wholesale prepara- 
 tion of artists' colours is not an unmixed boon. The question 
 of media or colour vehicles will be discussed in another part 
 of this chapter ; for the present it is sufficient to predicate 
 of the medium that it shall have no immediate appreciable 
 effect on the appearance of the colour, and in most cases 
 that after the colour is effectually fixed on the receptive 
 surface its tint shall remain unaltered, or that in special 
 cases the effect shall be certain and easily estimable. 
 
 Granted the possession of the quality of workability, it 
 is necessary that the colours at the artist's disposal be 
 iris-hued, capable either separately or judiciously mixed of 
 imitating the colour or the colour effect of any object which 
 the eye has seen or can conceive. Unless this is so artistic 
 effort must be confined to monochrome (which, though giving 
 considerable scope for a master of form and light and shade, 
 has, it must be confessed, much the same effect on the eye 
 as a Gregorian chant in music, or a very severe adherence 
 to a very obvious metre in poetry, has on the ear), or to a 
 very crude colour scheme which is less pleasant and certainly 
 less artistic than monochrome. In this respect, so far as 
 the representation of objective effects are concerned, our 
 known pigments leave very little to be desired, as an examin- 
 ation of the works of the great pre- and post-Kaphaelites 
 (and Kaphael himself) of the Italian schools, of the Dutch 
 school, especially some of the still-life examples, and, though 
 last, not, in many respects, least, of our great English land- 
 scape painters, and of those two masters of atmospheric 
 effect, Claude and Turner, will convince one. The suggestion 
 of the subjective phenomena of interference and diffraction 
 colours has indeed not presented insuperable difficulties to 
 some of our colourists. It is not, however, sufficient for the 
 
THE APPLICATION OF PIGMENTS. 21 
 
 highest kind of artistic work that colours should be capable 
 of easy application to the prepared surface and be sufficiently 
 diverse and brilliant for purposes of imitation, but, in justice 
 to the labours of the artist, they must, under reasonable 
 conditions, be permanent. In this respect the artist is, rela- 
 tively to the poet or musician, very unfortunately placed in 
 regard to posterity ; the effect sought to be produced by either 
 of the latter is entirely independent of the manner of repro- 
 duction. The writings of Homer, Shakespeare or Milton, 
 the musical compositions of Palestrina, Purcell, Ahn or 
 Mozart, and those fragments of ancient music we possess 
 are not only (except for corruption of text or score) in the 
 same verbal form as the original copy issued from the 
 author's hand, but, thanks to writing, musical notation 
 and printing, capable of indefinite reproduction. By reason 
 of this fact there seems no reasonable possibility of such 
 works being either lost or, saving for alterations of taste and 
 habits, failing to produce the same emotions and sensations 
 as they have always been capable of doing. With the artist 
 things are entirely different, he appeals to the feelings, not 
 through the ear, nor through the eye as a mere signalling 
 instrument, but through the eye in all its powers of convey- 
 ing sensations of form, colour, light and shade ; his work, as 
 laborious, as poetical as that of the writer or composer, can- 
 not be reproduced in such a way as to convey its full effect, 
 and consequently he can only appeal to a limited number 
 of people (and only in one place). Not only is this the 
 case, but he is working with materials the entire suitability 
 of which can never be satisfactorily determined, for whereas 
 we can decide that such a work is fading, or the surface 
 cracking, or the high lights going, and so being lost to 
 posterity, we can never be sure that another work now in 
 good preservation may not in the future show signs of such 
 decay. The materials used by artists are also only perman- 
 
22 CHEMISTRY OF PIGMENTS. 
 
 ent when properly kept, so the safe custody of the one only 
 example of each work of the artist becomes a matter of the 
 highest moment. 
 
 The ideal of permanence required of artists' colours is very 
 comprehensive. The surface must not only remain intact in 
 spite of the action of air, moisture, light and some variations 
 of temperature (not usually great), but all the colours must 
 retain to a very great degree, if possible to the end of time, 
 their original tint, however delicate. The bright colours and 
 the high lights must retain their brilliance, and the darker 
 colours and shadows their obscurity, or the contrast of light 
 and shade, the chiar'oscuro as it is called, will be destroyed, 
 and the objects which, when the picture left the painter's, 
 hands stood out, as it were, from the picture, and those which 
 were in the distance, appear to be but little separated, and 
 the whole seems flat and lacking in atmospheric effect. 
 
 That this permanence of colour and shade has been very 
 closely approximated to by many old masters is shown on an 
 examination of their works. The earliest examples in the 
 National Gallery are a series of portraits, either Greek or 
 Graeco-Bornan, taken by Mr. Flinders Petrie in 1888 from 
 mummy cases discovered in an ancient cemetery at Hawara 
 in the Fayyum, Egypt. Ten of these are painted on wood 
 panels in the encaustic method, the remaining one being 
 apparently in tempera on canvas ; this specimen is not in 
 very good preservation, rather the result of rough usage than 
 natural deterioration.. The others are still pleasing looking, 
 the flesh colours being fairly good, and the white used for 
 some of the draperies and high lights, two shades of 
 (Tyrian?) purple, blue and crimson drapery, blue, red and 
 green stones, set in gold, and other gold ornaments retaining 
 sufficient of their original brilliancy to be convincing. Alto- 
 gether, these ten pictures well illustrate the permanence of 
 colours in so inert a medium as wax, though it must be 
 
THE APPLICATION OF PIGMENTS. 23 
 
 borne in mind that from the nature of the case the portraits, 
 being preserved in the dark and in the dry atmosphere of 
 Egypt, had everything in their favour. It remains to be 
 seen what effect the light of a gallery and our moister climate 
 will have on them. A painting by Margaritone (died 3 293), 
 in the conventional Byzantine style, of " The Virgin and 
 Child, with Scenes from the Lives of the Saints" (No. 564) 
 is not at all satisfactory. The colours are very dingy, and in 
 some cases absolutely changed beyond recognition. The 
 picture is in tempera on linen fastened to wood, and it is 
 probable that part of the dark appearance is due to the 
 unsatisfactory medium used. A painting school of Giotto 
 (circa 1330), who introduced white of egg as a medium of 
 "The Coronation of the Virgin" (No. 568) is still in very 
 good preservation. The iris-hued wings of attendant angels, 
 a green and a scarlet, still look fairly bright. Another 
 painting of the same subject by Orcagna (died 1368), in 
 which a great many figures are represented, shows such 
 varied colours as crimson, scarlet, green and blue in very 
 good preservation, and some very varied and pleasing flesh 
 tints, from the delicate pink of the principal figures to quite a 
 swarthy sunburnt hue. The swords in the hands of some of 
 the saints, however, look very black, probably owing to 
 serious changes in the pigment used. "A Baptism" by 
 Taddeo Gaddi (died 1366) shows the following colours : two 
 purples, crimson, a bright red, a colour like raw sienna, a 
 sage green, blue, and two flesh colours, coarse and delicate, 
 and the steel of a sword, all but the latter satisfactory. A 
 "Virgin and Child" (No. 283) by Gozzoli (died 1498) shows 
 good flesh tints, and two goldfinches still looking well 
 coloured. His " Kape of Helen " (No. 591) shows good flesh 
 colours, scarlet and blue ; the landscape, with sea forming 
 the background of this, is fairly good, but the green (probably 
 vegetable) of the trees is very dull. Sandro Botticelli (died 
 
24 CHEMISTKY OF PIGMENTS. 
 
 1510) is represented by six pictures, all in tempera : No. 275, 
 " The Virgin and Child, St. John Baptist and an Angel," is 
 perfect in colour, the principal colours being delicate and 
 swarthy flesh tints, and gold (brocade). No. 626, "Portrait 
 of a Young Man in Brown Dress and Light Ked Cap," 
 is characterised by a rather tallowy (perhaps accurate !) 
 flesh colour and a fine red. No. 915, "Mars and Venus 
 and Four Young Satyrs," shows a very wide range of 
 colours ; very varied flesh tints, delicate for Venus, swarthy 
 for the satyrs, white, gold, crimson, steel (armour), a reddish- 
 brow r n conch shell and the dark rich green of the myrtle, a 
 very fine picture. By the side of this is a picture (No. 651), 
 "Venus, Cupid, Folly and Time," by Bronzino (died 1572) 
 in which varied flesh tints, blue drapery, a russet apple (of 
 Discord), red roses, a crimson cushion and the white doves 
 of the Paphian goddess appear with a remarkable freshness. 
 "A Virgin and Child" and a "Virgin Adoring the Infant 
 Christ," by Lorenzo di Credi (died 1537), show a brilliance of 
 colouring both of the figures and drapery and of the landscapes 
 in the distance which time would have done well to soften, 
 though in their way they are perfect. The " Portrait of Julius 
 II." (No. 27), "St. Catherine of Alexandria" (No. 168), the 
 Garvagh and Ansidei Madonnas and the ancient copy of the 
 Bridge water Madonna of Kaphael (died 1520), " The Holy 
 Family" (No. 4), " Venus and Adonis" (No. 34) and " Bacchus 
 and Ariadne " (No. 35) of Titian (died 1576), " The Portraits 
 of Jean Arnolfini and His Wife," by Jan Van Eyck (one of 
 the earliest oil painters), painted in 1434, and many other 
 works of masters of the early Italian and Flemish schools 
 might be quoted as examples of beautiful fresh colouring, 
 retaining, so far as may be judged, correct relationship of tone ; 
 but as this is a work rather on the materials used by artists 
 than on their works, the mention of a few works by masters 
 of light and shade and atmospheric effects, which would be 
 
THE APPLICATION OF PIGMENTS. 25 
 
 entirely marred by the fading of dark masses or the deteriora- 
 tion of high lights, must conclude this examination of pictures 
 which have stood the test of time. The portrait by (and 
 of?) Andrea del Sarto, Andrea senza errori (Andrea without 
 faults) as he is called, would, if the beautiful soft light on the 
 cheek or the white of the shirt were to darken, or the shade 
 over the rest of the face and the darker background fade, be 
 a dull, flat picture, though still beautiful, instead of being, as 
 it is, perfect. The "Agony, after Correggio," with its peculiar 
 illumination of the two figures in the darkness, requires abso- 
 lute permanency in the high lights. The " Walk to Emmaus," 
 by Lelio Orsi (died 1586), is another early work in which the 
 whole effect is due to the chiar'oscuro : a burst of light through 
 a dark sky lights the figures, throwing the folds of their gar- 
 ments and their faces into violent relief and reflecting gleams 
 from a dagger hilt and the top of a walking stick. The later 
 examples of Rembrandt, especially the marvellous " Adora- 
 tion," with its natural and supernatural illumination, the 
 heavenly light from the Child and the dull glimmer of the 
 shepherds' lantern ; of the Dutch landscape painters (especi- 
 ally Hobbema); of the French landscapists, Claude Lorraine 
 ("Gelee") and Gaspard Dughet (" G. Poussin "), nearly all 
 works depending for their highest beauty on very subtle 
 schemes of light and shade and atmospheric effect, most of 
 them over two centuries old, tend to show that it is possible 
 to produce works of a very high degree of permanence both 
 of colour and of tone. At the same time it must be admitted 
 that some of the colours used by the earlier masters, as, for 
 example, bitumen, were highly unsatisfactory both as per- 
 manent colours and on account of their injurious effect on 
 the surface ; and again, possibly, a process of natural selection 
 has weeded out many once beautiful works from the front 
 rank and turned them into the "speculative pictures" and 
 "doubtful old masters " of the auction room and the would- 
 
26 CHEMISTRY OF PIGMENTS. 
 
 be art patron. It is, notwithstanding, a matter of great regret 
 that we do not know more of the methods both of preparation 
 and working of the old masters. That we know so little is 
 not a matter for surprise ; the secret process is not yet dead 
 in chemical works (though it is usually a secret shared un- 
 consciously with most other similar works) and the whole 
 tendency of the middle ages, a tendency not seriously modi- 
 fied by the Renaissance, w r as for members of a guild or 
 confraternity (of craftsmen) to keep their methods very 
 secret, the master not always fully initiating his pupils, far 
 less trusting his methods to paper or to his fellow, and rival, 
 artists. Though in many ways to be regretted this is very 
 natural on the part of those who had probably with great 
 labour prepared their colours and discovered secrets they 
 did not reveal. The fact, however, remains that of the 
 methods of the ancients very little is known ; to attempt a 
 chemical examination of the works of acknowledged masters, 
 involving as it would their destruction or serious mutilation, 
 would be, apart from pecuniary considerations, an act of 
 most atrocious Vandalism and would probably be entirely 
 unsuccessful, both on account of the small amount of colour 
 actually applied to the surface and of the difficulty of such 
 examinations, particularly when it is desired to examine the 
 nature of the medium employed. It is, to an extent, possible 
 to form some idea as to the colours used on a certain picture, 
 but this does not always, even if the conjecture be correct, 
 convey much information, as permanence may be affected by 
 the presence or absence of accidental impurities and depends 
 on the pigment, the medium and the surface, even supposing 
 conditions of preservation to be the same. The study of 
 ancient pictures principally serves to remind us that it is 
 possible to obtain and to apply colours that will last for 
 centuries and still present to the eye such well-known hues 
 as those of human flesh, of sea and sky, and of those animate 
 
THE APPLICATION OF PIGMENTS. 27 
 
 and inanimate living things which we know have not altered, 
 and this not merely in a conventional manner (as the picture 
 writing of certain ancient nations), but with that force of 
 imitation or suggestion which almost convinces the eye of 
 their reality. This test of the fidelity of colour of natural 
 objects (making due allowance for the bluish flesh of one 
 period, the brown tree of another, and other obvious manner- 
 isms) seems, where applicable, the fairest to apply in judging 
 of the permanence of colours as colours ; the test of the 
 conviction produced by arrangements of light and shade the 
 best for that kind of permanence which is the result of fixity 
 of intensity or that quality which alone would appeal to the 
 colour-blind. 
 
 In the absence of this information concerning the per- 
 manent pigments of the earlier painters, and in face of the 
 lamentable condition of many modern pictures (particularly 
 those of Stothard, and, it is to be feared, some of Turner's 
 and Landseer's), the desirability of an extended series of ex- 
 periments on the action of light, air, moisture, heat and 
 products of combustion is evidently great. Such experiments 
 should include an examination of many (analysed) specimens 
 of each pigment with a view to determining the influence of 
 impurity and of variation of composition, and of the speci- 
 mens used in different media on such surfaces as are generally 
 considered suitable for the several media. So far as the 
 modern and beautiful method known as "water colour," in 
 which our countrymen have always excelled, is concerned, 
 some most highly interesting experiments have been carried 
 out in a manner remarkably free from empiricism by Dr. 
 W. J. Russell and Captain (now Sir) W. de W. Abney, who 
 in 1888 presented a report to the Science and Art Depart- 
 ment " On the Action of Light on Water Colours ". The 
 interest of the report is enhanced by the circumstance that 
 these gentlemen were advised and supplied with colours by a 
 
28 
 
 CHEMISTRY OF PIGMENTS. 
 
 I I I II II I I I I I I I I 1 I I ! I 1 I ll I i I I I II I I I I I I I, 
 
 ^ 
 
 a 
 
 'pH 
 
 a> co a> 
 
 CO O 
 O O 
 
THE APPLICATION OF PIGMENTS. 
 
 29 
 
 I I 
 
 ll 
 
 o fl'sj 
 
 jj ..- u; 
 
 a a 
 
 c3OOOOOOO 
 
 feOOOOOOO 
 
 ,d 
 
 03 03 ^3 
 
 fflOO^i 
 
 03 03 O) 03 03 03 "^ 
 
 d d d d d d ^ 
 
 O O O O O O 03 
 
 OOOOOOPn 
 
 oo 
 
 ccfl 
 
 03 d 
 
 d 
 
 &D O 
 
 fl tiD 
 
 ?S a -^ 
 
 
 
30 CHEMISTRY OF PIGMENTS. 
 
 committee of water-colour artists, including the late Sir F. 
 (Lord) Leighton, Sir E. J. Poynter (now P.R.A.), Sir Alma 
 Tadema, Mr. Sidney Colvin and others, and that forty- 
 six distinguished artists who used water colours furnished 
 the authors with lists of the colours they were in the habit of 
 using in their work. 
 
 The authors made a series of experiments with thirty- 
 nine colours, in the first place, exposed to the full action of 
 air and daylight. " The colours to be tested were applied by 
 a practised hand to the paper in a series of washes. ... In 
 most cases as many as eight washes were applied, giving thus 
 a complete series of eight tints." These strips were divided 
 so as to give two equal strips each with the eight tints ; 
 these two strips were both placed in a glass tube open at 
 each end and bent at the top, so that, while the complete 
 action of air was ensured, the tubes, which were placed 
 against a wall facing nearly south, were protected from the 
 entrance of wet and dirt. One half of the tube was bound 
 round with American cloth in order to protect one strip from 
 the action of light. " The two pieces of identically tinted- 
 coloured paper were therefore under exactly the same con- 
 ditions in all respects, except that one was exposed to light 
 and the other was in the dark." The papers were exposed 
 from May, 1886, to March, 1888, and were observed on 14th 
 August, 1886, in December, 1886, and in July and in No- 
 vember, 1887, and finally in March, 1888. It should be stated 
 that a very careful approximation of the relative illuminat- 
 ing powers of bright sunlight, the light from the sky, and 
 of diffused light from clouds was made, so that the authors 
 were able, knowing the hours of sunshine at Kew and Green- 
 wich Observatories during the period of their experiments, 
 and taking the mean of these as representing the sunlight at 
 Kensington, to state that between May and August, 1886, 
 they considered that the pigments received a total illumination 
 
THE APPLICATION OF PIGMENTS. 
 
 31 
 
 equal to 2,225 hours of average blue sky. " This, of course, is 
 only an approximate estimate." They also consider this to 
 be equivalent to 100 years in a gallery illuminated similarly 
 to those at Kensington. The results of the first and last 
 examination of the tints are given in the preceding table 
 (Table I. of the Keport). 
 
 A second series of experiments was made in hermetically 
 sealed tubes, with dried tinted paper and dry air. The 
 results obtained are epitomised in the following table (Table 
 III. of the Eeport) : 
 
 Name of Colour. 
 
 
 
 Dry Air. 
 
 Carmine ...... 
 
 
 
 Faded to 7 
 
 Crimson Lake .... 
 
 
 
 Gone to 5 
 
 Scarlet Lake ..... 
 
 
 
 Faded and darkened 
 
 Vermilion 
 
 
 
 Gone black 
 
 Rose Madder ..... 
 
 
 
 No change 
 
 Madder Lake 
 
 
 
 No change 
 
 Indian Bed ..... 
 
 
 
 No change 
 
 Venetian Red .... 
 
 
 
 No change 
 
 Brown Madder . . . . 
 
 
 
 Faded to 4 
 
 Burnt Sienna ..... 
 
 
 
 No change 
 
 Gamboge . 
 
 
 
 Faded to 3 
 
 Aureolin ...... 
 
 
 
 No change 
 
 Chrome Yellow .... 
 
 
 
 No change 
 
 Cadmium Yellow .... 
 
 
 
 No change 
 
 Yellow Ochre . . ' . 
 
 
 
 No change 
 
 Naples Yellow .... 
 
 
 
 No change 
 
 Indian Yellow .... 
 
 
 
 Faded to 4 
 
 Raw Sienna ..... 
 
 
 
 No change 
 
 Emerald Green .... 
 
 
 
 No change 
 
 Terra Verte 
 
 
 
 No change 
 
 Chrom. Oxide .... 
 
 
 
 No change 
 
 Olive Green ..... 
 
 
 
 No change 
 
 Antwerp Blue .... 
 
 
 
 Faded to 3 
 
 Prussian Blue .... 
 
 
 
 Faded to 5 
 
 Indigo Blue ..... 
 
 
 
 Faded to 7 
 
 Cobalt Blue 
 
 
 
 No change 
 
 French Blue 
 
 
 
 No change 
 
 Ultramarine Ash .... 
 
 
 
 No change 
 
 Leitche's Blue .... 
 
 
 
 Faded to 5 
 
 Permanent Blue .... 
 
 
 
 No change 
 
 Payne's Grey 
 
 
 
 No change 
 
 Violet Carmine .... 
 
 
 
 Faded and brown 
 
 Purple Carmine .... 
 
 
 
 Faded 
 
 Purple Madder .... 
 
 
 
 Faded to 4 
 
 Sepia . 
 
 
 
 No change 
 
 Vandyke Brown .... 
 
 
 
 V. si. faded 
 
 Burnt Umber 
 
 
 
 No change 
 
 Brown Pink 
 
 
 
 Faded to 4 
 
32 CHEMISTKY OF PIGMENTS. 
 
 Of thirty-seven colours exposed to the action of moist air, 
 only the following ten withstood the action of light under 
 this condition : Indian red, Venetian red, burnt sienna, yellow 
 ochre, raw sienna, emerald green, terra verte, chromium oxide, 
 cobalt, and ultramarine ash ; both Prussian blue and Antwerp 
 blue were entirely destroyed. Of twenty-nine mixtures only 
 two were unchanged raw sienna and Venetian red, and 
 cobalt and Indian red. 
 
 A further series was made in which the colour was ex- 
 posed to the action of moist hydrogen, so as to obviate the 
 action of oxygen. Of thirty-six colours " no less than twenty- 
 two remained unchanged; even carmine and crimson lake 
 did not alter, neither did madder lake, Indian red, Venetian 
 red, brown madder, burnt sienna, chrome yellow, yellow 
 ochre, raw sienna, terra verte, chromium oxide, olive green, 
 indigo, cobalt, French blue, ultramarine ash, permanent blue, 
 Payne's grey, sepia, Vandyke brown, and burnt umber ". 
 
 Thirty-nine experiments were made with single colours 
 exposed in a (Sprengel) vacuum. "Violet carmine and 
 purple carmine slightly darkened ; Prussian blue and purple 
 madder and sepia slightly bleached ; but in all cases the 
 action was very feeble. Twenty-four experiments were made 
 with mixed colours, and the results are of much interest 
 and importance. The mixtures containing Prussian blue 
 changed, the other colours becoming dominant. Vermilion 
 also blackened. With other mixtures hardly any change 
 occurred." 
 
 The actions of the electric arc light, of heat without light, 
 and of the light and products of combustion of coal gas were 
 examined, and experiments were also made with body colours 
 and with coloured light transmitted through red, green and 
 blue glasses ; in this latter series colours exposed under blue 
 glass were acted on to almost as great an extent as those 
 under white glass, the difference being due to the opacity 
 
THE APPLICATION OF PIGMENTS. 33 
 
 of the blue glass. This fully confirms expectations based 
 on theoretical considerations that the blue rays, from their 
 greater oscillation frequencies approximating to those of the 
 constituent atoms of substances, cause more decomposition 
 than rays nearer the red end of the spectrum. 
 
 The conclusions arrived at by Dr. Russell and Captain 
 Abney from these experiments are that 
 
 " Mineral colours are far more stable than vegetable 
 colours, and amongst those colours which have remained 
 unaltered, or have only very slightly changed after an ex- 
 posure to light of extreme severity, a good ganmt is available 
 to the water-colour artist. . . . 
 
 " The presence of moisture and oxygen is in most cases 
 essential for a change to be effected even in the vegetable 
 colours. ... It may be said that every pigment is per- 
 manent when exposed to light in vacuo. . . . 
 
 " The effect of light on a mixture of colours which have 
 no direct chemical action on one another is that the unstable 
 colour disappears and leaves the stable colour unaltered 
 appreciably. 
 
 " Our experiments also show that the rays which produce 
 by far the greatest change in a pigment are the blue and 
 violet components of white light, and that these, for equal 
 illumination, predominate in light from the sky, whilst they 
 are less in sunlight and in diffused cloud light, and are 
 present in comparatively small proportion in the artificial 
 lights usually employed in lighting a room or gallery. The 
 experiments have also shown that about a century of ex- 
 posure would have to be given to water-colour drawings in 
 galleries lighted as are those at South Kensington before 
 any marked deterioration would be visible in them, if painted 
 with any but the more fugitive colours ; and that when the 
 illumination is of the same quality as that of gaslight, or of 
 
 the electric glow light rendered normally incandescent, and 
 
 3 
 
34 CHEMISTEY OF PIGMENTS. 
 
 of the same intensity as that employed in those galleries, an 
 exposure to be reckoned by thousands of years would have to 
 be given to produce the same results. We have not taken 
 into account the action, if any, which might arise from the 
 products of combustion where gaslight is the illuminant, and 
 which our experiments so far have shown to have but 
 a trifling effect, nor of any modification of hue which might 
 be due to change in the whiteness of the paper on which the 
 paintings were made, but simply to the change in the colours 
 themselves." 
 
 A suggestion as to the use of yellowish glass in galleries 
 is also made in this report. 
 
 (B) Decorative Uses, 
 
 Under this heading we must include all those applications 
 of pigments in which the suitable adornment of useful or 
 quasi -useful objects is the principal purpose to be served, 
 considerations of pictorial accuracy or effect or of protection 
 of surface being subordinated to this in a greater or less 
 degree, according to the peculiar circumstances of the case. 
 These applications would comprise all kinds of mural decora- 
 tion, including coloured-glass windows, the adornment of 
 keramic ware of all kinds, of glass and of indoor (to a certain 
 extent of outdoor) woodwork, and in some cases of metal 
 work ; the media employed in these cases are, of coarse, most 
 varied in their nature. 
 
 The requirements of pigments to be used for decorative pur- 
 poses are, naturally, somewhat allied to those of the artist on 
 the one hand, and to those of the strict utilitarian on the other. 
 A choice not so great as the artist demands, for the decora- 
 tor's depictive efforts are more conventional than imitative 
 of colours is obviously needful, as is also permanence of rather 
 a different kind to that to which the artist endeavours to 
 attain. The conditions under which decoration is employed 
 
THE APPLICATION OF PIGMENTS. 35 
 
 are usually more trying, both as regards atmospheric and 
 other influences, because decoration is, after all, necessarily 
 subordinate to human comfort and convenience. A painted 
 ceiling, however lovely, is the top part of a room which 
 should serve a useful purpose ; a beautiful vase, however 
 useless, is the descendant, though perhaps very remote, of a 
 jar used to hold water, corn, or wine, or oil, or some other of 
 the possessions of early communities, and still in many ways 
 approximates to these more useful members of its family ; a 
 stained-glass window should be a means of letting in light 
 and keeping out rain and wind from a building ; a painted 
 panel of a door or cabinet is primarily part of a structure, and 
 though in many cases these things have been used by the 
 artist as means by which he can exercise the pictorial art, 
 they cannot be considered as the most suitable. The kind of 
 permanence, therefore, required is rather of surface than of 
 tint. A colour which will adhere well to the material and 
 allow of the surface being cleaned, will, if it retain its tint 
 fairly well, be preferable to one which, retaining its tint 
 better, is more susceptible to atmospheric influences or 
 wear. 
 
 It must be borne in mind that, whereas the pictorial artist 
 subordinates his surface and methods to his subject, choosing 
 the most suitable surface and medium, he who seeks to excel 
 in decoration must adapt everything to the surface or thing 
 to be decorated ; the colours, the medium, must be such as 
 on a certain object will produce the best effect and most en- 
 during. The question of cost is also, considering the often 
 extensive nature of such work, one which must not be 
 neglected ; also a due sense of proportion must be exercised in 
 deciding to what extent perfection and permanence are likely 
 to be required, or elaborate and costly schemes justified. 
 
 As the suitability of pigments for this class of work so 
 much depends on the nature of the surface to be decorated 
 
36 CHEMISTEY OF PIGMENTS. 
 
 and the consequent colour-vehicle to be employed, it will be 
 more convenient to consider the matter under the heading of 
 methods employed in applying pigments rather than in this 
 place; it always being remembered that the perfection to be 
 sought in this sort of work is not of that absolute kind which 
 is always desirable for serious artistic work, except in the 
 very highest kind of decoration, which, in our opinion, is only 
 legitimate in those cases where the permanence and proper 
 treatment and receptive condition of the building or structure 
 to be decorated can be well guaranteed. A painted ceiling, 
 which is quite legitimate at Hampton Court or Greenwich, 
 where the conditions are favourable, might be prepared and 
 executed with much more costly and carefully selected pig- 
 ments, media and surface than would be justifiable in a 
 private house, which is liable to demolition for local improve- 
 ments, or to premature senile decay. (What is true of 
 materials is still more true of the worker !) 
 
 (c) Protective Uses. 
 
 From the purely utilitarian point of view these are the most 
 important uses to which pigments may be pat. The principal 
 materials treated with paint for this purpose are wood and 
 iron, and such treatment in each case becomes necessary 
 only when exposure to moist or otherwise specially active air, 
 or to water, is liable to cause deterioration of the surface with 
 its subsequent general decay ; and in the case of wood when 
 it affords an easily cleaned surface. So far as we know, wood 
 or iron exposed to perfectly dry air would be unaltered for an 
 infinitely long period, but as this cannot be the case with 
 articles in common use, or exposed to the weather, or im- 
 mersed in water, the use of paint or varnish must be resorted 
 to in all work that is intended to be of a permanent character, 
 except, perhaps, in the case of very hard woods, which often 
 have very high weathering qualities. 
 
THE APPLICATION OF PIGMENTS. 37 
 
 The object of painting or varnishing iron- or wood-work 
 is, apart from considerations of appearance, to form a surface 
 coating, impervious alike t6*air and water, which will prevent 
 iron from rusting and wood from becoming waterlogged, 
 swelling, and perhaps, on drying, cracking, and in course 
 of time becoming rotten, water and air having no action, 
 either direct or indirect, on the surface. 1 This coating in 
 many cases, as ships' sides and iron- and wood-work and all 
 work which must be handled much, must be not only 
 impervious but tough, and not easily rubbed off, and in all 
 cases must be fairly permanent, so that renewal is not 
 frequently necessary ; this is especially the case in large 
 engineering work, where the difficulty of getting at the parts 
 of a structure is often great. 
 
 Protective applications for such work may be considered 
 under the following groups : 
 
 (1) Asphaltic varnishes. 
 
 (2) Oil varnishes. 
 
 (3) Paints. 
 
 (a) Presumably inert to the medium in which used. 
 
 (b) Active in forming a varnish with the medium. 
 
 (c) Antifouling by reason of their own erosion. 
 Concerning the relative value of members of the above 
 
 groups opinions vary greatly, and, unfortunately, in this, as 
 in many other cases, opinion has been allowed to take the 
 place of definitely ascertained facts : a certain coating has 
 
 1 It seems probable that many substances are less protective than might, 
 at first, be expected when applied to metal-work, owing to one or both of the 
 following reasons : (a) small quantities of soluble salts are through faulty 
 preparation contained in the pigment which may either act directly on the 
 surface in the presence of moisture, or which may absorb water and, producing 
 minute crystals of different volume and form from the original salt, tend to 
 weaken the coating by mechanical action ; (b) the pigment may contain 
 constituents which are decidedly electro-negative to the metal coated, and so 
 set up electro-chemical action with erosion of that metal. 
 
38 CHEMISTRY OF PIGMENTS. 
 
 done well under one set of conditions, and is therefore con- 
 sidered by its user as the protective coating par excellence, 
 while another coating, under totally different conditions, is 
 found by another individual to be satisfactory, and he is of 
 opinion that this is the material to be used in all cases. Some 
 attempts have, however, been made from time to time by 
 chemists and engineers to attack the problem of protection of 
 iron-work from some other standpoint than the mere weather- 
 ing of some isolated iron structure, possibly under abnormal 
 conditions. A paper, in which most of the work done in this 
 direction is examined and discussed, and a new series of 
 valuable experiments described, was read by Mr. Harry 
 Smith, F.I.C., before the Newcastle Section of the Society 
 of Chemical Industry in December, 1899. 
 
 It would appear from this paper that most writers on the 
 subject agree (1) that the work to be treated should be as 
 clean and free from scale as possible ; this to begin with 
 ensures the absence of any particles much more electro-nega- 
 tive than iron ; (2) that a treatment with hot (or cold) linseed 
 or boiled linseed oil is desirable both as a protective coating 
 and for the paint to adhere to more firmly than it will to the 
 untreated iron (Mr. Smith's and some other experiments do 
 not show this). Beyond these two points there is very little 
 agreement on the part of the various experimenters, as the 
 following quotations will show : 
 
 Iron oxide paints adhere better to Iron oxide paints should not be 
 
 ironwork than lead paints. Asphal- used on iron, as the pigments them- 
 
 tum paints are not satisfactory. selves act as carriers of iron and 
 
 E. GESLER. produce rusting. 
 
 A. H. SABIN, 
 
 The red paint known as oxide of Toltze obtained the best results 
 
 iron, and which was claimed to be with genuine asphalte varnish es. 
 a rust preventative, possesses no in- 
 herent quality of that kind. 
 
 Engineer. 
 
 The method of experimenting adopted by Max Toltze, and 
 
THE APPLICATION OF PIGMENTS. 39 
 
 later by Mr. Smith himself in his second series of experiments, 
 was as follows (Toltze's description) : 
 
 " The iron dishes were "about twelve inches in diameter 
 and about half an inch deep, having a capacity of about half 
 a pint. The scale or skin was carefully removed before 
 painting, so as to have a clean surface of iron exposed to 
 the paint. Two dishes were painted with each kind of paint, 
 one of them receiving one coat, the other two coats, the first 
 coat having dried thoroughly (for at least a week) before the 
 second coat was applied. After the second coat had com- 
 pletely dried and hardened these dishes were exposed to the 
 so-called water-and-moisture test, in which a given amount 
 of water is placed in the dishes and allowed to evaporate to 
 dryness at the ordinary temperature of the room. This is 
 repeated a number of times until the inside of the dishes 
 begins to show more or less rust. All dishes were carefully 
 examined before each refilling. After most of the water has 
 evaporated there remains at the junction round the edge a 
 thin film of water, which, in contact with the carbonic and 
 other acids in the air, acts on the paint in such a way that the 
 iron under the paint begins to rust. The rust thus formed 
 develops more and more after each evaporation, in some cases 
 practically covering the whole dish in a short period." 
 
 Mr. Smith carried out experiments with forty-nine dif- 
 ferent preparations under the conditions described hereunder 
 by himself : 
 
 " The tests were carried out in three different ways : 
 
 " 1. By painting shallow iron dishes and exposing them to 
 the action of slowly evaporating water as described in Mr. 
 Toltze's experiments quoted above. 
 
 " 2. By exposing a set of painted iron plates to the con- 
 tinuous action of the weather for a period of twelve months ; 
 and 
 
 " 3. By exposing painted iron plates to the continuous 
 
40 CHEMISTKY OF PIGMENTS. 
 
 action of water in a similar manner to the tests made by 
 Mr. Thomson and myself in 1894. 
 
 " 1. The paints employed were prepared by grinding the 
 pigments with linseed oil on granite rollers to a stiff paste 
 in the proportions given below ; these were thinned to the 
 consistency of ordinary paint with boiled linseed oil of the 
 best quality, and capable itself of yielding a dry film on a 
 glass plate in about seven hours under ordinary conditions 
 of temperature, etc. 
 
 "Each plate or dish was given two coats of paint, the 
 second being applied after the first had become thoroughly 
 dry ; the tests were commenced when the second coats all 
 appeared to be dry and firm. 
 
 " Let us take the dishes first. Each dish was about 
 five inches wide by half an inch deep, and was filled with 
 ordinary town water ; they were placed side by side upon a 
 table, and were not touched during the three months over 
 which the trial extended ; but as soon as the water had 
 completely evaporated from each dish it was immediately 
 refilled with fresh water. During the three months each 
 dish dried and was refilled six times. 
 
 "In most cases all traces of paint have disappeared, and 
 there is present a thick deposit of rust mixed with the sus- 
 pended and soluble impurities present in the evaporated 
 water. 
 
 " The dishes painted with the following paints are 
 practically unaffected, and have withstood the very severe 
 conditions of the trial : 
 
 Bed lead paint 
 
 ' A ' Red lead paint 
 
 * ~R * 
 
 " . " " \. Practically unaffected. 
 Orange lead ,, 
 
 Vermilionette ,, 
 Scarlet red 
 
THE APPLICATION OF PIGMENTS. 41 
 
 " The following are slightly rust-stained, and are placed 
 in order of merit. 
 
 Zinc white (oxide) paint 
 
 ' A ' Zinc white ,, 
 
 ' f 1 ' 
 
 Lithopone ' I Slightly rust-stained ; placed in 
 
 White lead 
 
 'A' 
 
 '0' 
 
 "As to the thirty-six other paints tried in this way, all 
 ^appear to have suffered equally ; but it was noticed that 
 the dish painted with boiled linseed oil simply was the 
 first to show deterioration, and has apparently produced 
 the greatest amount of rust. 
 
 "2. The forty-nine iron plates, which were painted and 
 exposed to weather for twelve months, all stood this test 
 remarkably well, showing that all the paints were of fairly 
 .good quality under moderate conditions. 
 
 r ' There was one exception, however; the plate which re- 
 ceived two coats of boiled oil speedily became spotted with 
 rust, and at the end of the year was much corroded. All 
 the painted plates became very much darker in colour owing 
 to the deposit of soot from the air, but most of this I have 
 ^since removed by rinsing the plates under the water-tap. 
 
 " 3. In these experiments I painted strips of sheet-iron as 
 before ; and when the second coats were all dry and hard 
 -each plate was placed in a wide- mouthed glass bottle, and 
 the same volume of ordinary tap water was added in each 
 case. The bottles were then placed on a shelf immediately 
 below the laboratory bench, so that the open mouths of 
 the bottles were about one-eighth of an inch from the under 
 side of the table ; in this way the entrance of dust was almost 
 entirely prevented, and evaporation was greatly checked, but 
 ihere was access of air to the interior of each bottle. 
 
 " In this third series the tests were made in duplicate for 
 
42 CHEMISTRY OF PIGMENTS. 
 
 the sake of greater accuracy ; the figures given below in- 
 the third column are the mean of two results, and the 
 duplicates agreed very closely with each other in almost 
 all cases. 
 
 " The bottles were now allowed to remain untouched for 
 three months. After about seven days several of the plates 
 were perceptibly affected ; this was shown by a turbidity in the 
 water ; as oxidation proceeded a red precipitate of ferric 
 oxide, or rust, appeared and slowly subsided to the bottoms 
 of the bottles. After three months' exposure the plates were 
 removed, and the amount of iron present in the liquid, 
 and the deposit of rust in each bottle, were determined 
 by analysis, and the total amounts of ferric oxide obtained 
 in each case were calculated to pounds weight of rust per 
 1,500 square feet of painted iron surface ; but, of course, this 
 is rather under than over the total amount of corrosion, 
 as a certain quantity of corroded iron was loosely attached 
 to each plate and to the film of paint. The results obtained, 
 and the composition of the paint in each case, are shown 
 in the following table, and it must be understood that these 
 paints are the same as those employed (1) on the shallow iron 
 dishes, and (2) on the plates which were exposed to the 
 weather for twelve months : 
 
THE APPLICATION OF PIGMENTS. 
 
 Paint. 
 
 Composition. 
 
 Rust from 
 1,500 
 Sq. Yards. 
 
 Bed Lead 
 Red Lead 
 
 Per Cent. 
 
 88-88 
 11-12 
 
 Lb. 
 
 JNone 
 
 ' A ' Red Lead- 
 Red Lead . 
 
 45-00 
 
 j 
 
 Barytes 
 Raw Linseed Oil ....... 
 ' B ' Red Lead- 
 Red Lead .... 
 
 45-00 
 10-00 
 
 22-00 
 
 l r None 
 | 
 
 Barytes ........ 
 
 66-00 
 
 rNone 
 
 Raw Linseed Oil 
 Orange Lead 
 Orange Lead . 
 Raw Linseed Oil . 
 Vermilionette ] 
 Barytes 
 
 12-00 
 
 88-88 
 11-12 
 
 33-33 
 
 58-80 
 
 f 
 JNone 
 
 /-None 
 
 Raw Linseed Oil 
 Scarlet Red 2 
 Scarlet Red 
 
 7-87 
 88-88 
 
 J 
 X-w 
 
 Raw Linseed Oil 
 Pure Zinc White- 
 Zinc White (Zinc Oxide) . . . 
 Refined Linseed Oil 
 ' A ' Zinc White- 
 Zinc White 
 Barytes 
 
 11-12 
 
 87-30 
 12-70 
 
 45-00 
 45-00 
 10-00 
 
 VNone 
 | Traces 
 
 ^Traces 
 
 ' C ' Zinc White- 
 Zinc White 
 
 27-27 
 
 
 Barytes 
 Refined Linseed Oil 
 White Lead- 
 White Lead 
 Refined Linseed Oil 
 ' A ' White Lead- 
 White Lead 
 
 63-63 
 9-10 
 
 92-56 
 7-44 
 
 53-78 
 
 Traces 
 
 }" 
 
 Barytes 
 Refined Linseed Oil 
 Pale Oxide- 
 Pale Oxide (about 52 per cent. Fe 2 3 ) 
 Boiled Linseed Oil 
 Lithopone 
 Lithopone (Zinc Sulphide, Zinc Oxide, Barium 
 Sulphate) 
 
 40-33 
 5-80 
 
 83-60 
 16-40 
 
 87-50 
 12-50 
 
 80 
 
 }* 
 
 J90 
 
 ' C ' White Lead- 
 White Lead 
 Barytes 
 Refined Linseed Oil 
 
 50-52 
 42-10 
 
 7-38 
 
 ^95 
 
 1 ' Vermilionette ' is a pigment composed of Orange Lead on which has 
 been precipitated about 10 per cent of Eosine. 
 
 2 'Scarlet Red' is Red Lead on which has been precipitated Aniline 
 Scarlet. 
 
44 
 
 CHEMISTRY OF PIGMENTS. 
 
 Paint. 
 
 Composition. 
 
 Rust from 
 
 1,500 
 Sq. Yards. 
 
 ' A ' Red 
 
 Per Cent. 
 
 Lb. 
 
 Barytes and Calcium Carbonate .... 
 
 78-80 
 
 1 
 
 Ferric Oxide (95 per cent. Fe 2 O 3 ) 
 
 8-47 
 
 Ul8 
 
 Raw Linseed Oil 
 
 12-73 
 
 J 
 
 ' C ' Red 
 
 
 
 Barytes 
 
 80-57 
 
 ^ 
 
 Ferric Oxide (95 per cent. Fe 2 O 3 ) 
 
 7-55 
 
 -123 
 
 Raw Linseed Oil 
 
 11-88 
 
 J 
 
 Deep Oxide 
 
 
 
 Ferric Oxide (96 per cent. Fe 2 O 3 ) 
 Raw Linseed Oil . . . . 
 
 86-89 
 13-11 
 
 ]-123 
 
 Middle Oxide- 
 
 
 
 Ferric Oxide (94 per cent. Fe 2 3 ) 
 Raw Linseed Oil 
 
 86-89 
 13-11 
 
 }l34 
 
 J 
 
 Extra Bright Oxide 
 
 
 
 Ferric Oxide (90 per cent. Fe 2 3 ) 
 Boiled Linseed Oil 
 
 82-35 
 17-65 
 
 J137 
 
 Barytes 
 
 
 
 Barytes (Natural Barium Sulphate) . 
 Raw Linseed Oil 
 
 88-00 
 12-00 
 
 }l55 
 
 Pure Oxide ' C ' 
 
 
 J 
 
 Ferric Oxide (90 per cent. Fe 2 3 ) 
 Boiled Linseed Oil 
 
 76-30 
 23-70 
 
 j-160 
 
 ' C ' Celestial Blue 
 
 
 
 Barytes and Calcium Carbonate .... 
 
 78-04 
 
 ^ 
 
 Celestial Blue (a form of Prussian Blue) 
 Raw Linseed Oil 
 
 9-74 
 12-22 
 
 keo 
 
 ' B ' Prussian Blue 
 
 
 
 Prussian Blue 
 
 22-76 
 
 ^ 
 
 Barytes 
 
 45-52 
 
 
 Raw Linseed Oil 
 
 31-72 
 
 / 
 
 Pure Middle Chrome Yellow 
 
 
 
 Middle Chrome Yellow . . 
 
 83-58 
 
 
 Raw Linseed Oil 
 
 16-42 
 
 177 
 
 Pure Raw Sienna 
 
 
 
 Raw Sienna 
 
 74-66 
 
 
 Raw Linseed Oil 
 
 25-34 
 
 197 
 
 Pure Graphite- 
 
 
 
 Graphite 
 
 69-56 
 
 > 
 
 Raw Linseed Oil 
 
 30-44 
 
 J 
 
 Pure Prussian Blue 
 
 
 
 Prussian Blue 
 Raw Linseed Oil 
 
 48-27 
 51-73 
 
 J221 
 
 Pure Indian Red 
 
 
 
 Indian Red (70 per cent. Fe 2 O 3 ) . 
 Raw Linseed Oil 
 
 82-35 
 17-65 
 
 \227 
 
 ' A ' Vandyke Brown 
 
 
 
 Barytes 
 Raw Linseed Oil 
 
 56-00 
 13-33 
 
 1 230 
 J 
 
 
 
 
 ' B ' Middle Oxide 
 
 
 
 Barytes 
 
 76-22 
 
 1 
 
 
 12-30 
 
 [244 
 
 Raw Linseed Oil 
 
 11-48 
 
 J 
 
THE APPLICATION OF PIGMENTS. 
 
 45 
 
 Paint. 
 
 Composition. 
 
 Rust from 
 
 1.500 
 q. Yards. 
 
 Ivory Black 
 
 Drop Black (Charcoal Black) 
 
 Boiled Oil 
 
 Turkey Red 
 
 Turkey Red (95 per cent. Pe 2 3 ) . 
 
 Raw Linseed Oil 
 
 ' A ' Celestial Blue 
 
 Barytes and Calcium Carbonate . 
 
 Celestial Blue 
 
 Raw Linseed Oil 
 
 ' B ' Chinese Blue 
 
 Chinese Blue (another form of Prussian Blue) 
 
 Barytes 
 
 Raw Linseed Oil 
 
 ' A ' Italian Ochre Paint 
 
 Italian Ochre 
 
 Barytes ....... 
 
 Raw Linseed Oil 
 
 ' A ' Middle Brunswick Green l 
 
 Barytes and Calcium Carbonate . 
 
 Superior Middle Brunswick Green 
 
 Raw Linseed Oil 
 
 ' C ' Middle Green 
 
 Barytes 
 
 Superior Brunswick Green .... 
 
 Raw Linseed Oil ...... 
 
 Superior Yellow 
 
 Barytes and Calcium Carbonate . 
 
 Chromate of Lead ..... 
 
 Umber 
 
 Raw Linseed Oil 
 
 English Umber 
 
 English Umber 
 
 Raw Linseed Oil 
 
 ' A ' Black 
 
 Barytes and Calcium Carbonate 
 
 Carbon Black ...... 
 
 Manganese Dioxide . . . . 
 
 Boiled Linseed Oil 
 
 Burnt Turkey Umber 
 
 Burnt Turkey Umber . . 
 
 Raw Linseed Oil 
 
 ' C ' Yellow 
 
 Barytes and Calcium Carbonate 
 
 Chromate of Lead 
 
 Raw Umber 
 
 Raw Linseed Oil ...... 
 
 ' C ' Black 
 
 Barytes and Calcium Carbonate 
 
 Carbon Black 
 
 Manganese Dioxide 
 
 Raw Linseed Oil 
 
 Per Cent. 
 60-00 
 40-00 
 
 81-16 
 
 18-84 
 
 80-56 
 
 11-83 
 
 7-61 
 
 22-76 
 45-52 
 31-72 
 
 38-74 
 19-00 
 42-26 
 
 69-99 
 18-24 
 11-77 
 
 78-32 
 
 9-79 
 
 11-89 
 
 63-07 
 
 22-51 
 
 3-31 
 
 11-11 
 
 57-51 
 42-49 
 
 68-99 
 8-42 
 2-46 
 
 20-13 
 
 59-20 
 40-80 
 
 79-28 
 8-31 
 1-72 
 
 10-69 
 
 79-30 
 4-35 
 1-30 
 
 15-05 
 
 Lb. 
 
 -266 
 
 275 
 
 296 
 
 309 
 
 .322 
 
 -326 
 
 -336 
 
 -369 
 
 *392 
 
 1 A mixture of Lead Chromate and Prussian Blue. 
 
46 
 
 CHEMISTRY OF PIGMENTS. 
 
 Paint. 
 
 Composition. 
 
 Rust from 
 1,500 
 Sq. Yards. 
 
 Middle Purple Brown 
 
 Per Cent. 
 
 Lb. 
 
 Barytes and Calcium Carbonate 
 
 65-52 
 
 ) 
 
 Oxide of Iron 
 
 27-03 
 
 1-398 
 
 Raw Linseed Oil 
 
 10-45 
 
 ) 
 
 ' A ' Ultramarine 
 
 
 
 Ultramarine 
 
 52-63 
 
 
 Barytes 
 
 26-32 
 
 425 
 
 Raw Linseed Oil 
 
 21-05 
 
 
 Burnt Sienna 
 
 
 
 Burnt Sienna 
 
 56-00 
 
 (.4.QQ 
 
 Raw Linseed Oil 
 
 64-00 
 
 r ^rOi7 
 
 Chinese Blue 
 
 
 
 Chinese Blue 
 
 48-27 
 
 ( AA-I 
 
 Raw Linseed Oil 
 
 51-73 
 
 - 441 
 
 Boiled Linseed Oil 
 
 
 / 
 
 Boiled Linseed Oil 
 
 
 
 500 
 
 Raw Turkey Umber 
 
 
 
 Raw Turkey Umber 
 Raw Linseed Oil 
 
 51-85 
 48-15 
 
 1 510 
 
 " I think that these three series of experiments, carried out 
 under such widely different conditions, and yet yielding such 
 similar results, go to show that red or orange lead form the 
 best basis for paint pigments amongst those which are in 
 every-day use for iron work, especially in situations where 
 excessive moisture is likely to be met with. 
 
 ''At the same time it must be said that, owing to the 
 vigorous chemical action set up in such paints, it is necessary 
 that the mixing process shall immediately precede the actual 
 painting. 
 
 " Red-lead paints have not quite the same degree of firm- 
 ness as a good oxide of iron paint, which will withstand a great 
 amount of rough usage when once it is perfectly dry, and 
 this tough and elastic coating yielded by genuine oxide of 
 iron paints has much to do with their undoubted popularity 
 for outdoor work ; the colour also is far more pleasing to the 
 eye than the crude, harsh tone possessed by red lead paints. 
 
 " Zinc oxide appears to have a very high protective value 
 as a pigment for use on iron, and stands better in this respect 
 
 
THE APPLICATION OF PIGMENTS. 47 
 
 than white lead ; also, zinc-white paint, when pure, has a 
 good body and covering power, and has the great advantage 
 of being non-poisonous to the workers. 
 
 "In a somewhat similar, but less severe, series of trials 
 made in 1897, I got a better result with graphite paint than 
 in these experiments. A pure graphite paint was used and 
 the result showed more corrosion than with pure zinc-oxide 
 paint, but less corrosion than with pure oxide of iron paint ; 
 red-lead paints in these experiments also gave the best results, 
 and still show no rust after two years' immersion. 
 
 "It is interesting to note the effect produced by the inert 
 pigments, barytes and Paris white. I believe the best 
 treatment for iron structures is to give them one or two 
 coats of genuine red-lead paint freshly ground ; and I would 
 follow this up with at least two coats of either a genuine 
 oxide of iron paint, or, in some cases, of zinc-white paint 
 made from pure zinc oxide and genuine linseed oil." 
 
 These experiments of Mr. Smith's are extremely interesting 
 and, as he says, certainly show very definitely the marked 
 superiority of red lead and zinc white over most other pig- 
 ments. White lead l occupies a high place on the list, as do 
 most of the iron-oxide pigments. The amount of difference 
 of action in the case of barytes and raw linseed oil and boiled 
 linseed oil alone is remarkable ; it is not easy to see why so 
 inert a substance as barium sulphate should have any other 
 than the merest mechanical action on oil ; the difference is 
 probably due to either the mechanical formation of a cement 
 more impervious than a layer of oxidised oil alone, or 
 to raw oil drying more slowly than boiled oil, forming 
 a tougher coating less liable to crack and allow erosion to 
 commence. The differences between Prussian blue alone 
 and diluted with barytes, and Chinese blue alone and 
 
 1 Mr. Smith in a private communication to one of us describes the white 
 lead as made by the Dutch process. 
 
48 CHEMISTRY OF PIGMENTS. 
 
 similarly diluted, in each case with raw oil, suggest that the 
 Chinese blue was not washed very free from alkaline salts 
 in its preparation, or possibly contained traces of free acid 
 or bleaching powder, which is sometimes used for oxidation. 
 Some other differences, as those between raw and burnt 
 sienna, are very remarkable, and in our opinion, having 
 regard to the fact that "the duplicates agreed very closely 
 with each other in almost all cases," the question of soluble 
 impurity will be found to have a very important bearing on 
 the preservative powers of pigments. 
 
 It is worthy of note that the materials which stand highest 
 on Mr. Smith's list, the red and orange lead, zinc white and 
 white lead, are all likely to have a considerable chemical 
 action on oil, red lead having probably both an oxidising 
 and hydrolysing action, and zinc white and white lead both 
 being likely substances to saponify linseed oil, in each case 
 of course only to a very slight extent. The inferiority of 
 pure carbonate of lead to ordinary white lead (a mixture of 
 carbonate and hydroxide) is well known. The following 
 remarks of Prof. Church illustrate this : "I tried com- 
 parative experiments with . . . pure lead carbonate and the 
 Dutch-made lead hydrated carbonate, or ordinary flake white. 
 The two lead pigments were washed thoroughly with dis- 
 tilled water, and dried before being ground in linseed oil. 
 The oil-paints thus prepared were spread in duplicate series 
 upon glass, paper and primed canvas. One set was kept in 
 a dark box ; the other was exposed to strong light. So 
 decided was the superiority of the ordinary flake white over 
 the pure carbonate, when both series of specimens were 
 examined after the lapse of various intervals of time, that 
 I was reluctantly compelled to abandon my recommendation 
 of the latter. Ease in working, solidity of body and rapidity 
 of drying were not the only points of superiority, for the films 
 of paint, after having been kept a year, showed differences. 
 
THE APPLICATION OF PIGMENTS. 
 
 49 
 
 in hardness and in smoothness of surface, which were all 
 in favour of the hydrated carbonate. No discoloration was 
 observed in the specimens "exposed to light, except in the 
 case of the pair upon paper ; the absorbent ground had 
 withdrawn some of the protecting oil, and both specimens 
 had equally darkened. In darkness all the specimens had 
 become of a somewhat greyish yellow, the discoloration 
 being about equal in all the pairs, the pair spread on paper 
 having, as in the previous case, become darker than the 
 others." l 
 
 II, METHODS OF APPLICATION OF PIGMENTS, 
 
 In the following table the authors have included most of 
 the better-known methods of applying colours to recipient 
 surfaces, and have indicated for each method the medium 
 used and the surfaces on which it can be suitably employed, 
 together with the purposes, as distinguished in the preceding 
 part of this chapter, for which the method is used, namely: 
 
 (a) Artistic (depictive) uses. 
 
 (b) Decorative uses. 
 
 (c) Protective uses. 
 
 Method. 
 
 Medium. 
 
 Purposes 
 Used for. 
 
 Surface on which Used. 
 
 Crayon, Pastel . 
 
 Chalk and Gum 
 
 a 
 
 Prepared (usually backed) 
 
 Water Colour . 
 
 used solid 
 Water with Gum, 
 
 a 
 
 Paper 
 Pure sized Paper 
 
 
 etc., and Gly- 
 
 
 
 
 cerine 
 
 
 
 Tempera . . . 
 
 Albuminous or 
 
 a, b 
 
 Prepared Wood, Canvas, 
 
 
 Gelatinous 
 
 
 Plaster 
 
 
 Matter 
 
 
 
 Fresco (and Secco) 
 
 Lime Water, Ba- 
 
 a,b 
 
 Prepared Plaster 
 
 
 ryta Water, 
 Water Glass 
 
 
 
 Encaustic . . . 
 
 Wax 
 
 a 
 
 Wood 
 
 CJiemistry of Paints and Painting, p. 271. 
 
50 
 
 CHEMISTRY OF PIGMENTS. 
 
 Method. 
 
 Medium. 
 
 Purposes 
 Used for. 
 
 Surface on which Used, 
 
 Oil (or varnish) . 
 
 A drying oil, 
 
 a, b, c 
 
 (a) Prepared Wood, Can- 
 
 
 thinned 
 
 
 vas, Copper ; (b and c) 
 
 Keramic 
 
 
 
 almost all Surfaces 
 
 1. Pastes . . 
 
 Clay 
 
 b 
 
 
 
 2. Glazes . . 
 
 A Glass 
 
 b,c 
 
 Porcelain or Earthenware 
 
 3. Majolica.Del- 
 
 An Opaque Tin 
 
 b,c 
 
 Earthenware (an Opaque 
 
 la Robia . 
 
 Enamel 
 
 
 Enamel is also used on' 
 
 4. Under Glaze 
 5. On Glaze . 
 
 ] Ground Coloured 
 1 Glass Paste ap- 
 j plied with Re- 
 | sinous Medium 
 
 ); 
 
 Glass) 
 Porcelain, Earthenware 
 
 Enamel .... 
 
 An easily fusible 
 
 a, b, c 
 
 Metal (usually Copper for 
 
 
 Glass or Frit 
 
 
 a) 
 
 Stained Glass 
 
 Glass 
 
 b ' 
 
 
 Painted Glass . 
 
 An Organic Me- 
 
 b 
 
 Glass 
 
 
 dium on Glass 
 
 
 
 Mosaic .... 
 
 
 
 b 
 
 Cement 
 
 Pastels and Crayons, 
 
 Crayons proper, as used for drawing, e.g., the first sketch 
 or outline of an oil painting, or for crayon studies, are usually 
 of three colours black, white and red. The black and red 
 are used for outline and shading, the white to heighten lights. 
 
 The gradation of shade in crayon drawings may be made 
 either in the same way as in pencil drawing, by hatching, or 
 by rubbing the hatching lines together into uniform, or 
 graduated tints, resembling washes, either by the finger tips 
 or by the use of a "stump" a pointed roll of paper or 
 leather. 
 
 Fine charcoal, such as is prepared by burning vine twigs, 
 is frequently used as a black pigment for such drawings. 
 
 Coloured chalks, crayons or pastels are used in a similar 
 manner, so far as the production of graduated or uniform 
 tints is concerned, to the black and red chalks. Very 
 beautiful soft effects may be produced by the use of soft 
 pastels, and by employing a large number of these little 
 crayons a great variety of tints are available, so that a fairly 
 correct colour effect may be obtained. 
 
THE APPLICATION OF PIGMENTS. 51 
 
 Pastels are made of colouring materials diluted with a 
 white base, which not only gives the required set of tints by 
 the use of varying amounts, but brings the pigment into a 
 suitably friable condition. 
 
 Each colour is made in a series of graduated tints, usually 
 as many as six, from the fullest workable tint to quite a pale 
 shade. When fine strokes with a tint not to be found in the 
 set of colours are required, fragments of two or more pastels 
 may be crushed under a " muller " on a glass plate, moistened, 
 and then rolled up into small pastels between the fingers, 
 and allowed to dry in the sun or before the fire. For such 
 mixed tints on larger surfaces streaks of two or more pastels 
 may be rubbed together by the finger in a homogeneous or 
 graduated whole like a " wash "in water colour or a 
 " softened " part of an oil painting. 
 
 One point about pastels to be remembered is that they 
 are fragile ; it is very easy to break them. The angles thus 
 produced are extremely useful for giving fine touches, and 
 the fragments can be made use of for rubbing in large sur- 
 faces of colour. In addition to these accidental sharp edges, 
 the usual methods of cutting and grinding on glass paper may 
 be adopted. 
 
 It is not possible by the use of such a method the appli- 
 cation of a diluted pigment to a white or only slightly tinted 
 surface in isolated particles, not bound together by any dense 
 medium causing much internal reflection to obtain the rich 
 full colours of an oil painting. Such drawings or paintings 
 must, from the enormous amount of white light reflected, 
 always have a weak unsaturated appearance, but for por- 
 traiture, especially female heads, certain kinds of landscape 
 and flower painting, pastel drawing may be used with con- 
 siderable success, 
 
 The following soft pastel crayons of French manufacture 
 have been qualitatively examined by us : 
 
- 52 CHEMISTRY OF PIGMENTS. 
 
 
 || 
 
 | 
 
 Composition. 
 
 Colour. 
 
 SI 
 
 ftj 
 
 Pigment. 
 
 White Base. 
 
 
 
 
 
 
 
 1 
 
 3-7 
 
 
 
 A Rosy Scarlet . 
 
 2 
 3 
 4 
 5 
 
 3-4 
 3-0 
 2.2 
 2-2 
 
 Eosin and Red 
 Lead 
 
 Calcium Carbonate 
 
 Pale Brick Red . j 
 
 1 
 
 2 
 
 3-9 
 2-6 
 
 A Ferric Oxide pig- 
 ment with Red 
 Lead 
 
 Calcium Carbonate 
 
 
 1 
 
 2-1 
 
 Do. do. do. 
 
 
 
 2 
 3 
 
 2-1 
 2-5 
 
 . The amount of Red 
 Lead greater in 
 
 
 
 
 4 
 
 2-8 
 
 the lighter tints 
 
 
 / 
 
 1 
 
 1-2 
 
 
 
 Black to Whitish) 
 Grey . . .) 
 
 2 
 3 
 
 1-6 
 
 1-9 
 
 f Bone or Ivory Black 
 
 Calcium Carbonate 
 
 I 
 
 4 
 
 2-0 
 
 | 
 
 
 
 1 
 
 1-7 
 
 
 
 
 2 
 
 1-9 
 
 
 
 Blue .... 
 
 3 
 
 2-0 
 
 " Prussian Blue 
 
 Calcium Carbonate 
 
 
 4 
 
 2-0 
 
 
 
 
 5 
 
 2-0 
 
 1 
 
 
 
 1 
 
 1-05 
 
 I 
 
 
 Purple 
 
 2 
 3 
 
 1-5 
 1-9 
 
 ICochineal and Ul- 
 | tramarine 
 
 Calcium Carbonate 
 
 
 4 
 
 2-0 
 
 J 
 
 
 r 
 
 1 
 
 2-7 
 
 (" 
 
 
 Yellow . . J 
 
 2 
 3 
 4 
 
 to to to 
 
 M tO 05 
 
 Lead Chromate 
 
 Calcium Carbonate 
 
 \ 
 
 1 
 
 3-6 
 
 ) 
 
 
 
 2 
 
 3-5 
 
 Red Lead 
 
 Calcium Carbonate 
 
 
 3 
 
 2-9 
 
 
 
 
 1 
 2 
 
 3-2 
 3-3 
 
 (Brunswick Green 
 
 
 Green 
 
 3 
 
 2-8 
 
 (Prussian Blue & 
 
 Calcium Carbonate 
 
 
 4 
 
 2-3 
 
 Chrome Yellow) 
 
 
 
 5 
 
 2-1 
 
 
 
 
 1 
 
 1-5 
 
 'V 
 
 
 
 2 
 3 
 
 1-7 
 1-8 
 
 I A Carmine Lake 
 
 (1 Apparently undiluted 
 Calcium Carbonate 
 
 
 4 
 
 1-9 
 
 J 
 
 
 Pale Reddish Brown J 
 
 1 
 2 
 3 
 
 2-4 
 2-1 
 2-2 
 
 \A Peroxide of Lead 
 j and Oxide of Iron 
 
 Calcium Carbonate 
 
 White 
 
 
 
 2-9 
 
 White Lead and Ca 
 
 Icium Carbonate 
 
 
 
 
 
 
 Brown Yellow (Ochre) J 
 
 ') 1 
 2 
 3 
 4 
 
 \ 
 
 2-8 
 3-5 
 2-5 
 2-2 
 
 V Ferric Hydroxide 
 
 j. White Lead 
 /Calcium Carbonate 
 
 
THE APPLICATION OF PIGMENTS. 53 
 
 The use of eosin in colours intended for permanent work 
 is certainly not to be recommended. The other colours, with 
 the exception of the violet and crimson, might reasonably be 
 expected to be highly permanent except, in some cases, in a 
 sulphuretted hydrogen atmosphere. 
 
 The determinations of the "apparent specific gravity" 
 given in the above table are useful as indicating the relative 
 proportions of colour and base, and were found very useful 
 in directing the qualitative examination. 1 
 
 The fullest crimson appeared to be an undiluted lake. 
 
 A quantitative analysis was made of the palest tint of 
 blue, which had the following composition : 
 
 Prussian blue ........ 10'7 
 
 Calcium carbonate 78'0 
 
 Alumina 2-0 
 
 Other matters soluble in acid 0*6 
 
 Insoluble siliceous matter 8'7 
 
 100-0 
 
 As the qualitative examination had indicated, the base 
 was almost entirely carbonate of lime probably a mixture 
 of prepared chalk and china clay. 
 
 Water Colour. 
 
 This, in its generally recognised form, purely modern 
 method of painting, in which our countrymen have so greatly 
 excelled, is essentially a staining process. The colours, ground 
 in water, with a suitable gummy medium are applied to the 
 surface, a pure sized paper, in thin washes, the high lights 
 being left uncovered, or only thinly washed with the appro- 
 priate colour ; the darker parts are treated with denser washes, 
 or two or more washes are applied until the desired colour 
 is obtained. Very beautiful atmospheric effects are produced 
 by this means, and good water-colour paintings have a light 
 
 1 The apparent specific gravity of chalk (CaC0 3 ) as used for blackboard 
 drawing is 1'30. 
 
54 CHEMISTRY OF PIGMENTS. 
 
 effect, which is not usually seen in oil paintings, owing to 
 the reflected light containing a very much larger proportion 
 of white light, as has been stated in the previous chapter. 
 The rough surface paper often used contributes greatly to 
 this result. It is not always that this peculiarity of water 
 colour contributes to artistic effect. For interiors and most 
 pictures where richness of colour is desirable oil is a more 
 suitable medium. Nevertheless, a comparison of the tinted 
 drawings of the early water colourists, pleasing as they are, 
 with the more mature efforts of recognised masters, will 
 show what can be done by this method in the way of colour 
 imitation (not mere suggestion). There is one thing about 
 water colour : it is impossible to reduce or paint out work 
 which is too heavy, or requires other alteration. A method 
 of obtaining small streaks of high lights, which seems to 
 be regarded by masters as legitimate, is to scratch the already 
 tinted surface of the paper with a knife, and so expose a 
 fresh white surface. 
 
 Many modern works painted with colour ground in an 
 aqueous medium are rather paintings in body colour than 
 pure water colour. Of this type we may instance an imitation 
 of one of the Chantry pictures (which may not be copied 
 in oils), which was exposed for sale in London some few 
 years ago. This, it is fair to state, was in avowed imitation 
 of oils, but many works called water colours are painted 
 more or less in this rather unsuitable manner a sort of 
 revival of tempera. 
 
 A report on the permanence of water colours by Dr. W. 
 J. Eussell and Captain Abney has already been alluded to at 
 some length. Paintings by this method must of necessity be 
 more susceptible to atmospheric influences than works in 
 which the colour is imbedded in some protective material (as 
 varnish) which, itself inert, more or less effectually precludes 
 the access of moisture or air. 
 
THE APPLICATION OF PIGMENTS. 55 
 
 Tempera Painting, 
 
 This ancient method of painting appears to have been 
 practised from very early times, but is not much used now for 
 artistic purposes. That its capabilities were great is shown 
 by the beautiful specimens we still possess of pictures painted 
 by this method, which have not only retained all their beauty 
 of colour, but in which effect has been obtained in a masterly 
 manner. For artistic purposes, however, it is not difficult 
 to see why it has been supplanted by the more convenient 
 methods of oil and water-colour painting. Tempera, or dis- 
 temper painting, is, to describe it briefly, water-colour painting 
 in body colour. The surface employed was usually wood, 
 sometimes linen stretched on wood, occasionally plaster. In 
 the case of wood (or linen) the suitably smoothed surface was 
 primed with whitening applied in a suitable aqueous medium 
 (this prepared surface was called gesso) and the colours to be 
 used in the picture applied in a similar medium to this surface 
 when it had dried. The media of the early Byzantine school 
 were very unsatisfactory in that they were far from colour- 
 less ; honey, glue and such sticky substances were used by 
 them, but Giotto, one of the early Florentines before alluded 
 to in this chapter, appears to have introduced a less coloured 
 medium, probably white of egg or white and yolk. With 
 this more satisfactory medium, or with pale sizes and fish 
 glues, tints could be prepared of much greater purity and 
 more approximating to those obtained by the painters of 
 classical antiquity. Considerable care must have been re- 
 quired in this method of painting to avoid, in applying colour 
 to parts already partly painted, any stirring up of the former 
 tint ; it would seem that the application of washes to modify 
 tint, as in water colour, or of glazing or painting over a sur- 
 face with thin layers of transparent colour, as in oil painting, 
 must have been extremely difficult with a method in which 
 
56 CHEMISTEY OF PIGMENTS. 
 
 the whole picture and the gesso could be washed off the 
 surface. Be this as it may, the process in the hands of 
 masters has proved most satisfactory, if it may be judged 
 in the usual way, by its results ; in fact, from some attempts 
 made by ourselves we think the manipulative weaknesses of 
 the method are more apparent than real. 
 
 The finished tempera painting being a very delicate and, 
 for reasons discussed in the previous chapter, a somewhat 
 weak and chalky-looking production, was treated in many 
 cases with a coat of linseed oil or other varnish, which not only 
 acted as a preservative, but imparted considerable brilliance 
 to the picture. 
 
 From the standpoint of permanency, the principal objec- 
 tions to this method of working are : (1) the putrescible nature 
 of the medium; (2) its hygroscopic nature, rendering the 
 surface liable to considerable expansion and contraction in 
 a moist atmosphere, and, therefore, to cracking and scaling ; 
 and (3) the chemical nature of the medium, which, containing 
 sulphur, is likely on the least putrefaction to evolve sulphu- 
 retted hydrogen, and cause blackening of some mineral 
 colours. All these objections are much reduced when varnish 
 has been applied to the painting, as thus it is rendered less 
 hygroscopic, and, consequently, less liable to any sort of 
 chemical change, and is also rendered much more tough and 
 tenacious. In the dry pure air of Italy tempera paintings 
 have preserved their beauty for centuries, and it is to be 
 hoped that, under glass in a gallery of fairly uniform tem- 
 perature, those specimens which are in our public collections 
 may, as things of beauty, be joys for ever ! 
 
 Fresco (Italian, Fresh}. 
 
 This favourite style of mural painting (for which it is 
 particularly well adapted) is also a most ancient one, having 
 been used by the Egyptians, Greeks and Komans. Anton 
 
THE APPLICATION OF PIGMENTS. 57 
 
 Mengs, an artist and writer of the eighteenth century, 
 expressed his conviction, after having passed the winter of 
 1772-73 at Naples, that the jaural paintings at Pompeii and 
 Herculaneum were executed in the method " biion fresco ". 
 More recent scientific investigations confirm the correctness of 
 this decision. These paintings, some 1,800 years old, having 
 survived many vicissitudes, present abundant testimony to 
 the permanence and suitability of this method for mural 
 painting. 
 
 Euon fresco is so called in distinction from secco, a less 
 .satisfactory method of working ; in the former method the 
 painting is performed on the wet ground or intonaco, as it is 
 called, in the latter the receptive surface is allowed to dry, 
 hence the term secco. 
 
 The wall to be adorned in fresco should be dry and well 
 .built, and as far as may be free from vibration. It is first 
 well damped with water, preferably free from any saline 
 matter other than lime salts, and then the coarser plaster 
 applied. This should consist of clean, sharp sand, mixed 
 with pure lime l paste prepared by slaking lime from chalk, 
 
 1 The following analyses of some Italian, Bavarian and English limestones 
 which furnish a suitable lime for buon fresco may be of interest. They were 
 -undertaken by Mr. E. Phillips for Sir C. Eastlake. 
 
 Travertine. Genoa. 
 
 Carbonate of lime . . 99-4 Carbonate of lime . . 63 
 
 Alumina with a trace Carbonate of magnesia . 36 
 
 of oxide of iron . . -6 Earthy matter, oxide \ 
 
 of iron j- 1 
 
 Bituminous matter J 
 
 100-0 100 
 
 Brought down from Bavarian Alps Durdham Down, Bristol. 
 
 by the Isar. 
 
 Carbonate of lime . . 80 Carbonate of lime . . 99'5 
 
 Carbonate of magnesia . 20 Bituminous matter . -3 
 
 Earthy matter . . "2 
 
 1(J(J 
 
 100-0 
 
 A limestone containing calcium sulphate should not be used for preparing 
 lime for fresco. 
 
58 CHEMISTEY OF PIGMENTS. 
 
 good limestone or marble, with so much water as will form a. 
 creamy paste, and then allowing this to stand for, say, two 
 months, loosely covered, in order that it may absorb carbon 
 dioxide from the air and so become partially carbonated. 
 According to Sir H. Davy's researches (confirming a statement 
 of Vitruvius) on the paintings at Herculaneum and Pompeii, 
 the ground used by the ancients was crushed marble cemented 
 by lime paste. Pumice, asbestos fibre, infusorial earth, or 
 any permanent binding substance, may be similarly used to 
 impart firmness to the lime plaster. Each coat of this is 
 allowed to set before another is applied, and is moistened in 
 order to prepare it for the next coat. The final surface, or 
 intonaco? is laid on by the plasterer day by day, only so much 
 being applied as can be painted over at a sitting. This final 
 coat is, of course, laid very flat, and when it is set the outline 
 of the design is marked off from a cartoon. The colours 
 mixed with lime water or the lime paste are then applied ; if 
 they dry in too quickly that part of the surface should be 
 sprayed with lime water, which will assist in binding them 
 to the surface. Most careful precautions are necessary in 
 fresco painting, both as to manipulation and the choice of 
 colours ; when these are duly observed the work is extremely 
 permanent. 
 
 Owing to the alkaline nature of the medium the palette 
 of the fresco painter is limited, and it is partly to this fact 
 only the most inert colours being admissible that fresco 
 paintings are so enduring. The following list of suitable 
 colours may be of interest : 
 
 1 The Italians usually applied three coats : the rizzaffato, or rough coat ;, 
 the arriciato, or sand coat ; and the intonaco, or fine surface. 
 
THE APPLICATION OF PIGMENTS. 
 
 59 
 
 Bed. 
 
 Yellow. 
 
 Green. 
 
 Blue. 
 
 " All kinds of 
 
 All kinds of Ochres 
 
 Terra Verte or 
 
 Ultramarine, real 
 
 Burnt Ochres " 
 
 (H.,C.) 
 
 Verona Green 
 
 (H.) ; factitious 
 
 (H.) 
 
 Raw Sienna (H.) 
 
 (H.) 
 
 (H.) 
 
 Burnt Sienna (H.) 
 Oxides of Iron (H.) 
 
 Cadmium Yellow 
 (C.) 
 
 Cobalt Green (H.) 
 Chrome Green 
 
 Cobalt (H.) 
 Some Ultrama- 
 
 Lake -coloured 
 
 Cobalt Yellow (C.) 
 
 (H.,C.) 
 
 rine & Cobalts 
 
 Burnt Vitriol 
 
 
 Guignet's Green 
 
 (C.) 
 
 (H.) 
 
 
 (C.) 
 
 
 " All the Iron 
 
 
 
 
 Beds" (C.) 
 
 
 
 
 Some varieties of 
 
 
 
 
 Vermilion (C.) 
 
 
 
 
 (H.) Hess of Munich, an eminent fresco painter of the early nineteenth 
 century. 
 
 (C.) Prof. Church. 
 
 Any colour which is altered by caustic alkalies, as Prussian 
 blue, gamboge or chrome yellow, is unsuitable. 
 
 The chemistry of the process is tolerably obvious. The 
 picture is painted on and becomes fixed in a ground of mixed 
 lime and carbonate of lime, which, at the same time drying 
 and absorbing carbon dioxide from the air, though mostly 
 probably still containing free lime, becomes converted on the 
 surface into a hard layer of calcium carbonate. This, being 
 only to a very slight degree hygroscopic, and absolutely 
 unacted on by any of the constituents of the air (carbon 
 dioxide and water a solution of carbonic acid would 
 slowly dissolve it, but this would only occur in the open air 
 or in very badly constructed rooms), not only remains intact, 
 but is, by suitable means, easily cleaned when exposure to a 
 smoky or dust-laden atmosphere has impaired its pristine 
 freshness. 
 
 Owing to the nature of the surface and the limited palette 
 at his disposal, the works of the fresco painter have usually 
 a somewhat sombre effect, this in London being usually 
 heightened in a short time by a surface film of carbona- 
 ceous matter. Still, for important historical works and 
 
60 CHEMISTRY OF PIGMENTS. 
 
 mural decoration generally buon fresco is a most suitable 
 process. 
 
 Yasari (Lives of the Painters} states of buon fresco that it is 
 " truly the most virile, most sure, most resolute and durable 
 of all modes ". 
 
 Buon fresco, from its durable nature, possesses the advan- 
 tage of being easily and safely cleaned. Bread, water and a 
 sponge, wine (white?), and, it is said, vinegar 1 (!) may be 
 used. Frescoes on unsuitable walls can also be transferred by 
 glueing cloth to them and stripping off cloth and colour and 
 re-transferring to another cloth. This apparently very heroic 
 method has been used with considerable success ; some 
 transferred frescoes may be seen in our National Gallery. 
 
 Secco, or painting on an already dried but re-damped 
 plaster ground, in colours mixed with lime water, is, as the 
 picture is only 011 and not in the receptive surface, less 
 suitable for serious artistic work ; it was, however, to some 
 extent used by the old masters. 
 
 Encaustic Painting, 
 
 This very ancient method of painting is chiefly of interest 
 on account of its antiquity. From the very few details and 
 very few specimens we possess of such work it would appear 
 that colours mixed with wax were applied hot to the receptive 
 surface probably primed with a mixture of wax and white 
 on which the design had been traced with a point, and the 
 colour masses were softened by local applications of heated 
 tools. The method, though apparently eminently unsuitable 
 for very artistic work, certainly had its advantages so far as 
 permanence is concerned, as a comparison of the encaustic 
 and the tempera painting brought by Mr. Flinders Petrie 
 from Egypt will show. 
 
 1 It seems obvious that any acid liquid is undesirable. 
 
THE APPLICATION OF PIGMENTS. 61 
 
 Oil-Colour Painting, 
 
 Though for decorative purposes colours ground in " drying" 
 oils have been used from relatively early times, the' adoption 
 of an oil or varnish medium as a colour vehicle in artistic 
 painting is usually attributed to the brothers Van Eyck, of 
 whom it appears that the elder, Hubert, was born in 1366 
 and John or Jan in 1390 ; though the latter is more commonly 
 credited with the discovery, it seems that Hubert was also a 
 master of this development of the art, as a great part of their 
 masterpiece (in oils), the "Adoration of the Lamb" at St. 
 Bavon's, Ghent, is known to be painted by him. Be this as 
 it may, it is certain that to these great brothers artists are 
 greatly indebted, at any rate, for very great improvements in 
 this method of painting, improvements which fitted it for 
 the finest artistic work, as an examination of the picture 
 " Jean Arnolfini and His Wife " by Jan will show. Of the 
 Florentine painters Antonio Pollaiuolo was one of the first to 
 adopt this medium. An example of this painter's work in 
 oils is to be found in the National Gallery, " The Martyrdom 
 of St. Sebastian " (No. 292). 
 
 The works of these early painters in oils, especially those 
 of Van Eyck, were executed, it is evident, in a manner some- 
 what different to that practised by many modern artists. 
 The three pictures by Van Eyck in the National Gallery 
 (Nos. 186, 290 and 292) are remarkable for the flatness of 
 the surface ; they are all on panels, and though in the cele- 
 brated "Jean Arnolfini" (No. 186) some very clever effects, 
 e.g., the mirror, the chandelier and the crystal rosary, are 
 produced, these are entirely due to colour, not at all to 
 raised surface (of the put-on- with-a-palette-knife kind). On 
 looking at the pictures very obliquely the differences in 
 level of the outlines of objects are perceptible to a slight 
 extent only. The surfaces in each case are covered with 
 
62 CHEMISTRY OF PIGMENTS. 
 
 minute cracks, especially where blackish brown (bitumen?) 
 and green (Prof. Church suggests verdigris) have been 
 used ; there is also some evidence of a repair on the mirror 
 in No. 186, but this looks more like the results of an acci- 
 dent than the effects of time. These pictures of Van 
 Eyck were probably painted with a slower drying medium 
 than oil and turpentine ; perhaps a transparent balsam or 
 gum resin entered largely into its composition. The exquisite 
 finish is not, as Prof. Church well says, compatible with hurry. 
 These pictures, No. 186 to a less extent than the others, 
 have a rather highly varnished though not exactly shiny 
 appearance, due probably to the peculiarity of the medium. 
 The painting by Pollaiuoli is very large (9' 6" h. x 6' 7|" w.), 
 is considered to be his most important and characteristic 
 work and is painted in a much bolder style than Van Eyck's 
 careful work ; the colour surfaces are much more denned 
 and the differences in level more noticeable ; still there is no 
 evidence of any attempt to obtain effect by loading parts of 
 the surface with clots of colour ; the differences in level are 
 merely due to the use of different colours with different 
 proportions of medium, and perhaps painted over more in 
 some cases than others and consequently drying down 
 differently. The blackish parts of this picture have become 
 very blotchy and the whole picture is covered with minute 
 cracks and some long ones, which latter have either not 
 parted or have been satisfactorily repaired. The picture at 
 close quarters presents a rather "sticky" appearance, due 
 either to a varnishy medium or a liberal use of varnish after 
 finishing : it is well preserved and still a fine bright picture. 
 Oil paintings are usually executed on prepared wooden 
 panels or stretched canvas, in the case of less important 
 pictures on prepared millboard, sometimes, as in the case of 
 mural paintings after this method, on a prepared secco or 
 dry plaster. Wood appears to have been the favourite surface 
 
THE APPLICATION OF PIGMENTS. 63 
 
 for small works in early times, and wood was particularly 
 suitable to the delicate work of so many early masters. 
 Panels should be of well-seasoned wood which has been cut 
 up some time before it is finally planed and glass-papered, so 
 that both back and front surface may be equally dry and 
 seasoned. It is recommended by some ancient authorities 
 that the wood should now be boiled. Prof. Church sug- 
 gests soaking in water raised to 50 C., and then steaming; 
 by this means soluble matters are extracted and albuminoids 
 precipitated. When dry he recommends a wash on both sides 
 of corrosive sublimate (we suppose very dilute say 1-1,000) 
 in methylated spirit. After this treatment, which renders it 
 unfit for the growth of any organisms, the panel is dried in 
 a warm-air chamber for some time, re-glass-papered and 
 primed with white lead, copal varnish, and boiled oil (pre- 
 pared in manganese salts, not lead). When this coat is quite 
 dry another coat in the transverse direction is applied. Then 
 coats of oil and white lead alone, and, finally, zinc white and 
 drying oil. Each coat is allowed to dry hard, and is rubbed 
 down with pumice powder before another is applied. Both 
 sides should be treated alike to prevent warping owing to 
 exposure of the back, but of course the rubbing with pumice 
 stone is not necessary for the back. W r hen compound panels 
 were used by the old painters linen cloth, or less frequently 
 parchment, vellum or tinfoil, was often stretched over them 
 to receive the colour, and also, of course, the gesso or paint- 
 ing ground. Probably the use of a linen surface in this 
 manner led to the now almost universal use of canvas 
 stretched on a wooden wedged frame for oil painting. The 
 following list of surfaces used for oil painting is compiled 
 from the catalogue of the National Gallery : 
 
64 CHEMISTEY OF PIGMENTS. 
 
 Panels. Metal. Textile. 
 
 Deal. Copper (in many cases). Canvas. 
 
 Oak. Silver (1). Linen. 
 
 Poplar. Silk. 
 
 Beech. Paper on canvas. 
 
 Chestnut. 
 
 The oil usually used for grinding colours in is pure linseed 
 oil ; in the case of badly drying colours, " boiled " or other 
 quick-drying linseed oil is used. The following oils are also 
 used to some extent in artistic work, though for decorative 
 and protective .purposes the cheaper linseed oil is always 
 used. 
 
 Callemantia oil. 
 
 Hemp-seed oil. 
 
 Walnut oil (this is used by artists as less liable to cracking than 
 
 linseed). 
 Poppy-seed oil (this is used by artists as less liable to cracking than 
 
 linseed). 
 Niger-seed oil. 
 
 Fir-seed oil (used for varnishes). 
 Japanese wood oil (used for varnishes). 
 
 Colours ground in oil are, without dilution of some kind, 
 too stiff, and sometimes too deep coloured for use alone. It 
 is, therefore, common to dilute the pigment with a suitable 
 white " base " to the required shade, and to reduce to a 
 workable consistency with some volatile liquid miscible with 
 oil. This liquid is usually " oil " or " spirit " of turpentine, a 
 tolerably pure mixture of terpenes, with only a small propor- 
 tion of oxidised product (resin), but of late years various- 
 turpentine substitutes, mostly of the nature of petroleum 
 spirit, have to some extent come "into use. It is also cus- 
 tomary with both artists and decorators to use to a greater or 
 less extent materials known as " driers," or " megilp," which, 
 containing compounds of lead or manganese as their active 
 constituents, facilitate the oxidation and " drying " of the 
 oily vehicle. 
 
THE APPLICATION OF PIGMENTS. 65 
 
 A surface having been covered with a coat of paint pre- 
 pared as above, two actions at once begin. The turpentine 
 or other volatile thinning material evaporates more or less 
 rapidly, and while this is going on the oil, especially if drying 
 materials have been added, or the colour itself or the white 
 diluting material, has high drying properties, becomes more 
 viscous, and a film of hardened oxidised oil forms with the 
 colour imbedded in it. This film, unless too much driers 
 has been used, is tough and durable, and in the space of 
 twenty-four hours or more is sufficiently established for a 
 second painting. This convenient property of oil colour is 
 of the greatest value to the artist and to the house painter ; 
 it enables the former to obtain very fine effects by the 
 superimposition of thin " glazes " of transparent colour, by 
 " stippling " and various other artistic devices ; it also enables 
 him to make alterations, to heighten lights and to run 
 different colours close to one another in one painting in a 
 way which is impossible to the water colourist ; the house 
 painter on his priming or first coat of good tough full-bodied 
 paint can apply further protective and final decorative coats, 
 the latter in colours which could not themselves be used as 
 priming on account of their poor covering power and opacity. 
 
 In mixing paint care should be taken that too much 
 thinning material is not used on the one hand, or, on the 
 other, an excess of oil. In the former case, the solid particles 
 are likely not to remain properly in suspension in the mass 
 while it is being applied, and the result is that, though flat, 
 the coat is of uneven tint and also dries very dull and 
 chalky-looking owing to insufficiency of oil, while an excess 
 of oil renders the paint difficult to work, slow drying, or, 
 rather, forming only a surface skin with " tacky " paint 
 underneath, and altogether unsuitable either for painting 
 over or for protective purposes. The aim should be to use 
 
 pigment, oil and turps in such proportions that a smooth 
 
 5 
 
66 CHEMISTRY OF PIGMENTS. 
 
 layer of pigment, perfectly imbedded in a thoroughly dried 
 and resinified layer of oil varnish, is the result. In the case 
 of artistic work and frequently in decorative work any de- 
 ficiency in this respect is repaired by an application to the 
 properly dried work of one or more coats of good transparent 
 copal or other varnish. This not only increases the durability 
 of the work by firmly cementing the colour particles in filling 
 in the interstices caused by shrinking of the oil film, but by 
 its high refractive index causes much of the white light which 
 would be reflected from the unvarnished picture to be lost by 
 internal reflection, and so gives that full mellow appearance 
 and purity of tint which one associates with a finished oil 
 painting. In the case of decorative work varnishing not only 
 adds to its appearance, but gives to the paint a much greater 
 durability by reason of the waterproof nature of the varnish. 
 
 Keramic Art. 
 
 A very important use of colours is to decorate pottery, 
 and for this purpose the colours must be very carefully 
 selected and applied in a highly specialised manner. We 
 can only most briefly touch on some of the most important 
 processes by which keramic ware is decorated. In the first 
 place it is obvious that, in view of the high temperature to 
 which all pottery is exposed in manufacture, the only colours 
 admissible are those which are purely inorganic in their 
 nature and which are non-volatile, at least at a red heat. 
 Colours may be used in the following ways : 
 I. Coloured pastes. 
 
 II. Colours on the paste. 
 
 (a) Glazes or transparent coloured glasses. 
 
 (b) Enamels or opaque glasses. 
 
 (c) Underglaze colours. 
 
 (d) On glaze colours. 
 
THE APPLICATION OF PIGMENTS. 67 
 
 It will be seen from this classification that two principal 
 methods are adopted : the use of a coloured paste, which of 
 course is the same colour adl through, and the application of 
 surface colours. We will consider these methods briefly. 
 
 I. Coloured Pastes. 
 
 All pastes containing fusible as well as plastic materials 
 can be beautifully stained by the addition of suitable metallic 
 oxides before firing. We give some proportions used in the 
 following table : 
 
 Colour. Colouring Material. Parts. 
 
 Pale Blue . Oxide of Cobalt .... 5 
 Deep Blue . ,, .... 10 
 
 f 5 
 
 Green ' ' ( Chromium . 10 
 
 Blue Green . J Cobalt .... 1-25 
 Zinc 1-25 
 
 2-5 
 
 Paste to make up 
 
 100 parts in each" 
 
 Bronze Green Calcined Oxide of Nickel . . 5 
 Brown ,, Iron . . 15 
 
 Yellow . . Oxide of Titanium . . .10 
 
 f ,, Iron 7 
 
 Black . . < 
 
 I Cobalt .... 3 
 
 Such coloured pastes would be used for mosaic tiles and 
 tesserae, coloured porcelain, etc. 
 
 II. Colours on the Paste. 
 
 (a) Coloured Glazes. These are applied either by dipping 
 or with a large camel-hair brush to the surface of the 
 " biscuit " or unglazed pottery. These glazes are largely 
 used for coloured glazed tiles and self-coloured ware gener- 
 ally. A French glaze given by Salvetat, Dictionnaire des 
 Arts et Manufactures, is 
 
 Red lead 2,000 parts 
 
 Flint 1,000 
 
 Borate of lime 500 
 
 coloured by 40 to 125 parts cobalt oxide for blue, 100 to 500 
 
68 CHEMISTKY OF PIGMENTS. 
 
 parts copper oxide (CuO) for blue greens, 70 to 200 parts ferric 
 oxide for ivory to strong yellow, 70 to 125 parts oxide of. 
 manganese (Mn 3 4 ) for madder- to purple-brown, etc. The 
 mixture is coarsely ground, melted, poured out into water 
 and grouad fine. An English mixture, rather less fusible, 
 is made from flint 100, China stone 90, red lead 360, borax 
 40 parts, coloured similarly to the above. 
 
 A very lovely turquoise blue frit used by the Egyptians 
 and Assyrians was examined by Sir H. Davy, who found it 
 to be a frit of soda, silica and cupric oxide in the proportions : 
 carbonate of soda 15, silica 20, copper 3. Vitruvius says it 
 was made by mixing copper filings, alkali and finely ground 
 sand, making into balls with water and fusing in a glass 
 furnace. Salvetat gives the following : 
 
 Body. Glaze (fritted). 
 
 Silica . . . . 93-0 Sand 900 
 
 Alumina . . . . 4'0 Sodium bicarbonate . . 400 
 
 Lime 2'0 Chalk 100 
 
 Potash .... 0'5 Cupric oxide . . . 135 
 
 (b) Enamels. These semi-vitrified, opaque materials are 
 really stanniferous glazes glazes made opaque by reason of 
 their containing oxide of tin. Majolica and Delia Robbia wares 
 were decorated with such enamels. A revival of this kind 
 of decoration has set in during this century, but, judging 
 from the precautions taken in the winter for protecting the 
 celebrated majolica fountain of the 1851 Exhibition, now 
 outside the Bethnal Green Museum, the majolica of to-day 
 is not a very suitable material for outdoor work in a variable 
 and damp climate. A few enamels by Deck are taken, as are 
 most of the recipes in this section, from the article " Pottery," 
 in Thorpe's Dictionary of Applied Chemistry, by Mr. W. Barton. 
 
 White, lead and tin ashes, 44; sand, 44; soda, 2; common salt, 8; red 
 
 lead, 2. 
 Yellow, white as above, 91 ; oxide of antimony, 9. 
 
THE APPLICATION OF PIGMENTS. 69 
 
 Blue, white as above, 95 ; cobalt oxide, 5. 
 
 Green, white as above, 95 ; cupric oxide, 5. 
 
 Yellow-green, white as above, 94 ; cupric oxide, 4 ; antimoniate of lead, 2. 
 
 Violet, white as above, 96 ; manganese dioxide, 4. 
 
 (c) Underglaze Colours. Colours used for painting on the 
 biscuit, which is subsequently glazed, must, when mixed with 
 their silicious base, be sufficiently infusible and insoluble in 
 the glaze to remain under (and protected by) it, and not to 
 run into it, and must also be of such a nature as to hold to 
 the glaze and not cause it to chip or crack. Underglaze 
 colouring is the most satisfactory way of applying colours 
 locally to porcelain or other keramic ware which is intended 
 for use. We give some mixtures (from the article referred 
 to): 
 
 Black. Eight parts native chromate of iron, 3 parts of 
 Mn 3 4 , 3 parts of CoO, 1 part of flint ; calcined together 
 strongly, and then ground fine. 
 
 Dark Blue. Four parts of CoO, 1 part of flint, 1 part of 
 chalk ; ground together. 
 
 Azure Blue. Sixty parts of ammonium alum, 3 parts of 
 CoO ; calcined strongly, then ground and washed thoroughly 
 till free from traces of acid. 
 
 Blue-Green. Twelve parts of borax, 12 parts of chalk, 12 
 parts of oxide of zinc, 24 parts of green oxide of chromium, 4 
 parts of oxide of cobalt; calcine well together and grind till fine. 
 
 Dark Brown. Eight parts of native chromate of iron, 4 
 parts of oxide of zinc, 2 parts of oxide of iron ; ground well 
 together, calcined strongly and re-ground. 
 
 Red-Broiun. Six parts of precipitated chromate of iron, 
 20 parts of oxide of zinc, 3 parts of litharge; calcine together 
 strongly, and then grind till fine. 
 
 Pink Colour. One hundred parts oxide of tin, 34 parts 
 chalk, 1 part oxide of chromium, 5 parts silica ; mixed well 
 together, calcined strongly and ground. 
 
70 CHEMISTEY OF PIGMENTS. 
 
 Yellow. Three parts oxide of antimony, 6 parts red lead, 
 2 parts flint, 1 part oxide of tin ; calcined together and then 
 ground. 
 
 In all these colours great importance is to be attached to 
 the grinding of the ingredients before, and the colour after, 
 calcining. 
 
 (d) On Glaze Colours. These colours are really fusible 
 glasses, which, when applied to the glazed surface of the 
 article (usually painted or printed with a resinous medium 
 or thick boiled oil) and raised to a red heat, adhere before 
 the glaze itself is remelted. They are by no means entirely 
 satisfactory ; unless the coefficients of expansion of glaze 
 and colour are almost equal, the colour is liable to crack and 
 splinter. Work done in this way is less brilliant-looking 
 and less artistic than underglaze work, besides being less 
 permanent. 
 
 These colours are divided into two classes, regular kiln 
 colours and hard kiln colours, according to the temperature 
 of firing, the latter requiring the higher temperature. The 
 composition of several fluxes, both Continental and Stafford- 
 shire, are given in the article in Thorpe's Dictionary, as also 
 are several colours, including, in addition to the colouring 
 materials already mentioned, oxides of uranium (black and 
 yellow), antimoniate of potash, purple of Cassius (finely 
 divided reduced gold), silver and oxide of gold. 
 
 The above brief outline of the methods of colouring 
 keramic ware, and of the preparation and nature of the 
 colours available for this purpose, will serve to indicate to 
 some extent the requirements and scope of this kind of work. 
 It is unnecessary to dilate on the extreme permanence which 
 may be expected of suitable colours suitably applied to such 
 durable materials, especially when either diffused through 
 the entire mass, or in or under the glaze or enamel. 
 
THE APPLICATION OF PIGMENTS. 71 
 
 Enamel, 
 
 This method of applying colours, though strictly including 
 the various methods of glazing and painting on keramic ware, 
 is, in its restricted sense, the decoration or protection of 
 metals by means of a coating of glaze which may or may 
 not be used as the surface for further decoration. 
 
 Enamel painting, a method but little practised by artists 
 on account of its difficulties and uncertainties, is really paint- 
 ing on enamel ; a metal plate, usually copper, in some cases 
 gold, is annealed and then covered with white enamel powder 
 on both sides, the powder being an easily fusible glass with 
 stannic or arsenious oxide or calcium phosphate suspended 
 in it. This is then fired, cooled, and the coat of enamel 
 which is formed ground smooth, a further coat is then burnt 
 on the face to be painted, and a more fusible transparent flux 
 then burnt on and ground. The painting is done with 
 powdered coloured " frits," or glasses, in suitable media, and 
 each colour burnt in separately. It will be seen that most 
 subjects would require several paintings and firings. When 
 it is considered that each of these operations is likely to result 
 in failure, either through an inappropriate shade being burnt 
 in, for the colour is only properly developed by firing, or by 
 cracking in cooling, which, in the case of a large plate, is a 
 serious risk, it will be understood that the art is but little 
 practised. 
 
 Cloisonne is a method of decorating copper and other 
 metal vessels in which the design is traced on the metal, 
 and the different parts which should take different colours 
 separated by strips of metal, or wires, fastened to the surface 
 (by brazing). The low level surfaces thus formed are filled 
 with enamel, and the whole is then fired, and when cold the 
 surface ground smooth. The colours are in this kind of 
 work separated by metal bands, or fillets, which show, like 
 
72 CHEMISTKY OF PIGMENTS. 
 
 the leading of a painted window. Another method, champ 
 leve, practised in Germany and at Limoges, a town cele- 
 brated for its enamel paintings on convex copper plates in 
 grey and white on a blue ground, was to trace the design 
 on copper and then cut away the parts to be enamelled with 
 a graver, filling in these hollows, firing, and then grinding 
 smooth. In this case, as in that of cloisonne, raised metal 
 surfaces are visible and must be treated as part of the design. 
 
 Enamel is used largely now on iron for advertising pur- 
 poses. Iron sheets enamelled blue and white or other colours 
 have largely supplanted the poster for permanent advertise- 
 ments and notices. The method of working is similar to that 
 for copper. 
 
 In any case it is desirable that the coefficients of expansion 
 of metal and enamel should be so adjusted by experiment as 
 not to be very different. If this is not the case chipping off 
 is likely to occur on cooling. 
 
 The colours used for enamel work are very similar to those 
 described as being used for the decoration of keramic ware ; 
 a description of many of these is given in the section devoted 
 to that branch of art. 
 
 Stained and Painted Glass, 
 
 Glass is, as is w r ell known, a mixture of various silicates 
 obtained by fusion and subsequent cooling, this process being 
 conducted so (relatively) rapidly that crystallisation does not 
 take place, and the resulting product is (usually) transparent. 
 
 Mixtures of the silicates of soda and lime, potash and lime 
 and potash and lead are used for the production of coloured 
 glass, the colour being imparted by the addition of small 
 proportions of various metallic oxides. The student of 
 chemistry in a very early period of his career is taught to 
 form deductions as to the nature of substances from the 
 
THE APPLICATION OF PIGMENTS. 73 
 
 colour imparted by them to " borax beads ". The borax 
 "pastes" thus produced are used in the manufacture of 
 artificial gems for theatriced and other purposes. Speaking 
 .generally, the oxides which impart a colour to borax impart 
 a similar colour to glass. We give a list of substances used 
 for colouring glass which will indicate the general composi- 
 .tion of coloured glasses. 
 
 Blue glasses are produced, the lighter sky-blue colours, by 
 the addition of 0*8 to 1*2 per cent, of cupric oxide (CuO); the 
 deeper, more violet glasses, by the addition of oxide of cobalt 
 {about 0*15 per cent.), or zaffre (0*35 to 0*4 per cent). A pale 
 blue or blue-green glass is produced by partial oxidation of 
 glass coloured by iron. 
 
 Amethyst coloured glass contains 2 to 2*5 per cent, of 
 manganese-dioxide (pyrolusite), mixed with about twice that 
 amount of nitre to prevent reduction to the manganous state. 
 (This agrees with the behaviour of manganese in borax in 
 the oxidising and reducing flames respectively.) 
 
 Yellow glasses are obtained in a variety of ways : by the 
 addition of wood or of charcoal, in which case carbon appears 
 to be the pigment; by the addition of sulphur (not to lead 
 .glass, as this would produce lead sulphide, which is black), 
 in which case a yellow alkaline sulphide appears to be pro- 
 duced or with manganese dioxide and ferric oxide, or by 
 antimoniate of lead (antimoniate of lead is used as a yellow 
 pigment by artists under the name of Naples yellow). Uranic 
 oxide also produces a fluorescent yellow glass, the appearance 
 of which is pleasing and is well known, somewhat resembling 
 that of an alkaline solution of fluorescein. 
 
 Orange-coloured glass is prepared by using manganese 
 dioxide, and ferric oxide, the ferric oxide being slightly in 
 excess. 
 
 Bed glass is coloured by cuprous oxide, Cu 2 (rose 
 copper), in which case great care must be taken to avoid 
 
74 CHEMISTRY OF PIGMENTS. 
 
 oxidation to cupric oxide with formation of a blue or green- 
 glass. Metallic iron (1 to 1'5 per cent.) and cupric oxide (about 
 1 per cent.) are added, and the mixture is melted and stirred 
 with an iron rod. The glass is colourless when taken out 
 of the crucible, but turns red on cooling. A more crimson 
 glass is obtained by the use of gold, which is added to the 
 sand of which the glass is to be made, in the form of chloride. 
 Not more than 0*1 per cent, gold is used, and even less than 
 this gives a fine rich ruby red. The colour, like that of the 
 purple of Cassius is due to the presence of finely divided gold. 
 
 Green glass is obtained by using a mixture of oxide of iron 
 and oxide of copper, with the addition of nitre to maintain 
 these in the higher state of oxidation. Chromium oxide also 
 produces a green, as does a mixture of antimonious oxide and 
 cobalt. Bottle green is produced by ferrous oxide, iron being 
 added as iron filings, and dissolved by the glass to a ferrous 
 oxide. 
 
 Black glass is produced by the use of mixtures of oxides 
 as cobalt, copper, iron or manganese, one of these being in 
 sufficient excess to remain undissolved as dark particles. 
 
 The addition of sulphur (7 to 10 per cent.) by forming 
 ferrous sulphide also produces a black glass. This is prepared 
 in Bohemia, and is known as hyalithe. 
 
 White glass, opal or translucent glass is prepared either by 
 the use of stannic oxide with lead oxide produced by heating 
 the metals together ; by arsenious oxide in a lead potash or 
 lead potash lime glass, or by calcium phosphate, or by the 
 use of fluorides as cryolite or, better, sodium fluoride. 
 
 Aventurine glass contains either finely divided cuprous 
 oxide, or finely divided copper. It is, at any rate, a yellow 
 glass full of sparkling red metallic-looking particles. It is 
 prepared according to Hautefeuille from such mixtures as 
 the following : 
 
THE APPLICATION OF PIGMENTS. 75 
 
 Crystal 2,000, saltpetre 200, copper turnings 125, ferric oxide 60 parts. 
 Or, 
 
 Sand 1,500, chalk 357, anhydrous carbonate of soda 801, carbonate of 
 potash 143, saltpetre 200, copper turnings 125 parts. 
 
 Or, 
 
 White soda glass 1,200, sand 600, carbonate of soda 650, saltpetre 200, 
 copper turnings 125. 
 
 When the glass is liquid, 38 parts of iron filings rolled up 
 in paper are thrown into the pot, and the mixture stirred with 
 a red-hot iron. The glass becomes blood red, opaque, and 
 full of small bubbles, the furnace draught is stopped, the pot 
 covered, heaped with ashes and allowed to cool very slowly. 
 Next day the crucible is broken, and aventurine found to 
 have been produced. It is difficult to produce a good article, 
 as the product is liable to become streaky, to contain bubbles, 
 or the crystals may be too fine. 
 
 Chromium aven-turine was discovered by Pelouze in 1865. 
 It is produced by heating sand 250, carbonate of soda 100, 
 calc spar 50, bichrome (bichromate presumably) 20 to 40 
 parts. The chromium oxide resulting on fusion is in greater 
 amount than will dissolve to form a green glass, and this 
 excess is suspended in the glass as brilliant green crystals. 
 
 Speaking generally, it is admitted by glass-makers them- 
 selves that the glass of to-day, though certainly very superior 
 to that of the early and middle part of last century, is 
 decidedly inferior to good old glass in richness of tint, and 
 probably in weathering qualities. 
 
 Painted glass such as is seen in windows is produced by 
 shading and burning in the shades on coloured glass. 
 Briefly, the process is this : The design is drawn full size 
 from the coloured sketch on white paper in black chalk, or 
 (in France) in white on blue paper, the different colours 
 being marked on the parts. The coloured glasses are then 
 
76 CHEMISTRY OF PIGMENTS. 
 
 selected, agreeing as nearly as possible with the brightest parts 
 of the respective colours in the coloured sketch, and are cut to 
 shape with a diamond, shaded first in water colour, then in 
 oil with an oxide of iron paint, a little borax being used as a 
 flux. In some cases actual painting with similar colours to 
 those used for tinting glass is resorted to. The plates are 
 then placed on shelves covered with powdered lime in a 
 furnace, which is heated sufficiently to so soften them that 
 the shading sinks in and becomes incorporated with the 
 glass. Various methods of shading, as smudging, stippling, 
 and hatching with lines are adopted ; pieces of high light are, 
 where necessary, wiped out of the shading before it is burnt 
 in, and in some cases flashed glass (coloured and colourless 
 glass welded together) is etched locally with hydrofluoric 
 acid until only the colourless glass is left. The process is 
 difficult and complicated, and the above is only the crudest 
 outline. Much modern glass seems to be too soft to with- 
 stand the erosive effect of town atmosphere. 
 
 Mosaic, 
 
 Mosaic is a method of decoration in which small coloured 
 dice or tesserae imbedded in cement are arranged to form 
 a pattern or design. It is, provided the cement is good, an 
 absolutely permanent kind of work, as the tesserae are usually 
 composed of natural-coloured stones, or of marbles, or of fired 
 earthenware. Speaking generally it is rather a method of 
 utilising coloured substances for decoration than of applica- 
 tion of pigments in the ordinary sense of prepared pigments, 
 and needs no more than a passing notice here, though as 
 a method of decoration, especially under the trying conditions 
 which prevail in modern towns, its importance is very great. 
 
CHAPTEK III. 
 
 INORGANIC PIGMENTS. 
 
 I WHITE PIGMENTS, 
 
 White Lead (Synonyms Cerussa Alba, Cremnitz White, Flake 
 
 White). 
 
 OF all white pigments this is the most, widely used and most 
 important ; it is also one of those most frequently sophisti- 
 cated, being sometimes adulterated, and frequently replaced 
 by other lead whites. Its great covering power, ease of 
 working with oil and permanence in that medium, combined 
 with its good drying qualities, render it most suitable both for 
 use alone and for diluting other (coloured) pigments. 
 
 It is, we believe, entirely correct to state that none of the 
 many artificial white leads or other white compounds of lead 
 possess to anything like the same extent the all-round good 
 qualities of white lead which has been prepared according to 
 the so-called Dutch or stack process ; even in those cases in 
 which the chemical composition of the white as shown by 
 analysis is correct the physical condition does not appear to 
 be so satisfactory. One objection brought against white lead 
 (principally by those interested in other whites) is that it is 
 more or less blackened by exposure to air contaminated with 
 sulphuretted hydrogen. This impeachment, so far as it goes, 
 is correct, but under ordinary conditions serious alteration 
 does not occur, and, a fact often disregarded, white lead on 
 
78 CHEMISTRY OF PIGMENTS. 
 
 exposure to light and pure air recovers in course of time. 
 Very old pictures in which white lead has been used often 
 exhibit an ivory-like yellowness, owing probably to combina- 
 tion with the oil or varnish of the medium, but this yellow 
 colour is seldom sufficient to spoil an effect, and usually is by 
 no means unpleasant. 
 
 This property of white lead, of entering into combination 
 with linseed oil, is a most valuable one, as to it is probably 
 due in no small degree the toughness and imperviousness of 
 the coat obtained. The experiments of a maker of whites, 
 quoted by Mr. A. P. Laurie in his Cantor Lectures, in which 
 strips of canvas were painted with various whites and allowed 
 to flutter in the breeze, and in which it was found that, after 
 wind and weather had caused all the other whites to peel and 
 crack, the canvas painted with white lead was still well 
 coated, are particularly interesting in this connection. 
 
 The most ancient and most satisfactory method of 
 preparing white lead is the so-called Dutch process, or stack 
 corrosion. In this, lead in the form of coils or gratings is 
 stacked up over pots containing dilute acetic acid or vinegar 
 and imbedded in fermenting horse dung or spent tan ; sev- 
 eral layers of pots are stacked one over the other in large 
 brick chambers or sheds capable of holding several tons of 
 lead. The temperature of the stack rises considerably as a re- 
 sult of the fermentation of the dung or tan, the temperature of 
 the mass reaching from 140 P. to 150 F. according to circum- 
 stances. Acetic acid vapours and carbon-dioxide are evolved, 
 which attack the surface of the lead in the presence of aqueous 
 vapour, forming first a film of lead oxide which is gradually 
 converted into basic acetate of lead. This, acted on by carbon- 
 dioxide, becomes white lead and normal lead acetate. The 
 normal acetate and fresh lead oxide re-form basic acetate, 
 which is again decomposed and re-formed, the resulting 
 compound at the end of some months, when the heating 
 
INOKGANIC PIGMENTS. 79 
 
 effect has passed off and chemical action ceased, being the 
 mixture or compound of lead hydroxide and carbonate known 
 as white lead. This forms, a thick crust on the surface of 
 the, by this time, much corroded lead plates, etc. This is 
 detached and ground and levigated in order to obtain the 
 requisite degree of fineness. The percentage of lead converted 
 depends on its state of aggregation and on the details of 
 working; it varies from 50 to 70 per cent. Some makers 
 prefer to cast the lead into rather thick coils, stars or 
 gratings, as it is easier to detach the white lead when the 
 percentage of corroded lead is low. 
 
 In England tan is usually used, in Holland dung, to 
 produce the carbon dioxide and to cause the requisite in- 
 crease in temperature ; it is also more common in England 
 to use dilute acetic acid from pyroligneous acid rather than 
 vinegar, otherwise the processes in general use in the two 
 countries are similar. This process of stack corrosion is 
 extremely slow, the operation, as has been already stated, 
 extending over several months, but the product is, for reasons 
 which will be considered below, most satisfactory. 
 
 A process closely allied to the stack process, and which 
 may be considered as a bond-fide method of preparing white 
 lead, is that used in Germany, originally at Kremsnow, but 
 to a greater extent at Klagenfurt. Thin sheets of lead are 
 exposed in wooden boxes, heated artificially to about 85 C., 
 and submitted to the vapours rising from a mixture of 
 wine lees and vinegar spread on the bottom of the boxes. 
 A modification of this process consists in suspending the 
 sheets of lead in chests or chambers on the floors of which 
 are placed vessels of acetic acid. Air and carbon-dioxide are 
 passed into these chambers, and in either case the German 
 method is more rapid than either English or Dutch. The 
 product, however, is not so satisfactory. 
 
 The French or Clichy method is altogether different from 
 
80 CHEMISTEY OF PIGMENTS. 
 
 either of the above processes. It was devised by the well- 
 known chemist, Thenard, and is one of the earliest of the 
 many precipitation processes. Basic acetate of lead is formed 
 by digesting litharge (PbO) with acetic acid of 1'056 specific 
 gravity. The mixture is kept agitated by a mechanical device, 
 and litharge added until the solution has a specific gravity 
 of 1*145. The liquor is then run into a settling tank where 
 any insoluble matters deposit, and the clear solution is trans- 
 ferred to a vessel where it is treated with carbon-dioxide 
 prepared by heating a mixture of chalk and coke in a kiln ; 
 the kiln gases are drawn off by a fan and forced through a 
 scrubber, and then through pipes into the precipitating tank. 
 In about twelve or fourteen hours the conversion is as 
 complete as is possible that is, white lead and normal acetate 
 are formed. The latter is pumped off and digested with 
 litharge to re-form basic acetate, the first washings of the 
 white lead being used again, as they also contain acetate. 
 The white lead formed is carefully washed and ground. This 
 process is in some respects very similar to the dry processes,. 
 but the product is not so satisfactory as a pigment. 
 
 In Milner's process a basic chloride of lead is produced 
 by the interaction of litharge, salt and water. The mixture 
 at the ordinary temperature becomes white and pasty ; a 
 considerable evolution of heat occurs, and the solution be- 
 comes alkaline owing to the formation of sodium hydroxide.. 
 The decomposition is usually effected in mills, and the 
 proportions used are 1 of salt, 4 of litharge, and 16 of water. 
 The agitation is continued for about three hours (if for a 
 shorter period the mass is too pasty), and after this time the 
 entire mass is creamy, and can be run out. The carbonation 
 is effected in an iron lead-lined vessel with hemispherical ends r 
 placed upright. At the top is an opening through which the 
 basic chloride mixture is introduced, and another by means 
 of which the pressure is regulated ; an opening near the 
 
INOEGANIC PIGMENTS. 81 
 
 bottom serves to draw off the white lead and samples which 
 are examined from time to time during the conversion. The 
 carbon-dioxide is, as in tfre French process, prepared from 
 coke and chalk, and is scrubbed in coke water towers. When 
 the action is complete a test sample is no longer alkaline, as 
 all the chlorine of the chloride has combined with the sodium 
 previously existing as hydroxide, forming common salt ; and 
 if shaken in a glass vessel the creamy homogeneous mass 
 leaves a frosted appearance on the sides, and in a few minutes 
 the white lead has separated out, leaving a clear liquid above, 
 and branching patterns on the sides of the vessel which were 
 coated. Any further addition of carbon -dioxide causes a de- 
 terioration in quality of the product, which becomes granular. 
 The white thus obtained is washed free from salt, and though 
 inferior to stack lead, is well suited for use as a paint. 
 
 Many other processes, as precipitation from a solution 
 of basic nitrate by C0 2 , action of C0 2 , air and water on finely 
 divided lead, action of C0 2 on a paste of litharge and lead 
 acetate, have been suggested and made the subject of patents. 
 So far, however, none of these have yielded so satisfactory 
 a product as that obtained by the older processes, though in 
 many cases closely approximating in chemical composition. 
 
 Whatever process may be adopted, if a product at all 
 satisfactory be required, it is necessary that very pure lead, 
 such as is prepared by the Pattinson or Kogan processes, 
 or by a modification of the Parkes zinc process, should be 
 used for the preparation of white lead, as the presence of 
 even very small quantities of other metals is likely to affect 
 the colour of the product. A slight pink tinge, which is 
 sometimes observable in corrosions, is said to be due to 
 the presence of a suboxide of lead ; others attribute it to 
 the presence of minute quantities of silver compounds. The 
 tan also, either by touching or by liquid from it falling on 
 the deposit, is likely to cause discoloration. It must be 
 
82 CHEMISTEY OF PIGMENTS. 
 
 remembered that basic acetate of lead is an extremely good 
 substance for removing colouring matters from liquids, and 
 that any drippings from boards used in stacking are likely 
 to give up any trace of yellow or brown colour extracted 
 from the wood to the " corrosion ". A discoloration, if not 
 serious, is sometimes corrected by the addition of a very 
 minute quantity of Prussian blue, which gives a bluish tinge, 
 and makes the white appear very pure in tone. 
 
 A most important objection to the stack process, or 
 indeed to any dry process of preparing white lead, is the 
 deleterious effect the very fine dust raised has on the human 
 system. This is certainly a serious drawback, and one which 
 has in the past called for protective legislation on behalf of 
 the work-people, who, in too many instances, require much 
 supervision to induce them to take needful precautions. 
 
 We give below in full the special rules prescribed under 
 the Factory and Workshop Acts, 1878-91, for observance in 
 white-lead works : 
 
 " DUTIES OF OCCUPIEES. 
 
 " 1. They shall provide respirators, overall suits and head 
 coverings, to be worn by the persons employed in the depart- 
 ments enumerated below, under ' Duties of Persons 
 Employed '. 
 
 " 2. They shall take care that every stack is fitted with a 
 standpipe, or movable hose, and an adequate supply of 
 water, distributed by a very fine rose or watering can, for 
 damping the white bed before stripping. 
 
 " 3. They shall see that no female shall be employed 
 without a certificate of fitness from a medical man, to be 
 obtained within one week from the date of employment. 
 
 "4. They shall see that no person shall be re-employed 
 after absence through illness without a certificate from a 
 medical man. 
 
INORGANIC PIGMENTS. 83 
 
 "5. They shall provide overalls for females in all blue beds 
 where the returns are used without being remelted, and 
 overalls and head coverings for females in all other parts of 
 the works except the casting shops. 
 
 " 6. That the wearing of shoes and stockings be optional, 
 but that no females shall be permitted to wear the same shoes 
 and stockings in the works as they wear in going to and from 
 the place of employment. 
 
 " 7. They shall provide sufficient bath accommodation for 
 all men and women employed. 
 
 "8. They shall provide dressing-rooms, a dining-room, 
 lavatories, and a cloak-room in which the ordinary clothes of 
 all workers are to be kept apart from their working clothes. 
 
 "9. They shall arrange for a weekly visit by a doctor, 
 who shall examine every worker individually, and who shall 
 enter the result of each examination in the proper register. 
 
 " 10. They shall cause such a register to be kept, and 
 shall have entered in it the date when each worker com- 
 mences and leaves employment, and the date when each 
 worker takes a bath. 
 
 "11. They shall cause every case of illness from lead 
 poisoning to be reported both to H.M. Inspector of Factories 
 for the district, and to the Certifying Surgeon. 
 
 " 12. They shall cause each man or woman to take a bath 
 at least once a week, and to wash in the lavatory before 
 bathing. 
 
 "13. They shall deliver to the persons employed the 
 articles of clothing which are required to be worn, and they 
 shall see that they are put on. At the end of every day's 
 work they shall collect and have thoroughly washed all those 
 which have been used in the stoves, and those which have 
 been used in other departments, once a week. 
 
 " 14. They shall see that the general lavatory is thoroughly 
 cleansed and supplied with clean towels after every meal. 
 
 s/ry 
 
84 CHEMISTRY OF PIGMENTS. 
 
 " 15. They shall have the dressing-rooms, baths, and 
 w.c.'s brushed and cleansed daily. 
 
 "16. They shall not allow the workers to leave any 
 clothes in the dining-room, or their ordinary clothes in any 
 work-room. 
 
 "17. They shall see that the supply of hot and cold water, 
 soap, brushes, and towels is sufficient in the bath-room and 
 lavatories. 
 
 " 18. They shall see that there are kept in close proximity 
 to the workers in each department washing conveniences and 
 a sufficient supply of approved sanitary drink, and they shall 
 cause the people to take it. 
 
 "19. They shall set apart, and cause to be entered in a 
 notice affixed in each department, a period of at least ten 
 minutes, in addition to the regular meal-times, for washing 
 immediately before each meal-time, and also before the end 
 of the day's work ; and they shall see that it is observed. 
 
 " 20. They shall see that at the doctor's weekly visit the 
 proper entries are on each occasion made in the register. 
 
 "21. Upon any person complaining of being unwell, they 
 shall with the least possible delay give an order upon the 
 doctor ; and upon any person desiring medicine, they shall 
 give a dose of the prescribed medicine kept at the works. 
 
 " 22. Managers, etc., shall report immediately to the firm 
 any instance which comes under their notice of any worker 
 neglecting the regulations hereinafter mentioned. 
 
 " 23. They shall examine all persons going out of the 
 works, and shall not allow them to leave unless they are 
 properly cleansed from lead. 
 
 " DUTIES OF PERSONS EMPLOYED. 
 
 " 24. Each man or woman before commencing work in 
 any of the following departments shall wear as follows, 
 having received the same from the person in charge : 
 
INOKGANIC PIGMENTS. 85 
 
 "Blue beds Every woman to wear an overall suit 
 in all blue beds where the returns are used without 
 being remelted^ 
 
 " White beds One overall suit and head covering. 
 Women inside the white beds to wear respirators 
 also, but the ' Carriers ' not. 
 
 "Washing and crushing 'One overall suit and head 
 covering. ' Koller ' women to wear respirators 
 also. 
 
 " Grinding One overall suit and head covering, 
 " Setting stoves One overall suit and head covering. 
 " Drawing stoves One overall suit, head covering, 
 
 and respirator. 
 
 " Paint-mixing One overall suit and respirator. 
 "25. Each man or woman working at any white bed, or 
 in setting or drawing stoves, or in the washing and crushing, 
 grinding, or paint-mixing departments, before going to break- 
 fast, dinner, or home, or before entering the dining-room for 
 any purpose whatever, must 
 
 " Put off the overall suit, etc., and give the same to 
 the person in charge, or leave it in the clothes 
 room. 
 " Brush every particle of lead dust from his or her 
 
 clothes. 
 
 " Thoroughly wash face and hands in the lavatory, and 
 be particular that no dust remain underneath the 
 finger-nails. 
 " If not wearing stockings and boots, thoroughly wash 
 
 the feet. 
 
 "26. Each man or woman must bathe at least once a 
 week, and must wash in the lavatory before bathing. 
 
 " 27. Each man or woman must receive and drink, at 
 such times as may be stated in a notice affixed in the factory, 
 such sanitary drinks as may be prescribed in such notice. 
 
86 CHEMISTRY OF PIGMENTS. 
 
 " 28. Every white bed must be adequately watered on 
 removal of the boards, and all trays of corrosions shall be 
 well saturated with water before passing through the rollers. 
 " 29. No person shall smoke or use tobacco in any work- 
 place, or room, or take food in any part of the works, except 
 in the dining-room. 
 
 " 30. No person may seek employment under an assumed 
 name, or under any false pretence. 
 
 " Respirators A good respirator is a cambric bag 
 with or without a thin flexible wire made to fit 
 over the nose. 
 
 f Sulphate of magnesia, 2 oz. 
 
 I Water, 1 gallon. 
 Sanitary drink suggested <; . 
 
 Essence of lemon, sufficient 
 
 I to flavour. 
 " Prescribed medicine. 
 
 " The following Departments to be specially Ventilated. 
 
 "(1) Washing and crushing. 
 " (2) Grinding in water. 
 "(3) Paint (grinding in oil). 
 " (4) Drawing stoves. 
 
 "R. E. SPKAGUE ORAM, 
 " H.M. Chief Inspector of Factories. 
 
 " Under Section 9, Factory Act, 1891, any person who is 
 bound to observe any special rules, as well as the occupier, is 
 liable to penalties for non-compliance with such special rules." 
 
 The composition of white lead varies somewhat, according 
 to the method of preparation, as has been very frequently stated 
 by different authorities. It may be represented by the general 
 formula, xPbC0 3 yPb(OH) 2 , a hydrated basic carbonate of lead. 
 Some samples approximate in composition to the normal 
 carbonate ; others contain a rather excessive amount of 
 hydroxide. The general opinion as to the normal composi- 
 
INORGANIC PIGMENTS. 87 
 
 tion of this substance is that it contains two molecules of 
 carbonate to one of hydroxide, 2PbC0 3 Pb(OH) 2 . The excess 
 of carbonate is usually supposed to be caused by the presence 
 of free acetic acid towards the end of the process, as it would 
 appear that it is only under such conditions that the normal 
 carbonate forms, the product otherwise always being basic. 
 A certain amount of normal acetate of lead is always present 
 in unwashed white lead. One object of the washing is to 
 remove this, but the amount is usually less in lead prepared 
 by the English or Dutch processes than in that obtained by 
 other methods, and it is in these two processes that the 
 vinegar or pyroligneous acid is allowed to evaporate quite to 
 dryness, and fermentation of the dung or tan to go on for 
 a further period, during which C0 2 is evolved and most of 
 the normal acetate converted into basic acetate, and then 
 to basic carbonate. 
 
 We give in the following table the composition of several 
 samples of genuine white lead ground in oil, the composition 
 of the oil-free white being given in the lower part of the 
 table, and also the approximate molecular proportions of 
 carbonate and hydroxide : 
 
 WHITE LEAD GEOUND IN OIL. 
 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 Oil, moisture, etc. 
 
 6-5 
 
 6-5 
 
 7-2 
 
 10-3 
 
 7-3 
 
 5-5 
 
 Lead carbonate . 
 
 71-3 
 
 64-0 
 
 66-3 
 
 66-5 
 
 67'0 
 
 65-4 
 
 Lead hydroxide . 
 
 22-2 
 
 29-1 
 
 25-2 
 
 23-2 
 
 25-7 
 
 28-7 
 
 Other matters 
 
 
 
 4 
 
 1-3 
 
 
 
 
 
 0-4 
 
 100-0 100-0 100-0 100-0 100-0 100-0 
 
 DRY MATTER. 
 
 I. II. III. IV. V. VI. 
 
 Lead carbonate . 76-4 68-5 71'5 74-2 72-3 69-2 
 
 Lead hydroxide . 23-6 31-1 27'2 25-8 27'7 30-4 
 
 Other matters . -4 1-3 0-4 
 
 100-0 100-0 100-0 100-0 100-0 100-0 
 Molecular ratio 
 
 Pb(OH) 2 : PbC0 3 1 : 2-94 1 : 1-99 1 : 2-37 1 : 2-59 1 : 2-35 1 : 2-06 
 
88 CHEMISTRY OF PIGMENTS. 
 
 The foregoing figures may be taken as representing the 
 composition of average samples of white lead prepared by 
 dry corrosion. It will be seen that the molecular ratio, 
 PbC0 3 :Pb(OH) 2 , varies from almost 3:1 to 2:1. Samples 
 have been examined by various authorities in which the 
 ratio was as high as 5:1, but these are evidently quite 
 abnormal. 
 
 A sample of " flake white " sold for decorators' use in 
 large tubes had the following decidedly abnormal composi- 
 tion : 
 
 Oil-Free Matter. 
 
 Lead carbonate 94 ! 
 
 Lead hydroxide 3-3 
 
 Calcium carbonate, etc 2-2 
 
 Fatty acids from lead soap . . . 0-4 
 
 100-0 
 
 It was ground with 9 per cent, of oil. 
 
 We have examined samples in which the ratio, 
 
 PbC0 3 :Pb(OH). 2 , 
 
 was very much lower than 2:1, but it is probable that none 
 of these were stack-corroded. Some, we know, were pre- 
 pared by other patent processes. We give the composition 
 of some such samples : 
 
 Oil, moisture, etc. . . . 7-40 6-34 7'04 
 
 Lead carbonate . . . 50-11 49-96 57'02 
 Lead hydroxide . . . 42-49 43'70 35-94 
 
 100-00 100-00 100-00 
 
 The following is a type of the enormous number of adul- 
 terated samples that are frequently met with : 
 
 Oil 11-23 
 
 Sulphate of lead 53-84 
 
 Sulphates of lime and baryta . . 28-83 
 
 Zinc oxide 6-10 
 
 100-00 
 
INORGANIC PIGMENTS. 89 
 
 A pigment of astounding composition, sold as granitic 
 flat white and ground in oil, contained 
 
 Oil .' . . " 7-9 
 
 White lead 42-7 
 
 Zinc sulphide 9-5 
 
 Barium sulphate 39-9 
 
 100-0 
 
 This on treatment with dilute acid evolved sulphuretted 
 hydrogen with blackening of the pigment. It is a most un- 
 suitable mixture for a white pigment. 
 
 Undoubtedly much of the excellence of white lead as a 
 pigment is due to its peculiar composition ; lead carbonate is 
 a very fine opaque white of remarkable covering power, but 
 alone it is neither chemically nor physically permanent as 
 an oil colour, as is shown by Prof. Church's experiments 
 quoted in chapter ii. (p. 48), and the experiments quoted 
 by Mr. Laurie, and referred to in our introductory remarks 
 on this pigment ; lead hydroxide, though not possessed of 
 great pigmentary value, confers on the substance the most 
 useful property of really combining with the oil in which it 
 is ground, and, on drying, forming a hard and tough varnishy 
 coat of oxidised oil and lead soap. 1 It is for these two reasons 
 that a white lead, containing an excessive amount of car- 
 bonate, though beautifully white, is not very durable in oil 
 on the one hand, and one too rich in hydroxide is possessed 
 of but little covering power or opacity on the other. 
 
 1 On grinding with oil some increase of temperature is usually noted ; it 
 is generally supposed that this is indicative of some saponifying process being 
 set up, and when one reflects that lead plaster is prepared by warming litharge 
 and olive oil, it is not surprising that a (probably) much more active substance, 
 finely ground lead hydroxide, should act in this way. That some sort of 
 .saponification goes on is certain ; ether will not extract the oil completely 
 from white lead, but when the apparently oil-free powder is decomposed with 
 acid some traces of oil are usually found. 
 
 The preference by painters for old white lead is easily explained when 
 we consider that more saponification may be supposed to have taken place 
 in such samples than in the freshly ground material. 
 
90 CHEMISTRY OF PIGMENTS. 
 
 One reason, it would appear, of the superiority of stack 
 corroded over precipitated white lead is that the former is 
 always amorphous, while the latter is usually crystalline ; 
 this being the case, however finely the pigment is ground, it 
 is more transparent than the amorphous variety, and probably 
 more light is lost by internal reflection, so that the brilliance, 
 which is always desirable in a white pigment, is somewhat 
 reduced. 
 
 The high price of white lead, consequent on the use of a 
 somewhat costly raw material, and the lengthy nature of the 
 process of manufacture, offers great incentive to adulteration 
 and substitution. Various substitutes have been proposed 
 and are sold as better than white lead, and a good deal is done 
 in the way of dilution, or, as it is called, lowering with other 
 white pigments, of which barium sulphate is one of the most 
 used (and cheapest). This fact renders the examination of 
 this material a matter of some importance, and we therefore 
 give a brief scheme for its analysis. 
 
 The objects of an analysis of white lead being twofold, 
 (a) to determine the presence and, if present, the nature of im- 
 purities ; and (b) to ascertain the proportion of hydroxide and 
 carbonate. The following scheme will be found sufficient : 
 
 Determination of Oil. A portion of 4 to 7 grams of the pig- 
 ment ground in oil is weighed into a glass tube of about 30' 
 cc. capacity and 20 cc. of ether added. The tube is corked, 
 and agitated until the white is uniformly diffused in the liquid, 
 and then it is placed in an upright position for some hours 
 until the pigment has settled to the bottom, and then 5 cc. is 
 pipetted off into a weighed beaker without disturbing the 
 deposit, and the oil weighed after all the ether is evaporated. 
 This method is sufficiently accurate for this purpose, though 
 no correction is made for the volume of the oil present in 
 the paint. How small this would be is shown by the follow r - 
 ing example : 
 
INORGANIC PIGMENTS. 91 
 
 Suppose 4 grams of a sample containing 8 per cent, of 
 oil were treated with 20 cc. of ether and 5 cc. pipetted off and 
 considered as J. Eight per cent, of 4 grams is '32 grams or 
 '34 cc. of oil. If this dissolved in ether suffers no contrac- 
 tion of volume, the whole volume of liquid will be 20*34 cc., 
 and 5 cc. will be '246 of the whole instead of '250, and the 
 weight of oil obtained will be '079 gram, equal to a result 
 of 7*9 per cent, instead of 8'0 per cent., well within other 
 errors of experiment ! The rest of the ether should be poured 
 off this extracted portion of white, and one or two washings 
 added to free from mechanically adhering oil, and the lead 
 and carbonic anhydride determined in this. 
 
 Determination of Lead, etc. (1) About 1 gram of the pig- 
 ment, either oil-free or ground in oil, is weighed into a 
 beaker and treated with dilute nitric acid, the solution of the 
 lead being hastened by warming either over a small flame or 
 in the water bath. It is necessary that the beaker should be 
 covered, as otherwise loss may occur by effervescence. When 
 all action is judged to be over the liquid is filtered from oil and 
 any other insoluble matter. The filter is washed with hot 
 water and ignited with any insoluble matter (unless there is a 
 great deal, when it should be burnt apart, and the insoluble 
 matter added to the ashes) in a porcelain crucible. Occasion- 
 ally a trace of lead is retained by the oil, and appears as in- 
 soluble matter, in which case its amount should be added to the 
 total lead. If more than 1 per cent, of insoluble matter is 
 found its nature should be determined. Lead sulphate would 
 be sufficiently soluble in strong hydrochloric acid to give a pre- 
 cipitate of barium sulphate with barium chloride and of lead 
 sulphide with sulphuretted hydrogen in very dilute solution. 
 Barium sulphate would be entirely insoluble in HC1, but on 
 fusion with alkaline carbonates (fusion mixture) would yield 
 barium carbonate and alkaline sulphates, and either the Ba or 
 the S0 3 determined as BaS0 4 would give the actual weight of 
 
92 CHEMISTRY OF PIGMENTS. 
 
 barytes present. The nitrate and washings will contain 
 all the lead (except part of any existing as sulphate) and 
 other metals present. It should be diluted somewhat, 
 nearly neutralised with sodium carbonate, and sodium 
 acetate added, so that any acidity is due only to acetic 
 acid. An excess of neutral potassium chromate is added to 
 the warm solution, which is allowed to stand until the 
 yellow precipitate of lead chromate has subsided, when the 
 supernatant liquid should be poured off through a weighed 
 filter and the precipitate washed once or twice by decantation 
 with hot water, brought on to the filter and w r ashed there, and 
 when free from all salts, as shown by evaporating a few 
 drops of the filtrate on a glass slip, precipitate and filter 
 may be dried in the water oven until of constant weight. 
 The precipitate can, if preferred, be detached from the paper 
 as completely as possible, the latter burnt carefully and the 
 ash moistened with nitric acid and gently incinerated, and 
 then the whole precipitate added to the (porcelain) crucible 
 and gently ignited. The weight of lead chromate obtained 
 X 0-689 - PbO or x 0'639 = Pb. The filtrate from the 
 lead should be tested with ammonium oxalate for lime, which 
 if present can be estimated by collecting the precipitate 
 of calcium oxalate and weighing as CaC0 3 or CaO. The 
 following mode of procedure (2) is perhaps more satisfactory 
 in the case of adulterated samples. About 1 gram of the 
 sample is treated with diluted hydrochloric acid on the water- 
 bath in a moderate-sized beaker, and the liquid, when all 
 action has ceased, diluted with boiling water and either kept 
 on the water-bath or boiled over a flame. The hot liquid is 
 filtered, the filter paper washed, any insoluble matter examined 
 as above, and the filtrate largely diluted and cooled. To 
 the cooled liquid sulphuretted hydrogen solution is added, 
 or (better) the gas is passed through it until it smells 
 strongly. The precipitate is collected on a filter and washed 
 
INORGANIC PIGMENTS. 93 
 
 with water with a little H 2 S dissolved in it, dried, transferred 
 as completely as possible to a crucible and either treated with 
 HC1 to convert into PbOi 2 , or with H 2 S0 4 to convert into 
 PbS0 4 . The former should be dried at 200 C., the latter may 
 be gently ignited until all free S0 3 is evolved. Lead sulphide 
 precipitated in HC1 solution is never free from PbCl. 7 , con- 
 sequently it is best to convert to PbCl 2 or PbS0 4 . 
 
 PbCl 2 x 0-802 = PbO. 
 PbS0 4 x 0-735 - PbO. 
 
 The filtrate from the PbS should be examined for lime, 
 which if present should be determined. 
 
 Precipitation as sulphate of lead in the possible presence 
 of lime is inadmissible ; if, however, S0 3 is found to be present 
 in the sample it is best to treat a 'weighed portion with 
 HC1 or HN0 3 , dilute, filter if necessary, and determine the 
 S0 3 either (with the addition of alcohol) as PbS0 4 or (much 
 better) by addition of barium chloride and precipitation as 
 BaS0 4 . The weight of SO 3 found should be added to any 
 found in the insoluble portion as PbS0 4 , and according as 
 PbS0 4 , or lime, is present, calculated as lead sulphate or 
 calcium sulphate. 
 
 Determination of Carbonic Anhydride. A portion of 4 to 6 
 grams of the oil-free pigment is either decomposed in a small 
 flask and the C0 2 , after being freed from HC1 by copper sul- 
 phate (on pumice) and dried by sulphuric acid, is absorbed 
 by caustic potash or soda lime, the increase in weight of 
 potash balls or soda-lime tubes being equal to the amount of 
 C0 2 present, or (less satisfactorily) a loss apparatus of the 
 Schrotter type is used. The percentage of C0 2 is calculated 
 back to the original white in oil, 
 
 C0 2 x 6-066 = PbOO 3 . 
 
 All the CO 2 found, except in cases where lime is present 
 and SO 3 absent, is calculated as PbC0 3 , but should lime be 
 
94 CHEMISTEY OF PIGMENTS. 
 
 present and no SO 3 , all the C0 2 not required to form CaC0 3 
 is calculated as PbC0 3 , and the excess of lead oxide over the 
 amount required for the CO. 2 calculated to Pb (OH) 2 ; PbO X 
 1-08 = Pb (OH) 2 . The ratio PbC0 3 : Pb (OH) 2 is thus obtained. 
 Lead sulphate, lime compounds, barytes or china clay can only 
 be regarded as adulterants ; the only object of adding them is 
 to reduce the cost, and their presence and amount should be 
 stated with, we think, a decidedly adverse comment should 
 calcium sulphate be present, as this is more or less liable to 
 be acted on by water. The others are quite inert, and 
 though they decrease the covering power of the pigment, in 
 some cases the lower price of the article may be considered 
 as a set-off against this ; any amount of such diluents is, in 
 our opinion, objectionable, as by their presence the peculiarly 
 good qualities of white lead are reduced. 
 
 White lead is usually used in oil, both as a white paint 
 and as priming or preliminary coats to a new surface which 
 is finally to be coloured. The colouring matter or "stain" is 
 seldom applied alone, but is diluted with white, in most cases 
 preferably white lead, to the required tint. By this means 
 colours of poor covering power or bad drying properties will 
 form an opaque, quick drying, tough and impervious coat. 
 It is as an oil colour that the peculiar excellencies of white lead, 
 both as a protective coating to wood or iron and as a covering 
 substance from the colour. point of view, are most apparent. 
 White lead will, however, work well in water, and was 
 formerly used considerably when a white pigment was re- 
 quired for water colour. It is not, however, nearly so suitable 
 for this purpose as other white pigments which will be dealt 
 with in this chapter. White lead is known to the artist in 
 oils as flake white and is one of his most important pigments, 
 being used both as a priming for his ground, for diluting other 
 colours and for putting in high lights, either white or white 
 glazed over with other transparent colours. It works well 
 
INORGANIC PIGMENTS. 95 
 
 with most other colours, but is inapplicable in conjunction 
 with coloured sulphides which are liable to cause blackening 
 by formation of lead sulphide. The yellowing by age of flake 
 white in oil paintings has been before alluded to ; it seems to 
 be rather a change of the lead-oil varnish than any ordinary 
 deterioration, and is not often so pronounced as to be un- 
 pleasant. 
 
 Zinc White, 
 
 This extremely brilliant white pigment was introduced 
 some years ago in the hope that it might replace white lead. 
 This it has altogether failed to do ; it is nevertheless a very 
 fine pigment and possesses very fair covering power, not, 
 however, equal to that of white lead. Its colour is rather 
 a bluish white. It works well in oil and extremely so in 
 water, and is the water-colour white par excellence. 
 
 Zinc white is the only definitely known oxide of zinc ; its 
 composition, expressed by the formula ZnO, corresponds to the 
 known salts of zinc. It is prepared by distilling zinc in clay 
 retorts connected with a series of chambers through which 
 air is blown. The zinc volatilises and combines with oxygen 
 in so doing, and the clouds of zinc oxide formed collect on 
 the walls of the receiving chambers as an amorphous deposit 
 easily reducible to powder. This is levigated to separate from 
 any unaltered zinc, and the settled and finely ground oxide 
 collected and dried. It is then ready for mixing with either 
 oil or water. Zinc white can also be prepared by oxidising 
 zinc in large muffles. 
 
 As it is a very high-priced material, zinc oxide is subject 
 to considerable adulteration with other less expensive whites. 
 The following scheme will suffice to detect and determine any 
 ordinary adulteration : 
 
 Determination of Oil. As suggested for white lead (p. 90). 
 
96 CHEMISTEY OF PIGMENTS. 
 
 A correction should be made for the volume of oil in solution' 
 in the manner suggested. 
 
 Determination of Zinc and of Impurities. A portion of 1 to 
 2 grams is digested with dilute hydrochloric acid on the 
 water bath or over a flame until all is dissolved (except 
 oil) or until no further solution takes place. The liquid is 
 then filtered and the filter paper with any insoluble matter 
 ignited and the nature of this insoluble portion determined as 
 described under white lead (p. 91). The filtrate is diluted 
 to a known bulk and the zinc determined in a portion cor- 
 responding to from '5 to I/O gram of the original, either (1) by 
 titration with potassium ferrocyanide or (2) by precipitation 
 as sulphide. 
 
 (1) Titration with ferrocyanide. A solution of potas- 
 sium ferrocyanide containing 41*25 grams of the salt per litre 
 is standardised by means of pure zinc. About '5 gram of 
 zinc foil is carefully weighed and dissolved in dilute HC1. 
 The solution is raised to boiling, two or three drops of a 
 solution of uranium nitrate or acetate added and the ferro- 
 cyanide solution run in from a burette until the brown colour 
 which at first forms and disappears almost at once becomes 
 more persistent. When this is the case portions are taken 
 out of the vessel on the end of the rod used for stirring and 
 tested with uranium on a tile until a reddish brown colour 
 is produced. This indicates excess of ferrocyanide ; the 
 volume used should be noted, '1 cc. deducted for the amount 
 required to produce the colour and the value of 1 cc. in zinc 
 calculated ; this should be "01 gram almost exactly. The 
 titration of the solution containing zinc should be made in 
 exactly the same way as that with pure zinc. The method 
 is expeditious and accurate, copper and iron being the only 
 interfering substances. Neither is likely to be present in 
 zinc white, but copper gives a chocolate and iron a blue 
 precipitate with ferrocyanide, so their presence would soon be 
 
INORGANIC PIGMENTS. 97 
 
 noted. When the zinc ferrocyanide has settled and left a 
 clear supernatant liquid this can be decanted and tested 
 for lime. The addition of sulphuretted hydrogen to another 
 portion of the original liquid will indicate the presence or 
 absence of lead. Any other white than white lead or calcium 
 carbonate would be found in the insoluble portion. 
 
 The zinc found is of course calculated as ZnO. The 
 percentages of zinc oxide, oil and insoluble matter should 
 add up to 100 approximately, if no calcium carbonate or white 
 lead be present. Should either lime or lead be found and it 
 is desired to determine their amount by a direct method 
 
 (2) A definite portion of the HC1 solution is treated with 
 sulphuretted hydrogen, being previously considerably diluted 
 if it is not already fairly dilute. Any precipitate in this acid 
 solution is probably lead sulphide. This should be collected 
 on a filter, washed with H.,S water (diluted), dried and 
 weighed as sulphate. This can be examined qualitatively 
 if desired. The filtrate is made alkaline with ammonia, 
 allowed to stand for some time, and the resulting precipitate 
 of zinc sulphide collected on a filter, washed, redissolved in. 
 dilute HC1 and zinc carbonate precipitated by Na. 2 CO 3 . This 
 is collected, washed, dried and ignited (the filter being ignited 
 separately and the ash added), and weighed as ZnO. Or the 
 dissolved zinc sulphide may be titrated with ferrocyanide as 
 above (1). 
 
 We give the results of examination of some samples of 
 this pigment which have come under our notice. 
 
 Oil . . . . l r '93 17-72 19-17 20'6 
 Zinc oxide . 82-07 82-28 80-83 79-4 
 
 100-00 100-00 100-00 100-00 
 
 The above samples as will be seen were all pure. The 
 amount of oil necessary for grinding to a pasty consistency 
 
 varies a few per cent, either side of 20 (of the whole, or 25 
 
 7 
 
98 CHEMISTEY OF PIGMENTS. 
 
 per cent, of the weight of white). The following is the com- 
 position of an adulterated sample we have recently met with. 
 
 Oil 14-0 
 
 Zinc oxide 56'S 
 
 Zinc sulphide 21'0 
 
 Barium sulphate ...... 8'2 
 
 100-0 
 
 Zinc sulphide is sometimes used as zinc white and its 
 use seems quite legitimate, but this sample is also diluted 
 w r ith barium sulphate. It looks like an order made up \vhen 
 the stock of oxide had run short. The reduced proportion 
 of oil is very marked, though the sample was quite as pasty 
 as is usually the case. The sample was of a very bluish 
 white. 
 
 The following is typical of many samples we have met 
 with : 
 
 Zinc oxide 56-0 
 
 Barium sulphate 34*5 
 
 Chalk 9-5 
 
 One advantage of zinc 'oxide is its absolute permanency 
 in sulphur-laden atmospheres. Mr. H. Smith's experiments 
 quoted previously show that as a protective colour zinc white 
 takes a very high rank, and this notwithstanding the general 
 opinion that it is absolutely inert to linseed oil. It would 
 certainly at first sight appear that the oxide of so strongly 
 electro-positive a metal as zinc should have some saponifying 
 action on oil and not be, as is supposed, merely suspended in 
 the hardened oxidised oil coating. 
 
 Zinc white in water colour is usually known as Chinese 
 white. 
 
INOKGANIC PIGMENTS. 99 
 
 Enamel white (Blanc Fixe, Permanent White, Barytes White, 
 Barium Sulphate). 
 
 Barium sulphate occurs in nature as barytes, barite, heavy 
 spar, or schwerspath, in crystals of the orthorhombic series. 
 
 It should be fairly pure, and require no further preparation 
 than grinding to a fine powder and treating with hydrochloric 
 acid to remove any soluble matters. 
 
 Barytes is used to some slight extent as an oil white, 
 but is too crystalline, and, therefore, transparent, to be of 
 much use. Its principal use, or abuse, is to dilute white 
 lead and other expensive colours. Its specific gravity, 4*3 
 to 4' 72, is in its favour for such purposes. 
 
 It should be entirely insoluble in hydrochloric acid ; any 
 effervescence would indicate the presence of carbonate. The 
 insoluble matter, on fusion with mixed carbonates of potash 
 and soda, should, on extracting with water and treating 
 the aqueous solution with hydrochloric acid until acid, and 
 then precipitating with barium chloride, yield its own weight 
 of barium sulphate, or the insoluble portion dissolved in 
 hydrochloric acid and precipitated with sulphuric acid should 
 also yield its own weight of barium sulphate. 
 
 On fusion 
 
 Ba S0 4 + M' 2 C0 3 = Ba C0 3 + M 2 S0 4 ; 
 
 therefore the weights of barium sulphate obtained by either 
 precipitating the Ba or the S0 4 should be equal. 
 
 Whitening, Chalk (Calcium Carbonate). 
 
 Prepared chalk or whitening obtained from native chalk 
 by a process of washing over is used to some extent as a 
 diluent in oil colours, and also for tempera (" distemper ") 
 and whitewash. It is, as sold, tolerably pure calcium car- 
 bonate, CaCO 3 . It should be entirely soluble in dilute hydro- 
 chloric acid (absence of sand, clay, etc.) to a colourless 
 
100 CHEMISTEY OF PIGMENTS. 
 
 solution, give no precipitate when ammonia is added in slight 
 excess to this solution in the presence of ammonium chloride 
 (enough of this is usually formed in neutralising the excess 
 of hydrochloric acid), indicating the absence of iron and 
 alumina. More than traces of iron would spoil the pure 
 white of calcium carbonate. It should, on determination of 
 CaO and CO 2 , agree closely with the composition : 
 
 CaO 56 
 
 CO 2 44 
 
 100-0 
 
 II OXIDES OF LEAD, 
 
 Red Lead (Synonym Minium Pb ;3 4 ). 
 
 This very brilliant scarlet, or rather perhaps scarlet-pink 
 lead pigment is not now very much used alone, but prin- 
 cipally mixed with white lead as a priming coat. It is 
 possessed of remarkable drying properties in oil, and forms 
 a splendid varnishy compound with it. It is usually used 
 with raw linseed oil, as it dries too quickly and with a too 
 brittle surface if used with boiled oil. 
 
 Red lead is prepared by heating massicot or litharge 
 (PbO) in furnaces to a temperature not exceeding 300 C. 
 Under these conditions it absorbs oxygen from the air, and is 
 converted into the red powder known as red lead. It is 
 usually supposed to have the composition Pb a 4 = 2PbO 
 Pb0 2 , but Mulder has found samples of the composition 
 Pb 4 5 = 3PbO Pb0 2 . 
 
 We have examined many samples of this pigment, and 
 have found the percentage of lead to correspond tolerably 
 well with Pb 3 4 , though the difference in percentage composi- 
 tion of the two oxides is not great, as the following figures 
 show : 
 
INORGANIC PIGMENTS. 101 
 
 Pb 3 4 Pb 4 5 
 
 Lead 9O66 91-18 
 
 Oxygen . . . . 9'34 8'82 
 
 100-00 100-00 
 
 The following percentages of lead were obtained by us in 
 some of the samples examined : 
 
 89'90 S 90-28, 89'60, 91-38, 91-09, 89'94. 
 
 Amounts of insoluble matter never greater than 1 per cent, 
 have been found by us ; this insoluble matter appeared to be 
 sand or clay, and was without doubt accidental. 
 
 Ked lead has a specific gravity of 8'62 9'19, is 
 crystalline in structure, darkens on heating, but recovers its 
 colour, and on heating very strongly gives off oxygen. It is 
 not entirely dissolved, but is darkened, by nitric acid, which 
 dissolves out the monoxide as lead nitrate, and leaves the 
 dioxide Pb0 2 as a purple-brown powder. 
 
 Red lead will dissolve easily in nitric acid if a little sugar 
 or starch is added. This is oxidised partly at the expense of 
 the lead dioxide, and if the acid is somewhat dilute the lead 
 passes into solution as plumbic nitrate ; if the acid is concen- 
 trated the nitrate separates in crystals, but can be dissolved 
 by dilution with water. The lead can be determined in this 
 solution, after filtration from any insoluble matter, which 
 should be weighed, by either of the methods recommended in 
 the section on white lead. Red lead also dissolves in hydro- 
 chloric acid with evolution of chlorine. If it is decided to 
 determine the lead either as chloride or sulphide, hydrochloric 
 acid is a suitable solvent. The action of hydrochloric acid 
 on red lead affords a means of determining the proportion of 
 dioxide. When lead dioxide or red lead is treated with 
 hydrochloric acid, 
 
 Pb0 2 + 4HC1 = PbCl 2 + C1 2 + 2H 2 0, 
 Or 
 
 Pb 3 4 + 8HC1 = 3PbCl 2 + C1 2 + 2H 2 0. 
 
102 CHEMISTEY OF PIGMENTS. 
 
 If the chlorine thus liberated be passed into a solution of 
 potassium iodide, using a suitable form of distilling and ab- 
 sorbing apparatus to ensure complete absorption, then an 
 equivalent amount of iodine is liberated, 
 
 2K1 + C1 2 = 2KC1 + I 2 . 
 
 This iodine may be titrated with standardized thiosulphate 
 and so, indirectly, the amount of peroxide contained in the 
 red lead determined. For technical purposes it is usually 
 sufficient to ascertain that it is a pure oxide of lead of the 
 right shade. 
 
 Litharge (Massicot, Lead Monoxide, PbO). 
 
 In addition to the hydrated carbonate and the red oxide 
 of lead, the monoxide, litharge or massicot, is used to some 
 extent. This is prepared by heating lead to above its 
 melting point in the open air. It forms a reddish-yellow 
 scaly mass, or an amorphous powder, according to whether 
 the temperature has been sufficiently high to cause fusion. 
 It possesses marked basic properties, and easily enters into 
 combination with oils to form lead soaps. For this reason 
 it is used with linseed oil as a " drying " material. It dries 
 too well to be suitable for use as a pigment, as the coat 
 formed is too hard to wear well. Its principal use is as a 
 drying material for paints and oil varnishes. 
 
 Some other lead pigments but little used now are : 
 
 Red-brown, formed by the fusion in a clay crucible of 1 
 part red oxide of iron with 10 parts of red lead. 
 
 Orange mineral, a variety of red lead formed by the 
 calcination of white lead. Mulder gives its composition 
 as : 
 
 Lead monoxide (PbO) 73 
 
 Lead dioxide (PbO 2 ) 25 
 
 Carbonic anhydride (C0 2 ). .... 2 
 
 100 
 
INOBGANIC PIGMENTS. 108 
 
 Mr. A. P. Laurie in his Cantor Lectures says of red lead : 
 " It was prepared by roasting white lead. It is now, I 
 believe, usually prepared- from litharge. No doubt the 
 minium prepared from white lead would be a finer pig- 
 ment." 
 
 Ill MERCURY PIGMENTS, 
 
 Vermilion-, 
 
 This very fine scarlet pigment is a sulphide of mercury 
 corresponding in composition with the mineral cinnabar 
 mercuric sulphide HgS, in fact ; occasionally specimens of 
 cinnabar are found sufficiently bright for use as a pigment, 
 more often, however, vermilion is prepared artificially from 
 mercury and sulphur. 
 
 There are two classes of processes by which this pigment is 
 prepared dry processes in which the combination is effected 
 by means of dry heat, and the product prepared by sublima- 
 tion, and wet processes in which both the combination and 
 further preparation are effected by the aid of liquids. 
 
 The procedure in both processes is first to prepare the 
 substance known as Ethiops mineral, a blackish sulphide of 
 mercury with uncombined sulphur, and then by suitable 
 treatment to produce some molecular change by which the 
 substance becomes of a bright scarlet colour. 
 
 We give some examples of each class of processes : 
 
 Dry Processes. 
 
 At the mines in Idria the following process is adopted 
 85 parts of mercury and 15 parts of sulphur are ground 
 together in revolving tuns for some hours until combination 
 appears to be complete. The " Ethiops " thus formed is 
 then heated in cast-iron cylinders and sublimed thence into 
 clay condensers. 
 
104 CHEMISTRY OF PIGMENTS. 
 
 The process used in Holland is said to consist in preparing 
 the " Ethiops " with 1 part sulphur, 2 parts mercury + 2'5 
 per cent, finely divided lead or red lead. Lots of about 
 100 kilos are sublimed and the sublimate allowed to cool 
 slowly during twenty hours, and then finely ground and 
 levigated. 
 
 Another process is to gently heat 75 kilos sulphur, and 
 540 kilos mercury on a shallow iron pan, and break up the 
 " Ethiops," which is kept in jars until it is wished to sublime 
 it. The contents of two or three jars are emptied into a tall 
 clay pot, the bottom of which is heated in a furnace to a dull 
 red. The substance inflames as it is thrown in owing to 
 the combustion of the excess of sulphur, and as the flame 
 goes down a stout well-fitting iron cover is placed on the 
 pot. A fresh charge is added every four to five hours, and the 
 heating continued for thirty-six hours. After cooling the pot 
 is broken, and the vermilion scraped from the lid and top 
 of the pot. The sublimate is then finely ground and levi- 
 gated. 
 
 The shade is sometimes modified by treating with hot 
 alkaline solutions which, perhaps by removing traces of un- 
 combined sulphur, possibly by favouring some molecular 
 change, brighten and purify the colour. 
 
 The object of sublimation appears to be twofold, firstly, to 
 remove excess of sulphur, which as being the cheaper material 
 is always used in considerable excess, as the percentage com- 
 position of mercuric sulphide shows : 
 
 Mercury . . . 86'2 , 
 Sulphur . . . 13-8 I S 
 
 100-0 
 
 and, secondly, to cause the change which results in the 
 formation of a scarlet sulphide. 
 
INOKGANIC PIGMENTS. 105 
 
 Wet Processes. 
 
 In China vermilion of # high quality has been prepared 
 probably for many centuries. The process used is sup- 
 posed to be a wet one. 1 
 
 We give some examples of European wet processes : 
 
 Kirchojfs Process. Three hundred parts mercury and 68 
 
 parts sulphur are moistened with a little potassium hydroxide 
 
 (caustic potash), and ground together for some time. The 
 
 black " Ethiops " which forms is then mixed with 160 'parts 
 
 1 The following process, which is certainly not a wet one, is given in 
 Thorpe's Dictionary of Applied Chemistry as that by which Chinese vermilion 
 <( is said to be prepared". 
 
 " About half a bottle (38 lb.) of mercury and 17 lb. of sulphur are 
 mixed in an iron pan about twenty-five inches wide and seven or eight inches 
 deep, heated by charcoal. When melted it is stirred with an iron spatula, 
 and the remainder of the bottle of mercury is gradually added. When the 
 metal has disappeared it is removed f iom the fire, cooled by the addition of 
 a little water, rapidly stirred and coarsely powdered. The reddish or black 
 semicrystalline powder, which contains free mercury and sulphur, is placed 
 in a fixed iron pan, and covered with porcelain tiles eight inches in diameter 
 {many of which are broken), arranged in the shape of a dome. The whole 
 is covered by a pan four inches in diameter less than the fixed one, to which 
 it is luted by clay, leaving four holes in the luting for the escape of gases. 
 The charcoal fire is then lighted and kept fiercely burning for eighteen hours ; 
 blue flames are seen burning round the holes, showing loss of sulphur and 
 of mercury. The fires are then allowed to die out, and the pans to cool. 
 Most of the vermilion is found adherent to the porcelain and is removed. 
 That attached to the iron is inferior, and is made with the other waste 
 into cakes with alum and glue-water, dried and resublimed. The sulphide 
 on the porcelain is blood red and crystalline. It is powdered and ground 
 with water in a hand-mill between stones, and washed in a vessel. At the 
 close of a day's work, a solution of alum and glue (1 ounce of each to 1 
 gallon of solution) is stirred well with the powder, and the whole is allowed 
 to stand until morning. The glue tends to lengthen the period of deposition, 
 and to render the stratification into the various qualities more perfect. The 
 alum is said to improve the colour. The liquid is decanted, and the upper 
 portions of the deposit are set aside. The lower parts are reground and 
 treated as before, the grinding being sometimes repeated several times. The 
 fine vermilion is stirred in water and settled, and the water is decanted. 
 The residue is dried in the open air, powdered, sifted through muslin and 
 packed in papers holding about 1^ ounce each." 
 
106 CHEMISTKY OF PIGMENTS. 
 
 of potassium hydroxide dissolved in a very little water and 
 heated to boiling for thirty minutes. Water is added to keep 
 up the volume of the pasty mass, which is stirred well, and 
 first becomes brown and gelatinous and then red. This 
 mass is stirred until cold, and then washed free of alkali, 
 ground and levigated. 
 
 Briinner's Process. Three hundred grams mercury, 114 
 grams sulphur and 75 grams potassium hydroxide dissolved 
 in 450 cc. water are taken. The mercury and sulphur are 
 ground together, and the alkali poured on the mixture in 
 small portions until all is added. The mass is well stirred, 
 and then heated for seven to eight hours at a temperature 
 of 45 to 50 C., he volume being maintained by additions of 
 water. The mixture, which is black to begin with, under 
 the action of the alkali becomes brown, red, and finally scarlet. 
 The vermilion is well washed from all alkali, ground and 
 levigated. 
 
 Jacquelin used a similar process, but the following propor- 
 tions, 90 parts mercury, 30 parts sulphur, 20 parts potassium 
 hydroxide, 30 parts water, and heated to 80 for one hour 
 instead of seven to eight hours at 45 to 50. 
 
 Firmerich prepared a very fine vermilion by the action of 
 (penta) sulphide of potassium on mercury. 
 
 Potassium sulphide is prepared by igniting potassium 
 sulphate with charcoal, extracting with water and concen- 
 trating to remove unaltered sulphate, which, by reason of 
 its somewhat sparing solubility, crystallises out. The solu- 
 tion of sulphide thus prepared is boiled with sulphur. By 
 this means the polysulphide is formed. This method is 
 found to be more satisfactory than fusion of potassium 
 hydroxide or carbonate with sulphur, as in these methods 
 other products than penta- or other poly-sulphides are formed. 
 Five parts of mercury, 1 part of sulphur, and 2J parts of 
 sulphide solution (on the basis of 2 parts K. 2 S to 7 parts 
 
INOKGANIC PIGMENTS. 107 
 
 water) are placed in bottles, moderately heated to start action, 
 and continually shaken for three and a half hours ; a greenish- 
 brown product results. This is cooled and kept for two to 
 three days in the " stoveroom " at a temperature of 45 to 50 
 C. ; after cooling, the vermilion is carefully treated with sodium 
 hydroxide to remove unaltered sulphur, and the alkali is 
 then removed by washing with water. 
 
 The object of the addition of sulphur to the mixture of 
 polysulphide and mercury is to replenish the former sub- 
 stance, which acts as a carrier of sulphur, and to effect a 
 combination which would otherwise require the aid of a dry 
 heat. In the other wet processes the solution of potassium 
 hydroxide used, by causing the formation of sulphides and 
 other sulphur compounds, enables the whole, or nearly the 
 whole, of the mercury used to be converted into sulphide. 
 
 Various means are used to improve and to fix the colour 
 of vermilion prepared by either process. Treatment with 
 nitric acid to remove any uncombined sulphur ; with a mix- 
 ture of potassium sulphide and hydroxide with hydrochloric 
 acid, which should remove any alkalies ; and with hot potas- 
 sium hydroxide solution, which is said to give a violet tinge, 
 are processes which have been recommended for these pur- 
 poses. The main object seems to be to obtain a very pure 
 red material corresponding, as far as is reasonably possible, 
 to pure HgS. This, whatever tint may be obtained, is 
 less likely to alter in tint than a substance which is not a 
 chemical individual. 
 
 The examination of vermilion is not usually a matter of 
 great difficulty. It is generally sufficient to agitate a portion 
 with alcohol, and allow to settle, filter off the alcohol, 
 and notice the colour of the solution, and determine the 
 amount of ash left on ignition at a moderately low tempera- 
 ture. The former test indicates the presence or absence of 
 eosin, which would give a pink colour and coppery fluores- 
 
108 CHEMISTRY OF PIGMENTS. 
 
 cence to the alcohol, or of other dyes which might be used 
 to brighten the pigment, while the presence or absence of 
 any amount of ash is a criterion of the amount of inorganic 
 adulteration. 
 
 Ked lead and scarlet antimony sulphide are, we believe, 
 used more or less as adulterants. These, unless present in 
 considerable quantity, have no great effect on the colour of 
 the pigment, though, are of course, undesirable. A mixture 
 of barium sulphate, red lead, a little vermilion, and eosin to 
 brighten the mixture, forms a not uncommon substitute for 
 vermilion. If any residue over 1 or 2 per cent, is left in igni- 
 tion it is well to examine its nature with a view to detecting 
 adulteration or carelessness in manufacture. Small quan- 
 tities of ferric oxide (under 1 per cent.) are frequently found in 
 vermilion. This is, doubtless, derived from the vessels used 
 in manufacture, and in such small quantities must be 
 regarded as accidental and allowable, though a treatment 
 with warm dilute hydrochloric acid should remove the greater 
 part of this impurity. Alkali, or alkaline salts, other than 
 mere traces, would indicate imperfect washing and probable 
 formation by a wet process. 
 
 Eosin is sometimes added to a pure vermilion, not, in 
 this case, to cover the admixture of a white substance, but 
 to brighten a badly prepared and probably over-heated 
 pigment. In any case its fugitive nature renders its presence 
 in colour intended for any but the most temporary purposes 
 extremely undesirable. 
 
 Chinese vermilion, which is greatly esteemed for its 
 beautiful full colour, usually contains a small quantity of 
 organic matter, apparently glue, but not in sufficient quantity 
 to be in any way objectionable. 
 
 Should it be considered in any way desirable to determine 
 the mercury in this substance, a portion of, say, 10 grams 
 should be mixed with pure quicklime and " burnt in a com- 
 
INORGANIC PIGMENTS. 109 
 
 bustion tube packed in the usual manner. The arrangement 
 of the ingredients in the tube, starting from the front end, is 
 
 as follows : 
 
 Lime and iron or copper. 
 
 Vermilion and lime. 
 C0 2 mixture. 
 
 The best plan is to weigh the vermilion on to 10 to 20 
 grams of freshly ignited lime in a glass or porcelain 
 mortar, and then fill in, either by a funnel or by scooping 
 with the tube itself into a clean dry combustion tube of about 
 f to inch internal diameter, closed at one end, and with 
 2 to 3 inches of a substance to evolve CO.,, 1 already filled 
 into the closed end, and plugged down with asbestos. 
 
 tn 
 0* 
 
 FIG. 4. 
 
 The mortar is then rinsed out with one washing of lime, 
 and a plug of asbestos inserted in the tube, after which a further 
 portion of lime is filled in. A layer of copper turnings, gauze 
 
 1 The following substances are suitable to use for the evolution of CO 2 : 
 
 1. A mixture of 3 parts fused potassium bichromate with 1 part of ignited 
 anhydrous sodium carbonate, both finely powdered, and then intimately 
 mixed. This is a very good and sensitive mixture. On ignition 
 
 K 2 Cr 2 7 + Na 2 CO, = K 2 Cr0 4 + Na 2 CrO 4 + C0 2 . 
 
 2. Sodium bicarbonate. On ignition 
 
 2NaHC0 3 = Na-jCO, + H 2 + C0 2 . 
 
 3. Magnesite. On ignition 
 
 MgCO., = MgO + C0 2 . 
 
 4. Oxalic acid, anhydrous. On ignition 
 
 coon - co * + co + OH - 
 
 1 and 3, which give dry C0 2 , are preferable. 
 
110 CHEMISTEY OF PIGMENTS. 
 
 or spirals of wire, or of iron nails or wire, about 3 inches 
 long, is then filled in, and .the tube drawn out obliquely 
 and (when cooled) placed in a combustion furnace, the drawn- 
 out part dipping well below the surface of water in a flask 
 or beaker. The heating is started from the open end of 
 the tube, and when 3 to 4 inches of lime are red hot, 
 one burner at a time should be lit, and also one burner 
 at the back under the plug of asbestos by the C0. 2 mixture 
 to prevent sublimation back, and to start a stream of CO.,, 
 which should be maintained, so as to secure constant bubbling 
 of gas through the water (thereby preventing a back rush 
 of water). When the whole of the lime is red hot all 
 the burners should be lit so as to sweep over all the mercury 
 vapour. Then, when no more globules of mercury condense, 
 the curved part of the tube is broken by touching it with a 
 wet file or glass rod, and any mercury which may have 
 accumulated in this front part is washed into the flask and 
 gently agitated to cause the globules to cohere, the water 
 poured off as completely as may be, and the mercury trans- 
 ferred to a weighed porcelain capsule, the visible water being 
 removed by blotting paper, and the mercury dried at a low 
 temperature in a desiccator and weighed. 
 
 The use of copper or iron is necessary in the case of 
 mercuric sulphide, as otherwise sulphide may sublime over, 
 or, if water vapour be present, sulphuretted hydrogen be 
 formed. In either case the heated metal retains the sulphur 
 and allows the mercury to pass over. 
 
 The action of the lime may be represented as follows : 
 
 2HgS + 2CaO - 2CaS + 2Hg + 2 . 
 
 Some of the calcium sulphide is probably oxidised to sulphate 
 by the oxygen liberated. 
 
 The action of the kon or copper is : 
 
 M" + HgS = M" S + Hg, 
 
 or 
 
 M" + H 2 S = M" S + Kg. 
 
INORGANIC PIGMENTS. Ill 
 
 This dry distillation method is very accurate indeed, but 
 in ordinary work is certainly seldom necessary. 
 
 When vermilion groud in oil is examined a portion 
 should be freed from oil, as recommended in the case of 
 white lead and other pigments, and eosin looked for in 
 the ethereal solution. The oil-free matter is ignited, and, 
 if necessary, the residue examined. When a determination 
 of the oil is not considered necessary, it will be sufficient to 
 shake up with ether and filter off the solution, examining its 
 colour, and to ignite a portion of the oily material. 
 
 The nature of probable adulterants of vermilion has been 
 indicated in the preceding paragraphs. Having regard to 
 the high specific gravity of vermilion, it is obvious that very 
 few adulterants could be used in any amount without so 
 seriously reducing the specific gravity of the material that it 
 would be apparent to the user. 
 
 We have occasionally examined adulterated samples of 
 vermilion, and also samples of mercuric sulphide brightened 
 with eosin ; doubtless these latter were badly prepared, and 
 "faked" in this manner to avoid the cost of resublimation. 
 The composition of two of these is given below : 
 
 Mercuric sulphide .... 5S-9 50 
 
 Barium sulphate .... 12-0 
 
 Lead sulphate . . . . 29-1 49 
 
 Eosin ...... 1 
 
 100-0 100 
 
 We also give the composition of some genuine samples : 
 
 Moisture 0-4 0-5 
 
 Loss on ignition (HgS) . . . 99'1 99'2 99-1 99'4 
 Non-volatile matter 0'5 0-3 0-9 0'6 
 
 100-0 100-0 100-0 100-0 
 
 The non-volatile matter was either clay or oxide of iron, 
 with traces of alkali in the case of the last sample ( = under 
 0'03 per cent. KHO). 
 
112 CHEMISTRY OF PIGMENTS. 
 
 Vermilion, notwithstanding its extreme brilliance and 
 good body, has a rather bad reputation for permanence. It 
 would appear to be somewhat liable to molecular change, 
 as it is stated that exposure to daylight has changed from 
 red to black vermilion letters in illuminated books exhibited 
 in museums, which had remained intact for hundreds of 
 years with the limited exposure incurred in use. It must 
 at the same time be admitted that vermilion frequently will 
 retain its colour for a long time and under trying circum- 
 stances. Being a very inert substance and a sulphide, it is 
 not easily changed in composition, or in any way chemically 
 affected by any reasonably possible use except, of course, 
 at very high temperatures, and, as we have before stated, 
 the liability to molecular change appears to be much reduced 
 by careful removal of impurities, and in the case of the dry- 
 formed material by condensation at a high temperature. 
 
 It must be remembered that vermilion is used for paint- 
 ing out-door work by both Post Office and Fire Brigade 
 authorities, and that it stands well on their carts and pillar- 
 boxes under very trying conditions. We know that in the 
 case of the Metropolitan Fire Brigade great care is exercised 
 in the selection of vermilion for this work, and doubtless 
 the Postal authorities exercise similar care. 
 
 We think that in many modern cases of serious deteriora- 
 tion of so-called vermilion, an examination of the colour 
 would have shown it to be a " vermilionette," the fancy 
 name for adulterated, brightened scarlets, some of which 
 are almost innocent of mercury. 
 
 Royal Scarlet (Mercuric Iodide). 
 
 This pigment is prepared by the double decomposition of 
 solutions of mercuric chloride and potassium iodide. It is, 
 as both these substances are expensive, desirable to use 
 molecular proportions. The proportions 4 mercuric chloride 
 
INORGANIC PIGMENTS. 113 
 
 to 5 potassium iodide agree very closely with those required 
 by the scheme. 
 
 HgCL, + 2KI * HgI 2 + 2KC1. 
 271 332 454 
 
 Though a very brilliant colour, mercuric iodide is not to 
 be recommended. 
 
 IV, THE CHROMIUM COLOURS. 
 
 Two series of colours owe their tints to the presence of 
 the element chromium, the chromium oxide greens and the 
 yellow and red chromates. The former contain as the colour- 
 ing group the oxide Cr. 2 O 3 , sometimes as hydroxide, some- 
 times as phosphate, while the latter owe their colour to 
 chromic anhydride Cr0 3 . 
 
 The Chromium Oxide Greens, 
 
 Chromium oxide, Cr 2 3 , prepared by ignition of the 
 hydroxide, or by the methods given below, is a sage green 
 coloured substance easily worked in water or oil, and abso- 
 lutely permanent as to tint, being not only unaffected by 
 light, but also unattacked by acids or alkalies. It is insoluble 
 in concentrated acids, and can only be brought into solution 
 by fusing with an oxidising mixture such as sodium carbonate 
 and potassium nitrate, or chlorate, when it is converted into 
 chromic anhydride, thus : 
 
 Cr 2 O, + 30 = 2CrO i . 
 
 This is found in the product of fusion as alkaline chromate. 
 
 On account of its permanency chromium oxide is a 
 colour much esteemed by artists. We give some methods 
 of preparing it ; they are mostly based on the reduction of 
 chromates and bichromates. 
 
 (a) By the ignition of mercurous chromate (the brick- 
 red precipitate obtained on adding a soluble chromate to a 
 solution of a mercurous salt) a very pure and fine-coloured 
 
114 CHEMISTBY OF PIGMENTS. 
 
 oxide is obtained. The process should be carried out in a 
 covered porcelain or earthenware crucible at a dull red heat. 
 4Hg. 2 Cr0 4 = 2Cr. 2 5 + 8Hg + 50 2 . 
 
 (6) Potassium bichromate is ignited with sulphur. Potas- 
 sium sulphate and chromium oxide are left in the crucible 
 and can be separated by washing. The following scheme 
 may represent the action : 
 
 K 2 Cr 2 7 + S = K 2 S0 4 + Cr,0... 
 
 (c) Potassium chromate and charcoal are ignited together 
 in a crucible. Potassium oxide and carbonate, and chromic 
 oxide remain. 
 
 The melt is treated with boiling water, and after disin- 
 tegration, the liquid is boiled to precipitate any hydroxide of 
 chromium which may have formed and dissolved in the free 
 alkali, and the insoluble part, after washing, is dried and 
 ignited. Chromium oxide prepared in this way is seldom 
 free from alkali. 
 
 (d) By the ignition of potassium bichromate with an 
 equal weight of ammonium chloride and a little sodium 
 carbonate a mixture of alkaline chloride and chromic oxide 
 is obtained. 
 
 (e) On the ignition of ammonium bichromate a violent 
 action with incandescence takes place, and a voluminous 
 green-tea-like residue of chromium oxide remains. 
 
 By all the methods described above the green oxide of 
 chromium Cr. 2 O 3 is obtained. Two other substances closely 
 allied to it are, however, used as green colouring matters a 
 hydroxide and a phosphate of chromium. 
 
 Guignet's green, vividian (veridian), Mittler's green, chromium 
 hydroxide, CV 2 3 2H 2 0. 
 
 This brilliant emerald green pigment is prepared by the 
 ignition of three parts of boric acid with one part of potassium 
 
INORGANIC PIGMENTS. 115 
 
 bichromate to dull redness for a suitable period. On the 
 small scale we have found one hour sufficient. A copious 
 evolution of oxygen anci violent frothing take place ; it is 
 therefore advisable to use a large crucible for the fusion. The 
 melt is washed out with hot water, and if the operation has 
 been carried out properly, only a very slight yellow colour 
 should be imparted to the wash water, the whole of the 
 chromate being reduced. It appears that a mixture of 
 potassium and chromium borates is formed, and the latter is, 
 on heating with water, decomposed and hydrolised into 
 chromium hydroxide and boric acid. 
 
 The product obtained by us in this manner was a full 
 brilliant green, and after careful washing and drying, first in 
 the air and then in a water oven, it lost on ignition 14' 1 per 
 cent. Cr 2 3 2H 2 requires 19'0, Cr 2 3 H 2 10'5. This sub- 
 stance would appear to be a mixture. 
 
 We found that by using less boric acid a dull green, 
 which only lost a trace on ignition, and was evidently Cr 2 3 , 
 was obtained, and the action was by no means complete, a 
 good deal of unaltered bichromate being present. This seems 
 to point to the need of sufficient boric acid to form chromium 
 borate in order that the hydroxide and not the oxide may be 
 formed. 
 
 A sample of Guignet's green, prepared by M. Kestner, 
 and analysed by a Mr. Shipton, one of Hoffman's pupils, 
 contained boric acid, and on drying at 100 had the following 
 composition : 
 
 Oxide of chromium . . . 76*47 
 
 Boric acid l 12-10 
 
 Water 11-43 
 
 100-00 
 
 A sample of " green oxide of chromium," sold by a firm 
 of artists' colourmen of repute, was examined by us. It 
 contained 
 
 1 By difference. 
 
116 CHEMISTRY OF PIGMEN-TS. 
 
 Oil 27-4 
 
 Chromium oxide . . . 66-0 
 
 Alumina 5'6 
 
 Lime salts, etc. . . . 1-0 
 
 100-0 
 
 The proportion of alumina seems larger than might 
 reasonably be present as impurity ; it was possibly added to 
 reduce the colour to a standard tint. 
 
 A sample of veridian examined by us, from the same maker 
 as the green chromium oxide just noticed above, contained : 
 
 Oil (loss on ignition less H 2 calculated) . 48-9 
 
 Chromium hydroxide 46'4 
 
 . , ( Matter soluble in water (alkaline chromate) 3-5 
 
 \Matter soluble in acid . 1/2 
 
 100-0 
 
 An actual determination of oil gave 50'3 per cent. This 
 rather tends to show that our calculation of chromium 
 hydroxide as Cr 2 O 3 2H 2 from the percentage of Cr 2 3 was 
 not justified ; we suggest this in view of the composition of 
 our own preparation. The unaltered chromate which, per- 
 haps, would brighten the green seems to point to insufficient 
 ignition and subsequent insufficient washings. Its presence 
 is, in our opinion, undesirable. 
 
 IVa THE CHROMATE COLOURS, 
 
 We believe we are correct in stating that all chromates 
 are coloured bodies, but only certain of these compounds, 
 from the beauty of their tint and other considerations, are 
 used as pigments. Of these the principal are the chromates 
 of lead, while less important members of the group are zinc, 
 barium, and strontium chromates. 
 
 The Chromates of Lead. 
 
 Lead forms two definite compounds with chromic acid 
 the neutral chromate containing one equivalent of chromic 
 
INORGANIC PIGMENTS. 117 
 
 anhydride and one of lead oxide (PbO), a yellow compound 
 varying in depth of colour according to the conditions of its 
 formation, and represented by the formula PbCr0 4 , and a 
 basic chromate containing two equivalents of PbO to one of 
 CrO a , Pb 2 Cr0 5 ( = PbCr0 4 , PbO), a beautiful red compound. 
 An intermediate substance, probably a mixture, is known as 
 orange chrome. 
 
 Normal Lead Chromate Colours (Chrome Yellow, Paris 
 Yellow, Cologne Yellow, etc.). 
 
 When a neutral or only slightly acid solution of a lead 
 salt is treated with a solution of a chromate a heavy yellow 
 pulverulent precipitate separates, and an alkaline salt is left in 
 solution. In the case of lead acetate and sodium chromate 
 the changes occurring may be represented by the equation 
 
 Pb (C 2 H,0 2 ) 2 + Na 2 Cr0 4 - PbCr0 4 + 2NaC 2 H 3 O 2 . 
 
 The compound thus produced is constant whatever the 
 conditions of precipitation ; a full yellow, such as pure 
 chromate, is not often used in commerce. Such pure colours 
 are not, however, entirely unknown, one examined by us, 
 ground in oil, had the composition- 
 Oil 25-0 
 
 Lead chromate (PbCr0 4 ) .... 75-0 
 
 100-0 
 
 It is more common to prepare a diluted pigment contain- 
 ing a greater or less percentage of some inert white sub- 
 stance ; by this means a range of colours from a full orange 
 yellow to the palest lemon can be obtained. 
 
 There are three types of these diluted yellows, (a) chro- 
 mate white lead yellows, (6) chromate lead sulphate yellows, 
 (c) chromates diluted with whites not containing lead. 
 
 (a) The first type of yellow, which seems, though not 
 very much used, to be. theoretically the most satisfactory, 
 having regard to the excellent drying and covering powers of 
 
118 CHEMISTRY OF PIGMENTS. 
 
 white lead, is prepared by treating dry white lead with a 
 quantity of dilute acetic or nitric acid insufficient to entirely 
 dissolve it, and precipitating with alkaline chromate, or more 
 usually bichromate, in insufficient quantity to attack all the 
 dissolved lead. By this means a mixture of lead chromate 
 and white lead is obtained, which varies in colour according 
 to the amount of white lead dissolved. This is allowed to 
 deposit, and washed free from soluble salts. 
 
 Two samples, evidently prepared by this method, and 
 called "pure chrome yellow," were almost pure lead chro- 
 mate of a full colour. 
 
 Lead chromate 92-2 93-4 
 
 White lead 7-8 6-6 
 
 100-0 100-0 
 
 Samples of lemon and orange yellow of this kind had the 
 following composition : 
 
 Lemon. Orange. 
 
 Lead chromate 31-5 47'7 
 
 White lead . .... 59-0 47 -2 
 
 Insoluble in acid 2'7 
 
 Difference 6-8 5-1 
 
 100-0 100-0 
 
 (b) The second type of colours, with lead sulphate as a white 
 base, is always considered by the trade as pure, consisting 
 only of lead compounds. Colours of this kind are usually 
 prepared by precipitating lead acetate or nitrate with mixtures 
 of alkaline bichromate and Glauber's salts (sodium sulphate) 
 or alkaline bichromate and sulphuric acid. Lead chromate 
 and lead sulphate are by this process simultaneously pre- 
 cipitated, and the proportions may be so adjusted as to 
 produce the requisite variety of shades. 
 
 Biot and Delisse precipitate lead sulphate by treating lead 
 acetate with sulphuric acid or sodium sulphate, and then 
 digest three parts of the washed precipitate with one part of 
 
INOEGANIC PIGMENTS. 119 
 
 potassium chromate in hot water. The conversion of the 
 chromate according to the following scheme 
 
 K 2 Cr0 4 +-bS0 4 = PbCr0 4 + K 2 S0 4 , 
 
 is almost complete, and the lead chromate is obtained mixed 
 or combined with the unaltered lead sulphate. By this 
 means a good yellow is produced of very high colour for the 
 amount of chromate used ; the covering power is, however, 
 less than that of the precipitated yellow. Lead chloride is 
 converted iiito chromate in a similar manner. 
 We have examined some of these colours : 
 
 Lead chromate . . . 57'3 Lead chromate . . . 50-4 
 
 Lead sulphate . . . 26'3 Lead sulphate . . .41-2 
 
 Calcium carbonate, etc. . 7-1 White lead .... 8-4 
 
 Insoluble in acid (BaS0 4 ) . 9'3 
 
 100-0 100-0 
 
 Oil 22-2 
 
 Lead Chromate . . . 38'8 
 
 Lead sulphate . . . 23-2 
 
 Sulphate of lime . . . 15-8 
 
 100-0 
 
 (c) The third class, comprising the cheaper chrome 
 yellows of the kind usually known as Cologne yellow, includes 
 all those colours where the required paleness of tint is 
 obtained by the addition of white substances other than lead 
 compounds, such as sulphate of barium. 
 
 Basic Lead Chromates. 
 
 The basic compounds (or rather, perhaps, mixtures of lead 
 chromate) include orange chrome and chrome red, the latter 
 being the more basic substance. 
 
 These substances are usually prepared by the action of 
 sodium hydroxide on yellow lead chromate, the alkali 
 abstracting the chromic anhydride from a portion of the lead 
 compound, forming alkaline chromate, while basic chromate 
 of lead remains. 
 
 2PbCr0 4 + 2NaOH = Pb 2 CrO 5 + Na 2 Cr0 4 + H 2 0. 
 
120 CHEMISTRY OF PIGMENTS. 
 
 Basic lead chromate is known as Derby red or Chinese 
 red. It is, when carefully prepared, a very beautiful colour, 
 somewhat resembling vermilion. It is, sometimes at least, a 
 crystalline substance consisting of single rectangular prisms, 
 and it is stated that the brightest shades owe their beauty to 
 the (relatively) large size of the crystals. It is desirable to 
 make small, roughly quantitative experiments to ascertain 
 the proportion of alkali and chromate required to prepare a 
 pigment of the desired colour and to use the same proportions 
 and dilution in the actual preparation. 
 
 Liebig and Wohler prepared vermilion-coloured reds by 
 dropping into a fusion of equal weights of potassium and 
 sodium nitrates, small pieces of chrome yellow. Ebullition 
 occurs and the mass becomes black ; it is heated until ebulli- 
 tion ceases. If it is overheated the product becomes brown 
 (? owing to formation of lead dioxide). The melt should be 
 w r ashed quickly. 
 
 Another process is to treat a solution of lead acetate with 
 a mixture of potassium hydroxide and chromate. 
 
 2PbO 2 (C 2 H 5 0) 2 + 2KOH + K 2 Cr0 4 
 - Pb 2 Cr0 5 + 4KOC 2 H 3 + OH 2 . 
 
 Prinvolt prepared a chrome red he called Persian red by 
 digesting 25 parts of lead carbonate with 10 parts of potas- 
 sium chromate dissolved in water, for two days. Basic lead 
 chromate and potassium bichromate (and carbonate) are said 
 to be formed. The liquid is boiled for half an hour, some of 
 the precipitate becomes decomposed and lead chromate is 
 formed, the precipitate turning violet. This is washed and 
 digested with sulphuric acid (1 in 100 water) and the red 
 pigment is the result. 
 
 We have examined several samples of Derby red, Chinese 
 red and orange chrome, of which we give the composition. 
 
INORGANIC PIGMENTS. 
 
 121 
 
 Chinese Red. 
 
 Water and volatile matter 
 Lead oxide (PbO) . 
 Chromic anhydride 
 Other matters . 
 
 Lead oxide . 
 Chromic anhydride 
 Other matters 
 
 Derby Red. 
 
 
 
 
 
 
 
 0-7 
 
 
 
 
 
 80-0 
 
 80-1 
 
 79-8 
 
 79-2 
 
 79-3 
 
 80-8 
 
 16% 
 
 17-2 
 
 17-8 
 
 18-1 
 
 17-5 
 
 17-6 
 
 3-2 
 
 2-7 
 
 *2-4 
 
 2-0 
 
 3-2 
 
 *l-6 
 
 100-0 100-0 100-0 
 
 100-0 100-0 100-0 
 
 79-4 
 
 14-3 
 
 6-3 
 
 Orange Chrome. 
 
 80-4 74-5 
 
 12-9 13-9 
 
 6-7 11-6 
 
 72-7 
 14-7 
 12-6 
 
 100-0 100-0 100-0 100-0 
 
 In most of the above samples the "other matters" con- 
 sisted of carbonate of lime, which in small quantity is 
 easily accounted for by the action of alkali on hard water 
 used in manufacture thus : 
 
 CaC0 3 , H 2 CO, + 2KOH = CaCO, + K 2 C0 3 
 + H 2 0' 
 
 The samples marked * were also brightened with eosin 
 (about O3 per cent.), which is an undesirable practice. 
 
 One sample of Derby red examined by us was not a 
 chrome colour at all. It had the following composition : 
 
 Water .... 
 Loss on ignition 
 Ferric oxide . 
 Alumina 
 
 Sulphate of lime . 
 Carbonate ot lime . 
 Insoluble siliceous matter 
 
 8-5 
 
 4-0 
 
 15-9 
 
 ri 
 
 42-3 
 
 3-9 
 
 24-3 
 
 100-0 
 
 a similar pigment to the colour known as light red, 
 which is very much cheaper than a lead chromate. 
 
 Zinc Chromate (ZnCr0 4 ), 
 
 This pigment is prepared by precipitating a solution of 
 zinc sulphate with a solution of sodium or potassium chro- 
 mate. It is necessary that the zinc salt should be fairly pure 
 
122 CHEMISTRY OF PIGMENTS. 
 
 and should be treated with sodium hydroxide or carbonate,, 
 which precipitates a small amount of zinc hydroxide or car- 
 bonate. The precipitate which is formed on the addition of 
 alkaline chromate is of a pale yellow colour, and only requires- 
 washing, drying and grinding to render it suitable for use. 
 
 E. Wagner gives the result of the examination of samples, 
 of English and German manufacture : 
 
 ENGLISH. 
 
 ZnCrO 4 .. 
 Chromic anhydride .... 14-94 55-2 
 
 Zinc oxide 75-35 44-8 
 
 Carbon dioxide . . . . . 3 '61 
 
 Water 6 -19 > 
 
 100-09 100-0 
 
 GERMAN. 
 
 Chromic anhydride . . . 11-88 9-21 
 
 Zinc oxide 45-78 61-47 
 
 Barium sulphate .... 42-34 29-32 
 
 100-00 100-00 
 
 It will be seen that the use of barium sulphate for " lower- 
 ing" purposes is not an exclusively English custom. All 
 these colours have evidently been prepared by previous pre- 
 cipitation of oxide or carbonate as there is but a very small 
 proportion of Cr0 3 present in any of the three. 
 
 Zinc chromate is, we believe, only used to a very small 
 extent in commerce. We have never yet examined a sample 
 of this pigment. 
 
 Silver Chromate (Ag,Cr0 4 ). 
 
 This blood-red pigment, prepared by the precipitation of 
 neutral solutions of silver nitrate with alkaline chromates r 
 is said to be used to some extent in miniature painting. It is 
 unnecessary to state that it is a very expensive substance, and, 
 
INOKGANIC PIGMENTS. 123 
 
 whatever its merits, only suitable for use on the very small 
 scale. 
 
 Mercury Chromates. 
 
 Mercurous chromate, Hg' 2 CrO 4 , prepared in a similar man- 
 ner to silver chromate, has been used as a pigment. It is 
 both costly and easily decomposed by light. It is of a brick- 
 red colour. 
 
 Mercuric chromate, Hg"CrO 4 , prepared by the precipitation 
 of a mercuric solution with alkaline chromate, is a light-red 
 pigment. 
 
 We believe neither of these substances has ever been used 
 to any extent as a pigment, nor are they suitable. For the 
 analyses of the chromates of lead and mixed colours contain- 
 ing these compounds the following scheme will be found 
 satisfactory : A suitable quantity (about 1 gram) of the 
 oil-free colour is weighed into a beaker, covered with hydro- 
 chloric acid, and the beaker, covered with a watch-glass, 
 placed in the waterbath to digest for fifteen to thirty minutes. 
 At the end of this time the chromate will have been reduced 
 to chromium salt in accordance with the scheme 
 
 CrO, + 6HC1 - CrCl, + 3H 2 O + 301. 
 
 The liquid is now diluted with boiling water. The cover and 
 the sides of the beaker are washed to prevent loss of spray 
 and the beaker heated on a flame, with stirring. If any in- 
 soluble matter remains it should be well washed with hot 
 water and its nature examined. It is most likely to be either 
 barium or lead sulphate, though the latter would be partly 
 dissolved by hydrochloric acid. The mixed filtrate and wash- 
 ings are treated with sulphuretted hydrogen (after dilution and 
 cooling) and the sulphide of lead collected and treated as de- 
 scribed on page 93 (white lead). The excess of H 2 S is removed 
 from the filtrate by boiling, a few drops of nitric acid added 
 to oxidise any iron, if present, and ammonium hydroxide 
 
124 CHEMISTEY OF PIGMENTS. 
 
 solution added. This precipitates chromium hydroxide, which 
 is collected, washed, ignited (still in the filter paper) in a pla- 
 tinum crucible and weighed as Cr 2 3 . If a preliminary test 
 has indicated the presence of iron this would also be included 
 in this precipitate as Fe. 2 O 3 and should be estimated by titra- 
 tion, after reduction with SnCl 2 , with bichromate. Barium 
 or lime would be found in the filtrate from the " ammonia 
 precipitate," which, in this as in all other cases, should after 
 the first precipitation be washed by decantation partly on to 
 the filter, given one or two washings, and then the contents 
 of the filter washed into the beaker used for precipitating, 
 redissolved in HC1, and reprecipitated by ammonia which 
 should be only added in slight excess, the excess being boiled 
 off. Unless this procedure is adopted lime is always likely to 
 be precipitated with the bases of the chromium group. Lime 
 can be determined in the mixed filtrates by precipitation with 
 ammonium oxalate and conversion to carbonate or oxide > 
 barium would also be precipitated by ammonium oxalate, 
 hence it would be well to dissolve the carbonate or oxide 
 when weighed in a large excess in fairly strong HC1, and add 
 sulphuric acid to the hot solution. Under these conditions 
 barium sulphate would be precipitated and calcium sulphate 
 remain in solution. It is, of course, impossible that barium 
 should be present in solution if a preliminary test on the 
 original pigment indicated the presence of sulphates soluble 
 in hydrochloric acid. If these be present the S0 3 should be 
 determined in a fresh portion of the pigment treated with 
 HC1, as already described, by precipitation with barium 
 chloride. Lead sulphate, though almost insoluble in water, 
 is moderately soluble in a large volume of hot HC1. 
 
 Having determined the amounts of lead, chromic acid 
 (Cr 2 3 corresponds to 2CrO a ), lime, barium and sulphuric 
 anhydride, if present, it now remains to combine these as they 
 really existed in the pigment. If the lead oxide is in excess of 
 
INOKGANIC PIGMENTS. 125 
 
 that required for PbCrO 4 , and the colour of the pigment does 
 not indicate the presence of basic chromate, and S0 3 is absent, 
 it is best to consider the excess as white lead. Lime would 
 be present as sulphate or carbonate, barium as chromate or, 
 if in the insoluble matter, as sulphate. If sulphuric acid is 
 present, and more lead present than required for all the Cr0 3 , 
 then the S0 3 should be calculated to PbS0 4 , and if this agrees 
 fairly well with the excess of lead, returned as such, but of 
 course some judgment is required to decide such points. In 
 the case of obviously basic chromates it is best to return PbO 
 and Cr0 3 together with such impurities as may be present. 
 
 In all cases it is a good plan to determine whether boiling 
 water extracts more than traces of alkaline and other soluble 
 salts, for the presence of these in any quantity is due to careless 
 washing. A sufficiently accurate method for the examination 
 of lead chromate colours is to treat a weighed quantity with 
 HC1, evaporate to dryness and wash with alcohol. Chromium 
 chloride and any chloride of calcium or other probable metals 
 are dissolved, leaving lead chloride, which is insoluble in 
 alcohol and can be weighed. The chromium can be deter- 
 mined in the nitrate, after evaporating off the alcohol, by 
 precipitation with ammonia, and is weighed as Cr 2 3 . Cal- 
 cium can be determined in the filtrate from the ammonia 
 precipitate. If S0 3 is present, a mixture of PbS0 4 and PbCl 2 
 will be left insoluble in alcohol, and a determination of the 
 S0 3 in a separate portion of the pigment should give figures 
 for calculating the actual amount of lead in the mixed 
 sulphate and chloride. 
 
 This method we have found more especially useful in the 
 case of chrome red and orange, which are usually fairly pure. 
 Its advantage is that the use of H.,8 is not necessary, an 
 advantage in a laboratory which is not isolated from the rest 
 of the world. 
 
 The percentage of Cr0 3 in chromates may be determined 
 
126 CHEMISTRY OF PIGMENTS. 
 
 by passing the chlorine evolved on treatment with HC1, into 
 potassium iodide solution, and titration of the liberated iodine 
 with sodium thiosulphate 
 
 B"Cr0 4 + 8HC1 = B"C1 2 + CrCL + 3C1 + 4H 2 
 KI + 01 = KC1 + I. 
 
 Brunswick Green, 
 
 This pigment is now a mixed colour, prepared by ad- 
 mixture of Prussian blue with lead chromate, a suitable 
 white diluent (usually barytes) being added in sufficient 
 proportion to produce a manageable pigment. It is a rather 
 dullish pure green, and under ordinary conditions is fairly 
 permanent, though chrome yellow has some action, in course 
 of time, on Prussian blue. Brunswick green is very largely 
 used for outdoor work, as painting ornamental ironwork, 
 bridges, railings, gates, etc. 
 
 There are two general methods of preparing this green, 
 (a) by mixing the constituents ready formed, (b) by pre- 
 cipitating the blue and yellow on the finely ground barytes. 
 
 The composition of samples of light, middle and dark 
 Brunswick green examined by us is given in the following 
 table : 
 
 Light. Middle. Dark. 
 
 Chrome yellow (PbCr0 4 ) . . . . 5 "59 1-16 10-11 
 
 Prussian blue 0'95 O66 4-96 
 
 Barium sulphate 91'74 90'39 79-40 
 
 Lime, salts, etc. . . ... . . 1-72 7'79 5-53 
 
 100-00 100-00 100-00 
 
 The following paragraphs from the paper on Prussian 
 blue published by us (Analyst, 225, 1896) sufficiently describe 
 the method of analysis found by us to be satisfactory : 
 
 "Two samples of Brunswick green ground in oil were 
 examined. Brunswick green is a Prussian blue-lead chromate 
 green mixed with barium sulphate (' barytes '). A portion 
 from which the oil had been extracted was gently ignited 
 
INOBGANIC PIGMENTS. 127 
 
 and treated with hydrochloric acid, the solution of lead, iron 
 .and chromium chlorides filtered from the barium sulphate, 
 and the lead precipitated -with sulphuric acid. In the filtrate 
 from the lead sulphate the ' ammonia precipitate ' containing 
 the mixed oxides of iron and chromium was determined. 
 The oxides were separated by fusion with alkaline carbonate 
 and nitrate and extraction of the fused mass with water, 
 Fe 2 3 being insoluble. Direct titration with K 2 Cr 2 7 was 
 difficult, as the colour of the chromium masked the reduction 
 of the iron with stannous chloride : 
 
 Light Green. Dark Green. 
 
 Oil 11-27 13-55 
 
 Prussian blue (Fe x 3 -03) . . . 1-01 4-21 
 
 Chrome yellow . . . . . 4'98 7'10 
 
 Barium sulphate .... 82-74 75-14 
 
 100-00 100-00 
 
 " The nitrogen was determined in each of these samples 
 in about 5 grams, and was '19 and '72 respectively, which, 
 using 4'4 as a multiplier, would give '83 and 3 '16 per cent, 
 of Prussian blue in these samples. We are much more 
 inclined to rely on a direct determination of this kind than 
 on the determination of the iron by the method described. 
 The method of analysis for these colours described by Hurst, 
 and due to Brown (Chem. News, 31st December, 1886), seems 
 still more unsatisfactory. The green is treated with hydro- 
 chloric acid to dissolve out the lead chromate (of course, as 
 lead and chromium chlorides). The residue, barytes and 
 Prussian blue, is ignited to decompose the blue, weighed, 
 treated with aqua regia to dissolve out oxide of iron (and 
 alkalies), and the insoluble portion again weighed. The 
 difference is to be taken as oxide of iron, and multiplied 
 by 2'212 to give Prussian blue. The lead and chromium 
 are of course determined in the original filtrate." 
 
128 CHEMISTEY OF PIGMENTS. 
 
 V IRON OXIDE PIGMENTS, 
 
 A most important class of colours, on account both of 
 their very general use, extending to remote antiquity, and of 
 their high intrinsic value, is that array of pigments the 
 colours of which are due to oxide and hydroxide of iron. 
 This class comprises both natural and artificial colours of 
 varied shades of yellow, red, brown and purple; of the 
 natural earths some are darkened in colour by roasting, 
 resulting in the loss of water of hydration and consequent 
 formation of a redder oxide ; most or all, however, of the 
 natural earths are also used in their unburnt state. 
 
 The composition of these colours is very variable ; some 
 of the red and purple pigments are nearly pure ferric oxide 
 (Fe. 2 3 ), others contain large amounts of silica and lime salts, 
 whilst not infrequently barium sulphate is found as a natural 
 admixture ; many of the browns owe their rich colour to 
 the presence of small quantities of oxide of manganese ; of 
 the yellows, most are hydrated oxides and silicates of iron, 
 usually considerably diluted by (natural) admixture with lime 
 salts. 
 
 In considering this group of pigments we propose to 
 give brief descriptions, first, of the natural earths, raw and 
 " burnt," and then of those members of the group which are 
 usually prepared by more artificial means. It will be con- 
 venient to consider the general properties and method of 
 analysis of these colours as a group rather than as individuals. 
 
 The Ochres, 
 
 There are two distinct series of colours known under the 
 name of ochres, namely, those which owe their colour to 
 hydrated oxide of iron the yellow and brown ochres, and 
 those which are coloured by the anhydrous oxide red ochres. 
 Members of the former class, by the simple process of roast- 
 
INOKGANIC PIGMENTS. 129 
 
 ing (and consequent dehydration), are converted into the 
 latter. 
 
 The ochres essentially consist of ferric hydroxide or oxide, 
 which is usually more or less mixed with clay, sand, lime 
 salts, and occasionally magnesia. The most used ochres are 
 those known collectively as yellow ochres. Yellow ochre is 
 the %/oa. known to the Greeks in the time of Apelles, used 
 also by the Egyptians and Eomans, and also by savage 
 nations in later times for painting their bodies. Its colour 
 is due to yellow haematite, xanthosiderite, Fe 2 3 , H 2 0, brown 
 haematite, limonite, 2Fe 2 O 3 , H 2 0, and bog-iron ore, lymnite, 
 Fe 2 3 3H 2 ; the brown haematite, according to Church, 
 being the most commonly occurring. 
 
 In England ochres are found in Cornwall, often associated 
 with tin and copper ore and separated from these by elutria- 
 tion, in Derbyshire and at Shotover Hill in Oxfordshire, not 
 to mention other localities. The beds are usually above the 
 oolite deposit, covered by sandstone and quartzose sands 
 more or less ferruginous, with plastic clays also containing 
 iron. The following sectional measurements of the Shot- 
 over deposit are taken from Dr. Ure's dictionary : 
 
 Ferruginous grit (forming summit of hill) . . 6 feet 
 
 Grey sand 3 ,, 
 
 Ferruginous concretions 1 ,, 
 
 Yellow sand 6 
 
 Cream-coloured loam 4 ,, 
 
 Ochre 6 inches 
 
 A further deposit of ochre occurs beneath a layer of clay. 
 A sample of this Oxfordshire ochre examined by Prof. 
 Church contained : 
 
 Hygroscopic moisture 7'1 
 
 Combined water 9'0 
 
 Ferric oxide . . 13-2 
 
 Alumina 6'3 
 
 Silica 61-5 
 
 Calcium sulphate 1*4 
 
 Undetermined 1*5 
 
 HXM) 
 
130 CHEMISTRY OF PIGMENTS. 
 
 A sample called Oxford ochre examined by us gave the 
 following figures : 
 
 Oil and water of combination 31 '32 
 
 Oxide of iron 9*04 
 
 Alumina 5'13 
 
 Lime salts 5 -20 
 
 Insoluble matter * .... 49 '31 
 
 100-00 
 1 Including barytes (BaS0 4 ) 20-62 per cent. 
 
 This differs from Church's sample in containing barytes. 
 Though native ochres are very largely used in England, 
 India, France, Italy, Spain and Germany also supply us 
 with considerable amounts of this valuable pigment. The 
 composition of some of these is given below. 
 
 Yellow ochre varies considerably in colour, the variation 
 being caused by the presence of different hydroxides of 
 iron and varying amounts of white matter (clay, etc.). It is 
 seldom that the clay contained in ochre is very ferruginous, 
 samples usually leave a fairly white residue on treatment 
 with strong hydrochloric acid. The colour varies from a 
 pale dull yellow to that now known in England, as it had 
 for years been in India, as khaki. 
 
 Yellow ochre, being a cheap pigment, is not much subject 
 to adulteration ; barium sulphate is sometimes present, but 
 it is difficult to decide whether this is not naturally occur- 
 ring, and, in any case, if the tint is suitable, its presence is 
 entirely harmless. Church states that occasionally ochres 
 are brightened by the addition of such organic colours as 
 turmeric. In this case a yellow colour would be imparted 
 to alcohol, or, if the pigment w r ere ground in oil, probably 
 a mixture of alcohol and ether would extract both colour 
 and oil, and the addition of alkali would, by causing change 
 of colour, indicate the presence of turmeric. 
 
INOEOANIC PIGMENTS. 
 
 131 
 
 Brown ochre is very similar to raw sienna, which is 
 also dealt with in this chapter. 
 
 An analysis of brown ochre sold by a firm of artists' 
 colourmen of repute gave the following figures : 
 
 Oil .... 
 
 Water of hydration, etc. 
 Ferric oxide . 
 Alumina 
 Lime salts, etc. 
 Insoluble siliceous matter 
 
 - 39-0 
 
 34-6 
 
 4-7 
 
 6-6 
 
 15-1 
 
 100-0 
 
 The following analysis of a New Zealand ochre, used 
 as a paint by the natives, given in Dundas Thomson's. 
 Cyclopedia of Chemistry, is of interest : 
 
 Ferric oxide 
 Silica . 
 Water . 
 Organic matter 
 
 64-36 
 13-92 
 20-2 
 4-72 
 
 103-20 
 
 This contained traces of alumina and lime, and gelatinised 
 with acids. The colour of this ochre is not stated. 
 
 COMPOSITION OF YELLOW OCHRES. 
 
 
 French 
 Ochre. 
 
 French 
 Ochre. 
 
 Stone 
 Ochre.* 
 
 " Yellow 
 Ochre." 
 
 Stone 
 Ochre* 
 
 Stone 
 Ochre.* 
 
 Stone 
 Ochre.* 
 
 Water . 
 Loss on ignition 
 
 0-39) 
 7-98 )" 
 
 9-87 
 
 127-8 
 
 1-70 
 4-15 
 
 38-31 
 
 23-37 
 
 23-72 
 
 Oxide of iron . 
 Alumina . 
 
 18-71 ( 
 2-78 t 
 
 33-50 
 
 f 11-21 
 
 I 4-6 f 
 
 13-95 
 
 43-64 
 
 24-75 
 
 22-31 
 
 Lime salts, etc. 
 
 64 
 
 
 
 1-2 
 
 3-20 
 
 8-05 
 
 3-28 
 
 0-88 
 
 Insoluble in HC1 . 
 
 69-50 
 
 56-63 
 
 55-2 
 
 77-00 
 
 10-00 
 
 48-60 
 
 53-09 
 
 100-00 100-00 100-0 
 
 Barium sulphate 
 
 * Stone Ochre. 
 Oil 
 
 Water ot combination . 
 Oxide of iron 
 
 Alumina .... 
 Lime salts, etc. . 
 Insoluble siliceous matter . 
 
 100-00 100-00 100-00 100-CO 
 ~38~62 51-05 
 
 24-5 
 
 3-3 
 11-2 
 
 4-6 
 
 1-2 
 55-2 
 
 100-0 
 
132 CHEMISTEY OF PIGMENTS. 
 
 The variation in composition of these samples, of which 
 those marked with an asterisk (*) were ground in oil, is 
 very remarkable considering that the variation of tint is 
 not great. The large amounts of barium sulphate present 
 in some of these may be naturally occurring, but have prob- 
 ably been added to a natural earth of full colour which 
 would bear lowering. The variations in the amount of ferric 
 oxide, or rather hydroxide, are equally remarkable. 
 
 Red ochre was also known to the Greek painters, who 
 obtained it from Cappadocia and called it sinopis ; it was also 
 known as rubrica, and now goes under a variety of names as 
 red haematite, ruddle, reddle, red chalk, bole, red-iron ore, 
 scarlet ochre, siniped miltos, terra rosa. Its colour is due 
 to anhydrous ferric oxide. A very remarkable feature about 
 this and other red oxide paints is the fact that the propor- 
 tion of ferric oxide is no indication of the depth of colour, 
 or, rather, affords but slight indication. Church quotes a 
 haematite from Cumberland which gave 
 
 Ferric oxide 94'7 
 
 Alumina 2-0 
 
 Silica 2-2 
 
 Moisture 1-1 
 
 100-0 
 
 Other " almost equally rich red ochres contain much less 
 iron oxide, a sinopis from Anatolia, analysed by Klaproth, 
 having been found to contain 21 per cent, only, and others 
 from other localities not above 40 ". 
 
 Four samples of Cornish ochres were examined by us 
 with the following results : 
 
 Ferric oxide .... 40-2 52-3 68*0 85-9 
 
 Manganese dioxide ... 0-8 1-2 1-4 0'6 
 
 Lime salts, etc 4'4 4-6 6-2 4-1 
 
 Siliceous matter . . . 54-6 41-9 24-4 9-4 
 
 100-0 100-0 100-0 100-0 
 
INOEGANIC PIGMENTS. 133 
 
 These were of a fine colour, but those containing more 
 than traces of manganese were somewhat of a reddish-brown 
 tinge instead of pure red. 
 
 Closely allied to red ochre are genuine Indian red and 
 Venetian red. 
 
 INDIAN KED should be a natural iron ore or haematite con- 
 taining over 90 per cent, of ferric oxide, and of a rich purplish- 
 red colour. Some of the red imported from India is obtained 
 by roasting lighter-coloured ores, but most specimens are 
 really natural ores. Church states that some is imported 
 from Ormuz in the Persian Gulf, and that some is an English 
 haematite from the Forest of Dean. The principal feature, 
 from the colour point of view, of this -pigment is the slight 
 purplish tint it possesses. 
 
 Indian red as sold is often an admixture of iron oxide with 
 other materials, probably the result of judicious blending of 
 purple brown, red ochre or " light red," and cheap white 
 substances. We give below the composition of samples of 
 the pigment, both in the dry state and ground in oil, which 
 have been examined by us : 
 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 Loss on ignition 
 
 
 
 22-29 
 
 
 
 30-12 
 
 0-75 
 
 14-00 
 
 Oxide of iron 
 Alumina 
 Lime salts, etc. . 
 
 94-00 
 l-88\ 
 3-42J 
 
 71-34 
 5-26 
 
 96-07 
 
 3-88 
 
 61-92 
 6-34 
 
 59-28) 
 _ / 
 1-15 
 
 53-75 
 28-21 
 
 Insoluble in H 01 
 
 0-70 
 
 1-11 
 
 0-05 
 
 1-62 
 
 38-82 1 
 
 4-04 
 
 100-00 100-00 100-00 100-00 100-00 100-00 
 1 35-82 per cent. BaSO 4 . 
 
 The two latter samples certainly were not entitled to the 
 name of Indian red, but the others, of which II. and IV. were 
 ground in oil, would appear to be genuine. The adulterated 
 samples seldom have the soft appearance of the genuine 
 Indian red. 
 
 VENETIAN KED (Rouge, crocus, colcothar, caput mortuum 
 
134 CHEMISTRY OF PIGMENTS. 
 
 vitrioli) originally was a similar produce to Indian red, but of 
 a purer red tone. Of late years various artificially calcined 
 iron oxides and mixed colours diluted ferric oxides have 
 been sold under this name. 
 
 The following three samples sold as Venetian red were 
 very satisfactory colours, but could hardly be described as 
 haematites, or even as calcined iron oxides : 
 
 Loss on ignition . . . . 1'50 (including oil) 19 '49 
 
 Oxide of iron 21-75 17-20 
 
 Alumina 5-00 2-11 J 24 ' 42 
 
 Calcium salts, etc 11-56 64-94 13-20 
 
 Insoluble in hydrochloric acid ! 60-19 15 75 42-89 
 
 100-00 100-00 100-00 
 
 1 This was barium sulphate. 
 
 We find, in fact, on looking over many analyses, that we 
 have not, in the case of pigments used on the large scale, 
 come across one sample which could be justly termed a 
 haematite. 
 
 Judging from one of its early names, caput mortuum 
 vitrioli, it would appear that calcined green vitriol, or ferrous 
 sulphate, the residue (caput mortuum of the alchemists) of 
 the preparation of Nordhausen sulphuric acid, was recognised 
 as a substitute for the true red earth sold in Venice, or, 
 probably, used by the Venetian school of painters. 
 
 Artificial oxides obtained in this and other ways will be 
 considered in a later section of this chapter. 
 
 Siennas and Umbers, 
 
 These beautiful yellow and brown earths, doubtless, 
 originally took their name from the localities in which they 
 were first found. The existence at Sienna and Umbria of 
 early schools of painters naturally led to the search for 
 suitable colours, and in the ferruginous clay of these districts 
 useful colours were found. The terms now have a more 
 
INORGANIC PIGMENTS. 
 
 135 
 
 extended use, and are applied to any earths having the same 
 general properties as those found in Sienna and Umbria. A 
 very valued variety of .timber, for instance, comes from 
 Cyprus, and is known as Turkey umber. 
 
 RAW SIENNA is usually a marl, occasionally a pure, or 
 nearly pure, clay, containing a considerable proportion of 
 ferric hydroxide, or rather, perhaps, hydrated ferric silicate. 
 It is a rather transparent colour, and works well in both 
 water and oil. Its usual tint is a dullish yellow or yellowish- 
 brown, somewhat like the real khaki. Its permanence under 
 all ordinarily possible conditions is absolute. 
 
 We give below the composition of some samples of this 
 pigment, both in the dry state and ground in water and oil, 
 which have been examined by us : 
 
 DRY SIENNA. 
 
 Hygroscopic water 
 
 Water of combination 
 
 Oxide of iron 
 
 Alumina 
 
 Lime salts 
 
 Insoluble siliceous matter 
 
 
 
 
 
 4-94 
 
 11-7 
 
 9-30 
 
 2-34 
 
 }a*l 
 
 30-72 
 
 30-18 
 4-65 
 
 33-1 ) 
 
 38-83 
 
 35-64 
 
 19-1 
 
 21-15 
 
 22-25 
 
 100-0 100-00 100-00 
 
 SIENNA GROUND IN WATER. 
 
 Water ..... 
 
 Water of combination 
 
 Oxide of iron 
 
 Alumina 
 
 Lime salts . 
 
 Insoluble siliceous matter 
 
 44-70) 
 
 
 42-27 
 
 47-59 
 
 3-90 i' 
 
 44-66 
 
 3-28 
 
 3-09 
 
 
 
 
 16-02 
 
 20-44 
 
 25-29 
 
 18-80 
 
 
 
 
 
 2*64 
 
 17-58 
 
 21-05 )" 
 
 24-30 
 
 19-02 
 
 13-33 
 
 9-00 
 
 11-35 
 
 1164 
 
 100-00 100-00 100-00 100-00 
 
 RAW SIENNA GROUND IN OIL. 
 
 Oil, water of hydration, etc. 40-61 43-12 54-15 
 
 Oxide of iron . . .j 27 . 8g 25 . ?3 31 . 63 
 Alumina . . . J 
 
 Lime salts .... 18-98 18-11 6-29 
 
 Insoluble siliceous matter . 12-52 13-04 7'93 
 
 34-39 24-3 
 14-20 30-3 
 7-3 
 2-9 
 26-34 35-2 
 
 25-07 
 
 100-00 100-00 100-00 100-00 100-0 
 
136 
 
 CHEMISTRY OF PIGMENTS. 
 
 It will be noticed that, speaking generally, the proportion 
 of siliceous matter is much lower in these earths than in the 
 ochres. Those ochres which contain only a small amount' 
 of silica are usually of a deeper, browner shade, more ap- 
 proaching these colours. In fact, the difference between 
 yellow ochre and raw sienna would appear to be rather one 
 of locality and depth of tint than of constitution, of degree 
 rather than kind. 
 
 BURNT SIENNA is, or should be, obtained by carefully cal- 
 cining raw sienna, until, by the expulsion of a portion or the 
 whole of the water of combination, a rich reddish-brown 
 pigment is obtained. This, like raw sienna, works well in 
 both oil and water, and from its pleasing colour and great 
 permanency is held in considerable esteem. Judging from 
 the composition of some samples we have examined, we 
 think it probable that any ferruginous earth of the requisite 
 reddish-brown shade is sold as burnt sienna. This substitu- 
 tion cannot altogether be regarded as fraudulent, as it is 
 difficult to see in what way the buyer is injured, provided the 
 tint is right and permanent. 
 
 The small amount of lime in some of these siennas is 
 very remarkable, and rather tends to support the opinion 
 expressed above as to substitution of any suitably coloured 
 earth. 
 
 We give the composition of samples of this pigment 
 examined by us : 
 
 BURNT SIENNA GROUND IN WATER. 
 
 Water (loss at 100) . 
 Water of combination 
 Oxide of iron 
 
 Alumina .... 
 Lime salts .... 
 Insoluble siliceous matter . 
 
 43-80 
 
 2-47 
 
 30-42 
 
 7-90 
 
 15-41 
 
 100-00 
 
 47-59 
 1-59 
 
 25-69 
 4-92 
 7-07 
 
 13-14 
 
 100-00 
 
INORGANIC PIGMENTS. 137 
 
 BURNT SIENNA GROUND IN OIL. 
 
 Oil 41-08 50-07 37-9 56-5 
 
 Water of combination, etc. .*" . 3-7 7-8 
 
 Oxide of iron 22-83 29'47 11-9 22-6 
 
 Alumina \ 4-83 0-7 1-3 
 
 Lime salts > 1-84 0-6 
 
 Insoluble siliceous matter . . 25-75 13-79 7-8 12-6 
 
 Barium Sulphate ... . . 37-4 
 
 100-00 100-00 100-0 . 100-8 
 
 UMBER (Levant umber, Turkey umber, Terra 'Ombre, 
 umbraun, umbra, Kolnische Erde, Terra Ombra). This brown 
 earth, most of which comes from Cyprus, owes its olive brown 
 colour, in which it differs from most of the iron colours, to 
 the presence of a considerable quantity of oxides of man- 
 ganese. An analysis by Church of a choice sample of 
 Cyprus umber will indicate the general character of this 
 pigment : 
 
 Water given off at 100 C 4-8 
 
 Water given off at a red heat 8-8 
 
 Iron oxide . 48*5 
 
 Manganese dioxide 19'0 
 
 Lime 1-4 
 
 Magnesia 0-5 
 
 Alumina 2-1 
 
 Phosphoric acid 0'9 
 
 Silica 13-7 
 
 Carbonic acid, etc 0-3 
 
 100-0 
 
 Prof. Church remarks that " this sample had the peculiar 
 greenish hue so much prized by artists," and that "it should 
 be stated that a part of the manganese probably existed as 
 Mn 3 4 ". 
 
 The pigment is prepared by levigation, and subsequent 
 drying at a temperature not much exceeding 100 C. If this 
 is exceeded, not only will the hygroscopic moisture be 
 expelled, but some of the water of combination, and a more 
 or less burnt umber will result. 
 
138 CHEMISTRY OF PIGMENTS. 
 
 Kaw umber is a very valuable pigment, as its colour is 
 not easy to satisfactorily imitate, and it is under all ordinary 
 conditions quite permanent : any changes in colour are more 
 probably due to yellowing of the oil used as a vehicle than to 
 alteration in the colour itself ; slight changes are also occa- 
 sionally noticed in water colour, probably attributable to the 
 use of a slightly bituminous earth, but in neither case is the 
 change serious. 
 
 We give below the composition of samples of raw umber 
 obtained from various sources and examined by us : 
 
 I. II. III. IV. V. 
 
 High class Oil- Pre- 
 
 artists' colour free Turkey English pared 
 
 in oil. Matter Umber. Umber. Umber, 
 of I. 
 
 Oil 47-6 
 
 Moisture . . . f 7.7 j^.g 4 ' 3 12 ' 6 5 ' 2 
 
 Water of combination . ( 6-9 8*3 11-0 
 
 Ferric oxide . . . 18-5 35-1 44-9 47'1 50'4^j 
 
 Manganese dioxide . . 11-2 21-3 14-0 10-5 13-8 f 
 
 Alumina . . . .1-8 3-4 5-8 3'1 
 
 Lime salts, etc. . . .4-5 9-1 4-8 3-0 3-6 
 
 Insoluble siliceous matter 8-7 16*5 19-3 15-4 16-0 
 
 100-0 100-0 100-0 100-0 100-0 
 
 The percentage of manganese is, it will be noted, highest 
 in the artists' colour and lowest in the English umber. We 
 are not aware what process the prepared umber had passed 
 through, but judging from its composition and colour we feel 
 justified in stating that it had not been ignited ("burnt"). 
 
 BURNT UMBER, as its name implies, is obtained by calcin- 
 ing the earth known as raw umber. It is slightly redder and 
 darker than the unburnt earth, the change being due to some 
 alteration in the hydration and constitution of the oxides of 
 iron and manganese present. Prof. Church justly remarks 
 that if the iron were present in umber to any considerable 
 extent as ordinary hydroxides a much redder product should 
 be obtained on calcination than is actually the case. Burnt 
 umber is more translucent than the raw earth, and is to all 
 
INORGANIC PIGMENTS. 
 
 139 
 
 intents and purposes absolutely permanent and inert to other 
 pigments. 
 
 We give some analytical figures which will sufficiently 
 indicate the composition of this colour : 
 
 Burnt Turkey Umber. Burnt Umber. 
 
 Moisture 
 
 Water of combination, etc. 
 
 Ferric oxide 
 
 Oxide of manganese . 
 
 Alumina 
 
 Lime salts, etc. . 
 
 Insoluble siliceous matter 
 
 2-5 
 
 4-2 
 
 45-9 
 
 15-6 
 
 2-5 
 
 3-8 
 
 25-5 
 
 100-0 
 1 Included with the ferric oxide. 
 
 BURNT UMBER IN OIL. 
 
 6-00 
 
 46-50 
 9-40 
 
 i 
 
 16-85 
 21-25 
 
 100-00 
 
 Oil . . . . . 
 
 Water of combination, etc. 
 
 Ferric oxide . 
 
 Oxide of manganese 
 
 Alumina 
 
 Lime salts 
 
 Insoluble siliceous matter 1 
 
 39-7 
 
 22-8 
 
 4-3 
 
 3-9 
 
 11-2 
 
 18-1 
 
 Burnt Turkey 
 Umber. 
 
 45-1 
 
 26-7 
 9-0 
 3-4 
 3-4 
 
 12-4 
 
 32-8 
 
 18-6 
 6-8 
 1-3 
 0-3 
 
 402 
 
 100-0 100-0 100-0 
 
 1 And BaS0 4 10'5 per cent., 2-5 per cent., 30*4 per cent. 
 
 The samples poor in manganese and containing barium 
 sulphate in quantity were probably not genuine Turkey umber, 
 but of English or Continental origin. They are seldom as 
 fine in colour as the real Turkey (Cyprus) earth and are not 
 by any means as costly or highly esteemed. 
 
 LIGHT BED-, a colour more in use for artistic than for utili- 
 tarian purposes, is, when genuine, a prepared ochre, a roasted 
 yellow ochre. It is usually lighter and brighter than red 
 ochre ; Church well defines its colour as scarlet, modified 
 by a little yellow and grey. 
 
 The colour of light red is obviously due to anhydrous 
 
140 CHEMISTRY OF PIGMENTS. 
 
 ferric oxide, and to obtain a good colour an ochre free from 
 organic matter, which is not easy to burn off without heat- 
 ing beyond the temperature required for a bright red, and 
 one not too rich in lime, should be used. The temperature of 
 roasting should not be too high ; a dull, red heat is sufficient. 
 It must be remembered that ferric oxide colours look very 
 much darker when hot than after cooling. The product is 
 thrown into cold w r ater, ground and w T ashed. 
 
 Light red is used in both oil and water-colour painting, 
 and is quite permanent. We give the composition of two 
 samples of this pigment ground in oil and sold by artists' 
 colourmen of repute, examined by us : 
 
 I. II. 
 
 Oil {_ 
 
 Water of combination j" 5} 
 
 Ferric oxide 6'0 22 -8 
 
 Alumina 3'8 5*7 
 
 Lime salts, etc 2-6 1-0 
 
 Barium sulphate. 3'5 
 
 Insoluble siliceous matter 32*5 26'6 
 
 100-0 100-0 
 
 The difference in the percentage of ferric oxide is very 
 remarkable, and, as the colours were of very similar tint, 
 shows how little colour depends on the amount of iron and 
 how much on its condition. Both samples might have been 
 and probably were obtained by calcining natural earths, the 
 small amount of barium sulphate present in I. being present 
 either as a natural or accidental ingredient of the earth, or 
 possibly added to reduce the pigment to a standard tint. 
 
 CAPPAGH BROWN (Euchrome Mineral Brown). This brown 
 earth, which in most respects resembles umber but is more 
 reddish, is found in the Cappagh mines on the estate of Lord 
 Audley near Skibbereen in Co. Cork. It gives off a good deal 
 of water at 100 and contains only traces of organic matter. 
 An analysis by Church is given below : 
 
INORGANIC PIGMENTS. 141 
 
 Water, given off at 100 C 18'7 
 
 Water, given off at a red heat ..... 11-6 
 
 Ferric oxide (Fe 2 3 ) 34-4 
 
 Manganese dioxide (Mn0 2 ) - 27'2 
 
 Alumina 2-6 
 
 Lime 1-1 
 
 Magnesia trace 
 
 Silica 4-6 
 
 Phosphoric acid O4 
 
 100-6 
 
 Prof. Church states that probably some of the man- 
 ganese exists as red oxide (Mn 3 4 ) and also, very sensibly, 
 suggests that "the large quantity of water present in this 
 mineral in a loosely attached form (hygroscopic), amounting 
 to nearly one-fifth of the weight of the pigment indicates the 
 the desirability of cautiously drying the substance previous to 
 grinding it in oil. A temperature of 60 C. should not be 
 exceeded." 
 
 Cappagh brown works well in oil, particularly if dried as 
 suggested. Church found that it became slightly redder on 
 exposure for one month to light, but the change did not 
 appear to increase after a further five months' exposure. 
 
 Red Oxide (Chocolate, Purple Brown, etc.). 
 
 For rough outdoor work, the protection of ironwork and 
 other purposes where it is desirable to obtain a cheap protec- 
 tive coating rather than a particularly rich or delicate colour, 
 coarse natural oxides are ground first roughly and then to a 
 fine powder and used, ground in oil, under the name of red 
 oxide, red oxide of iron, oxide, chocolate, etc. Those called 
 red oxide of iron are usually fairly pure, but the others fre- 
 quently contain considerable quantities of barium sulphate, 
 sometimes natural, sometimes added. The colours of these 
 oxides vary from a dark chocolate to a dull brickish red. 
 
 These natural oxides and their artificial allies are very 
 
142 CHEMISTRY OF PIGMENTS. 
 
 much used for painting bridges, girders and all sorts of iron 
 structures. So long as the oil with which these materials 
 are incorporated retains its tenacity and imperviousness to 
 water such coatings will be protective to ironwork, but 
 when water is able to make its way to the iron surface it 
 seems only too probable that the presence of iron oxide in 
 the paint is likely to cause corrosion by acting as the electro- 
 negative element in a couple, in the same way as a spot of 
 rust on the bright blade of a knife or razor will, if not rubbed 
 off, grow over the whole blade. 
 
 The artificial oxide reds are prepared by the calcination 
 of copperas (ferrous sulphate), or by the precipitation of 
 ferric oxide by means of milk of lime or alkaline solutions 
 from waste iron liquors. The shade of those produced by 
 ignition varies according to the temperature and time of 
 roasting, from a light red to a purple. The shade of colour is 
 also regulated by the presence (either added or naturally) 
 of more or less lime salts, or barium sulphate. It is re- 
 markable how little the shade of these colours seems to 
 depend on the amount of iron present, the physical changes 
 produced by roasting having apparently far more effect. 
 
 Below we give the composition of iron-oxide colours of 
 various shades, some dry, some ground in oil : 
 
 - 
 
 RED OXIDES. 
 
 I. II. III. 
 
 Oil ...... 12-3 
 
 Water of combination ... 0*4 0-6 
 
 Ferric oxide ..... 90'5 96-7 22-5 
 
 Alumina 
 
 Lime salts, etc 2-5 traces 23-6 
 
 Insoluble siliceous matter . . 6'6 2-7 5-2 
 
 Barium sulphate .... 36-4 
 
 100-0 100-0 100-0 
 
INOEG-ANIC PIGMENTS. 143 
 PURPLE AND CHOCOLATE. 
 
 +z C fl CD 
 
 .a a ^AF 
 
 ^ a 2 SJH2 Dark Purple Brown. i: Chocolate. 
 
 Hj^pq ^d,pq ^ 5 > p, s>^_^ 
 
 IV. V. VI. VII. VIII. IX. X. XI. XII. 
 
 Oil 22-6 14-0 14-6 10-0 
 
 Water of combination . - O5 
 
 Ferric oxide . . . 57-2 93-6 97-4 85-4 84-1 80-7 18-4 97'8 90-0 
 
 Alumina . . . - 2-9 - / _ , 5-3 
 
 Lime salts, etc. . 2-1 -6 i 3-2 -3 -4 1-0 
 
 Insol. siliceous matter . 18-1 3-0 2-0 7*2 1-9 1-5 5-7 1-8 3'7 
 
 Barium sulphate . . 65*6 
 
 100-0 100-0 100-0 100-0 100-0 100-0 100-0 100-0 100-0- 
 
 The difference in composition of similarly coloured 
 materials, and the similarity in composition of differently 
 coloured materials, are well illustrated in these examples. 
 Compare I. and II. with III. ; X. with any of the other 
 purples ; II. with VI. 
 
 The darker shades of colours, purple and chocolate, are 
 obtained by strongly igniting the red oxides, the higher 
 the temperature of ignition the deeper and more violet is 
 the colour obtained. 
 
 Mars Colours, 
 
 The Mars colours are a series of artificial oxide of iron 
 colours prepared by precipitating ferrous sulphate with milk 
 of lime, drying the resulting mixed precipitate of ferrous, 
 hydroxide and calcium sulphate in the air when the ferrous 
 hydroxide becomes oxidised to the ferric compound and 
 roasting or strongly igniting ; according to the temperature, 
 a yellow, orange or brown pigment is obtained. These colours, 
 like all the ferric oxide colours, are absolutely permanent. 
 
 Terre Verte (Green Verona Earth). 
 
 This natural green pigment is found at Verona, in Italy, 
 and at Cyprus. It is extremely permanent, and owes its. 
 
144 CHEMISTRY OF PIGMENTS. 
 
 colour to the presence of ferrous oxide, probably combined 
 as a silicate. We give the composition of two samples 
 examined by some rather ancient authorities : 
 
 Berthier or K- !_,, HI 
 
 Delesse. Kla P roth - 
 
 Verona. Cyprus. 
 
 Silica . ' . . . . . 51-21 51-5 
 
 Alumina 7 '25 
 
 Ferrous oxide 20-72 20'5 
 
 Magnesia 6-16 1-5 
 
 Soda 6-21 
 
 Potash 18-0 
 
 Water 4-49 8-0 
 
 Manganese oxide .... trace 
 
 96-04 99-5 
 
 These analyses are not very satisfactory, but both seem 
 to indicate that the substance is a ferrous alkaline silicate. 
 The presence of soda and magnesia in the Verona sample, 
 and of potash with only a small quantity of magnesia in 
 that from Cyprus, is of interest. 
 
 The Veronese earth is usually of a purer green than that 
 from Cyprus, which is of a verdigris to apple-green colour. 
 
 Prussian Brown. 
 
 This colour, which is not used to any great extent, is 
 prepared by the careful ignition of Prussian blue. It consists 
 almost entirely of ferric oxide. Prussian blue on ignition 
 gives off cyanogen and apparently leaves a residue of metallic 
 iron which, being in an extremely fine state of division, readily 
 burns, becoming red hot, to a brown oxide of iron. Should 
 the temperature become too high the product is too dark. As 
 Prussian blue is never pure ferric ferrocyanide but always 
 contains alkali-iron cyanide and usually other alkaline salts, 
 it is, even when using genuine samples of blue, not always 
 easy to ensure regularity of tint in the brown pigment. This 
 brown can be diluted to shade by means of the ever-useful 
 barytes or other white pigments. 
 
INOEGANIC PIGMENTS. 145 
 
 The analysis of the iron oxide pigments does not present 
 very great difficulties. In the case of red and yellow pig- 
 ments the following method of procedure should be adopted. 
 A suitable amount, say 1 to 2 grams, of the dry pigment is 
 weighed in a platinum or porcelain capsule and ignited to a 
 dull red heat. In the case of a dry pigment the loss repre- 
 sents the amount of moisture and water of hydration with, 
 in some cases, traces of organic matter. The residue after 
 ignition is scraped into a beaker and treated with concen- 
 trated hydrochloric acid, notice being taken whether effer- 
 vescence occurs (indicating presence of a carbonate). After 
 standing in the water-bath from half to three-quarters of an 
 hour the contents of the beaker are examined and, if the 
 insoluble residue does not appear reddish, diluted with water, 
 allowed to stand for any insoluble matter to deposit, and 
 filtered. The residue in the filter is washed, ignited without 
 drying, and weighed. It may be silica or clay, or barium 
 sulphate with one or both of these. Fusion with alka- 
 line carbonates will convert silica into alkaline silicates 
 soluble in water, clay into alkaline silicates and aluminates, 
 and barium sulphate into barium carbonate and alkaline 
 sulphates. It is usually only desirable to determine the 
 amount of barium, which, being usually weighed as sulphate 
 and occurring in pigments in this form, is returned as such. 
 
 If the residue from the HC1 treatment is coloured it 
 should be re-treated, after weighing, with acid and re-filtered. 
 The filtrate is mixed with the original filtrate and the in- 
 soluble matter again weighed. It can then be determined 
 whether a further treatment is necessary or not. The whole 
 of the filtrate and washings is diluted to 250, 500, or 1,000 c.c., 
 according to circumstances, and a convenient aliquot part, say 
 i, taken, diluted if necessary, and ammonia, in slight excess, 
 added. The liquid is heated to boiling to expel the excess 
 of ammonia. The precipitate is washed once or twice by 
 
 10 
 
146 CHEMISTRY OF PIGMENTS. 
 
 decantation, transferred to the filter and allowed to drain. 
 It is then re-transferred to the beaker, re-dissolved in large 
 excess of hydrochloric acid, suitably diluted and re-precipitated 
 with ammonia. By this means any co-precipitated lime is 
 removed and a precipitate consisting only of ferric oxide and 
 alumina (with possible traces of P 2 O 5 and Cr 2 3 ) obtained. 
 This is weighed. The iron can be determined in another 
 portion of the original liquid by titration with -^ K 2 Cr. 2 O 7 
 after reduction or in the redissolved weighed ammonia pre- 
 cipitate. The former is the more expeditious method. The 
 nitrate from the "ammonia precipitate" contains the lime, 
 magnesia, etc. These may be determined or not as desired. 
 The hygroscopic moisture should be determined in a separate 
 portion in a water oven at 100. 
 
 In the case of pigments ground in oil it is usually sufficient 
 to determine the total loss on ignition, and not to determine 
 the actual percentage of oil, though, of course, for scientific 
 purposes it is certainly better to do this. The determination 
 can be effected in the manner described under " white lead ". 
 
 The brown pigments present rather more difficulty, as 
 many of them contain manganese. The best method, in this 
 case, is to, in the original (filtered) hydrochloric acid solution, 
 adopt the method of separation based on the behaviour of 
 the acetates of iron and alumina on heating. The hydro- 
 chloric acid solution is nearly neutralised with ammonia, 
 care being taken, however, to leave a slight amount of free 
 acid, and then a saturated solution of sodium acetate added 
 in sufficiency to be in slight excess. The liquid, which was 
 yellow, becomes of a deep red colour, owing to the formation 
 of ferric acetate, and smells of acetic acid. This liquid on 
 boiling becomes turbid and deposits a flocculent precipitate of 
 basic ferric (and aluminic) acetate. The manganese remains 
 in solution. The basic ferric acetate (or mixed acetates as 
 the case may be) is collected and washed ; in very accurate 
 
INORGANIC PIGMENTS. 147 
 
 analyses, Fresenius recommends re-solution and precipitation, 
 but this is not usually at all necessary : the precipitate is 
 then dried, ignited, and re-dissolved in HC1, precipitated by 
 ammonia as hydroxide, collected, weighed, and the amount of 
 iron determined by titration, after reduction, with T ^ K 2 Cr 2 7 . 
 By this means the percentages of iron oxide and alumina 
 can be determined. In the nitrate from the basic acetates 
 manganese can be determined by making alkaline with 
 ammonia, with the addition of ammonium chloride, and 
 either passing sulphuretted hydrogen or adding ammonium 
 sulphide. Manganese is precipitated as sulphide. 1 The 
 precipitate is collected, washed, and weighed, either as 
 sulphide after ignition with sulphur in a current of H 2 S, or 
 re-dissolved in HC1 and precipitated by Na. 2 C0 3 as MnC0 3 , 
 which on ignition becomes Mn 3 4 . The filtrate from the 
 manganese may contain lime, magnesia, etc. Ammonium 
 oxalate, in slightly acetic solution, will precipitate the lime, 
 which can be weighed as carbonate or oxide, and the filtrate, 
 after concentration, can be treated with ammonia and sodium 
 or ammonium phosphate to precipitate the magnesia as 
 MgNH 4 P0 4 , which on careful ignition becomes Mg 2 P 2 7 ; but 
 this is seldom necessary. 
 
 VI. COBALT COLOURS. 
 
 The metal cobalt enters into the composition of some few 
 colours, in each case as the chromogenic constituent. These 
 cobalt colours may be considered as of three kinds : (a) pig- 
 ments formed of a white basic oxide with cobalt oxide ; (b) 
 
 1 It is desirable that a considerable quantity of ammonium chloride 
 should be present in the solution from which manganese sulphide is to be 
 precipitated, and that the solution should stand twenty-four hours after the 
 addition of ammonium sulphide before filtering. The sulphide should be 
 washed with water containing ammonium sulphide, and the funnel not 
 allowed to remain empty after each washing runs through, as otherwise 
 oxidation may occur, and manganese pass through the filter. 
 
148 CHEMISTRY OF PIGMENTS. 
 
 silicate of cobalt ; (c) cobalt potassium nitrite. We will con- 
 sider these three classes. 
 
 (a) Cobalt Oxide with a Basic Oxide, 
 
 COBALT BLUE (Cobalt Ultramarine, Thenard's Blue). Cobalt 
 blue is, according to its method of preparation, a mixture of 
 either oxide, phosphate or arsenate of cobalt with alumina, 
 and is a fine deep blue, somewhat like ultramarine, but with 
 a tendency to violet which is more marked in artificial light. 
 It is prepared by precipitating a solution of a cobalt salt 
 (the nitrate, acetate or chloride) with sodium phosphate or 
 arsenate. The gelatinous violet precipitate thus obtained 
 is washed well with water and mixed with three to five 
 times its volume (or more in the case of the arsenate) of 
 freshly precipitated and washed alumina. The mixture is 
 thoroughly incorporated and dried until brittle and in a suitable 
 condition for ignition. It is then transferred to a clay crucible, 
 which is well covered and ignited to a cherry red for about 
 half an hour. It is important that no reducing gases should 
 be allowed access to the ignited mass, and Regnault has sug- 
 gested the addition of a small quantity of mercuric oxide which 
 gives off oxygen on heating, and the mercury volatilising 
 leaves no residue to contaminate the product. It is important 
 that the cobalt salt and the alumina used should be free from 
 all other metals, the oxides of which are coloured, e.g., iron 
 nickel, manganese. 
 
 Another process by which a similar but inferior colour is 
 obtained is, the co-precipitation of the oxides of cobalt and 
 aluminium from a mixture of the salts, e.g., cobalt nitrate and 
 alum, by means of sodium carbonate. The precipitate of 
 mixed oxides is washed, dried and ignited as is, in the former 
 method, the mixed phosphate or arsenate and alumina. 
 
 Binden recommends that cobalt chloride should be treated 
 
INORGANIC PIGMENTS. 149 
 
 with ammonia to precipitate the oxide, which, after washing, 
 is mixed with alumina^ and ignited. 
 
 Cobalt blue is permanent, non-poisonous and a fine colour,, 
 though, as already stated, somewhat inclined to violet. It 
 lacks the brilliance of ultramarine, which as a blue is unsur- 
 passed. 
 
 COBALT PINK. This pigment is prepared by mixing mag- 
 nesium carbonate and a solution of cobaltous nitrate to a 
 paste and calcining the mixture, after evaporation to dryness, 
 in a covered crucible. 
 
 COBALT BROWN. A brown pigment is prepared by adding 
 ferric oxide to the mixture of alumina and cobalt salt used 
 for making the blue, or by igniting ammonia alum with 
 cobalt sulphate and ferrous sulphate ; a high temperature is 
 requisite for the carrying out of this latter process. 
 
 These cobalt-basic-oxide compounds, from the fact that 
 the presence of reducing gases in the crucible damages the 
 pigment, and that the addition of mercuric oxide or man- 
 ganese dioxide tends to improve the pigment, would appear to 
 be cobaltic compounds. 
 
 Another pigment which to some extent belongs to this 
 class is 
 
 Cceruleum (Calin, Bleu Celeste). 
 
 This pigment, which is lighter in colour than cobalt blue, 
 is apparently a stannate of cobalt, mixed with calcium 
 sulphate and silica. It is said to be in a state of purity, 
 
 3 (Sn0 2 CoO) + Sn0 2 . 
 
 An analysis given by an unknown authority is as follows : 
 
 Stannic oxide ' . . 49-66 
 
 Cobaltous oxide ....... 18-66 
 
 Calcium sulphate and silica 31-68 
 
 100-00 
 
 COBALT GREEN (Rinmanns Green). When cobalt oxide is 
 
150 CHEMISTRY OF PIGMENTS. 
 
 ignited with oxide of zinc instead of oxide of aluminium, a 
 green colour is obtained ; this fact is well known to those 
 who are accustomed to blow-pipe analysis. 
 
 This cobalt green is prepared by precipitating from a pure 
 cobalt salt in solution (10 per cent.) the phosphate or arsenate, 
 and, after washing, mixing the precipitate with zinc oxide, 
 and igniting. Sodium carbonate may, less satisfactorily, be 
 substituted for sodium phosphate or arsenate, or a mixed 
 solution of zinc sulphate and cobalt nitrate may be precipi- 
 tated by sodium carbonate. Another method is to mix a 
 solution of a cobalt salt with zinc oxide, evaporate to dry- 
 ness and ignite. 
 
 Some analyses of this pigment are given by E. Wagner. 
 One from the University of Wiirzburg had the following 
 composition : 
 
 Zinc oxide 88-040 
 
 Ferric oxide 0-298 
 
 Cobaltous oxide 11-662 
 
 100-000 
 
 This was a light green. 
 
 Two samples prepared by himself agreed more with what 
 might be expected from the former mode of preparation 
 described by us : 
 
 Zinc oxide 71'93 71-68 
 
 Cobaltous oxide 19-15 18-93 
 
 Phosphoric anhydride .... 8*22 8'29 
 
 Sodium oxide . 0-69 
 
 99-99 98-90 
 
 The sodium oxide was probably present as an impurity due 
 to imperfect washing. 
 
 (b) Cobalt Silicates. 
 
 SMALT (Bleu d'azur, Bleu de Saxe Saxon blue). Smalt is 
 a blue colour prepared in Saxony and in Norway, in the 
 
INOBGANIC PIGMENTS. 151 
 
 former country usually from smaltine (smaltite), an analysis 
 of which by Hofmann is given below : 
 
 4~ 
 
 SMALTINE FROM SCHNEEBERG. 
 
 Arsenic 70*37 
 
 Cobalt 13-95 
 
 Nickel 1-79 
 
 Iron 11-71 
 
 Copper 1-39 
 
 Sulphur 0-66 
 
 Bismuth . 0-01 
 
 99-88 
 
 The typical kind is (Co, Fe, Ni) As 2 . 
 
 In Norway cobaltite CoAsS (or CoS 2 + CoAs. 2 ) is the ore 
 used. 
 
 Smalt is a silicate of cobalt and potassium, and is pre- 
 pared by fusing a crude cobalt oxide with potassium carbonate 
 and quartz. The process is conducted in several stages. 
 
 The ore is first carefully selected and all casual impurities 
 rejected, and is then placed in charges of about three cwt. in 
 a layer five or six inches thick, on the bed of a reverberatory 
 furnace or in a muffle, the object being to roast it in a current 
 of air. By this means the sulphur and a great part of the 
 arsenic is expelled as S0 2 and As 2 3 respectively, the latter 
 oxide being collected in condensing chambers. The roasting 
 should be continued until only sufficient arsenic is left to 
 combine with the less oxidisable metals, the cobalt being 
 converted into oxide. Test portions are taken out from time 
 to time until the tint of the glass obtained is satisfactory, 
 when the roasting is stopped. 
 
 Pure quartz ignited, then slaked and crushed, is washed 
 by levigation from any iron oxide or other impurities. This 
 is mixed with pure potassium carbonate, about one part of 
 the latter being used for three parts of roasted ore and the 
 same quantity of quartz, and some arsenious oxide added to 
 oxidise any ferrous oxide present. The exact amount of 
 
152 CHEMISTRY OF PIGMENTS. 
 
 these ingredients required is ascertained by making small 
 tests. 
 
 Very refractory melting pots are used and placed in a 
 furnace similar to that of a glass oven. This is raised to a 
 very high temperature and in about eight hours the mass fuses. 
 It is from time to time stirred to thoroughly mix and to break 
 up any crust which may form on the surface of the melt. At 
 a white heat the cobalt oxide begins to be attacked by the 
 silicate and a blue glass is formed. The mixed arsenides of 
 the other metals with some cobalt sink to the bottom of the 
 pot and form a brittle metallic-looking speiss. The mass 
 is left for some time at a white heat to allow this to settle 
 completely and the smalt ladled out into vessels of cold water. 
 An easily pulverised glass is thus obtained. The speiss, which 
 begins to be scooped up with the smalt as the bottom of 
 the vessel is neared, is more fusible and may be poured 
 out from under the blue into a niche connected with the 
 furnace chimney, thus allowing the fumes of arsenic to 
 escape. 
 
 The glass is now crushed, ground fine and levigated. As 
 it is a more or less transparent substance the portions of 
 medium fineness are more suitable for colouring purposes 
 than the very finely ground portions, which must be re- 
 smelted. 
 
 The presence of other oxides than those of cobalt and 
 potassium is prejudicial to the colour of the product ; baryta 
 gives a deep indigo tint, sodium, calcium and magnesium 
 produce a reddish shade, iron a blackish green, manganese 
 violet, nickel a less intense violet ; copper, zinc, bismuth and 
 antimony give dull shades. 
 
 The composition of three samples of smalt examined by 
 Ludwig (from Thorpe's Dictionary) is given below : 
 
INOKGANIC PIGMENTS. 153 
 
 Norwegian German German 
 
 deep-coloured deep pale 
 
 sample. coloured. coarse. 
 
 Silica . . . ' \ . 70-86 66-20 72-12 
 
 Potash and soda . . . 21-41 16-31 20-04 
 
 Cobaltous oxide . . . 6-49 6-75 1-95 
 
 Alumina .... 0-43 8-64 1-80 
 
 Protoxide of iron . . . 0-24 1-36 T40 
 Arsenious acid . . . trace 4 08 
 
 Water and carbonic acid 0-57 0'92 0-46 
 
 100-00 100-18 l 97-85 
 (c) Aureolin (Potassio Cobaltic Nitrite). 
 
 This deep lemon-yellow pigment is prepared by adding 
 potassium nitrite to a cobaltous solution acidified with acetic 
 acid. Nitrogen is set free and the salt separates as a yellow 
 crystalline powder 
 
 Co 2 (N0 2 ) 6 6KN0 2 + nH 2 O. 
 
 It is desirable to use strong solutions, as otherwise relatively 
 large crystals are formed and the pigment has little covering 
 power. 
 
 Aureolin, sometimes called Indian yellow, is a very per- 
 manent yellow, but from the nature of its constituents is 
 expensive and only suitable for artists' use. It works well 
 in both oil and water. It is quite a modern colour. 
 
 VII. COPPER PIGMENTS. 
 Copper Greens, 
 
 The hydrated and some other compounds of copper are, 
 as is well known, usually of a blue or green colour, and 
 some of these have from very early ages been used as green 
 colours. The compounds principally used are the basic 
 carbonate, the basic acetate, and the arsenite and aceto- 
 arsenite ; the basic chloride was also formerly used under the 
 
 1 This total is given in the Dictionary as 101 '18. 
 
154 CHEMISTRY OF PIGMENTS. 
 
 name of Brunswick green, which name is now applied to^ 
 Prussian blue green, a chromate. We will consider these 
 colours individually. 
 
 MALACHITE (Basic Carbonate of Copper, Green Verditer, 
 Green Bice, Mountain Green Vert de Montague, Berggrun}. 
 This pigment is the most ancient of all the copper greens ; 
 Sir H. Davy in his researches on the pigments found in the 
 baths of Titus and Flavia and other ruins at Eome and 
 Pompeii found this pigment used for mural decoration. 
 
 Malachite is a mineral found in various localities in 
 Europe, Africa, America and Australia. The following list 
 is from Dana : The Urals ; at Chessy in France ; at Schwatz 
 in the Tyrol ; in Cornwall and in Cumberland ; Sandlodge 
 Copper Mine in Scotland ; Limerick, Waterford and else- 
 where in Ireland ; at Grimberg, near Siegen, in Germany ; 
 at the copper mines of Nischne Tagilsk ; at Bembe on the- 
 west coast of Africa ; with the copper ores of Cuba, Chili, 
 Australia, and in New Jersey, Pennsylvania, Winsconsin and 
 California. 
 
 The mineral which is highly valued for ornamental 
 purposes is named from yLtaXa^r?, mallows, in allusion to its. 
 green colour ; and its composition corresponds to CuC0 3 Cu. 
 (OH). 2 . This corresponds to 
 
 C0 2 19-9 
 
 CuO 71-9 
 
 H 2 8-2 
 
 100-0 
 
 Malachite only requires careful selection of pure pieces 
 free from ochreous matter, and grinding to render it fit for 
 use as a pigment. 
 
 Church states that "Malachite as an oil paint has often 
 proved to be permanent, although it may seem to acquire 
 a dull, brownish hue, owing to the darkening and yellowing 
 
INOEGANIC PIGMENTS. 155 
 
 of the oil ; sometimes, however, it becomes somewhat olive 
 in colour ". 
 
 *- 
 
 Various artificial preparations have from time to time 
 been proposed in place of this very expensive mineral for 
 use as pigments. We give in the next sections a description 
 of the preparation of some of these and of similar blue 
 substances. 
 
 BREMEN GREEN (Green Verditer). This colour, which is 
 now but little used except, we believe, by artists and paper 
 stainers, consists chiefly of basic carbonate of copper, mixed 
 with alumina and calcium carbonate. According to Bley r 
 a fine blue-green colour is obtained by dissolving copper 
 sulphate in 10 parts of water, adding a little nitric acid, 
 leaving the solution to itself for a week, then filtering, adding 
 fresh lime water, precipitating with filtered solution of pearl 
 ash and mixing the washed product with gum water to give 
 it lustre (Watt's Dictionary of Chemistry). The object of adding 
 nitric acid is to prevent precipitation of copper carbonate by 
 the lime salts in the water used for solution, and the pro- 
 longed keeping of the solution facilitates the precipitation 
 of any insoluble impurities. Another action of nitric acid 
 would be to oxidise any ferrous salts present as impurities, 
 which means that any precipitate due to iron is yellow ferric 
 hydroxide, which is permanent, and not greenish ferrous 
 hydroxide, which will become yellow. 
 
 At Bremen and Cassel this pigment is, according to 
 Gentele, prepared by grinding 225 Ib. of sea salt with 222 Ib. 
 of crystallised copper sulphate and water to a thick paste. 
 With this, 225 Ib. sheet copper, cut into pieces about 1 in. 
 square, is mixed in strata in a wooden chest made without 
 nails, and digested for three months, with stirring about once 
 a week. At the end of this period the undissolved metal is 
 removed and the precipitate washed with the minimum 
 amount of water. One hundred and eighty pounds of this 
 
156 CHEMISTRY OF PIGMENTS. 
 
 is thrown into a tub with 12 Ib. of hydrochloric acid of 13 
 Baume, well stirred and left for twenty-four to thirty hours ; 
 to 6 volumes of this, 15 volumes of sodium hydroxide (19 
 Baume) and afterwards 6 volumes of water are added. The 
 precipitate is washed, filtered, exposed to the air, and dried. 
 
 Another method, described by Habich, is to treat copper 
 sheathing with about equal parts of potassium sulphate and 
 sodium chloride, forming a paste of the mixture and stirring 
 for some months, or to treat 100 parts of copper with 60 parts 
 of salt and 30 parts of sulphuric acid diluted with three times 
 its volume of water, exposing for some time to the fresh air, 
 and in either case to treat the magma (100 kilos) with copper 
 sulphate (7 kilos) and concentrated soda solution (40 kilos) ; 
 then stir vigorously and pour into 150 kilos of sodium hy- 
 droxide (20 Baume) wash, pass through hair sieves and 
 dry at a temperature not above 78 F. 
 
 In these processes, which appear to be unnecessarily com- 
 plicated, it would seem that under the influence of air and 
 hydrochloric acid, or air and alkaline chloride, copper becomes 
 converted into basic chloride or copper oxy-chloride, which is 
 then converted into an hydroxide which may or may not be 
 allowed to carbonate. 
 
 In the process described by Gentele it is conceivable that 
 a double decomposition occurs thus : 
 
 CuS0 4 + 2 NaCl = CuCl 2 + Na 2 SO 4 , 
 
 upric chloride acting on copper forms cuprous chloride 
 
 CuCl 2 + Cu = Cu 2 Cl 2 . 
 
 This, on oxidation, may become an oxy-chloride 
 Cu 2 Cl 2 + = CuCl 2 CuO. 
 
 The object of adding hydrochloric acid to this is difficult to see, 
 and the addition of caustic soda should result in the formation 
 of cupric hydroxide and not carbonate. Unless it is the case 
 
INOEGANIC PIGMENTS. 157 
 
 that a certain amount of oxy-chloride is left in the colour it is 
 most difficult to understand why such complicated processes 
 are used apparently only txr produce cupric hydroxide. 
 
 SCHEELE'S GREEN (Cupric Arsenite, Swedish Green, Mittis 
 Green, Scheele's Griln, Vienna Green, Veronese Green}. This 
 pigment, discovered by Scheele in 1778 is an arsenite of 
 copper containing an excess of copper oxide, prepared by 
 precipitation. Scheele's original process was to dissolve 
 1 part of arsenious anhydride and 2 parts of potassium 
 carbonate by boiling in 35 parts of water, filtering if 
 necessary, and adding until no further precipitation occurs 
 to a solution of 2 parts of copper sulphate in water. The 
 precipitate was collected, washed and dried at a gentle heat 
 (it will not bear ignition). Church recommends that solu- 
 tions of arsenious acid and copper sulphate should be mixed 
 and potassium carbonate added until the maximum intensity 
 of colour is obtained. Various other methods have been 
 adopted, but the pigment is not much used now, having 
 become very much discredited owing to its poisonous nature 
 and inferiority to other copper-arsenic compounds. It is a 
 pale bat not very bright green and can be readily distin- 
 guished from malachite on the one hand and emerald green 
 on the other by giving a reaction with Marsh's test, a sub- 
 limate of arsenious acid on heating, and not effervescing 
 with dilute mineral acids (differences from malachite), and by 
 not giving off acetic acid vapours on heating with strong 
 sulphuric acid (difference from emerald green). 
 
 EMERALD GREEN (Cupric Aceto- Arsenite, Schweinfurt Green, 
 Paris Green). This pigment, which has now almost super- 
 seded Scheele's green, is a most brilliant colour. It is a 
 mixture or compound of arsenate and acetate of copper 
 supposed to correspond to 
 
 3 CuO As 2 O 3 Cu(C 2 H 3 O 2 ) 2 . 
 
158 CHEMISTRY OF PIGMENTS. 
 
 Various methods of preparation are employed, of which the 
 following are of interest. 
 
 Five parts of verdigris (basic acetate of copper) made into 
 a thin paste with water are added to a boiling solution of 
 more than 4 parts of arsenic trioxide in 50 parts of water, the 
 solution being kept boiling during the addition, and acetic 
 acid being added if a yellowish-green precipitate separates. 
 On further boiling for a few minutes the precipitate becomes 
 crystalline and of the characteristic bright green colour. 
 
 Boiling concentrated solutions of arsenious oxide and 
 copper acetate are mixed in such proportions that equal 
 weights of the two substances are present, when a bulky 
 olive-green precipitate falls the liquid is diluted with an 
 equal volume of water and the mixture placed in a flask 
 which is rilled to the neck to prevent any pellicle which 
 forms on the surface from falling and starting premature 
 crystallisation. 
 
 The colour thus prepared separates out in the course of 
 two or three days and owes, it is supposed, much of its beauty 
 to the gradual nature of its formation. 
 
 We give the composition of some samples of emerald 
 green examined by us : 
 
 Deep. Light. 
 
 Moisture 1-6 1-1 
 
 Arsenious oxide .... 56-6 52-7 49-4 46-8 
 
 Cupric oxide 35-0 31-5 28-2 26-2 
 
 Acetic anhydride, etc . . . 8-4 14-2 14-6 13-1 
 Insoluble in acid .... 7-8 12-8 
 
 100-0 100-0 100-0 100-0 
 
 These samples were most brilliant colours ; the light 
 greens were "lowered" with barium sulphate. 
 
 The ratio of arsenious oxide to cupric oxide in each of 
 these four samples is approximately 2 molecules to 3 mole- 
 cules. The actual figures work out 
 
 1:1-55, 1:1-50, 1 : 1'44, 1 : T40. 
 
INORGANIC PIGMENTS. 159 
 
 The ratio calculated from the formula ascribed to the pure 
 compound is 3As. 2 3 : 4CuO, and the percentage composition 
 
 As 2 3 . . '.*" . ' 58-7 
 
 CuO 31-2 
 
 (C 2 H 3 O) 2 O 10-1 
 
 100-0 
 
 The excess of copper found is probably due to the presence 
 of verdigris or other basic-copper compounds. 
 
 Emerald green is dissolved by acids without effervescence 
 to a blue or green solution ; on warming the solution acetic 
 acid is evolved. Marsh's and Reinsch's tests indicate the 
 presence of arsenic. On ignition it is blackened with evolu- 
 tion of acetous vapours and formation of a white sublimate 
 of arsenious anhydride. 
 
 The analysis of the copper-arsenic colours presents no 
 great difficulty. A portion, not more than 1 gram, is treated 
 with hydrochloric acid and nitric acid or potassium chlorate 
 added to oxidise the arsenious to arsenic acid, the liquid 
 diluted, and, if necessary, filtered from any insoluble matter, 
 which should be weighed. The filtrate, in the known absence 
 of lead or other heavy metals, is made strongly alkaline 
 with ammonia and excess of magnesium mixture added. 
 Magnesium ammonium arsenate forms, and after some hours 
 standing, with frequent stirring, precipitation is complete. 
 The precipitate is filtered off and washed, until free from 
 dissolved matter, with dilute ammonia. The magnesium 
 ammonium arsenate may be weighed as such after very long 
 drying at 105 C. or, better, is slowly ignited at a gradually 
 increasing temperature until all NH 3 is expelled, and the 
 residual magnesium pyroarsenate Mg 2 As 2 7 weighed. The 
 filtrate from the arsenic contains all the copper as blue 
 ammonio-cupric salt. This is concentrated and acidulated 
 with hydrochloric or sulphuric acid, transferred to a weighed 
 platinum dish and zinc added. The copper is precipitated 
 
160 CHEMISTRY OF PIGMENTS. 
 
 on the platinum and when all the zinc is dissolved, and the 
 liquid carefully poured off, the spongy copper is pressed to- 
 gether and washed repeatedly with hot water, then with alcohol, 
 and lastly with ether. This should be done quickly and the 
 dish dried in the water oven. The increase in weight gives 
 the weight of copper present in the amount of green taken. 
 The supernatant liquid from this operation should be tested 
 with a fresh piece of zinc and a few drops of acid, for any 
 copper not precipitated. If carefully carried out this process 
 is very accurate ; excess of zinc is necessary to precipitate all 
 the copper and excess of acid to dissolve all the zinc. A test 
 with zinc and acid alone should show no residue insoluble in 
 acid ; if this is found the zinc is unsuitable for the purpose. 
 
 If lead is present it can be removed by precipitation with 
 a large excess of diluted sulphuric acid. The lead sulphate 
 should be washed twice with dilute sulphuric acid to remove 
 arsenic and copper, and then with alcohol to remove sul- 
 phuric acid. Any precipitate with ammonia should be filtered 
 off and examined before precipitating the arsenate. Lead 
 chromate, which might be used to lighten the pigment, 
 would, after solution in HC1 give a precipitate of chromium 
 arsenate under these conditions. 
 
 VERDIGRIS (Vert de Gris, Griinspan). Under the name 
 verdigris several of the acetates of copper are included ; 
 those which are of importance as pigments are blue verdi- 
 gris dibasic cupric acetate, and green verdigris a mixture 
 of di- and tri-basic acetates, or a sesqui-acetate. Blue verdi- 
 gris is prepared at Montpellier and other parts of France by 
 exposing copper plates to the air in contact with fermenting 
 wine lees or marc. The acetous fermentation sets up, and 
 verdigris forms. The plates are, after about three weeks' 
 action, taken out, placed in an upright position to dry,, 
 dipped in water about once a week for six or eight weeks, 
 and the verdigris, which swells up, is scraped off. The plates. 
 
INORGANIC PIGMENTS. 161 
 
 are then again treated with wine lees and re-treated until 
 entirely corroded. When the plates are new action is facili- 
 tated by brushing theirTwith a solution of normal acetate of 
 copper. 
 
 Blue verdigris is also formed by exposing copper plates to 
 damp air in contact with a paste of the normal acetate and 
 water. 
 
 It is obvious that, whatever process is used, old corrugated 
 copper plates will give a better yield by reason of the greater 
 surface they present than new bright plates. 
 
 Verdigris forms silky blue needles and scales which grind 
 to a beautiful blue powder. It is CuO, Cu(C 2 H 3 2 ) 2 + 6H 2 0. 
 On heating to 60 C. the water is given up and a green mixture 
 of a more basic salt and the neutral acetate is formed 
 
 2CuO Cu(C 2 H 3 2 ) 2 = Cu(C 2 H 3 2 ) 2 + Cu(C 2 H 3 2 ) 2 2CuO. 
 
 Eepeated exhaustion with water causes the formation of 
 normal cupric acetate with two other basic acetates thus : 
 
 5(C 2 H 3 O 2 ) 2 Cu, CuO = 2(C 2 H 3 2 ) 2 Cu, 2CuO + (C 2 H 5 O 2 ) 4 Cu2, CuO + (C 2 H,0 2 ) 2 Cu. 
 
 The composition of samples examined by Berzelius and 
 Phillips is given in Watts' Dictionary of Chemistry. 
 
 Phillips. 
 
 Theoretical French. English 
 
 for (C 2 H 3 O 2 )2 CuCuO, GHaO. Berzelius. Crystallised. Compressed. 
 
 CuO . . . 43-24 43-34 43-5 43-25 44-25 
 
 (C 2 H 3 0) 2 . . 27-57 27-45 29-3 28-30 29-62 
 
 6H 2 . . 29-19 29-21 25-2 28-45 25-51 
 
 Impurities . 2-0 0-62 
 
 100-00 100-00 100-0 100-00 100-00 
 
 Green verdigris, which according to Berzelius is the salt 
 2(C 2 H 3 2 ) 2 Cu, CuO + 6H 2 with small quantities of bi- and 
 tri-basic acetates and sometimes cuprous acetate, is prepared 
 at Grenoble by sprinkling copper plates with vinegar and 
 keeping in a warm damp room, and in Sweden by packing 
 copper plates and flannel alternately and moistening with 
 
162 CHEMISTKY OF PIGMENTS. 
 
 vinegar. The greenest kind, Berzelius stated, contains 49'9 
 per cent. CuO and 13'5 per cent, water and impurities, while 
 the pure sesqui-acetate contains 43 '5 per cent. CuO. 
 
 Brunswick Green. 
 
 The pigment formerly known by this name was oxy- 
 chloride of copper Cu 4 Cl 2 O 3 , 4H 2 = CuCl 2 3CuO, 4H 2 0, pre- 
 pared by moistening copper turnings with hydrochloric acid 
 or a solution of ammonium chloride and leaving them in 
 contact with the air. The oxy-chloride forms on the surface, 
 and is washed off with water and dried at a gentle heat. 
 
 The much used pigment now known by this name is 
 of very different composition, namely, Prussian blue and 
 chrome yellow diluted with barium sulphate. 
 
 A preparation of copper oxy-chloride from copper turnings 
 and ammonium chloride gave after drying in the air and then 
 over H 2 S0 4 
 
 lost at 100 . . ' ...... 1-4 
 
 H 2 lost at 175-85 . . . . . . 15'7 
 
 CuCl 2 .......... 23-0 
 
 CuO .... ...... 60-4 
 
 100-5 
 
 It was a blue-green which became greener on drying at 
 100 and darkened at higher temperatures. It is more basic 
 than required by the formula Cu 4 Cl. 2 3 , 4H 2 
 
 4H 2 ..... ..... 16-2 
 
 CuCl 2 .......... 30-3 
 
 3CuO . ...... . . ..... 53-5 
 
 100-0 
 
 Our preparation agrees fairly closely with 2CuCl 2 9CuO, 10H 2 0. 
 It seemed to be a very poor pigment of very little colour- 
 ing power when ground in oil. 
 
INORGANIC PIGMENTS. 163 
 
 Non-Arsenical Green. 
 
 A green brought otft in Germany to supersede emerald 
 green consisted mainly of malachite brightened by lead 
 chromate. It is said to be obtained by mixing copper blue 
 (basic carbonate) with chrome yellow, chalk and ferric oxide. 
 We give an analysis by C. Struse : 
 
 Lead chromate 13*65 
 
 Malachite 80-24 
 
 Ferric oxide O77 
 
 Calcium carbonate 2-65 
 
 Water . 2-58 
 
 99-89 
 
 It never, we believe, came much into use and in no way 
 equals the brilliance of copper aceto-arsenite. 
 
 Copper Blues, 
 
 MOUNTAIN BLUE (Blue Ashes, Lime Blue, Copper Blue}. 
 The name mountain blue is given to the mineral azurite, 
 a native carbonate of copper, and also to a blue prepared 
 by precipitating copper hydroxide with lime crearn. When 
 cupric sulphate is treated with calcium hydroxide, 
 
 CuS0 4 + Ca(OH) 2 := Cu(OH) 2 + CaS0 4 , 
 
 the pigment contains copper hydroxide with precipitated 
 calcium sulphate, and when, as is sometimes done, potassium 
 carbonate is mixed with the lime, calcium carbonate also 
 remains in the washed blue. This blue is, we believe, used 
 to some extent for distemper work, but we have never seen 
 a commercial sample. 
 
 This substance in the moist condition has, under the name 
 " bouille Bordelaise," been used with success as a spray for 
 checking the ravages of the potato disease, phytophthyra 
 infestans. It is a very pure sky-coloured blue. 
 
 By precipitating cupric nitrate with chalk and adding 
 
164 CHEMISTEY OF PIGMENTS. 
 
 to the precipitate 8 to 10 per cent, freshly burnt lime, a blue of 
 this kind is obtained. Without the lime a green pigment 
 results. 
 
 A peculiar blue described by Halich is obtained by dis- 
 solving cupric oxide in nitric acid and treating with K 2 CO 3 
 until almost but not quite all the copper is precipitated ; then 
 washing the precipitate with water, and introducing it into 
 a solution of copper nitrate. An insoluble heavy green basic 
 nitrate is formed, which, digested with a solution of zinc 
 oxide in potash, forms a dark blue of great body but little 
 weight, which contains both zinc and copper, and is apparently 
 a double oxide with basic copper nitrate. 
 
 VIII ULTRAMARINE, 
 
 Eeal ultramarine is obtained from a somewhat rare 
 mineral, lapis lazuli, a variety of Haiiynite thus described by 
 Dana : " Not a homogeneous mineral, according to Fischer 
 and Vogelsang. The latter calls it a mixture of granular 
 calcite, ekebergite, and an isometric ultramarine mineral, 
 generally blue or violet. Much used as an ornamental 
 stone." It is, as the two following analyses will show, of 
 very variable composition : 
 
 Gmelin. Fuchs. 
 
 Silica .... 49-0 Phosphoric acid . . 41-81 
 
 Alumina . . . .11-0 Alumina . . . 35'73 
 
 Lime .... 16-0 Magnesia . . . 9-34 
 
 Soda and potash . . 8-0 Silica .... 2-10 
 
 Oxide of iron . . . 4-0 Protoxide of iron . . 2*64 
 
 Magnesia . . .2-0 Water .... 6'06 
 Sulphuric acid . . . 2-0 
 
 97-68 
 
 92-0 
 
 These analyses are rather ancient, and though by men 
 eminent in their day, seem very inconclusive. Speaking 
 roughly it would appear to be an aluminium-sodium silicate 
 containing sulphur in some form. It is of a blue colour 
 
INORGANIC PIGMENTS. 165 
 
 varying according to circumstances. Lapis lazuli is the 
 "sapphire" of the ancients and is evidently the material 
 referred to in Revelation xxi. 19. It is occasionally found with 
 gold-like fragments of iron pyrites interspersed through its 
 substance. To prepare the pigment, the mineral is broken 
 into small pieces, freed as much as possible from mechanic- 
 ally adhering impurities, heated in a crucible and thrown 
 into cold water or very weak vinegar. It is then washed by 
 decantation, dried, ground and then purified by elutriation, 
 by which process various grades of colour, from the finest 
 blue to grey ultramarine ash, are obtained. Ultramarine is 
 the purest and most beautiful blue pigment known and most 
 closely approximates in tint to the pure blue of the sky. 
 Real ultramarine, on account of the rarity of lapis lazuli and 
 the troublesome process of preparation, is a most expensive 
 colour. 
 
 In the year 1828 Guimet, stimulated by a prize of 6,000 
 francs offered by the Societe d'Encouragement de France, 
 discovered a method of preparing artificially a blue similar in 
 properties and composition to natural ultramarine. Alkali 
 makers had previously noticed spots of ultramarine on their 
 furnaces, and efforts had been made to determine the con- 
 ditions of formation of this pigment. Gmelin, whose analysis 
 has been quoted, also discovered at about the same time a 
 method of formation. 
 
 Blue ultramarine was formerly solely made by the " in- 
 direct process," in which sulphate of soda, kaolin and char- 
 coal are ground together and burnt in crucibles in a suitable 
 oven for six to nine hours. The mass is then turned out and 
 is of a dull green colour. It is then crushed and heated on 
 a roasting furnace with powdered sulphur, the mass being 
 continually stirred until the sulphur has burnt off and a 
 bright blue mass is left. Though the materials are cheap 
 the process is troublesome and the result is somewhat uncer- 
 
166 CHEMISTEY OF PIGMENTS. 
 
 tain. The product obtained is poor in silica, and though of 
 pure tint is of very weak colour. 
 
 The direct process, which is now adopted very largely, 
 requires great care both as to details and in the selection 
 of materials. The mixture consists of about 100 parts of 
 china clay, 90 of soda, 110 of sulphur, 20 of charcoal and a 
 variable amount of infusorial earth, the amount of this latter 
 material depending on the quality of ultramarine required. 
 The china clay must be very pure and free from sand and 
 other rough matters. The soda is the best soda ash, known 
 as carbonated ash, and should test 58 per cent, (total alkali as 
 Na. 2 0). The raw materials are intimately mixed and finely 
 ground. The ignition is conducted in ovens of either of two 
 patterns, "crucible" or "mass" ovens, of which the latter 
 is the newer, and, in the opinion of some, the better form. 
 The names explain themselves sufficiently ; in the former 
 pattern the mixture is filled into crucibles twelve to sixteen 
 inches high, the lids being luted on and rows of these 
 crucibles piled into the furnace, the heat of which is gradu- 
 ally raised to a bright red which is maintained for some 
 hours, the time varying with the size of the crucibles and 
 the nature of the materials used. Air is as far as possible 
 excluded at the close of the operation, and the mass allowed 
 to slowly cool. The crucibles are taken out and opened and 
 the ultramarine carefully turned out and pieces of overburnt 
 material chipped away from the beautiful blue colouring 
 matter. The " mass " ovens are arranged with a permanent 
 floor and back or bridge ; the mixture is put on the floor and 
 banked up until level with the bridge, and is then covered 
 with thin tiles luted together with a mixture of sand and 
 clay. A hole is left in front for observing the courses of the 
 operation and another smaller one for removing samples of 
 the burning from time to time. Both these can be closed 
 with loose bricks or clay plugs. The temperature is slowly 
 
INOEGANIC PIGMENTS. 167 
 
 raised to a bright red, when sulphurous flames are seen to 
 rise from any cracks or faults in the luting ; these at first 
 increase, and as the Reaction becomes complete disappear. 
 The temperature is maintained at its highest point for twelve 
 to eighteen hours or until, in the opinion of the operator, all 
 action has ceased. The sample, if properly burnt, is of a 
 greenish blue and evolves sulphur dioxide in the air without 
 actually burning, and spread on a tile soon cools and be- 
 comes a slightly greenish blue. The colours assumed by the 
 mixture while burning are successively a yellowish grey 
 (initial) brown, green, blue ; the brown colour is unstable and 
 in the air, and the material burns to a greenish blue. The 
 green is also unstable. If the sample is satisfactory the oven 
 is luted up and the mass allowed to cool. This takes a week 
 or ten days ; on opening, the mass is a deep blue, the lower 
 portions, having been more or less heated, being less brilliant 
 than the upper layers. The loss in weight is usually about 
 one third, and some considerable shrinkage takes place. The 
 mass is washed with hot water in vats with perforated false 
 bottoms and coarse filter surfaces to remove sodium sulphate 
 and other soluble salts, and is ground between upright stones, 
 settled first to remove dirt and unground matter, and then 
 the finer matter fractionally settled out, the latter portions 
 which settle more slowly being the finer colours. The 
 liquid, which still contains colouring matter, is precipitated 
 with lime, which, by coagulating the particles, renders their 
 removal by filtration more easy. The mixing of the various 
 shades so as to ensure uniformity of product is a matter of 
 considerable importance as, of course, this considerably 
 affects the reputation of the manufacturer. 
 
 Most of the details given above are taken from the article 
 by G. W. Rawlings in Thorpe's Dictionary of Applied Chemistry. 
 
 We give the results of analysis of some samples examined 
 by us and some given in the article mentioned above : 
 
168 
 
 CHEMISTRY OF PIGMENTS. 
 
 German. 
 
 English. German, 
 
 Parry and Coste. 
 
 Moisture 
 
 0-7 
 
 Si0 2 . 
 
 . 38-90 
 
 39-61 
 
 42-70 
 
 41-30 
 
 42-26 
 
 41-7 
 
 42-4 
 
 ALA. 
 
 . 29-50 
 
 23-95 
 
 24-50 
 
 24-30 
 
 26-79 
 
 25-2 
 
 24-0 
 
 Na^O. 
 
 . 21-02 
 
 19-15 
 
 19-95 
 
 17-40 
 
 19-49 
 
 18-8 
 
 18-7 
 
 S 
 
 . 10-84 
 
 13-10 
 
 13-04 
 
 14-80 
 
 12-01 
 
 14-2 
 
 15-4 
 
 100-26 101-66 100-19 101-30 100-55 99-9 101-2 
 
 Comparative analyses of three varieties of ultramarine 
 by E. Dollfus and F. G-oppelsroder (Butt, de Mulhouse, 1875, 
 May; Dingl. poL /., ccxx., 337, 431) are given below. These 
 are of a more ambitious nature than the others quoted by 
 us : 
 
 
 Green. 
 
 Blue. 
 
 Violet. 
 
 
 17-963 
 
 19-160 
 
 20-440 
 
 Aluminium . 
 
 17-702 
 
 13-925 
 
 12-735 
 
 Sodium as NagO . 
 
 10-487 
 
 10-088 
 
 11-110 
 
 Potassium 
 
 0-420 
 
 
 
 
 
 Sulphur as SO 3 
 
 0-292 
 
 0-500 
 
 0-877 
 
 Sulphur as S0 2 
 
 0-213 
 
 0-441 
 
 0-834 
 
 Sulphur as S 2 2 
 
 . 
 
 0-469 
 
 2-536 
 
 Sulphur as Na^S . 
 
 3-718 
 
 3-057 
 
 1-165 
 
 Free sulphur 
 
 3-491 
 
 8-977 
 
 6-964 
 
 Sodium as Na 2 
 
 5-345 
 
 4-395 
 
 1-676 
 
 Oxygen . 
 
 40-363 
 
 38-984 
 
 41-748 
 
 99-994 99-996 100-085 
 
 These would seem to show that the percentage of silicon 
 increases and that of aluminium decreases from the green to 
 the violet substance. The analyses, calculated as they are to 
 three places of decimals, add up to 100 remarkably closely. 
 
 The structure of ultramarine is crystalline, its form being 
 apparently single refracting crystals of the regular system. 
 This fact was first observed by E. Hoffmann, and the above 
 conclusion as to the structure arrived at by H. Vogelsang. 
 
 The true constitution of ultramarine is still a matter of 
 great doubt, though its composition and behaviour to reagents 
 have been the subject of investigation on the part of many 
 chemists. It is, to say the least, startling that a compound 
 
INORGANIC PIGMENTS. 169 
 
 containing only the elements silicon, aluminium, sodium, 
 sulphur and oxygen, none of which are recognised as possess- 
 ing chromophoric properties, should have so intense a colour. 
 The method of production, being of a somewhat violent nature, 
 serves only to a very slight extent to indicate the nature of 
 the pigment. That it is some sort of double silicate con- 
 taining sulphur is evident ; but the internal structure of the 
 blue molecule is, so far, merely a matter for surmise. 
 
 The action of reagents tends to throw more light on the 
 probable constitution of this pigment. Mineral acids, both 
 strong and dilute, attack ultramarine blue, discharging the 
 colour and causing an evolution of hydrogen sulphide with 
 liberation of sulphur. This seems to point to the existence 
 of a polysulphide. Solutions of alkalies do not attack blue 
 or green ultramarine but the violet becomes blue. A solution 
 of alum slowly decolourises blue ultramarine. Heumann dis- 
 covered this ; when blue ultramarine is heated to 120C. in 
 a sealed tube with a solution of silver nitrate for fifteen 
 hours a dark yellow amorphous body having the following 
 composition is formed : 
 
 Ag 47-97 
 
 Na 1-07 
 
 Al . . 9-1 
 
 Si 10-09 
 
 S . . . . 4-75 
 
 and H (? H 2 O) 0-61 
 
 Insoluble siliceous matter (clay) 0*81 
 
 74-40 
 
 It is to be presumed that the difference between 74*4 and 
 lOO'O is oxygen, which is not mentioned in this analysis. 
 
 It will be seen that in this compound nearly all the sodium 
 has been replaced by silver ; it is probable that all is replace- 
 able. This compound, silver ultramarine, forms the starting 
 point for organic derivatives as ethyl, benzoyl and amyl 
 ultramarines ; the existence of these substances, though of 
 
170 CHEMISTRY OF PIGMENTS. 
 
 interest, can scarcely be said to throw much light on the 
 constitution of the parent substance. In addition to these 
 organic ultramarines, potassium (blue), lithium (blue), barium 
 (yellowish-brown), zinc (violet) and manganese (grey) ultra- 
 marines may be formed. In all these cases the silver com- 
 pound is acted upon with the iodide or chloride of the radical 
 or metal to be substituted. The sulphur of ultramarine may 
 be replaced by selenium or tellurium. 
 
 When a mixture of chlorine and steam is passed over ultra- 
 marine blue or green heated to 160 to 180 a violet-coloured 
 substance from which sodium chloride may be extracted is 
 produced. The same substance is produced by the action 
 of hydrochloric acid gas and air at 150 to 230 C. This sub- 
 stance, ultramarine violet, contains the whole of the sulphur 
 of the original blue, but the sodium (partly removed as chloride) 
 is considerably reduced in amount. The long-continued action 
 of hydrochloric acid and air causes the violet substance to 
 become rose red, or the red colour may be prepared by passing 
 the vapours of nitric acid over the violet at 130 to 150 or by 
 the vapours of hydrochloric acid at 128 to 132. 
 
 The considerable variation in composition of ultramarines 
 of similar colour, and on the other hand the similarity in 
 composition of pigments of differing shades, seem to point 
 to the conclusion that ultramarine is not a simple substance,, 
 either being a mixture of blues of allied composition or of 
 a coloured with a colourless substance. 
 
 Notwithstanding the difficulties of the case various workers 
 have from time to time proposed formulae for expressing the 
 constitution, or, at any rate, the empirical formulae of 
 ultramarine substances. 
 
 K. Hoffmann (Ann., cxciv., 1-22) considers that the pale 
 blue kind, poor in silica, has the formula 4(Na 2 Al 2 Si 9 8 ) 
 + Na 2 S 4 , and that rich in silica and of a deep reddish tint 
 is 2(Na 2 Al 2 Si 8 O 10 ) + Na 2 S 4 . These, he supposed, are formed 
 
INOEGANIC PIGMENTS. 171 
 
 by the abstraction of sodium from a white compound, 
 thus : 
 
 White. Blue. 
 
 Blue, poor in silica 4(Na 2 Al 2 Si 2 O 8 + Na 2 S) - 6Na = 4(Na 2 Al 2 Si 2 O 8 ) + Na 2 S 4 , 
 Blue, rich in silica 2(Na. 2 Al 2 Si 3 10 + 2 Na 2 S) - 6 Na = 2(Na 2 Al 2 Si 3 O 10 ) + Na 2 S 4 , 
 
 the effect of this being to form polysulphides to which the 
 colour is probably in some way attributable. The latter white 
 ultramarine has not been discovered. 
 
 Griinzweig found that yellow ultramarine, rich in silica, 
 could be made from the blue to which the formula 2(Na 2 Al 2 
 Si 3 10 + Na 2 S) is attributed, by the abstraction of sulphur and 
 the addition of oxygen, thus 2(Na 2 Al 2 Si 3 10 ) + Na 2 S 3 4 is 
 formed, the yellow thus appears to be an oxidation product 
 of the blue. 
 
 Ungor considered that ultramarine contained nitrogen and 
 was Al 2 Si0 2 3 N 2 . 
 
 Endemann believes in the existence of a " colour nucleus," 
 which in the case of white ultramarine is AlNa 4 2 S 2 . 
 
 Bottinger (Ann., clxxxii., 305) holds that ultramarine may 
 be regarded as the last term of a series of molecular compounds 
 of an aluminium silicate with a sodium thio-silicate a silicate 
 in which more or less oxygen is replaced by sulphur. 
 
 Fiirstenau (Dingl. pol. J., ccxix., 269) finds that only the 
 silicates 4A1 2 O 3 , 9Si0 2 and A1 2 3 , 3Si0 2 are suitable ; these 
 treated with Na 2 S 2 or Na 2 S 5 give the following pigments : 
 
 (a) 4A1 2 CK, 9SiO 2 with Na 2 S 2 , pure clear blue of but little colouring 
 
 power. 
 
 (b) 4A1 2 3 , 9Si0 2 ,, Na 2 S 5 , pure dark blue with great covering power. 
 
 (c) A1 2 O,, 3Si0 2 ,, Na 2 S 2 , reddish, dingy-coloured product. 
 
 (d) A1 2 3 , 3SiO 2 NagS.j, dark violet blue colour with great tinctorial 
 
 power. 
 
 The former two products are free from alum, but the latter 
 two both contain this substance. 
 
 Considering the difficulties attending all investigations 
 into the constitution of inorganic compounds, it is not surpris- 
 
172 CHEMISTRY OF PIGMENTS. 
 
 ing that diversity of opinion should exist as to the true nature 
 of ultramarine ; we have endeavoured to indicate the views 
 of some workers on the subject, but cannot profess to have 
 any preference for the views of any one individual. There 
 is certainly an abundant field for work in this direction. 
 
 The method of analysis adopted by us was to treat a 
 portion of about 1 gram in a platinum or porcelain dish with 
 hydrochloric acid, carefully covering and, when effervescence 
 had ceased, washing back any splashes into the main liquid. 
 This was evaporated to dryness in the water bath, moistened 
 with hydrochloric acid and again taken to dryness. The dry 
 mass was moistened with hydrochloric acid, taken up with 
 water and the soluble part filtered from the residue of insolu- 
 ble matter and sulphur. This insoluble matter was ignited 
 and weighed, afterwards being examined to ascertain whether 
 pure silica or not. The alumina is precipitated by addition 
 of a slight excess of ammonia, collected, and weighed in the 
 usual way. The ignited alumina should be quite white, any 
 colour indicating the presence of impurity. The filtrate from 
 the alumina contains the alkali (as chloride). This may be 
 determined, after addition of sulphuric acid in excess and 
 evaporation to dryness in a platinum vessel, by cautiously 
 igniting at a very low temperature just sufficient to drive off 
 the ammonium salts and sulphuric acid ; the sodium is thus 
 obtained as neutral sulphate Na 2 S0 4 . It is better to weigh 
 as sulphate than as chloride, as the latter is volatile at a 
 relatively low temperature and loss is likely to occur. 
 
 For the determination of sulphur it is sufficient to evapo- 
 rate to dryness with concentrated fuming nitric acid or aqua 
 regia, which oxidises sulphur to sulphuric acid. This can be 
 determined in the filtered diluted liquid in the usual manner. 
 
 Various methods of examination as to quality have been 
 described by different workers. Some of the more reason- 
 able of these are described below. 
 
INOKGANIC PIGMENTS. 173 
 
 Guimet, the discoverer of artificial ultramarine, compared 
 blues as to colouring power by weighing out O'l gram of 
 a standard sample and rmxing it with O6 gram of pure 
 powdered chalk by means of a thin spatula, and diluting a 
 similar quantity of the sample to be examined with weighed 
 increments of the same chalk until equal tints were obtained. 
 Then if the sample under examination requires *7 gram 
 (7 times its own weight) to produce the standard tint, the 
 colour value standard : sample = 6:7, that is, the sample is 
 J better than the standard. 
 
 Another rather remarkable method of examination is to 
 ignite at a temperature of about 400 C. in a current of hydro- 
 gen. The best samples of the artificial blue become a greyish 
 green in about half an hour, the worst in a few minutes. 
 Lapis lazuli heated for as long as two hours retains its colour 
 in the presence of hydrogen. 
 
 Biichner adopts an alum test ; O05 gram ultramarine 
 is stirred up with a cold saturated solution of alum and the 
 time required for decolorisation, whether minutes, hours or 
 days, noted. The longer the blue resists the action of alum 
 the better it is likely to be. 
 
 The fineness of grinding and the glazing power of the 
 blue put on paper with size are matters of importance more 
 particularly to the paper maker. 
 
 IX CARBON PIGMENTS. 
 
 Carbon forms the base of most of the black pigments used 
 in the arts. In most of these it is employed in some amor- 
 phous form, but for the protection of metal-work and as a 
 grey paint the mineral graphite finely powdered is used, ground 
 in oil. Graphite (plumbago, black lead) is almost pure carbon ; 
 its value as a protective coating for iron-work has been 
 considered in chapter ii. (p. 47). It has the advantage oi 
 
174 CHEMISTRY OF PIGMENTS. 
 
 being an absolutely inert substance and can only act as a 
 body or rather, perhaps, a skeleton for the boiled oil varnish 
 which forms when the paint dries. When the paint becomes 
 waterlogged the fact of graphite being strongly electro-negative 
 to iron is hardly in its favour. 
 
 The various carbon paints have no great "drying" pro- 
 perties in oil, and require the use of " boiled " oil or of suitable 
 siccative materials. 
 
 IVORY BLACK (Bone Black}. By the ignition of ivory 
 (waste pieces, turning dust, etc.) or bone in a covered vessel 
 a good black pigment is obtained. The organic matter (ossein 
 and traces of fat) is charred to carbon, and a mixture of this 
 with phosphate and carbonate of lime left behind as either 
 ivory or bone black. The former, though much of the black 
 sold for ordinary purposes is called ivory black, is probably 
 only used by artists' colourmen, if, indeed, by them, and the 
 cheaper bone black sold for decorators' work. 
 
 We give the composition of average bones and of samples 
 of so-called ivory black : 
 
 Bones. Ivory Black. 
 
 Moisture .... 6-91 3-44 1-2 Oil 28-84 
 
 Organic matter (or carbon) . 39-31 20-03 13-0 12-82 
 
 Phosphate of lime . . 46-60) 7g . 47 Q ^, Q 49-10 
 
 Carbonate of lime, etc. . 5'78/ 3-24 
 
 Sand 1-40 3-06 1-0 6-00 
 
 100-00 100-00 100-0 100-00 
 
 Nitrogen . . . . 4-35 
 
 Ivory black is sometimes moulded into little conical masses 
 probably a little gum is used to give some coherence and 
 sold as soap black ; we give the composition of a sample 
 examined by us : 
 
 Moisture 3-29 
 
 Loss on ignition (black) 23-41 
 
 Phosphate of lime, etc 70-71 
 
 Insoluble siliceous matter 2-59 
 
 100-00 
 
INORGANIC PIGMENTS. 
 
 175 
 
 The peculiar manner in which the inorganic matter is 
 incorporated with the black in this dye, though diminishing 
 its pigmentary power, gives it a beautiful softness in working 
 which renders it a valuable colour. 
 
 LAMP BLACK (Soot Black, Vegetable Black). When organic 
 matters rich in carbon are burnt a great deal of unburnt 
 carbon escapes as "smoke " and condenses, or rather settles 
 
 FIG. 5. 
 
 out as " soot " on the cooler parts of the chimney or other 
 draught arrangement. To obtain such black in quantity resin 
 or tallow is burnt in a confined atmosphere and the carbon 
 liberated collected on the walls of a large chamber, which 
 are hung with canvas ; a cone suspended in this chamber, 
 on lowering, acts as a scraper and detaches the black which 
 falls on to the floor. The accompanying illustration represents 
 
176 CHEMISTRY OF PIGMENTS. 
 
 the manufacture of this pigment, the resin or tallow is burnt 
 in the iron pot A, heated by the furnace B. The soot is con- 
 densed in C and scraped off by the cone D. 
 
 Bistre. 
 
 This is a brownish-black pigment produced by extracting 
 with boiling water soot produced at a very low temperature, 
 and consequently containing a considerable amount of em- 
 pyreumatic matter. The residue, when this has been 
 extracted, is levigated and dried. It forms a warm brownish 
 black. It is said to be principally produced from beechwood 
 smoke or soot. 
 
 X VARIOUS UNCLASSIFIED PIGMENTS 
 
 (Naples Yellow}. 
 
 Under the name of Naples yellow various pale yellow 
 pigments are sold. The original Naples yellow (giallolini) 
 appears to have been the secret preparation of a Neapolitan 
 colour maker. Fongeroux de Bonduroy, who made some 
 investigations at Naples, where it was by some believed to- 
 be obtained from some volcanic product from the adjacent 
 mountain Vesuvius, gives the following method of preparation : 
 A mixture of 24 parts of white lead, 4 parts of " diaphoretic 
 antimony " (potassium metantimoniate), 1 part of ammonium 
 chloride and 1 part of alum are fused in an earthen crucible 
 at a red heat for three hours and the melt broken up on 
 cooling, ground and washed. 
 
 Thenard states that this pigment is said to be obtained 
 by the " calcination at the proper temperature of a mixture 
 of litharge, hydrochlorate of ammonia (sal ammoniac), dia- 
 phoretic antimony (a combination of peroxide of antimony 
 and potassa and alum)". Another method is to fuse 3 parts- 
 of massicot (litharge) with 1 of antimony oxide, or to fuse 2 
 
INORGANIC PIGMENTS. 177 
 
 parts of red lead, 1 of antimony and 1 of calamine (zinc 
 carbonate). 
 
 Brunner recommends slow fusion of 1 part of tartar 
 emetic with two parts of lead nitrate and washing the ground 
 melt with hydrochloric acid to brighten its colour. 
 
 From these processes, which are evidently variations of 
 one original method, it would appear that the pigment is a 
 more or less basic antimoniate of lead with various impurities 
 added according to taste. 
 
 In his Cantor Lectures (1891) Mr. A. P. Laurie describes 
 various pigments which have been included under the name 
 of Naples yellow. We quote the section on this pigment, of 
 lecture ii. : 
 
 " Giallolino. The history and nature of this pigment are 
 somewhat obscure. Cennino distinctly states that it is a 
 volcanic product. He states that it is not a brilliant yellow,, 
 though brighter than ochre, and never makes bright greens. 
 Mrs. Merrifield considers that several pigments were included 
 under this name. I cannot do better than quote her sum- 
 ming up of this matter. 
 
 " 1. 'A native mineral yellow pigment, known by the name 
 of giallolino, giallolino di Napoli, jaune de Naples, luteolum Napo- 
 litanum.' 
 
 " This is doubtless the yellow referred to by Cennino. All 
 trace of it seems to be lost, though probably a proper search 
 in a volcanic district would lead to its discovery. 
 
 " 2. ' An artificial pigment which was composed of the 
 yellow protoxide of lead, and which was called giallolino, giallo- 
 lino fino, giallolino di fornace di fiandra, luteolum Belgicum gcnuli 
 (the last is a Spanish term) and massicot, of which there are 
 two varieties, namely, the golden or yellow, and the white or 
 pale massicot.' 
 
 11 This pigment can be prepared by gently roasting white 
 lead. It is now known as Turner's yellow. It is apt to turn 
 
 12 
 
178 CHEMISTRY OF PIGMENTS. 
 
 black, like all lead pigments, the fault of our towns, not of 
 themselves. 
 
 "3. 'An artificial pigment made at Venice, composed of 
 giallolino fino and a certain kind of giallo di vetro, or vitreous 
 yellow, for which a recipe is given in the Bolognese MS. in 
 the Venetian dialect, and which appears to have been the 
 Hornaza of the Spaniards.' 
 
 " This recipe is worth quoting, and is as follows : 
 
 " ' To make yellow glass for paternosters or beads : Take 
 of lead 1 lb., of tin 2 Ib. ; melt and calcine them, and make 
 glass for paternosters. 
 
 " ' To make giallolino for painting : Take 2 lb. of this cal- 
 cined lead and tin., that is, 2 lb. of this glass for paternosters, 
 2J- lb. of minium, and \ lb. of sand pounded very fine ; put it 
 into a furnace and let it fine itself, and the colour will be 
 perfect.' l 
 
 " This pigment must have been a yellow lead frit. Prob- 
 ably effective on fresco walls, but of little or no use in oil. 
 Mrs. Merrifield then goes on : 
 
 " ' I consider it established that they used two kinds of 
 Naples yellow, namely : 
 
 " ' 1. A native mineral pigment found in the neighbour- 
 hood of volcanoes, the nature of which is not accurately 
 known, and which was called "giallolino di Napoli " and 
 " jaune de Naples," and which is synonymous with the first 
 kind of giallolino above mentioned. 
 
 " ' 2. An artificial pigment now in use (?) composed of the 
 oxides of lead and antimony, called " giallo di Napoli," " jaune 
 de Naples," and Naples yellow, and which was not known to 
 the old Italian artists.' 
 
 " Apparently the manufacture of the more modern artificial 
 Naples yellow has now ceased. I failed to find either that 
 
 1 " MS. of the fifteenth century in the library of the R. R. Canonica Rego- 
 lari, in the Convent of the S. Salvatore in Bologna." 
 
INORGANIC PIGMENTS. 179 
 
 it was made or that any one had ever heard of its being made 
 in Naples. The manufacture has long ceased, apparently. 
 The colour now sold as Naples yellow is, I understand, usually 
 a mixture of yellows. One sample I examined was massicot 
 pure and simple. A fine yellow can be made from lead and 
 antimony, and I have some here which I have made myself. 
 Possibly a search on Mount Vesuvius might result in the 
 rediscovery of the original Naples yellow." 
 
 Arsenic Sulphides (Orpiment, Eealgar). 
 
 Of the three sulphides of arsenic As 2 S 2 , As 2 S 3 and As 2 S 5 
 the first two are used as pigments, to some extent. They 
 may both be formed artificially, or suitable specimens of the 
 native mineral may be ground. 
 
 EEALGAE, Arsenic disulphide. This occurs native as an 
 aurora red or orange yellow mineral of the monoclinic 
 system, of resinous lustre, transparent to translucent, of uneven 
 conchoidal fracture. Specific gravity 3'4 to 3'6. It may be 
 obtained artificially by fusing 75 parts of arsenic with 32 
 parts of sulphur (it is probably better to use the proportions 
 2 : 1 as loss of sulphur is likely to occur on fusion). It is 
 distillable in a confined atmosphere but on heating in the 
 air burns to As 2 3 and S0 2 . 
 
 ORPIMENT (Auri pigmentum, King's yellow, Eoyal- yellow). 
 Arsenic trisitiphide. Orpiment occurs in nature as a lemon - 
 yellow substance found in foliated masses varying considerably 
 in shade. Its specific gravity is about 3'4 to 3 '5. It belongs 
 to the orthorhombic system. 
 
 It is usually prepared in the wet way by precipitating 
 solutions of arsenious acid containing free hydrochloric acid 
 with hydrogen sulphide 
 
 As 2 O 3 + 3H 2 S = As 2 S 3 + 3H 2 O. 
 
 It can also be prepared by fusing arsenic or arsenious 
 
180 CHEMISTEY OF PIGMENTS. 
 
 acid with the proper proportion of sulphur. In the former 
 case direct combination occurs, in the latter sulphur dioxide is 
 formed. 
 
 2As 2 O 3 + 9S = 2As 2 S 3 + 3S0 2 . 
 
 The sulphide sublimes to the cooler parts of the vessel. 
 
 Orpiment appears to be fairly permanent in oil though 
 liable to be blackened when used in tempera. Both orpiment 
 and realgar, being sulphides, .must be used with very great 
 caution in admixture with other pigments. Mercury, lead 
 and copper pigments should not be used in admixture with 
 these colours. 
 
 Cadmium Yellow, Radiant Yellow, Cadmium Sulphide CdS, 
 
 Cadmium sulphide, which is a brilliant yellow substance, 
 is used to a considerable extent as a pigment. It is usually 
 prepared by the precipitation of a solution of a cadmium 
 salt with hydrogen sulphide. In the case of the sulphate 
 
 CdS0 4 + H 2 S = CdS + H 2 S0 4 . 
 
 The bright yellow precipitate is collected, washed and 
 ground. It is not entirely permanent, as will be seen on 
 reference to Kussell and Abney's experiments already quoted. 
 
 Cadmium yellow is also prepared by fusion of cadmium 
 oxide with sulphur. 
 
 Vandyck Brown, 
 
 Vandyck brown is a name applied to various brown pig- 
 ments owing their tints to either ferric oxide or organic 
 matter (sometimes partially charred) or both. Church 
 describes three varieties : " The first is made by calcining 
 certain very ferruginous earths or brown ochres ; the second 
 is nothing more than a dark brown variety of colcothar ; 
 the third is a kind of brown earth, containing, along with 
 some iron oxide and hydrate, a good deal of organic sub- 
 stance in the form of humus, or bituminous matter. The 
 
INORGANIC PIGMENTS. 
 
 181 
 
 first and second kinds are permanent and innocuous, but 
 the third kind will not resist the prolonged action of light, 
 becoming paler and redder in course of time." 
 
 Prof. Church further states that most of the samples 
 now met with in England belong to the third kind. 
 
 We have examined some used for decorative purposes 
 and found them to belong to the third class. The figures 
 are given below. 
 
 Dry Brown. Brown in Water. Brown in Oil. 
 
 Moisture 
 
 Mineral matter 
 
 Organic matter 
 
 Oil . 
 
 Oxide of iron and alumina 
 
 Carbonate of lime, etc. 
 
 Insoluble in HC1 . 
 
 100-00 100-0 100-00 100-00 
 
 Two samples of artists' colours were examined with the 
 following results : 
 
 12-25 
 
 60-6 
 
 50-35 
 
 
 
 6-55 
 
 7-6 
 
 9-50 l 
 
 
 
 81-20 
 
 31-8 
 
 40-15 
 
 62-56 
 
 
 
 
 
 
 
 28-85 
 
 
 
 
 
 
 
 1-81 
 
 
 
 
 
 
 
 5-16 
 
 
 
 
 
 
 
 1-62 
 
 Oil . 
 
 Organic matter 
 
 Oxide of iron . 
 
 Alumina 
 
 Lime salts, etc. 
 
 Insoluble in acid 
 
 40-9 
 38-5 
 4-4 
 4-6 
 5-4 
 6-2 
 
 82-5 
 
 10-7 
 
 3-9 
 
 2-9 
 
 100-0 100-0 
 
 These are both rather organic than oxide of iron pig- 
 ments and their permanence may well be a matter for doubt. 
 
 1 Including 
 
 Oxide of iron and alumina 3-00 
 
 Carbonate of lime . 4-05 
 
 Insoluble siliceous matter . 2-45 
 
 9-50 
 
CHAPTEK IV. 
 
 ORGANIC PIGMENTS. 
 
 I PRUSSIAN BLUE. 
 
 THE pigment generally known as Prussian blue is a mixture 
 of double cyanides of iron, although a definite single com- 
 pound is known which has a claim to the name. In the 
 process of manufacture on a commercial scale, however, it 
 is impossible to prepare this pure compound, so that the 
 pigment is invariably a mixture. In this sense, then, Prussian 
 blue will be referred to in the sequel. Alone, or diluted with 
 an inert white base, it forms a very valuable paint, known 
 under the names Prussian blue, Paris blue, Antwerp blue, or 
 Chinese blue. When genuine it should not be diluted, and 
 under the above names one expects to receive the pure blue. 
 Several fancy names have been introduced for the diluted 
 pigment, and in estimating the value of these compounds it is 
 hardly necessary to say that their value is directly proportional 
 to the amount of the true pigment they contain. Prussian 
 blue also forms the base, together with lead chromate, of the 
 well-known Brunswick green paint. 
 
 History. The historical aspect of this important pigment 
 is of some interest on account of the fact that that of the 
 cyanogen compounds as a group may be said to have com- 
 menced with the manufacture of Prussian blue. This was 
 accidentally discovered in the early part of the eighteenth 
 
OBGANIC PIGMENTS. 183 
 
 century by a colour manufacturer of the name of Diesbach. 
 He shortly afterwards communicated the fact to the chemist 
 Dippel, who was an alchemist, and he carefully investigated 
 the conditions under which the colouring matter was formed. 
 Woodward first, however, published a method of making it. 
 He stated that it was obtained by heating equal parts of 
 cream of tartar and nitre, and heating strongly the resulting 
 alkaline mass with ox blood. The residue of the calcination 
 was then lixiviated, and green vitriol (sulphate of iron) added, 
 together with alum. A greenish precipitate was thrown 
 down, which on treatment with hydrochloric acid yielded the 
 blue colour (Phil. Trans., 1724). Various other animal matter 
 was soon shown to yield the same result. It is unnecessary 
 here to go into the various views which were in the early 
 days held as to the constitution of the pigment, all of which 
 were later proved to be erroneous. Macquer in 1752 showed 
 that the use of alum was not necessary. The first real 
 indication of its constitution was given by the last-named 
 chemist, who showed that when boiled with alkali it yielded 
 oxide of iron, leaving a new body in solution. To this sub- 
 stance, which we now know as potassium ferrocyanide, the 
 name phlogistigated potash was given. Towards the end of 
 the eighteenth century Scheele investigated the compound, 
 and the result was the discovery of that deadly poison, prussic 
 acid. A few years later Berthollet took up the investigation, 
 and to him and Guy-Lussac we owe our first real insight 
 into the molecular constitution of the double cyanides. 
 
 Before passing on to the study of the actual constituents 
 of the commercial pigment, we may briefly examine the 
 principles underlying the process of its manufacture. The 
 production of the pigment is intimately connected with the 
 manufacture of the well-known salt prussiate of potash (the 
 yellow prussiate, potassium ferrocyanide), so that it is neces- 
 sary to describe the manufacture of the latter. Animal matter, 
 
184 CHEMISTRY OF PIGMENTS. 
 
 such as the shavings of hoofs, horn, dried blood, skin or 
 hair, is used as the source of the carbon and nitrogen in the 
 compounds. Owing to the large quantity of nitrogen these 
 substances contain, they were sometimes calcined alone in the 
 first instance in order to obtain as much ammonia as possible. 
 Sufficient nitrogen, however, is retained for the production 
 of the cyanogen required for the prussiate. The charred 
 organic mass is mixed with potassium carbonate (this is 
 preferably added in strong solution, and the water afterwards 
 driven off). The mixture is then heated in a cast-iron retort, 
 the iron necessary being taken up from this, or, as preferred 
 by some manufacturers, scrap iron is added to the mass. The 
 mass is then extracted with water and the water filtered off 
 and boiled down. A series of recrystallisations is necessary 
 to obtain the prussiate in a state of purity, and excess of 
 carbonate of potassium should be avoided. For the manu- 
 facture of ordinary Prussian blue, however, the crude solution 
 is frequently employed, and it is only in the finer varieties 
 that the pure crystals are first separated. Processes have 
 been patented for the recovery of ferrocyanides from gas and 
 soda liquors, and at least one of the large gas companies is 
 now employed in the manufacture of Prussian blue. The 
 blue pigment is obtained in many different shades, and the 
 methods used are as variable in detail as is the composition 
 of the resulting pigment. In general the principle of the 
 process is the addition of either a ferric salt to the solution of 
 the prussiate, or of a ferrous salt, the resulting nearly colour- 
 less precipitate being treated with a suitable oxidising reagent 
 such as nitric acid, ferric chloride, or bleaching powder. 
 According to A. H. Allen the lighter shades are useful for 
 the manufacture of zinc greens and the darker for the pre- 
 paration of chrome greens. Gentele states that the best 
 blues are obtained by using a ferrous salt and oxidising the 
 ferrous ferrocyanide formed. In the process recommended 
 
ORGANIC PIGMENTS. 
 
 185 
 
 by Crowther and Kossiter the ferrous ferrocyanide is sus- 
 pended in strongly acidulated water, and submitted to electro- 
 lysis. A blue of extremely vivid violet reflex is obtained at 
 the anode. 
 
 Various allied compounds of iron and cyanogen, with or 
 without potassium, are well known. These result from the 
 treatment of ferrocyanide or ferricyanide with ferrous or 
 ferric salts. In theory, one definite compound may be stated 
 to result in a given reaction, but owing to the oxidation by 
 the atmosphere, to impurities in the salts, and to other uncon- 
 trollable circumstances, a mixture always results in practice. 
 The following table gives the well-defined members of this 
 series : 
 
 Compound. 
 
 Formula. 
 
 Common Name. 
 
 Reaction between 
 
 1. Potassio- ferrous- fer- 
 
 K 2 Fe 2 C 6 N 6 
 
 Everitt's salt 
 
 Ferrous salts and 
 
 ro-cyanide 
 
 
 
 ferrocyanide 
 
 2. Potassio- ferric-ferro- 
 
 KFe. 2 C 6 N 6 
 
 Williamson's blue 
 
 Ferric salts and 
 
 cyanide 
 
 
 
 ferrocyanide 
 
 3. Dipotassio - diferric - 
 
 K 2 Fe 4 C 12 N 12 
 
 Soluble Prussian 
 
 Ferric salts and 
 
 diferrocyanide 
 
 
 blue 
 
 ferrocyanide 
 
 4. Ferric ferrocyanide 
 
 Fe 7 C 18 N 18 
 
 Prussian blue 
 
 Ferric salts and 
 
 
 
 
 ferrocyanide 
 
 5. Potassio -ferrous- fer- 
 
 KFe 2 C 6 N 6 
 
 Williamson's blue 
 
 Ferrous salts and 
 
 ri-cyanide 
 
 
 
 ferricyanides 
 
 6. Ferrous ferricyanide 
 
 Fe 5 C 12 N 12 
 
 Turnbull's blue 
 
 Ferrous salts and 
 
 
 
 
 ferricyanides 
 
 Which of these bodies, 2 or 5, actually represents Williamson's 
 blue is not certain, but the two bodies are practically, if not 
 actually, identical. 
 
 For all practical purposes the blue sold on the market 
 under the name of Prussian blue may be regarded as a mix- 
 ture of iron and iron-potassium ferrocyanides. 
 
 The Analysis of Prussian Blue. -Full details as to the 
 methods of analysis of this important pigment were de- 
 scribed by us in a paper published in the Analyst (September, 
 1896), from which we quote the following description in full : 
 
186 CHEMISTRY OF PIGMENTS. 
 
 " We have found, and Dr. Williamson in every case found T 
 that alkali was present in so-called Prussian blue, not merely 
 as alkaline salts not washed away completely, but as an in- 
 tegral part of the cyanide. 
 
 " As we are frequently called upon to examine commercial 
 samples of Prussian blue, and of pigments containing this 
 substance, we have considered it desirable to make a more 
 complete examination than the method usually adopted would 
 afford of specimens of blue of known origin, with a view to 
 getting some more definite data for basing conclusions as to 
 the purity of samples of unknown make. 
 
 " It appeared to us that, more especially in the case of com- 
 plex pigments ground in oil, the determination of the nitrogen 
 would give valuable information as to the amount of Prussian 
 blue present. 
 
 " Dyer has shown (Chem. Soc. Journ., 1896, 811) that ferro- 
 cyanides and ferricyanides yield the whole of their nitrogen 
 as ammonia when treated by the Kjeldahl-Gunning-Arnold 
 method. We found that potassium ferrocyanide boiled with 
 sulphuric acid for a few minutes gave up all its nitrogen as 
 ammonia. A determination of the water of hydration (lost 
 at 180 to 200 C.) was also made. The results were : 
 
 Found. Theory. 
 
 N 19-64 19-95 
 
 H 2 12-79 12-71 
 
 " We therefore felt justified in assuming that equally 
 correct results would be obtained in the case of the allied 
 compounds contained in commercial Prussian blue, an ex- 
 pectation which was fully justified by the agreement of the 
 nitrogen determinations with the other figures obtained. 
 
 " The following is briefly the scheme of analysis adopted 
 by us : 
 
 " The moisture is determined at 100. The water of com- 
 bination if the term is here justifiable can scarcely be 
 determined unless the blue is ' burned ' and the water col- 
 
OEGANIC PIGMENTS. 187 
 
 lected, as we made several attempts to drive off the water in 
 a current of hot air, gradually raising the temperature until 
 at 230 C., when water appeared to be still coming off, the 
 pigment was decomposed with the formation of ferric oxide. 
 Dr. Williamson, in his classical paper, ' On the Blue Com- 
 pounds of Cyanogen and Iron,' determined the total water 
 in these pigments by combustion with plumbic chromate. 
 This is apparently the only way of obtaining a correct result, 
 as, on heating, part of the hydrogen is evolved as hydrocyanic 
 acid, the oxygen of the water going to form ferric oxide, as 
 stated. The nitrogen was determined as above described, 
 and was found to differ within small limits. A weighed 
 quantity was ignited, care being taken that the temperature 
 was sufficiently high to decompose the last traces of the blue, 
 but not too high to render the oxide of iron difficult of solu- 
 tion. It is necessary to ensure the complete oxidation of the 
 finely divided iron, as otherwise it is very difficultly soluble 
 in hydrochloric acid. 
 
 " In all cases on adding acid to the ' ash,' a marked effer- 
 vescence showed that alkaline carbonate (from the alkali- 
 containing ferrocyanide) was present. Pure blue leaves an 
 1 ash ' completely soluble in hydrochloric acid, but in the 
 case of adulterated Prussian blue or of diluted blues, barium 
 sulphate or other insoluble matter must be filtered off and 
 weighed before precipitating with ammonia. The iron in 
 the (weighed) mixed oxides was determined by titration with 
 potassium bichromate after reduction with stannous chlo- 
 ride, the alumina being of course estimated by difference. A 
 portion of the filtrate was evaporated to dryness, and, after 
 volatilisation of the ammonium salts, the alkaline salts were 
 weighed, and the chlorine therein determined by titration with 
 silver nitrate. In another portion of the nitrate the sulphuric 
 acid was determined, and from these data viz., the weight 
 of the alkaline salts, chlorine and sulphuric acid we were 
 
188 
 
 CHEMISTRY OF PIGMENTS. 
 
 enabled to show that in all cases the alkali-metal was almost 
 entirely potassium or sodium, and in no case a mixture of the 
 two metals. Another weighed quantity of the pigment was 
 boiled for a few minutes with aqueous potash, and the result- 
 ing precipitate of oxide of iron weighed, after ensuring its 
 complete conversion into Fe. 2 3 . This, multiplied by 0'7, 
 represents the * extra-radicle ' iron. 
 
 " The following tables represent the composition of eight 
 samples of blue sold by makers of repute as genuine Prussian 
 blue of good quality : 
 
 COMPOSITION OF EIGHT SAMPLES OF COMMERCIAL ' PURE ' 
 PRUSSIAN BLUE. 
 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 VII. 
 
 VIII. 
 
 Moisture (lost at 
 
 
 
 
 
 
 
 
 
 100 C.) 
 
 5-61 
 
 3-54 
 
 5-36 
 
 5-45 
 
 74-53 
 
 5-32 
 
 5-56 
 
 5-61 
 
 Water of combina- 
 
 
 
 
 
 
 
 
 
 tion, etc. 
 
 15-46 
 
 18-18 
 
 6-22 
 
 13-07 
 
 3-08 
 
 7-86 
 
 14-60 
 
 16-93 
 
 Cyanogen J 
 
 3772 
 
 41-10 
 
 42-97 
 
 37-90 
 
 10-64 
 
 39-91 
 
 40-19 
 
 40-86 
 
 Iron 2 
 
 29-48 
 
 32-16 
 
 34-27 
 
 30-32 
 
 7-97 
 
 30-94 
 
 31-94 
 
 31-25 
 
 Aluminium 
 
 1-82 
 
 52 
 
 
 3-17 
 
 72 
 
 I'OO 
 
 1-43 
 
 1-52 
 
 Alkali metal (Na) 
 Alkaline sulphate 
 
 7-60 
 2-31 
 
 (K) 4-50 
 
 (K) 7-72 
 3-46 
 
 (K) 2-25 
 
 7-84 
 
 (K) 1-06 
 2-00 
 
 (K) 11-31 
 3-66 
 
 (Na) 2-52 
 3-76 
 
 76 
 
 (Na) 3-07 
 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 1 Nitrogen . 
 
 20-31 
 
 22-13 
 
 23-14 
 
 20-18 
 
 5-73 
 
 21-49 
 
 a*64 
 
 22-00 
 
 2 ' Extra - radicle ' 
 
 
 
 
 
 
 
 
 
 iron 
 
 16-66 
 
 18-99 
 
 19-05 
 
 16-04 
 
 
 
 16-21 
 
 18-98 
 
 19-38 
 
 COMPOSITION OF DRY MATTER OF ABOVE SAMPLES (DRIED 
 
 AT 100 C.). 
 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 VII. 
 
 VIII. 
 
 Water of combination, etc. . 
 Cyanogen 1 ..... 
 
 16-38 
 39'% 
 
 18-85 
 42'61 
 
 6-58 
 45*41 
 
 13-87 
 
 40-06 
 
 12-03 
 41-77 
 
 8-35 
 42'14 
 
 15-46 
 42-55 
 
 17-95 
 43-29 
 
 Iron 2 
 
 31-23 
 
 33-34 
 
 36-21 
 
 32'05 
 
 31-30 
 
 32-67 
 
 33'82 
 
 33-09 
 
 
 1*93 
 
 54 
 
 
 
 2-90 
 
 1-03 
 
 1-52 
 
 1-61 
 
 Alkali metal 
 Alkaline sulphate .... 
 
 8-05 
 2-45 
 
 4-66 
 
 8-16 
 3-64 
 
 2-38 
 8-29 
 
 4-16 
 
 7-84 
 
 11-94 
 
 3-87 
 
 2-67 
 3-98 
 
 0-81 
 3-25 
 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 1 Nitrogen 
 2 ' Extra-radicle ' iron 
 Intra-radicle iron (found) 
 Intra-radicle iron (calculated 
 from nitrogen) .... 
 
 21-52 
 17-65 
 13-58 
 
 14-34 
 
 22-94 
 19-69 
 13-65 
 
 15-30 
 
 24-45 
 20-02 
 16-19 
 
 16-30 
 
 21-57 
 16-95 
 15-10 
 
 14-38 
 
 22-49 
 14-99 
 
 22-69 
 17-12 
 15-55 
 
 15-12 
 
 22-91 
 20-09 
 13-73 
 
 15-28 
 
 23-30 
 20-51 
 
 12-78 
 
 15-54 
 
ORGANIC PIGMENTS. 189 
 
 "In looking at these figures, it will be seen that the per- 
 centages of iron and nitrogen do not vary greatly. The 
 amounts of iron in the iron-cyanogen radicle, calculated from 
 the percentage of nitrogen and from the difference between 
 total and extra-radicle iron, do not agree closely in all cases. 
 We can offer no explanation of this. Taking the figures for 
 the dry matter, the greatest difference in iron was in the 
 cases of III. and I., 4'98 per cent., and the greatest difference 
 in nitrogen between III. and I. again 2*93 differences 
 which, calculated on the mean percentages, are under 16 
 and under 13 per cent, of the totals respectively. 
 
 " It will also be noticed that seven out of the eight samples 
 contained aluminium. This is not to be considered as an 
 adulterant, as alum is often added to the sulphate of iron 
 used in precipitating the ferrocyanide without any idea of 
 adulteration, but probably to cause the precipitate to settle 
 better and to dry in a more coherent manner. It probably 
 exists as aluminium ferrocyanide, a compound described by 
 Tissier (Comp. rend., xlv., 232). This has no colouring pro- 
 perties, and, of course, the iron and nitrogen in the iron 
 cyanogen radicle of this compound appear in the total iron 
 and nitrogen as determined. If merely the ammonia precipitate 
 is taken and called ' ferric oxide,' the alumina is included 
 as oxide of iron. 
 
 " We think that the addition of alum to the precipitating 
 tank is unnecessary, especially as the best sample of blue we 
 have examined contained none. 
 
 "Alkali metal, as iron-akali cyanide, is present in every 
 case. This agrees with the statement of Williamson and 
 others that a blue cannot be obtained free from alkali metal, 
 except when hydroferrocyanic acid is substituted for alkaline 
 ferrocyanide in the manufacture (the alkaline sulphate present 
 in each case is, of course, due to imperfect washing). 
 
 " In fact, Prussian blue, if by that term we mean ferric 
 
190 
 
 CHEMISTRY OF PIGMENTS. 
 
 ferrocyanide Fe 7 (CN) ]8 , is not known to the commercial 
 world. Commercial Prussian blue is a mixture of William- 
 son's blue with other iron-alkali cyanides, and often with 
 aluminium-iron cyanides, altogether a most complex sub- 
 stance. 
 
 "An examination of the watery extract showed, in the 
 cases of I. and VI., the presence of alkaline ferrocyanide. 
 This is rather remarkable, as with the quantities usually 
 taken the iron is in excess. We believe that these came 
 from, the same maker, but are sure, however, that both 
 samples were sent out as bond- fide Prussian blue. 
 
 "The following notes on appearance of the samples in lump 
 and in powder, depth of colour, etc., may be of interest : 
 
 
 
 Powdered Samples. 
 
 Condition. 
 
 Appearance. 
 
 Classifica- 
 
 
 
 
 tion in order 
 
 Quality 
 
 
 
 of Depth of 
 
 ot Tint. 
 
 
 
 Colour. 
 
 
 I. Lumps, conchoidal 
 
 Blackish copper glance, but not 
 
 2 
 
 6 
 
 fracture 
 
 a bright sheen 
 
 
 
 II. Lumps 
 
 Blue, pale-looking, no coppery 
 
 6 
 
 4 
 
 
 glance 
 
 
 
 III. Lumps, conchoidal 
 
 Rich blue, bright coppery sheen 
 
 4 
 
 1 
 
 fracture 
 
 
 
 
 IV. Lumps, conchoidal 
 
 Ditto, but not as good as III. 
 
 8 
 
 2 
 
 fracture 
 
 
 
 
 V. Paste 
 
 Dried, with coppery lustre 
 
 
 
 
 
 VI. Lumps, conchoidal 
 
 Blackish coppery glance, bufi 
 
 1 
 
 7 
 
 fracture 
 
 not a bright sheen 
 
 
 
 VII. Powder 
 
 
 
 7 
 
 5 
 
 VIII. Lumps 
 
 Light blue, no coppery glance 
 
 5 
 
 3 
 
 " The mean percentage of iron in the dry matter of these 
 eight samples was 32 "96. This w r ould give 3 '03 as the factor 
 for calculating iron to Prussian blue. The mean percentage 
 of nitrogen was 22 '73 ; this would give as a factor for calcu- 
 lating nitrogen to Prussian blue 4 '4. The following tables 
 show the accuracy to which these factors gave the percentage 
 of Prussian blue in the eight samples examined : 
 
ORGANIC PIGMENTS. 
 
 191 
 
 In Dry Matter. 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 VII. 
 
 VIII. 
 
 N x 4-4 
 
 94-69 
 
 100-98* 
 
 '107-58 
 
 94-91 
 
 98-95 
 
 99-83 
 
 100-80 
 
 102-52 
 
 Fe x 3-03 
 
 94-63 
 
 101-02 
 
 109-71 1 97-11 
 
 94-84 
 
 93-99 
 
 102-47 
 
 100-26 
 
 " Of course, these are merely empirical factors, based on 
 the examination of commercial samples of varying composi- 
 tion, and do not possess the accuracy of a factor to reduce 
 one definite chemical compound to terms of another, but, at 
 any rate, taken together they are of sufficient accuracy for 
 calculating the percentage of Prussian blue in pigments 
 containing that colour. The nitrogen alone in most cases 
 would be sufficient. 
 
 "We feel justified in stating that blue sold as Prussian 
 blue should contain at least 20 per cent, of nitrogen and 30 
 per cent, of iron calculated on the dry matter, and, after 
 burning, should be entirely dissolved by hydrochloric acid. 
 A ' dry ' blue should certainly contain under 7 per cent, 
 moisture. Another important point is that the sulphuric 
 acid used in the Kjeldahl nitrogen determination should 
 not be blackened. Pure cyanides dissolve in sulphuric acid 
 without any charring, which, if it occurs, indicates the pre- 
 sence of organic adulterants. A case of this kind will be 
 noted later. 
 
 " The watery extract should not indicate the presence of 
 excess of alkaline ferrocyanide. We consider that this is 
 evidence of defective manufacture, although it cannot, of 
 course, be regarded as adulteration. Still it containing as' 
 it does iron and nitrogen is partly included in the analysis 
 as Prussian blue, whereas it has no pigmentary value, and 
 its solubility in water does not add to the weathering qualities 
 of the colour. 
 
192 CHEMISTRY OF PIGMENTS. 
 
 " COMMERCIAL PIGMENTS. 
 
 " The following cases of examination of an adulterated 
 sample of Prussian blue (of German manufacture) and of 
 some colours ground in oil possess some interest. 
 
 " A rather pale-looking sample of dry powdered Prussian 
 blue, which we were told was a cheap sample of German 
 manufacture, gave only 14'35 per cent, of nitrogen. This 
 at once aroused our suspicions, especially as, instead of be- 
 coming colourless in a few minutes on boiling with sulphuric 
 acid, a decided blackening occurred. This clearly pointed 
 to the presence of an organic adulterant. On further exam- 
 ination, the following figures were obtained : 
 
 Moisture 11-35 
 
 Water of combination, organic adulterant, alkalies, etc. 37'76 
 
 Cyanogen i 26-65 
 
 Iron 22-67 
 
 Aluminium . 1-14 
 
 Insoluble -43 
 
 100-00 
 Per cent, nitrogen x 4-4 ....... 63'10 
 
 iron x 3-03 68-69 
 
 This sample not only contained more water than is usual, 
 but was clearly deficient in blue. We think that one is 
 justified in stating that it did not contain more than 70 per 
 cent, of Prussian blue. 
 
 " Two samples of ' celestial blue ' gave the following 
 results : 
 
 Dry. Ground in Oil. 
 
 Prussian blue 7'12 6-29 
 
 Barium sulphate 92-88 75-60 
 
 Oil 13-94 
 
 Undetermined 4-14 
 
 " In the case of colours ground in oil, the Kjeldahl method 
 is particularly applicable for the determination of nitrogen, 
 
 1 Nitrogen 14-35 
 
ORGANIC PIGMENTS. 193 
 
 and, as now it is very general to sell these colours in oil 
 instead of dry, we think that the nitrogen determination will 
 be found a very convenient method of ascertaining (approxi- 
 mately) the amount of Prussian blue in the many diluted 
 colours made from it. Adulteration with nitrogenous matter 
 is not probable, and so is not likely to lead to erroneous 
 results. We intend to continue the examination of all samples 
 which come under our notice by this method, which is rapid 
 (we have obtained a result in under one hour), and at once 
 points to any serious sophistication." 
 
 Prussian blue occurs in commerce as amorphous lumps 
 with a conchoidal fracture, and a strong coppery lustre, 
 which varies much in different samples, the best samples 
 showing a very strong lustre. It is so dark in this state 
 that its real colour value cannot be judged whilst the pig- 
 ment is in an undiluted condition. The actual value in this 
 respect can best be judged by comparing a carefully ground 
 mixture of 5 per cent, of a standard pure blue and 95 per 
 cent, of white lead with a similarly prepared mixture of the 
 given sample. More of the sample is added if necessary to 
 equalise the two shades, when the colour values are in the 
 inverse ratio to the amount of blue present in the mixtures. 
 
 Commercial samples, especially cheap German blues, are 
 often adulterated with barium sulphate, gypsum, chalk or 
 occasionally starch. Some very carelessly prepared samples 
 which have a very poor appearance are coated with a well- 
 prepared blue, so that it is necessary to make more than a 
 superficial examination. The adulterants usually met with 
 can be detected in the ordinary manner, and if the sample 
 be examined in the manner we have above described any 
 sophistication will be revealed. 
 
 Although largely employed, and of great value, Prussian 
 blue is not quite permanent in its nature. This is much 
 
 more marked in badly prepared samples, so that any Prussian 
 
 13 
 
194 CHEMISTEY OF PIGMENTS. 
 
 blue employed for artists' work should be of the highest 
 possible quality. 
 
 We have again recently come across samples of Prussian 
 blue which contained free potassium ferrocyanide. This is 
 clearly due "to imperfect washing, and in every case the pig- 
 ment was very poor in colour, and when diluted with a 
 white base more closely resembled a French grey than a 
 good blue. 
 
 One of these had the composition 
 
 Moisture 3-71 
 
 Prussian blue 89-29 
 
 Water-soluble matter (alkaline f erro or f erricyanides) 7-00 
 
 100-00 
 
 The presence of so much ferrocyanide is not only evi- 
 dence of incomplete washing, but also clearly shows that 
 ferric chloride was not used as an oxidising agent for the 
 Everitt's salt. The finest colour we have examined was 
 one prepared by oxidation with this reagent. 
 
 Two samples of Prussian blue, ground in oil, had the fol- 
 lowing composition : 
 
 Oil 9-96 24-61 
 
 Prussian blue 42-24 26-00 
 
 Calcium carbonate, etc. . . . 25-80 27-13 
 
 Insoluble in acid (BaSO 4 ) . . . 22-00 22-26 
 
 100-00 100-00 
 
 These more closely approximate in composition to Antwerp 
 blue, and it is certainly undesirable that such substances 
 should be sold as Prussian blue without some qualifying 
 description. 
 
 II. NATURAL LAKES, 
 
 This important group of pigments may be regarded as 
 compounds of some animal or vegetable colouring matter 
 with an inorganic base. The usual metallic base employed 
 
OEGANIC PIGMENTS. 195 
 
 in their preparation is alumina, or a mixture of that body 
 with lime, magnesia or oxide of iron. 
 
 The old-fashioned lak-es were prepared from such sources 
 entirely, the colour being derived from either an insect, such 
 as cochineal, or a plant such as logwood. To-day, however, 
 lakes are prepared from the coal-tar colouring matters, and 
 thus differ from the older lakes in the fact that their colour 
 principle is of artificial origin. Although frequently of very 
 beautiful colour, the lakes as a class suffer from one common 
 objection, which restricts their use, namely, the fact that 
 they are not permanent to light. They were used in very 
 early times, the Italian artists being very fond of them. 
 The origin of this class of colouring matters is said to be 
 as follows : In the early days of Italian dyeing, a colouring 
 material was used which was known as "lac". In the 
 process of. dyeing it was necessary to use a substance as a 
 mordant to develop and fix the colour on the fibre, and 
 salts of aluminium and tin were soon found to be the most 
 suitable for the purpose. During the process, combination 
 naturally took place in the vat liquid itself as well as on the 
 actual fibre. As a result the insoluble compound of colour 
 and base, which was of a very voluminous nature, floated to 
 the surface in the form of a scum. This was collected and 
 dried, and then sold to artists under the name of lacca. 
 This special name soon became generic, as other colours 
 were found to yield similar compounds, and so the name 
 passed into common use. As would be expected, in certain 
 well-defined cases the natural colouring matter is of an acid 
 nature, which accounts for its ready combination with bases. 
 This will be referred to in more detail in the sequel, but at 
 the present moment it may suffice to say that a " theoretical " 
 lake would consist of a compound between the acid and the 
 base in molecular 'proportions : such theoretical lakes, how- 
 ever, have no practical existence, and often a series of lakes 
 
196 CHEMISTBY OF PIGMENTS. 
 
 of a given colour exists, in which the tint depends entirely 
 on the proportion between the acid and the base, part of 
 which is in chemical combination, and part in a kind 
 of mechanical mixture. Although the processes used for 
 the preparation of these colours vary very much, and are 
 often carefully kept secret, the principle underlying their 
 preparation may be illustrated in the following example. A 
 decoction of the natural substance in water is prepared of as 
 high a strength as possible, and after filtering it from sus- 
 pended particles, a solution of the base is added to the liquid. 
 The exact conditions under which the base is added deter- 
 mine the resulting tint, and it is in a scientific appreciation 
 of these conditions that success depends. Some natural 
 colouring matters exist ready formed in the plant, etc., and 
 yield lakes which do not greatly differ in colour with the 
 nature of the base used : whilst others do not exist as 
 colours in the fresh plant, but are only developed when the 
 base is added, and therefore differ greatly in the resulting 
 colour of the lake, according to the nature of the base used. 
 
 Cochineal Lakes, 
 
 The Spanish conqueror, Cortes, and his comrades found 
 the cochineal insect used in Mexico ; and Prescott, the able 
 historian of the conquest, seems to be definitely of the opinion 
 that this was the first cause of the introduction of this colour 
 into Europe. 
 
 The coccus used in Europe and Asia Minor was probably 
 an insect, kermes, attacking the kermes oak (Quercus 
 coccifera). 
 
 The beautiful colouring matter known as carmine, with 
 its various lakes, is derived from the insect, Coccus cacti. 
 The variety usually employed appears to be the dried fecun- 
 dated female insect which has been reared on various species 
 of Nopalea. It has been stated that so long ago as in the 
 
ORGANIC PIGMENTS. 197 
 
 time of Moses a red colour was derived from an insect, and 
 used for dyeing the high priest's garment. This appears to 
 have been some species of Coccus, probably identical with the 
 Coccigranum of Pliny. The male insect does not furnish the 
 colour. 
 
 It is true that this colour does not find a very extensive 
 use except for a few special purposes, save in the dyeing 
 industry. Its value as a pigment is greatly diminished on 
 account of the action of light, possibly combined with that 
 of moisture. Outside work in carmine colours, whilst being 
 at first very beautiful, is not at all lasting. Further, it is 
 naturally much more expensive than most reds, so that its 
 use would be limited on that account alone. 
 
 The following preparations of this colour are, however, 
 of sufficient interest and importance to justify their being 
 shortly described. 
 
 Carmine. 
 
 It is uncertain when this beautiful pigment was discovered, 
 but the earliest recipe that can be traced is one given by 
 Homberg in 1656, when it was already a well-known colour. 
 According to Wiegler (Die natilrliche Magie, published in 
 Berlin in 1782) it was accidentally discovered in Florence 
 or Pisa by a Franciscan friar. It was said to have been 
 thus found by chance during its use in the preparation of 
 some medicine, in which form it had for some time enjoyed 
 a reputation. Its name has even been derived from the 
 same root as . " carminative " by enthusiastic etymologists, 
 assuming that its use in medicine was of this nature. 
 
 It may be regarded as the highest lake of the series to 
 which it belongs, that is, it is the nearest approximation to a 
 true compound without excess of base. The methods used 
 in its preparation are varied, and have in most cases been 
 kept as secret as possible. The following are some of the 
 
198 CHEMISTEY OF PIGMENTS. 
 
 published methods, but they must be accepted with reserve, 
 as in many cases misleading information has purposely been 
 published. 
 
 (1) One pound of crushed cochineal insects are boiled in 1 
 gallon of water for a quarter of an hour, and 1 oz. of ordinary 
 alum added, the boiling being continued for a short time 
 longer. After standing for a few hours the clear supernatant 
 liquid is decanted, and this after a few days deposits about 
 an ounce and a half of carmine. A crop of an inferior nature 
 is deposited after a short interval. The addition of a little 
 cream of tartar is said to assist in the deposition of the 
 carmine. (2) Two pounds of the insects are boiled with 
 water, and to the clear decoction, 2 oz. of alum and 3 oz. of 
 a saturated solution of stannous chloride with 2 oz. of sodium 
 carbonate are added, and the liquid allowed to stand for a 
 time until the carmine is deposited. (3) The following 
 method is the subject of a patent, dated 1856 : 9 oz. of car- 
 bonate of sodium, 8 oz. of citric acid and 27 quarts of water 
 are boiled together, a pound and a half of insects are added, 
 and the whole again boiled for an hour and a half. The liquid 
 is then strained and clarified. The clear solution is then boiled 
 and 9 oz. of alum are added. After again boiling for five 
 minutes, the fluid is allowed to stand, until the carmine is 
 gradually deposited, when it -is collected, washed and dried. 
 Without suggesting that these methods will give the best 
 results, it is not too much to say that they embrace the 
 general principles underlying the successful preparation of 
 carmine. 
 
 Pereira, about fifty years ago, stated that alum was no 
 good as a precipitant for carmine, but that such a substance as 
 chloride of tin must be used. This however is not in accord- 
 ance with almost universal experience, since alum is found to 
 be the base of most of the fine commercial carmines. 
 
 Carmine is a fine deep scarlet powder, of somewhat 
 
ORGANIC PIGMENTS. 199 
 
 variable tint, according to its quality, but always of a brilliant 
 fiery brightness. The best quality of commerce is known as 
 "nacarat carmine". It'fs insoluble in all the usual organic 
 solvents, but is soluble in ammonia and the caustic alkalies. 
 As a pigment it works well in oil or water, but is not per- 
 manent to light and air. 
 
 The Analysis of Carmine. The moisture should be deter- 
 mined in the sample, and, so long as it is pure carmine, the 
 value is of course proportional to the amount of dry pigment 
 it contains. As a general rule, one does not expect to find 
 more than from 15 to 18 per cent, of water in commercial 
 samples. Over 20 per cent, may be regarded as an unfair 
 addition. The ash should not only be determined, but it 
 should be as fully examined as possible. The bulk of it 
 should be alumina and lime, and there should be no insoluble 
 white pigments present such as barium sulphate or siliceous 
 matter. To determine whether excess of base in the un- 
 combined state is present, the sample should be exhausted 
 with dilute ammonia, which removes the true compound, 
 and leaves the uncombined alumina and lime, together with 
 some organic matter. Valuable information in regard to 
 the colouring matter itself is obtained by boiling a few wool 
 fibres for half an hour in the ammoniacal solution : aniline 
 scarlet dyes a red-orange tint, whilst carmine gives a distinct 
 purple red. 
 
 The presence of lakes of Brazil wood may be detected by 
 dissolving the sample in the minimum quantity of very dilute 
 ammonia and precipitating the carmine colour with excess 
 of lime water. If Brazil wood lake be present, the filtrate 
 after this treatment will have a purple or violet colour, as the 
 colouring matter is not precipitated under these circum- 
 stances. A compound of Biebrich scarlet with salts of tin 
 resembles pure carmine closely in colour and in general 
 characters. If tin be present in the colour, this body should 
 
200 
 
 CHEMISTRY OF PIGMENTS. 
 
 be looked for. It may be detected by boiling white wool in 
 the ammoniacal solution of the colour, when, if the scarlet 
 be present, the fibre assumes a red-orange colour, instead of 
 a pure red purple. 
 
 Dechan has given the following table of analyses of 
 a number of commercial samples of carmine (Pharm. Journ., 
 3, xvi., 511) : 
 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 VII. 
 
 VIII. 
 
 IX. 
 
 Moisture 
 
 22-1 
 
 16-1 
 
 2-0 
 
 22-3 
 
 20-2 
 
 23-5 
 
 10-0 
 
 21-2 
 
 13-0 
 
 Colouring matter . 
 
 46-1 
 
 69-2 
 
 34-1 
 
 65-7 
 
 60-8 
 
 69-5 
 
 72-0 
 
 18-4 
 
 67-5 
 
 Alumina and lime, 
 
 
 
 
 
 
 
 
 
 
 etc. (dissolved by 
 
 
 
 
 
 
 
 
 
 
 ammonia) . 
 
 8-0 
 
 9-8 
 
 11-4 
 
 12-0 
 
 9-0 
 
 7-0 
 
 8-1 
 
 4-4 
 
 10-0 
 
 Organic matter (in- 
 
 
 
 
 
 
 
 
 
 
 soluble in am- 
 
 
 
 
 
 
 
 
 
 
 monia) 
 
 21-8 
 
 2-5 
 
 18-5 
 
 
 
 9-8 
 
 
 
 8-0 
 
 52-4 
 
 9-5 
 
 Ash (insoluble in 
 
 
 
 
 
 
 
 
 
 
 ammonia) . 
 
 2-0 
 
 2-4 
 
 34-0 
 
 trace 
 
 0-2 
 
 trace 
 
 1-9 
 
 3-6 
 
 trace 
 
 Carmine is met with in commerce, adulterated with 
 various aniline colours and occasionally with such substances 
 as starch. Excess of mineral matter, generally uncombined 
 alumina, is also met with, and according to Dechan (Pharm. 
 Journ., 3, xvi., 511) there are also found vermilion and 
 chrome red. These adulterations are, however, we think, 
 almost apocryphal. 
 
 Lafar (/. prak. Chem., xliii., 130) has made a full analysis 
 of a very fine sample of carmine (nacarat-carmine) and gives 
 the following as his results. It contained 15 '5 per cent, of 
 w^ater, 6*87 per cent, ash, 23'26 per cent, of nitrogenous 
 matter and 52'37 per cent, of colouring matter. The com- 
 position of the ash was as follows : 
 
 Cupric oxide 
 Stannic oxide 
 Alumina 
 Calcium oxide 
 Magnesia . 
 
 0-35 
 
 0-14 
 
 40-48 
 
 44-20 
 
 0-61 
 
ORGANIC PIGMENTS. 201 
 
 Sodium oxide 5'40 
 
 Potassium oxide 3-20 
 
 Phosphoric acid 2-71 
 
 Silica . . .'" . ' 0-60 
 
 Carbonic anhydride . . . . . . . 2-31 
 
 Ferric oxide traces 
 
 In this, as in most cases, the ratio of the alumina to the 
 lime and magnesia is practically that of one molecule of the 
 former to two molecules of the latter. A very high-class 
 sample examined by Liebermann was found to contain 17 
 per cent, of water, and yielded 3'7 per cent, of nitrogen, 
 which may be taken as equivalent to about 23 per cent, of 
 nitrogenous matter. The dry carmine contained 8*1 per cent, 
 of ash, the composition of which was as follows : 
 
 Stannic oxide O67 
 
 Alumina . . 43*09 
 
 Lime 44-85 
 
 Magnesia 1-02 
 
 Sodium oxide 3'23 
 
 Potassium oxide ..... . 3'56 
 
 Phosphoric acid 3-20 
 
 Neither the alumina nor the lime is precipitated from 
 an ammoniacal solution of carmine by any of the usual 
 re-agents, it being necessary to examine the ash to detect 
 these metals. 
 
 Although the chemistry of the cochineal dye had been the 
 subject of researches by John (1813), Pelletier and Caventou 
 (1818), and by Preisser and Arppe, the earliest systematic study 
 of the body may be regarded as that of Warren de la Kue, in 
 1847. He did not succeed in preparing the acid in a crystalline 
 condition, and the formula which he assigned to it, C 14 H 14 O 8 , 
 must now be regarded as incorrect. Schutzenberger (Ann. 
 Chim. Phys., liv., 52) arrived at the conclusion that De la 
 Kue's acid was a mixture of several bodies, and assigned to 
 the pure acid the formula C 9 H 8 5 . Schaller later (1864) 
 analysed what he believed to be pure carminic acid and 
 
202 CHEMISTKY OF PIGMENTS. 
 
 assigned to it a formula differing from that of Schutzen- 
 berger's, only by containing one molecule more of water. 
 
 Hlasiwetz and Grabowsky (Annalen, cxli., 329) considered 
 that carminic acid was a glucoside which yielded on hydroly- 
 sis a sugar and carmine red. Von Miller and Kohde, however, 
 showed that this was not correct, as carminic acid did not 
 alter on boiling with dilute sulphuric acid. 
 
 These chemists originally held the view that the acid was 
 a naphthalene derivative, but have since modified their opin- 
 ions. They consider that the formula of carminic acid is 
 either C 24 H, 2 14 or C 22 H 20 O 13 . 
 
 The most modern researches, and those which are to be 
 regarded as the most reliable, are those of Liebermann and 
 of Schunck and Marchlewski. 
 
 Liebermann, who has recently devoted much attention 
 to the chemistry of the cochineal dye, considers that carminic 
 acid is an indene derivative of the formula C 2 . 2 H 22 O 13 . The 
 acid, which is easily soluble in water, readily passes into in- 
 soluble colouring matters, the change being accompanied by 
 elimination of water and increase of molecular complexity. 
 This change is characteristic of the bodies of the ketoindene 
 series. On oxidation by potassium persulphate, the dye 
 yields two other acids. These have been termed coccinic 
 acid, C 9 H 8 5 , a body very* soluble in alcohol, but nearly in- 
 soluble in water, melting at 293 with decomposition : and 
 cochinelic acid, G 10 H 8 O 7 , which forms crystalline needles 
 melting at 224 to 225. It is moderately soluble in cold water, 
 and' easily so in alcohol. The former of these acids has been 
 identified with the well-defined compound, hydroxy-uvitic 
 acid. A study of these acids and their derivatives has led 
 Liebermann to assign, provisionally, to carminic acid the 
 
 constitution 
 
 COOH, C 6 H, CH 3 (OH), CH, OH 
 
 CH(OH) -CH(OH). 
 
ORGANIC PIGMENTS. 203 
 
 Schunck and Marchlewski prepare pure carminic acid by 
 treating cochineal extract with lead acetate, decomposing the 
 lead salt with sulphuric acid in the presence of alcohol, and 
 evaporating the liquid to dryness at the lowest possible 
 temperature. The residue can be purified by dissolving in 
 alcohol and precipitating with ether or benzene. It is then 
 recrystallised from alcohol, when it forms small red prisms. 
 Aqueous solutions of carminic acid, when evaporated, give an 
 amorphous residue, but no crystals. According to Schunck,. 
 carminic acid possesses the formula C n H 12 6 or C n H 8 O 4 
 with two molecules of water of crystallisation. His prepara- 
 tion darkened at 130 and blackened without melting at 205. 
 In alcoholic solution it shows three ill-defined absorption 
 bands, one in the green and two in the blue. The barium 
 and calcium salts are brown, changing to violet with excess 
 of base ; the lead and aluminium salts are also violet, and 
 the stannous salt scarlet. An aqueous solution is at once 
 decolourised by animal charcoal, the latter increasing in 
 volume and becoming gelatinous. This mass seems to be a 
 compound which is not changed by alcohol, but is decomposed 
 by alkalies. The anilide of carminic acid is deposited in ruby 
 crystals from its solutions, and melts with decomposition at 
 189 to 190. 
 
 Crimson Lake. 
 
 This pigment, which produces very beautiful results, is a 
 more fully saturated lake of the colouring matter of cochineal 
 than ordinary carmine. It suffers from the same defect as 
 the last-named colour, namely, lack of permanency, so that 
 its employment is somewhat limited. Much of the so-called 
 crimson lake of the present day, however, is not a true 
 cochineal colour at ail ; this is especially true of the pigment 
 when used in oil, it then being generally supplied by the 
 artists' colourmen of repute, made from the coal-tar product, 
 
204 CHEMISTRY OF PIGMENTS. 
 
 alizarin. When so made it has the advantage of being pretty 
 permanent, but in chemical constitution it must not be con- 
 founded with the true crimson lake. When supplied as a 
 water colour, it is generally made from the insect. 
 
 Crimson lake may be regarded as a more basic compound 
 of carminic acid than ordinary carmine, with, of course, more 
 or less foreign matter present as well. The following receipt 
 has been given as producing a very fine shade of this exquisite 
 colour : Twenty parts of the powdered insects are boiled 
 with 400 parts of water and ten parts of cream of tartar. 
 After filtration, a solution of 300 parts of alum and a small 
 quantity of stannous chloride are added to the solution. The 
 precipitate first formed is exceedingly brilliant, but the 
 greater part of the colour is still in the solution. To effect 
 its precipitation a solution of carbonate of sodium is cautiously 
 added, when the alumina is completely precipitated, along 
 with all the colouring matter. One can hardly fix any 
 standard for the quality of this pigment, but it is necessary 
 that it should be the product of the true cochineal, and it 
 should, after allowing for the greater proportion of mineral 
 matter, correspond closely in its behaviour with genuine 
 carmine. 
 
 The following recipe is given by A. P. Laurie (Cantor 
 Lectures, 1891) as from a -MS. in the Library of the Univer- 
 sity of Padua, dated probably the middle of the seventeenth 
 century. 
 
 " ' To make a most beautiful purple lake. Take an ounce of 
 fine grana or cochineal, a quarter of an ounce of roche alum, 
 and about a bocale full of common water. Boil the water 
 with a quarter of an ounce of fennel seed until it is diminished 
 one-third ; then add the grana or cochineal finely pulverised, 
 and boil the whole over a slow fire for a quarter of an hour ; 
 then add the pulverised roche alum, and let it boil for another 
 quarter of an hour. After this, take it from the fire, strain it 
 
ORGANIC PIGMENTS. 205 
 
 through a linen cloth into a new and unglazed earthen por- 
 ringer, and leave it there for eight days. You must then decant 
 the water, or take it up gently with a sponge, evaporating the 
 little which remains, until the colour is condensed, which 
 you must afterwards keep in shells, adding to it a little lemon 
 juice.' ' 
 
 Mr. Laurie says : "I have tested this recipe, and find 
 that a precipitate is thrown down of a purple colour. The 
 addition of lemon juice referred to here, and in some other 
 recipes, causes the lake to become more of a crimson and less 
 of a purple." 
 
 Lac Dye Lake, 
 
 The substance known as lac dye is the product of Coccus 
 lacca, an insect which lives on the banyan and other trees, 
 especially those belonging to the genus Ficus. From the 
 mature impregnated female insect a resinous exudation flows, 
 which encloses the deposited ova. The twigs with the 
 attached resinous matter and enclosed animal substance are 
 broken off, and constitute stick lac. If the resinous mass 
 be extracted with water, the greater part of the colouring 
 matter present is dissolved, and the residue is known as seed 
 lac, which when melted and strained and thus purified is 
 sold as shellac. The colouring matter, or lac dye, is appar- 
 ently prepared by treating the stick lac with a weak alkaline 
 solution, and probably with a mixture of alumina and lime 
 salts. It is used to only a very small extent now, and at 
 most is only employed for pigmentary work in rare cases as 
 an artist's colour. 
 
 The composition of this colour has been investigated by 
 Schmidt (Journ. Soc. Dyers, etc., iii., 122), who called the 
 chief constituent laccainic acid, and pointed out its close 
 resemblance to carminic acid. He assigned to it the formula 
 C 16 H 12 O 8 , and described it as a brown-red crystalline powder 
 
206 CHEMISTRY OF PIGMENTS. 
 
 melting at 180. It is soluble in alcohol and acetic acid, and 
 to a fair extent in water. It is almost insoluble in ether. 
 
 It appears to be a dibasic acid, and the chief difference 
 between it and carminic acid is the difference in the absorp- 
 tion spectra when dissolved in sulphuric acid. The two 
 following analyses are given by Schmidt of two samples of 
 the dye. 
 
 Moisture 9-0 11-26 
 
 Mineral matter 15'7 18-24 
 
 Colouring matter 10-4 13-2 
 
 Other organic matter 64-9 57*3 
 
 A good lac lake is prepared by the use of alum as a pre- 
 cipitant, and tin is also a good base when a fine colour is 
 required. Samples of lac lake usually contain about 50 per 
 cent, of colouring matter, 40 per cent, of resin, and 10 per cent, 
 of alumina or of alumina and lime mixed. 
 
 Colours prepared from this dye are rather more permanent 
 than those from cochineal. 
 
 Scarlet Lake, 
 
 This pigment used to be a mixture of crimson lake with 
 more or less vermilion. The fugitive nature of the cochineal 
 colour, however, has caused it to be replaced very generally 
 by an alizarin colour. It thus becomes practically a per- 
 manent pigment. 
 
 Madder Lakes. 
 
 At one time the madder lakes were very largely employed, 
 and held in very high esteem. Their value has in no wise 
 diminished, but as the chemistry of the constituents of the 
 root became more and more understood until finally artificial 
 alizarin was an accomplished fact, the use of the natural 
 product gradually diminished, until to-day it is almost 
 entirely superseded by the artificial colours. Hence the 
 
OEGANIC PIGMENTS. 207 
 
 following short epitome of the chemistry of the madder lakes 
 becomes of little but historical interest. The root of the 
 madder plant (Rubia tirtctorium) contains a considerable 
 quantity of the colouring principle alizarin (q.v.) in the form 
 of a glucoside which is known as ruberythric acid. This 
 body has the formula C 26 H 28 14 , and under the influence of 
 either natural ferments or of dilute acids or alkalies it splits 
 up into alizarin and the sugar, glucose. The equation repre- 
 senting this change is as follows : 
 
 C 26 H 28 14 + 2H 2 = 2C 8 H M O e + C 14 H 6 2 (OH) 2 . 
 
 The closely allied body purpurin (q.v.) occurs in the root in a 
 similar condition. 
 
 The employment of madder has usually been in the form 
 of a madder extract or of garancin, or garanceaux, the 
 corresponding substance prepared from madder which has 
 been once used and still contains some of its colouring matter. 
 Garancin, obtained by treating the root with strong sulphuric 
 acid, has been more frequently employed for the preparation 
 of madder lakes than any other substance, and the following 
 are the outlines of several processes which may be said to 
 cover the general principles involved. Of course the details 
 have been varied without limit, and lakes of different shades 
 obtained accordingly. Khittel many years ago described the 
 method he employed, in the following manner. One part of 
 garancin is steeped in a solution of one part of sodium 
 sulphate in thirty-six parts of water, and after a time is 
 washed and pressed until all traces of the sulphate are 
 removed. The purified garancin is then ready for use. A 
 quantity of alum, free from the least traces of iron (which 
 darkens the resulting lake very much), equal in weight to the 
 garancin employed, is then dissolved in ten times its weight 
 of water, and boiled. The purified garancin is then added to 
 this solution. The mixture should not now be boiled, as the 
 
208 CHEMISTEY OF PIGMENTS. 
 
 resulting lake is darkened by too much heat. After about 
 half an hour, with repeated agitation, most of the colouring 
 matter is extracted. The liquid is then filtered from the 
 residue, and when the filtrate has cooled to about 45 C. 
 sub-acetate of lead is added in quantity equivalent to the 
 amount of alum used. On stirring the mixture sulphate of 
 lead is precipitated and rapidly subsides. The clear liquid is 
 then decanted before it has time to cool. It is then heated 
 for some time to nearly the boiling point, and then the first 
 fraction of the lake separates. This is of a very fine red tint. 
 After the first bright red lake has been deposited, the residual 
 liquid is divided into two equal portions, and to one is added 
 ammonium carbonate until a slight turbidity is apparent. 
 The two portions are now again mixed, and again heated, 
 when a fresh quantity of lake separates, which is not, however,, 
 so brilliant as the first fraction. Great care must be employed 
 in drying these lakes, as heat injures them considerably. 
 
 Sace described the following method of obtaining a fine 
 lake. He mixes 100 parts of an alcoholic extract of madder 
 with 50 parts of water, and allows the mixture to macerate 
 for twenty-four hours. More water is then added, and the 
 solution is separated from the solid residue by straining 
 through a silk sieve. A boiling solution of alum, containing 
 10 per cent, of the salt is then gradually added until pre- 
 cipitation takes place. 'Eb^lake has a fine deep-red tint. 
 By using sulphate of iron an almost black-violet lake results, 
 whilst alum containing a little iron yields intermediate colours. 
 
 Kopp treated the root in powder with a solution of 
 sulphurous acid and allowed the mixture to macerate for a 
 time. The hot filtered liquid is then treated with a solution 
 of aluminium acetate, or alum mixed with carbonate of sodium, 
 and the lake precipitated in fractions. The finer tints are 
 deposited first, the later fractions containing more and more 
 of the accompanying impurities. 
 
ORGANIC PIGMENTS. 209 
 
 The high value of the natural madder lakes caused them 
 to be often adulterated with cheaper colouring matters. The 
 following description of the methods used for detecting the 
 more usual adulterants is given by Chateau, and is repro- 
 duced from an interesting old treatise, On the Manufacture 
 of Colours by Malepeyre. We give an account of the 
 methods, but are unable to vouch that by following the 
 directions there given one will be able to detect all the 
 admixtures that may be present, although good indications 
 of the purity of the lakes can undoubtedly be obtained in this 
 manner. 
 
 " Bed and Pink Lakes of Madder. These lakes do not colour 
 water, either hot or cold. They colour ether and alcohol only 
 very slightly, and only after some time. By calcination they 
 leave a residue of alumina. 
 
 " Santaline. If the lake be dark it may contain santaline, 
 the colouring matter of red sanders wood (Pterocarpus santa- 
 linus), which is detected by the orange-red colour acquired 
 by the ether digested with the suspected lake. Alcohol under 
 the same circumstances would be coloured red. 
 
 " If the lake be of a pink hue it may be falsified by lakes of 
 Brazil wood or with (common) cochineal lakes. But as 
 madder lakes and, generally, all lakes are insoluble in water, 
 alcohol and ether, their colouring matter should be isolated, 
 and the following method is proposed. Every lake with 
 alumina for its base is soluble in hydrochloric acid, or in 
 acetic acid to which a few drops of the former have been 
 added, or in a solution of stannous chloride. After the lake 
 is dissolved, ether is added to the solution, and the whole is 
 shaken. All the colouring matter is dissolved in the ether, 
 which will acquire the colour of the matter forming the basis 
 of the lake. 
 
 " Lakes of Brazil Wood. If the lake be mixed with a lake 
 
 of Brazil, Pernambuco or Japan wood, the colouring matter 
 
 14 
 
210 CHEMISTEY OF PIGMENTS. 
 
 will be dissolved in the ether by the above process, and the 
 ether will be of a golden-yellow colour. 
 
 " Venice Lake. This lake, one of the finest of the Brazil 
 wood lakes, will disengage ammonia if heated in a test tube 
 with a solution of potash. A pure madder lake does not 
 yield any ammonia under these circumstances. 
 
 " Carmine Lake. Water will be coloured if cochineal lake 
 is present, and the colour is intensified by heating. Aqueous 
 solutions containing cochineal lake become violet when soluble 
 alkalies are added, and give a violet precipitate with lime 
 water, stannous chloride or zinc salts. Cochineal lake is 
 turned a cherry red by stannous chloride, and the solution 
 stains paper. Madder lake does not' behave in this manner. 
 
 " Campeachy Lakes. In the presence of these lakes the 
 addition of hydrochloric acid produces a crimson red colora- 
 tion. When extracted with ether as above mentioned, the 
 ether will be of a golden-yellow colour, which yields the 
 crimson red reaction with hydrochloric acid. 
 
 " Alkanet Lakes. The lake is dissolved in acetic acid and 
 the solution extracted by carbon bisulphide. If alkanet be 
 present, the carbon bisulphide is coloured an intense violet 
 red. This is characteristic of this colouring matter. When 
 heated, the lake gives off violet fumes if alkanet be present. 
 After dissolving the lake in acetic acid, and separating the 
 colour with ether, this is evaporated, and the residue is 
 treated with alcohol, which dissolves the colouring matter of 
 alkanet. The alcoholic solution gives a blue precipitate with 
 lead subacetate solution. 
 
 " Orchil. If orchil colouring matter be present, the colour 
 is yielded to hydrochloric as a deep red. If this solution be 
 shaken with ether, the orchil does not yield the least colour 
 to that solvent. 
 
 " Prussian Blue. In the case of this somewhat rare adul- 
 terant, the lake will be of a violet colour. This will be 
 
OEGANIC PIGMENTS. 211 
 
 changed to a green by hydrochloric acid, and the iron cyanide 
 compounds can be recognised and determined by the usual 
 methods (see Prussian Blue)/' 
 
 Alizarin Lakes. 
 
 The chemistry of this group of pigments is now of very 
 great importance, since the alizarin colours have practically 
 replaced the madder colours for dyeing purposes, and have 
 of recent years become of great importance as pigments for 
 certain kinds of work. In the dyeing industry they are 
 always employed in such a manner that they yield lakes as 
 the resulting compound, so that alizarin dyes differ but little 
 in theory from alizarin pigments. 
 
 Alizarin may be described as an anthracene derivative, 
 and as the number of colouring matters derived from this 
 coal-tar hydrocarbon is very limited, and since they all resemble 
 each other very closely in their chemical properties, the an- 
 thracene group may be looked upon as an isolated and naturally 
 related series of coal-tar colours. 
 
 They are of a strongly acidic nature, which explains the 
 fact that they form admirable lakes, and in dyeing they can 
 only be used in conjunction with mordants, or, in other words, 
 can only be employed in the form of lakes. They possess 
 the advantage of being very permanent to light, far more so 
 than most coal-tar colours, and they are also very fast on 
 fibres when used as dyes. 
 
 Commercial alizarin. The hydrocarbon anthracene is usu- 
 ally transformed into alizarin by means of three distinct 
 operations. It is first oxidised to anthraquinone by means 
 of chromic acid, and the resulting body is treated with sul- 
 phuric acid in order to convert it into a mixture of sulphonic 
 acids. These are melted in the last stage of the process with 
 caustic soda, when alizarin is produced. These steps in the 
 
212 CHEMISTEY OF PIGMENTS. 
 
 transformation are illustrated by reference to the following 
 diagrammatic formulae : 
 
 /CHv / co \ / co \ 
 
 C 6 H/ | XH, 6 H/ )>C 6 H 4 C fl H ' >C 6 H 2 (S0 3 H) 2 
 
 \OH/ NOO/ MXK 
 
 Anthracene Anthraquinone Anthraquinone 
 
 di-Sulphonic Acid 
 
 C 6 H 
 
 \ 
 
 Alizarin 
 
 Alizarian is, chemically, 1:2: dioxy-anthraquinone. It 
 forms orange-red needles melting at 290, and subliming at 
 higher temperatures. It is identical with the principal colour- 
 ing matter of the madder root (Rubia tinctorium), in which 
 it occurs as a glucoside known as ruberythric acid (identical 
 with morindin, from Morinda citrifolia). 
 
 Of the trioxy-anthraquinones, of which a number are 
 known, the most important are purpurin, flavopurpurin and 
 anthrapurpurin. These are all isomeric bodies related to 
 alizarin by having one of the hydrogen atoms (different in each 
 case) replaced by an OH group. 
 
 Alizarin, C U H 6 2 (OH) 2 , is prepared in the pure state by 
 melting pure anthraquinone-monosulphonic acid with caustic 
 soda. It can also be obtained from ordinary blue shade 
 commercial alizarin paste in the following manner. The 
 paste is dissolved in caustic soda, and the solution filtered. 
 A solution of barium chloride is added, and the whole is 
 heated to boiling point, when the barium compound of alizarin 
 separates out in a crystalline condition. This is collected on 
 a filter and washed, and finally decomposed by an acid. It 
 can be freed from the last trace of impurities by recrystallisa- 
 tion from glacial acetic acid or by sublimation. Alizarin has 
 also been obtained synthetically by several methods, but these 
 are not necessary to record here. Pure alizarin forms fine 
 
ORGANIC PIGMENTS. 213 
 
 orange-red crystals melting at 290. It is almost insoluble 
 in cold water and only slightly so in hot water, one litre 
 dissolving 0'31 gr. of alizarin at 100. It dissolves in sul- 
 phuric acid with a red-brown colour, but on dilution the 
 alizarin is precipitated in an unchanged state. When crystal- 
 lised from moist ether, alizarin contains three molecules of 
 water of crystallisation. If precipitated by acids from alkaline 
 solutions, it also contains water, which is driven off at 100. 
 Alizarin behaves towards alkalies as a weak acid. It dissolves 
 in caustic alkalies and in ammonia with a blue-violet colour, 
 but is precipitated from such solutions by dilute acids. With 
 calcium and barium salts, alizarin forms violet precipitates, 
 and with all other bases it yields practically insoluble lakes. 
 Those of alumina and tin are red, the others mostly of a 
 darker colour. Towards these bases alizarin behaves as a 
 strong acid, displacing even hydrochloric and nitric acids from 
 their combinations. 
 
 In commerce alizarin is always sold as a paste, which 
 contains the hydrates of alizarin and the allied colouring 
 matters in a fine state of division. The average quantity 
 of dry colouring material in these pastes is about 20 per cent., 
 but sometimes as much as 60 per cent, is met with. The 
 two most important commercial shades are those known as 
 alizarin blue shade (alizarin V) and alizarin yellow shade 
 (alizarin G). The blue shade results when the sulphonation 
 of the anthraquinone has not been carried beyond the mono- 
 sulphonic acid stage. The yellow shade contains little true 
 alizarin, but mostly anthrapurpurin and flavopurpurin. The 
 latter body is responsible for the yellow shade, the former 
 yielding a neutral red with alumina. 
 
 Purpurin, C 14 H 5 2 (OH) 3 , which is found associated with 
 alizarin in the madder root, crystallises with one molecule 
 of water, and melts at 253. 
 
 Anthrapurpurin (isopurpurin) has the same empirical 
 
214 CHEMISTEY OF PIGMENTS. 
 
 formula as the last-named body, merely differing from it by 
 the. orientation of the (OH) groups. It melts at 360. 
 
 Flavopurpurin is also isomeric with purpurin, and melts 
 at above 330. From the above brief descriptions of the 
 properties of the colouring matters of the alizarin group, it 
 will be easily understood how very numerous shades of lakes 
 are produced from them, many of these differing greatly in 
 tint, whilst being but slightly different in chemical composi- 
 tion. Of the varieties of these lakes, the following are best 
 known as commercial pigments : alizarin carmine, scarlet 
 lake, burnt carmine, Indian lake, permanent crimson, per- 
 manent violet, purple lake, sap green, olive green, olive lake, 
 and others known under various fancy names. 
 
 The chemical composition of these pigments cannot be 
 regarded as regularly constant, but as far as possible this is 
 indicated in the following paragraphs, in which a description 
 of the chief well-defined compounds of this nature is given. 
 
 Pure alizarin yields, as above mentioned, with calcium 
 and barium salts a series of violet lakes, which vary slightly 
 in tint according to the conditions under which they are 
 formed. With tin and alumina it yields good red lakes, but 
 with other bases the lakes are dark in colour. The slightest 
 trace of iron salts suffices to change the alumina red to a dull 
 red or even to a brown colour. When the commercial alizarin 
 is employed, the tint of the resulting lake necessarily depends 
 on the exact composition of the alizarin. Ordinary alizarin 
 red is the alumina lake of the yellow shade of alizarin, that 
 is, it contains a large quantity of the trioxyanthraquinone 
 lakes. Alizarin pink is prepared from the blue shade, and 
 contains more of the true alizarin compound. They can all 
 be obtained by dissolving the colouring matter in an alkali 
 and precipitating the lake by a solution of alum. By varying 
 the base or by using a mixture of tin and alumina, for example, 
 different shades are obtained. According to recent researches 
 
OEQANIC PIGMENTS. 215 
 
 of Liechti and Suida the composition of the normal alumina- 
 lime alizarin red lake is A1 2 O 3 , CaO, (C 14 H 6 O 3 ) 3 , H 2 O. Traces 
 of ferrous salts change the colour to a violet, and with ferric 
 salts the darkening is very pronounced, a brown being often 
 produced. A small quantity of chromium salt is sufficient to 
 change the alumina red into a fine puce colour. 
 
 In addition to the lakes of alizarin and its oxy compounds, 
 those of the sulphonated derivatives have a considerable 
 importance. 
 
 To prepare alizarin-sulphonic acid of the degree of sul- 
 phonation required for general work, one part of alizarin is 
 acted on by three parts of strong sulphuric acid containing, 
 about 20 per cent, of free sulphuric anhydride, at 100 to 150. 
 The heating is continued until a sample dissolves completely 
 in water. The reaction product is then dissolved in water 
 and the excess of sulphuric acid is removed by treatment 
 with barium or calcium hydroxide, and the filtered liquid is 
 evaporated, when the necessary alizarin-monosulphonic acid 
 is obtained. The free acid is soluble in water, and yields 
 three series of salts. Those of the general formula C 14 H 5 2 
 (OH) 2 S0 3 R are yellow or orange and are soluble in water. 
 The sodium salt is the commercial product used for the 
 preparation of many of the colours. The alkali salts of the 
 general formula C 14 H 5 2 (OH) (OK) SO 3 E are of a red-violet 
 colour, and those of the alkaline earths of a red-yellow colour. 
 Those salts where the three available hydrogen atoms have 
 been replaced, of the formula C 14 H 5 2 (OK) 2 S0 3 K, are the 
 most soluble, and are of an intense violet colour. 
 
 The acid forms excellent lakes, as would be expected from 
 its marked acidic properties, and the aluminium lake is of 
 a deep carmine colour. It forms the basis of the most 
 permanent of the crimson colours, and is known as "perma- 
 nent crimson " or " alizarin carmine ". With tin salts as the 
 base of the lake, orange shades are obtained. 
 
216 CHEMISTRY OF PIGMENTS. 
 
 Fine colours belonging to the series of lakes can also be 
 prepared by the use of nitro-alizarin. Two mononitro 
 derivatives of alizarin are known, that termed the /3-variety 
 being the most generally employed. This is obtained by 
 treating the blue shade of alizarin in a fine state of division 
 with nitrous fumes. The purified nitro compound has the 
 formula C 14 H 5 2 (OH).,(N0 2 ) and forms soluble red-coloured 
 salts with the alkalies. With alumina it yields a fine insoluble 
 orange, and with iron salts a red violet. 
 
 An alizarin blue is known, but it has not been used to any 
 great extent for pigment work. Several closely allied varieties 
 are recognised, but even the best of them is not so fast to 
 light as indigo, and is not fit to replace the latter. The 
 alizarin blues are yielded by heating nitro-alizarin with gly- 
 cerine and sulphuric acid, and appear to be quinoline-alizarin 
 compounds. Green colours are now used prepared from 
 alizarin. These are those sold under the names : sap green, 
 olive green and olive lake. Alizarin green is formed by 
 treating alizarin blue with a large excess of fuming sulphuric 
 acid, and subjecting the resulting product to the action of 
 either alkalies or acids. The colour thus obtained is known 
 as "alizarin blue-green," and if it be heated to 130 with 
 concentrated sulphuric acid alizarin green is formed, which, 
 after separation and washing with water, forms fine blue-grey 
 needles. As seen in commerce, however, it is a red-brown 
 solution of the colour, which smells of sulphurous acid and 
 when boiled gives a blue precipitate. This is used for dyeing 
 purposes and is usually mordanted with potassium bichromate. 
 
 For the detection of alizarin colours a spectroscopic exa- 
 mination is most useful, as they all give more or less 
 characteristic absorption bands which should be compared 
 with those yielded by colours of known origin. The alizarin 
 colours may be distinguished from madder colours by boiling 
 them with a solution of aluminium sulphate. In the latter 
 
OEGANIC PIGMENTS. 217 
 
 -case the solution is strongly fluorescent. Concentrated min- 
 eral acids remove the base from the lake, and the free acid 
 may then be examined. Bleaching powder destroys the 
 colour of most of the alizarin compounds, but in some cases 
 very slowly, especially in the case of the most permanent 
 reds. None of them can, however, withstand the simultaneous 
 action of an acid and chloride of lime. 
 
 Campeachy Lakes, 
 
 The Campeachy lakes, as they are usually called, are 
 lakes prepared from logwood (Hcsmatoxylon campechianum), a 
 tree abounding in the West Indies, Mexico and, generally, 
 in South America. When felled, the wood of the tree is 
 nearly colourless, but it soon assumes a dark reddish-brown 
 colour, which is deeper on the surface of the wood than in 
 the interior. It is evident, therefore, that the colouring 
 principle is the result of a chemical change after the felling 
 of the wood ; but whether this is merely an oxidation pro- 
 cess, or is at the same time accompanied by the hydrolysis 
 of a pre-existing gluQOside is not a matter of certainty. It 
 appears most probable that the glucoside is in the first place 
 split up into a sugar and hsematoxylin, and that the latter 
 is afterwards partially oxidised to haematin. An aqueous 
 extract of the wood is a well-known commercial article, and 
 whether used as a dye-stuff or for the precipitation of lakes, 
 it is important that the evaporation of the water be conducted 
 at as low a temperature as possible, and that oxidation be 
 not allowed to proceed too far. The fermentation, as it is 
 called, of the wood, by which the glucoside is decomposed 
 with the formation of haematoxylin, takes place best when 
 the wood is rasped into thin shavings and moistened. 
 
 Hcematoxylin, C 1(5 H 14 6 + 3H 2 O, the initial active principle 
 of logwood, crystallises in yellowish prisms having a sweet 
 taste. It is very soluble in water and in alcohol, and also in 
 
218 CHEMISTEY OF PIGMENTS. 
 
 alkalies. It can be obtained by treating the aqueous extract 
 of logwood, or the powdered wood itself, with ether, and 
 evaporating the liquid to a syrup, adding water and allowing 
 it to stand for several days. The hsematoxylin, in a fair 
 state of purity, is gradually deposited, containing three mole- 
 cules of water of crystallisation if in the prismatic form, but 
 only one if it occurs as fine granules. By heating to 100 a 
 portion of the water is driven off, but a higher temperature 
 is required to drive off all of it. Haematoxylin is not very 
 soluble in cold water, but is easily so in hot water, alcohol, 
 ether and carbon bisulphide. It contains several hydroxyl 
 groups, and forms several well-defined methyl and acetyl 
 derivatives (Monatshefte, xv., 139). It behaves as a weak 
 acid, dissolving readily in solution of ammonia and caustic 
 alkalies. These alkaline solutions are, when perfectly fresh, 
 almost colourless, but they rapidly absorb oxygen from the 
 air, with the formation of oxidation products, amongst which 
 the most typical is hsematin, and at the same time becoming 
 bluish, then a deep red-brown. The more or less pure alka- 
 line compounds can be prepared by "salting out " the alkaline 
 solutions. Lead acetate gives with haematoxylin a bluish 
 white precipitate, rapidly darkening on exposure to the air. 
 Tin salts produce a permanent rose-coloured precipitate 
 sometimes used as a pigment. Ordinary alum gives a bright 
 red colour, and aluminium acetate a fine purple ; there is 
 only a slight precipitation, however, unless other salts are 
 present to assist. 
 
 Hsematoxylin is very sensitive to alkalies and to acids,, 
 being used as an indicator in chemical analysis. With free 
 alkalies it yields a bluish colour, while with acids it is red. 
 It is especially sensitive to ammonia and to calcium carbonate. 
 Hence it is not to be regarded as a very permanent pigment,, 
 so far as its initial shade is concerned. Chalk should never 
 be used as a diluent. 
 
ORGANIC PIGMENTS. 219 
 
 H&matein, C 16 H 12 6 , is easily produced from hsematoxylin 
 by atmospheric oxidation, especially in the presence of an 
 alkali. It may be rapidly prepared by saturating an ammonia 
 solution with hgematoxylin, and allowing it to stand exposed 
 to the air. Haematein-ammonia, C 6 H n (NH 4 )O 6 , is formed, 
 from which acetic acid precipitates free hsernatein. This- 
 body is a reddish-brown powder with a metallic lustre of a 
 greenish hue. It is sparingly soluble in cold, but more easily 
 so in boiling water. It is only slightly soluble in alcohol 
 and acetic acid, and not very soluble in ether. Alkalies, 
 however, dissolve it with avidity, the solution being at first 
 blue or purple, but on oxidation by the air it darkens con- 
 siderably, becoming of a deep brown colour. 
 
 It forms a well-defined ammonium salt, which occurs as 
 a deep violet powder consisting of microscopic prisms, which 
 dissolve in water with a purple, and in alcohol with a red 
 colour. At 100 the ammonia is volatilised, or even at 
 ordinary temperatures in a vacuum over sulphuric acid. 
 With copper sulphate its solution gives a violet-blue precipi- 
 tate, and with stannous chloride a violet precipitate. It 
 reduces silver nitrate. By reduction with sulphurous acid 
 a portion at least of the body is converted into hsematoxylin. 
 A sulpho acid is obtained by treating it with cold concentrated 
 sulphuric acid, and is precipitated as an orange-red crystal- 
 line powder by adding acetic acid to the sulphuric acid 
 solution. It has the formula C 16 H n (S0 3 H)0 6 . 
 
 The reactions obtained from preparations of logwood 
 are due to the simultaneous existence of hsematoxylin and 
 haematein. Dilute acids turn the colour yellow, but excess 
 of strong acid gives a red colour. Sulphuretted hydrogen 
 decolourises the solution, and sulphurous acid turns it yellow. 
 Alkalies give at first a red, then a violet and finally a brown 
 colour. Lime, barium and most of the heavy metals pro- 
 duce characteristic precipitates. 
 
220 CHEMISTKY OF PIGMENTS. 
 
 Stannous hydroxide gives a well-defined violet lake, 
 whilst stannic salts behave as acids, turning the colour 
 red. Salts of iron yield a blue-black colour, so deep that the 
 iron compounds of logwood are employed with great success 
 as inks. Mercuric salts give an orange, antimony salts a 
 carmine, and bismuth salts a violet precipitate. Alum gives 
 at first a yellow colour, which becomes red after a time : 
 while aluminate of sodium gives a blue-violet precipitate 
 insoluble in excess of alkali. 
 
 This reaction is said to be so delicate that logwood colour 
 may by it be detected even when mixed with other colours. 
 Another very well-defined test is the colour produced by 
 bichromate of potassium. This test is best applied by boil- 
 ing a piece of wool in a solution of potassium bichromate, 
 and then immersing the wool in the colour decoction. In 
 the presence of logwood it will be dyed an intense black. 
 
 To isolate the colour principles the lake is acidulated and 
 the acid aqueous liquid is shaken with amyl alcohol. The 
 alcoholic liquid is then extracted by a solution of borax. To 
 purify the colour, the borax solution is rendered acid and 
 the colour again extracted with amyl alcohol, and the solvent 
 evaporated. 
 
 The best defined of the lakes of this important colour 
 (which, however, find their chief employment in the dyeing 
 industry) are the following : 
 
 Aluminium salts yield deep violet-grey shades, varying 
 according to the exact method of treatment adopted in the 
 manufacture. Ferrous salts give blue-black lakes of great 
 intensity, whilst numerous varieties are produced by using a 
 mixture of the two metals. With chromates, logwood de- 
 coctions yield black colours which gradually turn green on 
 exposure to light. By the use of potassium ferricyanide, etc., 
 in dyeing operations, very fine and permanent deep blue shades 
 can be obtained. 
 
ORGANIC PIGMENTS. 221 
 
 In the examination of the logwood lakes the following 
 points are to be noted. If to the lake a few drops of concen- 
 trated hydrochloric acid be added, the colour produced is a 
 cherry red. A spot of this is absorbed by blotting paper, 
 and touched with a solution of aluminate of soda, which at 
 once turns it blue. The blue and violet lakes leave on ignition 
 an ash consisting of alumina or alumina and iron oxide, 
 or the base may consist almost entirely of oxide of tin. 
 The black lakes leave an ash containing alumina with a large 
 amount of iron oxide, or, more usually, chromium or copper 
 oxide. Free chlorine (treatment with bleaching powder) 
 readily bleaches all logwood colours. By boiling with glacial 
 acetic acid, the colouring matter is dissolved, the acid having 
 a rose-red colour, changing to yellow on heating. On adding 
 ether and then sufficient water to cause the ether to separate, 
 any indigo present will be found either in the ether or at the 
 junction of the two layers, whilst the logwood will be present 
 in the lower layer, colouring it a reddish-blue. If the colour 
 is not very pronounced, a few drops of hydrochloric acid are 
 added. The aqueous layer will then be a fine red colour. 
 
 Quercitron Bark Lakes. 
 
 Amongst the natural yellow colouring matters, all of 
 which are of vegetable origin, the most important are the 
 lakes prepared from the bark of Quercus tinctoria or "black 
 oak," which is found abundantly in the southern parts of 
 the United States. The bark itself is a regular commercial 
 article, usually appearing in the market as a mixture of fibres 
 and coarse buff or yellow powder. A more concentrated 
 form of the colouring matter is that known under the name 
 "flavin," which is a preparation obtained by treating the 
 bark with sulphuric acid (somewhat analogous to garancin), 
 and which contains a large proportion of the colouring principle 
 of the bark, quercitrin, together with its decomposition pro- 
 
222 CHEMISTRY OF PIGMENTS. 
 
 duct quercetin. " Aurantine " and " patent bark " are similar 
 preparations. 
 
 Quercitrin, the active colouring principle of the bark, is a 
 glucoside, about the constitution of which much discussion 
 has arisen. It may be prepared in a state of purity by treat- 
 ing the coarsely powdered bark for six hours with 85 per 
 cent, alcohol at boiling temperature. The alcohol is recovered 
 from the extract, acetic acid is added, and a great deal of the 
 extraneous matter is precipitated by the addition of an alco- 
 holic solution of acetate of lead ; the excess of the latter re- 
 agent is removed by sulphuretted hydrogen, and the filtered 
 liquid is evaporated to dryness. The residue is dissolved in 
 alcohol, and the filtered solution precipitated by the addition 
 of water. The quercitrin is mostly thrown down by this, 
 and is purified by recrystallisation from boiling water. 
 
 Quercitrin crystallises from water or dilute alcohol in 
 small yellow glancing needles or tablets. It is easily soluble 
 in absolute alcohol, slightly so in cold water, but more so in 
 hot water. It is nearly insoluble in ether. When anhydrous 
 it melts at 169 and at higher temperatures is decomposed 
 with the formation of inter alia quercetin. The air-dried 
 preparation, containing possibly a molecule of water of 
 crystallisation, melts at 173 to 176. A solution of quercitrin 
 is coloured an intense green by ferric chloride solutions. 
 
 Its solutions are precipitated by lead acetate, but not 
 when much free acetic acid is present. It easily reduces 
 silver and gold salts in the cold. Quercitrin is easily dissolved 
 in alkalies, the solution however soon becoming brown on 
 exposure to the air. 
 
 Liebermann has assigned to it the formula C 36 H 38 20 , but 
 the more modern researches of Herzig (Monatshefte f. Chem., 
 xiv., 58) strongly support the formula C 21 H 22 O 12 or probably 
 C 2] H 20 O n + H 2 O. By the action of boiling dilute sulphuric 
 acid the body, which is clearly a glucoside, splits up into 
 
OKGANIC PIGMENTS. 223 
 
 quercetin and the sugar rharnnose. Assuming the formula 
 to be C 2] H 20 O n , when anhydrous the reaction may be ex- 
 pressed as follows : 
 
 C 21 H 20 O n + 2H 2 = C 6 H 14 6 + C 15 H 10 7 , 
 
 the products being hydrated rhamnose and quercetin. 
 
 According to Wachs, the so-called quercitrin found in 
 numerous other plants, such, for example, as Thuja and 
 Sophora, is a compound of quercetin with one molecule of 
 rhamnose and one of glucose, thus differing from normal 
 quercitrin by containing an extra molecule of sugar. 
 
 At all events no less than four well-defined glucosides 
 which yield quercetin on hydrolysis have been described. 
 These are (1) quercitrin, which yields on hydrolysis one 
 molecule of rhamnose ; (2) rutin, which occurs in ordinary 
 rue, and yields two molecules of rhamnose ; (3) Viola- 
 quercitrin, which is extracted from the flowers of viola tricolor 
 and yields dextrose on hydrolysis ; and (4) osyritin, from a 
 Cape sumach, osyris compressa, which yields dextrose, but in 
 different proportion to (3). 
 
 Quercetin, the product of the hydrolysis of quercitrin, forms 
 a yellowish-gold crystalline powder, which is insoluble in 
 cold and only very slightly soluble in hot water. 
 
 W. H. Perkin recommended the following method for the 
 manufacture of quercetin. The bark in powder is washed 
 with salt solution to remove impurities, and then extracted 
 with cold dilute ammonia. The extract when neutralised with 
 dilute sulphuric acid, deposits a brown amorphous precipitate 
 containing little or no colouring matter ; this is filtered off, 
 and the clear lemon-yellow solution which contains the 
 glucoside quercitrin is acidified and boiled, when crystals 
 of quercetin soon begin to separate. These are collected 
 while the mixture is still warm, in order to prevent their 
 contamination with a brown flocculent matter which after- 
 
224 CHEMISTRY OF PIGMENTS. 
 
 wards separates. The nearly pure quercetin can be com- 
 pletely purified by recrystallisation from dilute alcohol. It 
 is almost insoluble in ether. By rapid heating it melts 
 at about 250, or when anhydrous, according to Wachs, at 
 299. At higher temperatures it sublimes, part being decom- 
 posed and part undecomposed. The alcoholic solution gives 
 an intense green with ferric chloride solution, the colour 
 changing to dark red on warming. Acetate of lead gives a 
 red precipitate. Silver and gold salts are easily reduced in 
 the cold by it, and copper salts when boiled with it in solu- 
 tion. Corresponding to Liebermann's old formula for quer- 
 citrin, C 24 H 16 O n has been assigned to quercetin, but in the 
 light of modern researches there appears no doubt that 
 C 15 H 10 7 is the correct formula. 
 
 Quercetin has been obtained by Perkin and Pilgrim (Journ. 
 Chem. Soc., 1898, 267) from the Indian dye-stuff asbarg 
 (Delphinium Zalil), but the nature of the glucoside with which 
 it was probably in the first instance associated has not been 
 determined. It also occurs to a small extent in the root of 
 Podophyllum emodi (Dunstan and Henry, Journ. Chem. Soc., 1898,. 
 209), and also in the leaves of New South Wales sumach 
 (Rhus rhodanthema), and in various other plants, such as the 
 catechu-producing trees. 
 
 The most probable constitution of quercetin, which is 
 supported by a great deal of experimental work, is 
 
 H 
 
 c CH COH 
 
 OHC 
 
 HC 
 
 C C < )> C OH 
 
 COH 
 
 C H CH 
 
 COH CO 
 Perkin (Journ. Chem. Soc., 1896, 1447) has shown that 
 
OEGANIC PIGMENTS. 225 
 
 quercetin and its allies (such as fisetin, rhamnetin, etc.) form 
 well-defined additive compounds with acids. This property 
 may possibly be of use in, enabling one to distinguish between 
 this group of natural yellow colours and all other groups. 
 For example, a saturated boiling solution of quercetin in 
 acetic acid yields, on the addition of a few drops of sulphuric 
 acid, a glistening mass of yellow hair-like needles. On 
 separation and washing with acetic acid and drying at 100 
 they are decomposed quantitatively by water into sulphuric 
 acid and quercetin. 
 
 The lakes of these coloured principles are usually made 
 with an aluminium basis, the precipitate being of a very 
 beautiful yellow colour. No standard for the exact quality 
 of such a lake can be laid down, but it is important to deter- 
 mine that the ash does not consist of a neutral body that has 
 been used as a diluent. 
 
 If the compound be acidulated and the quercetin extracted 
 with alcohol the solution will give a green colour with ferric 
 chloride ; if acidulated and treated with sodium amalgam it 
 assumes a fine purple-red colour, and on concentration yields 
 red prisms which dissolve in alcohol and a little free alkali 
 with a green colour, the solution being rapidly reoxidised on 
 exposure to the air. Some samples will allow of fairly pure 
 quercetin being separated, which should then possess the pro- 
 perties given above. On fusion with caustic alkali, quercetin 
 yields protocatechuic acid and phloroglucinol, which may be 
 searched for. 
 
 Rhamnus Lakes, 
 
 The berries of various species of Khamnus, including the 
 common buckthorn, E. cathartica, yield green and yellow 
 colours of some importance in dyeing, calico printing, and 
 artistic work. 
 
 15 
 
226 CHEMISTRY OF PIGMENTS. 
 
 The following are used : 
 
 Name. 
 
 Fruit of. 
 
 Description. 
 
 Persian berries (from 
 
 R. amygdalina Size of a pea, greenish yellow, 
 
 Aleppo and Smyrna) 
 
 R. oleoiides 
 
 hard shrivelled surface, di- 
 
 
 R. saxatilis 
 
 visible along well-marked 
 
 
 
 depressions into four parts, 
 
 
 
 each containing a triangular 
 
 
 
 seed, bitter taste. 
 
 Avignon berries,graines 
 
 R. infectoria 
 
 Smaller than above, only two 
 
 d'Avignon (French 
 
 R. alaterna 
 
 seeds. 
 
 berries) 
 
 
 
 Spanish berries 
 Italian berries 
 Hungarian berries 
 
 R. saxatilis 
 R. infectoria 
 R. cathartica 
 
 }"Very similar to French 
 berries. 
 
 Others are obtained from the Morea, Wallachia, and 
 Bessarabia, but the real Persian berries are the most 
 esteemed, and these especially when gathered in the unripe, 
 yellowish-green condition, but not when they are pure 
 yellow or brown to black. 
 
 When an aqueous decoction of Persian berries is allowed 
 to stand, surface moulds grow, the liquid becomes ropy, and 
 fermentation takes place, with the separation of a bright 
 yellow insoluble powder. 
 
 Gellatly, and later Schiitzenberger, showed that these 
 berries contained the glucoside xanthorhamnin. Lieber- 
 mann and Hermann showed that this, by boiling with dilute 
 mineral acids, or by the action of the natural enzyme l 
 of the berries, forms isodulcite and a colouring matter, 
 rhamnetin. This latter was shown by Herzig to be a methyl 
 derivative of quercetin (he believed it to be a dimethyl 
 ether). Later he showed that quercetin was probably 
 
 1 This enzyme rhamninase is precipitated by alcohol from the cold water 
 extract of the fruit of R. infectoria as a pasty mass containing 28 to 50 per 
 cent, of solid matter ; it is very soluble in water, and its activity does not 
 diminish appreciably on keeping. The dry substance contains 17 per cent, 
 mineral salts, 53 per cent, substances coagulated by heat, and galactan. A 
 temperature of 70 is most favourable to its action, which is destroyed at 85 
 (C. and G. Tanret, Bull. Soc. Chim., 1899, in., 21, 1073-75). 
 
ORGANIC PIGMENTS. 227 
 
 C 15 H 10 7 , and rhamnetin probably C 16 H 12 7 (= C 15 H 9 O 7 CH 3 ). 
 Lefort, and later Schiitzenberger, showed that xanthorhamnin 
 was not a chemical individual, and the latter chemist 
 extracted two glucosides, a-rhamnegin (xanthorhamnin), 
 yielding rhamnetin, and /3-rhamnegin, yielding a colour more 
 soluble in alcohol and acetic acid. Herzig extracted a gluco- 
 side yielding a colouring matter, the acetate of which melted 
 at 169 to 171, whereas acetyl-rhamnetin melts at 183 to 185. 
 This he separated by alcohol into rhamnetin and quercetin, 
 and considered the glucoside to be a loose compound of 
 xanthorhamnin and a glucoside of quercetin, which he 
 named rhamnin. 
 
 Later, A. G. Perkin (Journ. Chem. Soc., 1895, 496), who has 
 done so much good work on natural colours, with J. G-eldard 
 took up the examination of Persian berries, and, allowing the 
 orange-brown liquid obtained by soaking the ground berries 
 (in a calico bag) with ten times their bulk of water to ferment, 
 obtained a yellow powder, separated by the action of the enzyme, 
 as was well known. When this precipitate no longer increased 
 in quantity and had settled, the clear liquid was removed 
 and the precipitate dried at 100, and digested with boiling 
 toluene. This gave a crop of brown needles agreeing fairly 
 in composition with C 17 H 14 O 7 , and melting at 214 to 215 
 identical with rhamnazin prepared by these authors from a 
 purchased rhamnus colour, " rhamnetine ". The residue from 
 the toluene extraction was crystallised from a large bulk of 
 alcohol, and gave, on recrystallisation in alcohol and acetic 
 acid, rhamnetin, C 16 H 12 7 , M.P. above 280, and sparingly 
 soluble. The alcoholic mother liquors and aqueous main 
 nitrate gave, on further treatment, minute yellow needles, 
 readily soluble in alcohol and acetic acid, and crystallisable 
 from ether and chloroform, agreeing in composition with 
 quercetin, C 15 H 10 7 , and yielding the characteristic acetyl 
 derivative colourless needles, M.P. 189 to 191. 
 
228 CHEMISTEY OF PIGMENTS. 
 
 The authors, in summing up, state : 
 
 " These results are interesting, and show that xantho- 
 rhamnin, together with the unknown glucoside of rhamnazin, 
 are readily decomposed at 40 by the ferment present in the 
 berries. This, on the other hand, exerts but little influence 
 on the glucoside of quercetin (quercitrin ?), which is also 
 present. 
 
 "The colouring matters obtainable from Persian berries are 
 therefore rhamnetin, or quercetin monomethyl ether, C 16 H 12 7 , 
 rhamnazin or quercetin dimethyl ether, C 17 H 14 7 , and quercetin, 
 C 15 H 10 7 , itself." 
 
 They are of opinion that Schiitzenberger's /3 rhamnetin 
 was quercetin. 
 
 Xanthorhamnin is prepared (Liebermann and Hermann) by 
 boiling for eight to ten hours powdered berries with three 
 times their weight of 85 per cent, alcohol. On allowing to 
 cool and stand for twenty-four hours a large quantity of 
 impure glucoside, with a little free colouring matter, is 
 deposited as a resinous mass. The clear solution allowed 
 to stand for some days in a cold place deposits pure xan- 
 thorhamnin in pale yellow cauliflower-heads, and in such 
 quantity as to render the liquid pasty. The total yield is 
 about 12 to 13 per cent. By recrystallisation several times 
 from alcohol, and then from alcohol with water and ether, 
 it may be obtained in distinct crystalline needles. It does 
 not crystallise from an aqueous solution. It is soluble in 
 water and alcohol, but not in ether, benzene or chloroform. 
 It should be dried rapidly over H 2 S0 4 in a vacuum, but not 
 by heat, as it melts at a low temperature when moist, but 
 above 130 (it contains 2 molecules alcohol, which it loses 
 at this temperature) when dry. The above authorities 
 assigned the formula C 48 H 66 29 to xanthorhamnin. Both 
 Fehling's solution and ammoniacal silver nitrate are reduced 
 by it. 
 
ORGANIC PIGMENTS. 229 
 
 Normal lead acetate turns a solution orange, but the 
 addition of ammonia precipitates an orange-coloured lake. 
 Alcoholic KOH causes 'the separation from the alcoholic 
 solution of a potassium derivative, C 48 H 62 29 K 4 . It is stated 
 by Schiitzenberger that twelve acetyl groups can be intro- 
 duced on acetylation ; fusion with caustic potash causes 
 formation of phloroglucin and protocatechuic acid, with an 
 acid body giving an intense red colour with the alkali. 
 Sodium amalgam causes the production of the former bodies, 
 but not of the coloured body. 
 
 Mineral acids effect the hydrolysis of xanthorhamnin, but 
 acetic acid does not, though the glacial acid be used. 
 
 The mixture of colouring matters known formerly as 
 rhamnetin, the nature of which was indicated by Perkin 
 and Geldard, is readily soluble in fixed alkalies, less readily 
 in ammonia, and only slightly in alkaline carbonates. Its 
 alcoholic solutions give a yellow precipitate with tin and 
 alum solutions, a reddish brown with copper acetate, and 
 an orange with lead acetate. 
 
 The behaviour of quercetin, rhamnetin and rhamnazin 
 to acids is characteristic. 
 
 Quercetin easily forms a sulphate, hydrobromide, hydro- 
 chloride and hydriodide by addition of the acid to a boiling 
 aqueous solution. 
 
 Rhamnetin forms a sulphate with difficulty, and no halides. 
 
 Rhamnazin requires a still greater excess of sulphuric acid- 
 to form an unstable sulphate, and forms no halides. 
 
 Those compounds are decomposed by water, and must be 
 washed with acetic acid to free them from excess of mineral 
 acid. In the case of the sulphates this must be done 
 quickly. 
 
 This property of forming salts is, as previously mentioned, 
 valuable in characterising the members of the quercetin group 
 from one another and from other substances. 
 
230 CHEMISTRY OF PIGMENTS. 
 
 Adopting the quinonoid formula previously given for 
 quercetin : 
 
 OH 
 
 /\ 
 OH 
 
 OH 
 
 OH 
 
 OH CO 
 
 rhamnetin becomes 
 
 o 
 
 /\ /\ 
 OH 
 
 OH 
 
 OH 
 
 OOH 
 
 OH CO 
 
 while in rhamnazin a further hydroxy group is replaced by 
 the methoxy group ; the addition of this group enfeebling 
 the acid-combining power of the pigment. 
 
 Bhamnose (isodulcite), CH 3 (CH, OH) 4 CHO + H 2 0. The 
 sugar of xanthorhamnin melts at 93 when anhydrous, and 
 at 122 to 126 when crystallised from acetone, and is also 
 laevorotatory ; whereas the /3 modification has a D = + 10, and 
 the 7 variety obtained by warming this to 90 has a D = + 20, 
 which after keeping goes back to + 10. 
 
 Persian berries are used principally in calico printing. 
 
 A steam yellow is obtained by the addition of alum to the 
 aqueous extract, thickening the lake with gum acacia and 
 adding stannous hydroxide. 
 
 Steam orange is obtained by the use of stannous chloride 
 and sodium acetate (equivalent of stannous acetate) as a 
 mordant or lake base. 
 
 Steam green is prepared by the use of stannous chloride 
 and alum with acetic acid and potassium ferrocyanide, and sul- 
 phuric or oxalic acid, gum being added to thicken (? should some 
 iron salt be added to form Prussian blue and thus a green). 
 
OEGANIC PIGMENTS. 231 
 
 Persian berry carmine is a brown or yellow tin lake. 
 
 The colours known as brown pink and stil de grain are 
 lakes produced from these berries. 
 
 These colours, generally speaking, are less fast and more 
 expensive than those obtained from quercitron. 
 
 Sap Green. The pigment known as sap green, used to 
 some extent by artists, as are the Persian berry lakes, is 
 prepared by fermenting the decoction of buckthorn berries 
 (R. catharticus), lime water and gum acacia being added. After 
 a week, alum is also added to the liquid strained from the 
 berries, and the mixture concentrated by evaporation and the 
 residue hung up in a pig's bladder to dry. This green buck- 
 thorn lake is mentioned by De Mayerne (1573-1655), a friend 
 of Rubens. 
 
 A similar but poorer green is prepared from the black 
 alder (R. frangula) and the evergreen privet. 
 
 An alizarin lake is also employed under the name of " sap 
 green " (vide supra). 
 
 Lokao, Chinese green, is said to be prepared from the 
 twigs of certain species of rhamnus (R. chlorophorm (globorus) 
 and R. utilis) by boiling the bark with water and immersing 
 cotton cloths, w r hich take up a colourless substance, this turn- 
 ing green on exposure to air. The process is repeated until 
 a quantity of colour has accumulated. It is then washed 
 with cold water and boiled with water in which cotton yarn 
 is laid. This takes up the colour, which is washed off and 
 collected on paper. 
 
 Charoin of Lyons prepared a green from rhamnus bark by 
 boiling it with water and adding lime water : on exposure to 
 air in shallow vessels a green precipitate formed, which was 
 increased by the addition of potassium carbonate. This 
 seems more plausible than the reported method of the Chinese, 
 and the product would appear to be a lake. 
 
 These greens, though of a rich colour, have not a good 
 reputation for permanence. 
 
232 CHEMISTRY OF PIGMENTS. 
 
 The sap-green of a well-known firm of artists' colourmen 
 was a chlorophyll-like looking colour, but as on ignition it 
 left a blue ash discoloured by hydrochloric acid and contain- 
 ing about 36 per cent, silica, it was probably gamboge and 
 ultramarine, a more permanent colour than real sap-green. 
 This was an oil colour. Sap-green is usually used in water. 
 
 Brazil Wood Lakes, 
 
 Brazil wood is the product of Ccesalpinia Brasiliensis, a 
 tree growing in the forests of Brazil. The red -dye woods 
 known in this country under the names Sapan wood, Lima 
 wood, Bahia wood, etc., are all products of various closely 
 related trees of the same natural order, and take their names, 
 as is evident, from the port of exportation. They all yield 
 similar colours, but that from Brazil wood is the one which 
 has been fairly thoroughly investigated, and whose chemistry 
 is best understood. The colouring matter appears to be 
 present in the form of a glucoside, which is probably identical 
 in all the woods above named. It is decomposed by the 
 action of a ferment in the presence of water, or by boiling 
 with dilute acids, into glucose and the colouring matter, 
 brazilin. This body is colourless itself, and appears to be 
 closely related to haematoxylin, from which it differs in 
 composition by only one atom of oxygen. 
 
 Brazilin forms white, shining needles of the formula 
 C 16 H 14 5 , and contains the equivalent of one and a half 
 molecules of water of crystallisation. It is soluble in water, 
 alcohol and ether : its solution on exposure to the air, espe- 
 cially in the presence of alkalies, is rapidly converted into 
 a bright red fluid, from which acids precipitate the analogue 
 of hsematein, namely brazilein. 
 
 Brazilein, C 16 H 12 5 , forms minute crystals of a greyish 
 lustre, containing one molecule of water of crystallisation. 
 It is formed from brazilin by several methods, such as the 
 
OEGANIC PIGMENTS. 233 
 
 interaction of the latter body with iodine, or by treating 
 brazilin in acetic acid with potassium nitrite. A careful 
 comparison of the brasilems prepared by the various methods 
 has proved conclusively that they are all identical (Berichte, 
 23, 1428). 
 
 When powdered, brazilein is of a reddish-brown colour, 
 and dissolves only slightly in cold, but more readily in hot 
 water; the solution is of a yellowish-pink colour with a 
 greenish-orange fluorescence. On the addition of an alkali 
 the solution becomes crimson red, ultimately turning brown 
 on exposure to the air. 
 
 Kopp has proposed the formula C 22 H 18 O 7 for brazilin, but 
 the researches of Schall and Herzig have conclusively proved 
 that the previously quoted formula is correct. A large num- 
 ber of bromine and alkyl derivatives have been prepared 
 and described which all support that formula, for details of 
 which the original papers must be consulted (see Berichte, 
 23, 1428 ; 21, 3009 ; 27, 524 ; Monatshefte, 15, 139 ; 14, 56). 
 
 The exact shade of the lakes formed from the extract of 
 Brazil wood, in which form the colour is usually found, 
 depends on the relative quantities of brazilin and brazilein 
 present. Brazilein gives a good red lake with alumina, a 
 greyish- violet to black with salts of iron, and browns with 
 mixtures of the two. Stannic chloride gives a red, and there 
 is also a lake of a fine dark crimson colour formed by the 
 action of potassium bichromate. This appears to be due to 
 the action of the chromic acid on the brazilin and brazilein, 
 with a partial reduction to a lower oxide of chromium, 
 which is of a basic character, and unites with the brazilein. 
 Lead salts give a dirty blue lake. One of the most success- 
 ful methods of obtaining these lakes is to pass a current of 
 air through a solution of brazilin containing the requisite 
 metallic salt, also in solution. 
 
 Brazilein and its derivatives can be reconverted into 
 
234 CHEMISTRY OF PIGMENTS. 
 
 brazilin and its derivatives by reduction by means of zinc 
 dust. 
 
 If these lakes are pure, the residue left on ignition will be 
 found to consist almost entirely of the metallic oxide with 
 which the brazilein is combined. Sometimes starch or chalk 
 will be found used as a diluent, but the use of the lakes is too 
 small to cause much adulteration to be practised. Strong 
 hydrochloric acid turns these lakes a pink colour, which is 
 materially altered on dilution with water. Hypochlorous 
 acid or chlorine rapidly bleaches them. 
 
 Alkanet Lakes, 
 
 Alkanet, as known in commerce, is the root or portions 
 of the root of Anchusa tinctoria. It contains a red colouring 
 matter of an acid nature which may be prepared by boiling 
 the root with water in order to remove all soluble matter, 
 drying it, and exhausting with alcohol. The alcoholic solution 
 has a violet colour and is slightly acidified with hydrochloric 
 acid, and evaporated to dryness. The dry residue is treated 
 with ether, and this, on evaporation, leaves the red colouring 
 matter in an impure condition as a dark red resinous mass. 
 
 This colouring matter was described so long ago as 1814 
 by Pelletier, who regarded it as a kind of fatty acid, and gave 
 to it its name anchusic acid. The formula assigned to it 
 (old notation) was C 35 H 20 O 8 . The same body appears to 
 have been described by John (Chemische Schriften, iv., 85) 
 under the name pseudo-alkannin, which he stated was 
 present in the root to the extent of 5 '5 per cent. The more 
 recent investigations of Carnelutti and Nasisi (Berichte, 13, 
 1514) are the basis of our present knowledge of the active 
 principle of the root. In preparing the acid, they exhausted 
 the commercial extract of the root with a solution of potash, 
 and from the alkaline solution they obtained an impurity 
 present by shaking with ether. The potash solution de- 
 
OEGANIC PIGMENTS. 235 
 
 posits the alkannin, as it is now called, on being saturated 
 with carbonic acid. It forms a dark red mass soluble in 
 chloroform and acetic aid, but only sparingly so in other 
 organic solvents.. The formula assigned to the acid was 
 C 15 H 14 4 . A crystalline diacetyl compound was obtained by 
 treating the acid with acetic anhydride and sodium acetate. 
 A barium salt containing two atoms of barium to three mole- 
 cules of alkannin was obtained by precipitating an alcoholic 
 solution with ammoniacal solution of barium chloride. 
 
 Alkannin appears to be related to the red colouring matter 
 of sanders wood. Liebermann and Homer (Berichte, 20, 2428) 
 investigated the compound in 1887, and after a series of 
 analyses they came to the conclusion that the formula of 
 the acid was either that proposed by the above-mentioned 
 chemists, or C 15 H 12 4 . They consider that alkannin is a 
 methylanthracene derivative, probably its dihydroquinone or 
 its dihydride. 
 
 The alcoholic solution of alkannin is of a crimson colour, 
 and is permanent to light and heat. It gives a blue colour 
 with alkalies, and a blue-violet precipitate with aluminium 
 salts, the acetate being the best to use for the preparation of 
 the lake ; a crimson precipitate with stannous chloride, and a 
 purple precipitate with stannic chloride. Lead acetate gives 
 blue, and iron salts violet, precipitates. 
 
 According to Allen, the best test for alkannin is an 
 examination of its absorption -spectrum. Its solution in amyl 
 alcohol gives the best results, and exhibits three equidistant 
 bands in the blue-green part of the spectrum. On adding 
 ammonia to this solution, these bands give place to two fresh 
 bands, one nearly coincident with, and the other on the red 
 side of the D line. Bujard and Klinger (Zeit. ang. Chem., 1890, 
 26) state that the alcoholic solution acidified with acetic acid 
 gives a well-defined absorption spectrum, the three character- 
 istic bands being as follows : the first is near and on the more 
 
236 CHEMISTRY OF PIGMENTS. 
 
 refrangible side of the D line ; the second commences at E 
 and extends to beyond b ; and the third, which is faint, is 
 close to F. On rendering the solution alkaline the blue 
 solution shows two bands, one of which is midway between 
 C and D, and the other commences at about D. 
 
 Alkannin resembles orchil (archil), but differs from the 
 colouring matter of logwood, Brazil wood, etc., by being 
 extracted from its ammoniacal solution by ether. 
 
 When natural madder lakes were articles of general 
 commerce, adulteration of the latter with alkanet lakes was 
 sometimes practised. A reaction said to be characteristic of 
 alkanet lakes, and which was used to detect the presence of 
 these bodies, was as follows : The lake was dissolved in 
 acetic acid and the acetic solution was extracted with carbon 
 disulphide ; if alkannin were present the carbon disulphide 
 solution was coloured an intense violet-red (see p. 210). 
 
 Santal-wood Lakes, 
 
 The wood of the so-called red sandal, Pterocarpus 
 Santalinus, must not be confounded with that of the yellow 
 sandal wood, Santalum album, from which the santal w r ood 
 oil of pharmacy is distilled. Ked sanders wood, as it is 
 more frequently called, together with the w r oods of the 
 allied trees which yield the so-called barwood, camwood 
 and caliatour wood, are used for certain tinctorial purposes, 
 but to-day the lakes from these woods are almost entirely 
 superseded by coal-tar colours. They all appear to contain 
 a colouring matter of the formula C 15 H 14 5 , and it is probable 
 that this is identical in all the woods. It is termed santalin. 
 It appears to be an acid, but its chemistry is not well 
 understood. 
 
 With stannous chloride the tinctures of the woods, espe- 
 cially those of santal and barwood, yield blood-red lakes, and 
 
OEGANIC PIGMENTS. 237 
 
 with ferrous salts a violet lake. A dark cherry-red lake is 
 yielded by the use of tartar emetic. 
 
 Archil Lakes. 
 
 These lakes are now practically never used, as the coal- 
 tar colours have superseded them, but the colouring matter 
 is still used for other purposes, and a few lines treating of 
 their general properties will not be out of place. Archil 
 is the product of several species of lichens, of which the 
 two principal are Eocella fuciformis and R. tinctoria. It 
 comes into commerce as a paste or as a liquid. It is usually 
 prepared by treating the finely chopped " weeds " with dilute 
 ammonia, keeping the mixture at about 20 till a dark violet 
 paste has been formed. This paste, when diluted with am- 
 monia and filtered, yields "blue archil," and this, on gently 
 heating to drive off the ammonia, yields the " red archil ". 
 
 The pigment known as French purple is a lake obtained 
 by treating the ammoniacal liquid with calcium chloride. 
 
 The pasty archil consists chiefly of ammonia combined 
 with a colouring matter called orcein. This body owes its 
 origin to the action of air and ammonia on the orcin present, 
 in the same way as haematein is formed from haematoxylin. 
 The lichens contain a considerable quantity of complex 
 ethers, from the decomposition of which orcin results. The 
 principal of these are the following : 
 
 Erythrin (Erythric acid), C 20 H 22 10 . This body when 
 boiled with alkalies yields orcellinic acid and picroerythrin, 
 the latter body being decomposed by further treatment into 
 orcinol and erythrol, with the evolution of carbon dioxide. 
 These reactions establish the constitution of erythrin as the 
 diorcellinic ether of erythrol. Orcellinic acid is a dihydroxy- 
 toluic acid, whilst erythrol is a tetratomic alcohol closely 
 related to the sugars. The relationships of these bodies are 
 shown in the following table : 
 
238 CHEMISTRY OF PIGMENTS. 
 
 Orcinol . . . C 6 H 2 (CH 3 )(OH) 2 H (methyl resorcinol). 
 Orcellinic acid . . C 6 H 2 (CH 3 )(OH) 2 CO,OH 
 
 Diorcellinicacid. /O.C 6 H 2 (CH 3 )(OH)CO,OH 
 
 \CO.C 6 H 2 (CH 3 )(OH) 2 
 
 Erythrin ^ / [OCO(OH) 2 (CH 3 )C 6 H 2 ] 2 
 
 \(OH) 2 
 
 Picroerythrin ^ /OCO(OH) 2 (CH 3 )C 6 H 2 
 
 \(OH) 3 
 Erythrol . . . C 4 H 6 (OH) 4 
 
 The special characters of these bodies are without interest for 
 our present purpose. 
 
 Orcinol (Orcin) is a methyl-resorcinol, and therefore has the 
 characters of a diatomic phenol. It occurs in the free state 
 in several of the lichens used in the preparation of archil, 
 but is chiefly a decomposition product of the above-described 
 complex ethers which are present to so large an extent in the 
 plants. It is a crystalline body melting at 58, and on treat- 
 ment with ammonia in the presence of atmospheric oxygen 
 it yields the colouring matter orcein. According to Lieber- 
 mann two compounds are formed, according to the conditions 
 of the reaction. He states that if ammonia be in excess 
 a body of the formula C 14 H 12 N 2 3 results, whilst if the reverse 
 be the case the compound has the formula C 14 H n NO 3 . 
 
 The researches of Zulkow*ski and Peters (Monatshefte, 
 11, 227-245), however, have shown that the previous formulae 
 of these colouring matters are incorrect, and were based on 
 the analysis of impure specimens. By careful procedure 
 they obtained three distinct colouring matters from orcinol 
 by the action of air and ammonia. They dissolved 50 
 grams of orc'inol in 200 c.c. of water and added 200 c.c. of 
 strong solution of ammonia. After standing for two months 
 the mixture was examined and after a series of separations 
 the orcein was obtained in the crystalline condition. It 
 
ORGANIC PIGMENTS. 239 
 
 forms a brown crystalline powder, of the formula C 28 H 24 N 2 7 , 
 insoluble in water, but soluble in acetone, acetic acid, and 
 alcohol. 
 
 French purple, as above stated, is a calcium lake of 
 orcein, but finds very little employment now. If an archil 
 lake be treated with hydrochloric acid and shaken with 
 ether no trace of colouring matter will be dissolved, if 
 the lake be made from pure archil. According to Slater, 
 the presence of most other vegetable colours may be 
 detected by treating 3 or 4 grams of the sample with 
 100 c.c. of water and 50 drops of a solution of stannous 
 chloride. On boiling the liquid a yellowish colour will 
 remain if the archil be pure, but if logwood be present 
 a bluish colour will persist, and if most other red woods 
 are present the colour will be reddish. 
 
 The colouring matter known as cudbear, or on the Con- 
 tinent as perseo, is obtained by the action of ammonia or 
 urine on various lichens, such as Lecanoria tinctoria and 
 Variolaria orcina, and is, therefore, very similar to orchil 
 in its properties. The colouring matter of this substance 
 appears to be either identical, -or very closely related to 
 that of archil, but sometimes the extract is considerably 
 richer than that of the rocella lichens. Hence, it is fre- 
 quently mixed with a considerable amount of mineral matter, 
 usually common salt, not so much as a wilful adulteration as 
 to bring the richer varieties down to one uniform standard. 
 
 Ill COAL-TAR LAKES. 
 
 The lakes produced from coal-tar colours have been 
 indicated when dealing with the madder lakes, but in the 
 present section it is proposed to deal with the lakes of the 
 artificial colours at some length, as they have now assumed 
 an importance which has gradually increased, with the 
 
240 CHEMISTEY OF PIGMENTS. 
 
 increase in our knowledge of the now universally employed 
 coal-tar colours. 
 
 The natural colour lakes may, in general, be regarded 
 as compounds of one or more natural colour acids with 
 inorganic bases, with, at times, more or less mechanical 
 admixture of excess of base or acid. Theoretically, however, 
 the lake may be regarded as the true compound in the sense 
 described. 
 
 In the same way the lakes of the artificial colours 
 must be regarded as true chemical compounds, although the 
 mechanical admixture plays an important part in the pre- 
 paration of the colours in actual practice. 
 
 For the purposes of the present chapter, artificial colouring 
 matters capable of forming lakes may be divided into three 
 groups. These are as follows : (1) The artificial colour base s 
 containing nitrogen in combination with hydrogen, so that 
 the base behaves as an ammonia derivative. (2) Artificial 
 colours of a purely acid nature, capable of combining with 
 an inorganic base. (3) Artificial colours in which both acid 
 and basic functions exist simultaneously in a well-defined 
 degree. Such bodies may be typified by a sulpho acid of an 
 amido compound. 
 
 In this sense then we understand a true lake, and it is 
 necessary to here draw attention to the somewhat free use of 
 the word " base " in connection with this subject. As we 
 are employing the word, it refers to a compound or an oxide 
 of a metal capable of uniting to form a definite compound 
 with an acid. The word is also employed (" lake base," etc.) 
 when referring to a neutral body, such as sulphate of barium 
 or china clay, which is employed as an absorbent, or as a 
 diluent for a colour, but in the present work the word will 
 not be employed in that sense. 
 
 At the same time it must be admitted that the principles 
 of lake formation are not altogether as well understood as one 
 
ORGANIC PIG-MENTS. 241 
 
 could wish. Although we have emphasised the importance 
 of recognising the principle of true chemical combination as 
 the basis of the formation of lakes, there is considerable room 
 for speculation as to the degree to which this combination 
 is carried in a great number of cases which must be regarded 
 as belonging to the class of true lakes. It is quite certain 
 that advantageous precipitations of colour bases take place, 
 when only a small proportion of the calculated molecular 
 equivalent of the precipitating acid is used. This is especially 
 the case when tannic acid is employed. Here, then, we have 
 a case in which, whilst there is certainly a true chemical 
 combination of the base and the acid, there exists in the 
 compound far more base than the theoretical combination 
 would require. It is usual to use the expression " mechanical 
 combination " in such cases, and to escape from the difficulty 
 of a lame explanation by the use of a term which is even 
 more difficult to define than the original problem is to 
 explain. In certain cases, where a voluminous precipitate, 
 such as that of alumina in the hydrated state, is thrown 
 down, a species of " mechanical combination " is not difficult 
 to assume. For example, when one adds a solution of 
 ammonia to a solution of alum mixed with a salt of calcium, 
 a voluminous precipitate is thrown down. It is of such a 
 bulky, gelatinous nature that together with the mass of 
 water which assists to make up the "jelly," there is a 
 considerable amount of lime salts : it is next to impossible 
 to completely remove these lime salts by ordinary washing 
 with water, and when the alumina is filtered off and dried, 
 it will be found that there still remains an appreciable 
 amount of lime in a state of intimate admixture with the 
 alumina. But the quantity is not sufficient to explain the 
 almost complete precipitation of a considerable excess of base 
 by a small quantity of the precipitating acid, as in the case 
 
 we have above quoted. 
 
 16 
 
242 CHEMISTRY OF PIGMENTS. 
 
 From a prolonged experience of compounds of the inor- 
 ganic elements, which are more easily manipulated than the 
 organic compounds from this point of view, we are acquainted 
 with well-defined basic compounds, i.e., compounds of a base 
 with an acid which are not of normal constitution, but 
 contain definite molecular proportions of the base in excess 
 of that required for the normal compound. In our present 
 imperfect state of knowledge concerning the exact nature 
 of the combination existing between many organic com- 
 pounds, it appears to us that the most feasible explanation 
 of the somewhat erratic combinations of these lake bodies 
 is the existence of an analogous series of compounds to those 
 which, as just mentioned, are well recognised between 
 inorganic elements. This, however, is merely a matter of 
 speculation, and need not, therefore, be further discussed 
 here. We now pass on to the consideration of the coal- 
 tar lakes, and in doing this we have arranged the lakes 
 in groups according to their colours, without taking their 
 chemical constitution into consideration, a practice which, 
 .as evident in the earlier chapters, would not have been 
 convenient when dealing with the pigments of inorganic 
 origin. 
 
 
 
 Red Lakes. 
 
 By careful manipulation practically any shade of red can 
 be obtained from various coal-tar derivatives. The method 
 of working will modify the shade to a very great extent, 
 in spite of the fact that the constitution of the resulting 
 colour will be practically unaltered. Hence, an accurate 
 knowledge of the working details of lake manufacturing is 
 indispensable to the manufacturer of this series of bodies, as 
 the processes are not merely those of " mixing ". 
 
 The principal colouring matters which are employed for 
 
OEGANIC PIGMENTS. 243 
 
 the preparation of the red lakes are members of the following 
 groups : 
 
 1. The rosaniline group, or derivatives of triphenyl- 
 methane, CH (C 6 H 5 ) a . 
 
 2. The rhodamine group, or derivatives of amido-phenol- 
 phthaleins. 
 
 3. Azines, including the safranines, and the eurhodines. 
 
 4. The sulphonated azo compounds, typified by crocein 
 scarlet. 
 
 5. The eosins, or halogen substituted phenol-phthaleins. 
 
 6. The alizarin group. 
 
 1. The Bosaniline Group. The principal member of this 
 group of colours, magenta, is that which is chiefly employed 
 in the manufacture of lakes. Commercial magenta is in 
 reality a mixture of the two colours, rosaniline and pararos- 
 aniline. The two bodies are, however, so nearly identical that 
 with the exception of briefly indicating the difference in their 
 constitution there is no need to further differentiate between 
 them. 
 
 The parent substance of the group is the hydrocarbon 
 triphenyl-methane, CH (C 6 H 5 ) 3 ; the basic properties of the 
 colours derived from this hydrocarbon being derived from 
 amido groups introduced into the phenyl radical. Kosaniline 
 is the triamido derivative of triphenyl-carbinol, of the con- 
 stitution C(OH)(C 6 H 4 NH,) 3 , and differs only from para- 
 rosaniline in the fact that the latter is the corresponding 
 derivative of tolyl-diphenyl-carbinol, of the constitution 
 C(OH)(C 6 H 3 . CH 3 . NH 2 )(C 6 H 4 NH 2 ) 2 . The colour (consisting 
 of a mixture of the two bodies) is manufactured by the 
 oxidation of ordinary aniline by either arsenic acid, mercuric 
 nitrate, or nitrobenzene. The bases are, when pure, quite 
 colourless, but they form salts (with the elimination of 
 water) with acids, which are the real colours employed. 
 
 The usual form in which magenta is seen in commerce is 
 
244 CHEMISTRY OF PIGMENTS. 
 
 as the hydrochloride, the rosaniline salt having the composi- 
 tion C 20 H 19 N 3 HC1, water being eliminated in the formation 
 .of the salt. It is then in the form of rhombic crystals 
 which have a metallic green colour in reflected light. The 
 solutions are crimson, and are not fluorescent. It is not very 
 soluble in pure water, but is readily so in acidified water and 
 in alcohol. Caustic alkalies .separate the colourless base in the 
 free state. Reducing agents, such as sulphurous acid, or zinc 
 and acetic acid, decolourise solutions of magenta, eliminating 
 the oxygen atom, with the formation of salts of leucaniline. 
 After reduction in this way the solution is not re-oxidised by 
 the action of the air (this distinguishes this colour from the 
 somewhat similar colours, Magdala red and the safranines). 
 Chloride of lime decolourises solutions of magenta. 
 
 Sometimes the acetate is found in commerce. It has the 
 advantage of being the most soluble of the rosaniline salts. 
 Magenta is a colour which should, when pure, consist only of 
 the two colouring matters mentioned. Impurities modify the 
 shade, and this is reproduced in the lake which is prepared 
 from it. It is sold under numerous names, amongst which 
 are the following : Magenta, azaleine, roseine, fuchsine, 
 rubine, etc. Magenta-violet is a frequently occurring colour, 
 and consists of a mixture of magenta and mauvaniline ; the 
 lakes prepared from this colour are of a much more violet 
 shade than those from the pure colour. Cerise is an im- 
 pure magenta salted out from the mother liquors after the 
 preparation of the pure magenta. It contains a certain 
 amount of a colouring matter called phosphine. Cardinal 
 and amaranth are also mixtures of magenta and various 
 impurities. 
 
 Isorubin, or " new magenta," as it is called, is the 
 corresponding hydrochloride of triamido - tritolylcarbinol, 
 C(OH)(C 6 H 3 . CH 3 . NH 2 ) 3 . It is a colour of recent intro- 
 duction, formed by the condensation of formaldehyde and 
 
ORGANIC PIGMENTS. 245 
 
 orthotoluidine. It resembles ordinary magenta in appearance 
 and properties, but gives colours of a bluer shade, and is 
 more soluble in water. 
 
 Maroon and grenadin are also more or less impure 
 magenta. 
 
 Many of the lakes in which magenta is the chief ingredient 
 are compound lakes manufactured from magenta mixed with 
 one or more other colours, such as various scarlets or cherry 
 reds. Amongst the best lakes of magenta are those prepared 
 with arsenious or resinic acid (the latter being a mixture of 
 various resin acids). The colour of these lakes is very bright, 
 but the arsenious acid compound is somewhat fugitive. The 
 tannic acid lakes are also fugitive, and somewhat dull. A 
 lake prepared with antimony salts and tannic acid is very 
 permanent, but not as bright as the arsenious acid lake. 
 The tannic acid lakes have the property of being soluble 
 in alcohol. 
 
 Magenta lakes, when undiluted, leave no ash, as they 
 consist of organic bases in combination with volatile acids. 
 Any ash present should be examined, and may be regarded 
 as a diluent either added to lighten tha shade, or as an 
 adulterant for the purpose of cheapening the colour. 
 
 The colour should be entirely removed by treatment with 
 sulphurous acid or by chloride of lime. In the former case 
 exposure to the air does not restore the colour as it will do 
 in the case of Magdala red and the safranines. If the lake 
 be treated with a strong solution of caustic alkali, the free 
 base may be dissolved out by ether. The colourless ethereal 
 solution will dye silk a fine crimson, combination taking 
 place between the base and some constituent of the fibre : 
 or it will yield a fine crimson colour with a trace of acetic 
 acid. 
 
 For a full recognition of the constituents of a compound 
 lake prepared from several coal-tar colours, special works on 
 
246 CHEMISTEY OF PIGMENTS. 
 
 the analysis of this group of colours must be consulted. The 
 enormous number of them, however, many of which are of 
 almost identical properties, renders the task a matter of 
 practical impossibility, unless the mixture is one of compara- 
 tive simplicity. 
 
 A colour known as acid magenta, magenta S,or rubine S, 
 is sometimes employed for lake manufacture. It is a trisul- 
 phonic acid of magenta, and forms lakes with bases instead 
 of acids. Its colouring power is not so good as the basic 
 colour, but it is very useful in combining with certain yellows 
 for mixed shades. It is known also as acid fuchsine, and in 
 an impure form as maroon S, grenat S, acid cerise, cardinal 
 S, acid maroon, etc. 
 
 2. The Rhodamine Group. When phenols are heated 
 with phthalic anhydride, a combination takes place accord- 
 ing to the following reaction : 
 
 / C0 \ / C = (C 6 H 4 OH) 2 
 
 C 6 H 4 / ;>0 + 2C 6 H 5 . OH = C 6 H 4 / \ o + H 2 0. 
 
 \co '' co 
 
 The resulting series of compounds are the phthaleins, 
 which will be further referred to under the eosins. If 
 amido derivatives of the phenols are treated in the same 
 manner, amido-phthaleins result, which constitute the series 
 of colours known as the rhodamines. Of these the body 
 known simply as rhodamine is the type. This is prepared 
 by the action of phthalic anhydride on diethyl-amidophenol. 
 The resulting compound, which possesses simultaneously 
 acid and basic properties, has the constitution 
 
 C = (C 6 H 3 N(C 2 H 5 ) 2 OH) 2 
 
 Here, as in the case of magenta, water is eliminated in 
 salt formation, the commercial product being the hydro- 
 
OBGANIC PIGMENTS. 247 
 
 chloride, of the formula Co 8 H 30 N 2 O 3 , HC1. The simplest 
 possible rhodamine, of course, would be that obtained by the 
 action of amidophenol *on phthalic anhydride, but by the 
 introduction of alkyl residues into the amidophenol the 
 colour of the resulting body is much intensified, so that the 
 compound above described is the body usually known under 
 the name, which is in reality generic. 
 
 The amidophenol employed in the preparation of the 
 rhodamines is the meta variety. 
 
 Commercial rhodamine forms a red powder, readily 
 soluble in water, with a fine crimson colour and a character- 
 istic yellow fluorescence, which is best observed in dilute 
 solutions. By heating the solution to about 90 this dis- 
 appears, and returns when the solution has cooled. 
 
 The free base is precipitated by the addition of caustic 
 alkalies, in red flakes, soluble in ether. With stannous 
 chloride, rhodamine gives a brilliant scarlet precipitate, which 
 in a fine state of division shows a remarkable blue colour, 
 somewhat resembling a fluorescence phenomenon. In strong 
 sulphuric acid rhodamine dissolves with a yellow colour, 
 which changes back to red on dilution with water. Khoda- 
 mine colours are very permanent to light. 
 
 In addition to the normal hydrochloride, the basic hydro- 
 chloride is well known under the name of rhodamine B. 
 Numerous rhodamines are known, being the corresponding 
 compounds of other alkyl-meta-amido-phenols. 
 
 Besides the ordinary rhodamine, the chief of those which 
 are used for the production of lakes are the following : 
 rhodamine B, the basic hydrochloride of diethyl-m-amido- 
 phenol-phthalein ; rhodamine S, the succinein (in which 
 succinic anhydride replaces phthalic anhydride) of dimethyl- 
 amidophenol ; rhodamine 6 G, the ethyl ester of diethyl- 
 rhodamine; and rhodamine 12 G, a still further alkylised 
 rhodamine. 
 
248 CHEMISTRY OF PIGMENTS. 
 
 In preparing the lakes of this group of colours, the best 
 results are obtained by the use of tannic acid and tartar 
 emetic, as the antimony and tannic acid lake is by far the 
 least fugitive of the series, and none of them can be regarded 
 as in any way permanent. These lakes are used to a certain 
 extent for tinting violet lakes. When used for this purpose 
 they are usually precipitated by a salt of phosphoric acid. 
 The usual diluent of this lake is a fine variety of barium 
 sulphate. 
 
 3. The Azines. (a) Safranines. These compounds have a 
 very complex constitution, all agreeing in containing two 
 nitrogen atoms united to each other. The lowest member 
 of the group is phenosafranine, the chloride of which pro- 
 bably has the constitution 
 
 
 C 6 H 5 C1 
 
 The bases themselves are very little known, the salts 
 of these being the colouring matters. As a rule they dis- 
 solve in strong sulphuric acid, with a fine green colour. 
 On adding water the colour gradually changes to a bluish 
 green, then to a distinct green. On further dilution violet 
 and red shades appear. 
 
 By reduction with a reagent such as tin and hydrochloric 
 acid, the colour is discharged, but it returns again on exposure 
 to the air, thus differing from the rosaniline colours. 
 
 Alcohol dissolves the colour, forming a red solution with 
 a yellow fluorescence. Dilute hydrochloric acid is without 
 action, whilst concentrated acid changes the colour to a blue- 
 violet. Ammonia and alkalies remove the colour, but without 
 much alteration. 
 
 Commercial safranine consists of a mixture of several 
 compounds, of which the best defined are the homologues, 
 C 19 H 17 N 4 C1, C. 20 H 19 N 4 C1 and C 21 H 21 N 4 C1. It is prepared in 
 
OKGANIC PIGMENTS. 249 
 
 various ways, and according to shade is known as : safranine, 
 safranine T, aniline pink, safranine extra G, safranine S, 
 safranine GGS, safranine GOOD, safranine FF, safranine 
 AG and AGT extra. 
 
 Dimethyl-phenosafranine is the base of the colour known 
 as fuchsia. Magdala red is a colour which is best classed 
 with the safranines, if it does not actually belong to that 
 class. It is a very useful colour, known also as naphthalene 
 red, napthalene rose, naphthalene scarlet, Sudan red and rose 
 pink. It has the formula C 30 H 21 N 4 C1 + H 2 0. It occurs in 
 commerce as a hydrochloride. It is very slightly soluble in 
 water, and is characterised by its cherry-red colour in alcohol, 
 with a cinnabar-coloured fluorescence. The solution loses its 
 fluorescence by the addition of ammonia. It is distinguished 
 from eosin by not being dissolved from its compounds by 
 alcohol, and by not being easily decomposed by strong alkalies 
 or dilute acids. 
 
 Reducing agents decolourise the solutions, the colour 
 returning on exposure to the air. 
 
 The only satisfactory lakes of the safranine group are 
 those prepared with tartar emetic and tannic acid. They 
 are much brighter than the corresponding magenta lakes, 
 and are also much faster. 
 
 (b) The Eurhodines. This group of colours might almost 
 be classed with the safranines, as they differ from them only 
 in that they are azines in which one atom of hydrogen has 
 been replaced by an amido group, whereas in the safranines 
 two atoms have been so replaced. The separation of the euro- 
 dines into a separate class is due to Otto Witt, whose classifi- 
 cation we follow in this respect. The chief colour in this group, 
 which is used for the production of lakes, is that known as 
 toluylene red, or neutral red. This compound is the hydro- 
 chloride of the base dimethyl-diamidotoluphenazine, of the 
 formula C 15 H 16 N 4 'HC1, and occurs as a greenish-black powder, 
 
250 CHEMISTEY OF PIGMENTS. 
 
 easily soluble in water, which turns bluer and finally loses its 
 colour on heating with reducing agents. The colour, however,, 
 returns on exposure to the air. It gives a fine red solution 
 in alcohol, with a brownish fluorescence. With hydrochloric 
 acid its solution becomes blue. It forms a* good lake with 
 tannic acid and tartar emetic, which has a blue-red tone. 
 The closely allied neutral violet, of the formula C 14 H 14 N 4 HCl r 
 is a homologue of the above colour, being the hydrochloride 
 of dimethyl-diamidophenazine. It is a violet colour, but the 
 tannic acid and tartar emetic lake is of a fine red-violet tint. 
 
 4. The Sulphonated Azo-compounds. The sulpho acids of the 
 azo colours are amongst the most important of all the coal- 
 tar colours, not only for lake production, but also for all 
 purposes for which the colours are used. They are so- 
 numerous, their number having increased to such an extent 
 of recent years, that it is impossible to do more than give 
 short details of the principal of those which are used for the 
 production of the more important of the red lakes. 
 
 It is necessary, in order to get a clear idea of the sub- 
 stances with which we now have to deal, to understand the 
 principles involved in the preparation of the several groups 
 comprising the azo colours. The fact that they may now be 
 regarded as the most important series $f the coal-tar colouring 
 matters, and have in themselves giver; a fresh impetus to an 
 already important industry, justifies a somewhat fuller treat- 
 ment than might at first appear necessary in a technical 
 work of the character of the present volume. 
 
 (4) Azo Compounds. The azo dyes form a well-defined and 
 well- understood group of compounds. They are prepared by 
 the action of diazo compounds on phenols or amines of the 
 aromatic series. The diazo compounds themselves result when 
 salts of primary amines of the aromatic series are treated with 
 nitrous acid. The typical reaction illustrating this important 
 change is that of nitrous acid on aniline, as follows : 
 
ORGANIC PIGMENTS. 251 
 
 C 6 H 5 . NH 2 . HC1 + HN0 2 C 6 H S .N : N.C1 + 2H 2 
 
 Aniline hydro chloride Nitrous acid Diazobenzene chloride Water 
 
 If aniline in alcoholic*' solution be treated with nitrous 
 acid, the resulting product is diazoamidobenzene. This 
 body may be regarded as due to the previous formation of 
 free diazobenzene, which then reacts with another molecule 
 of aniline, thus : 
 
 C 6 H 5 N:N.OH + C 6 H 5 NH 2 = C 8 H 6 N : N.NH.CH 5 + H 2 O. 
 
 Diazoamidobenzene 
 
 The diazo compounds are thus characterised by con- 
 taining the group N : N, which is combined with one carbon 
 atom and with one atom other than carbon. 
 
 The azo compounds, on the other hand, contain this same 
 important group, N : N, but it is combined with two carbon 
 atoms, this constituting the difference between the two series 
 of bodies. The simplest type of the azo compounds is ordin- 
 ary azobenzene C 6 H 5 N : NC 6 H 5 . 
 
 Azobenzene and its homologues can be obtained by the 
 reduction of the nitro derivatives of the corresponding hydro- 
 carbons. The most suitable reducing agents are sodium 
 amalgam, or zinc and alcoholic potash. The typical reaction 
 takes place as follows : 
 
 2C 6 H 5 N0 2 + 4H 2 = C 6 H 5 N:NC 6 H 5 + 4H 2 0. 
 
 The simple azo compounds are usually highly coloured 
 bodies, but they are not colouring matters, as they possess 
 no power of combining with either acids or bases. The real 
 colour bodies employed are amido or hydroxy derivatives of 
 the azo compounds. The types of these two series are : 
 
 C 6 H 5 N:NC 6 H 4 .NH 2 Amidoazobenzene 
 C 6 H 5 N:NC 6 H 4 .OH Hydroxyazobenzene 
 
 The amidoazo compounds can be employed as such when 
 they possess basic properties, combining with acids, and they 
 can also be used in the form of their sulpho acids, when they 
 
252 CHEMISTEY OF PIGMENTS. 
 
 are of an acid character. The preparation of benzene azo /3 
 naphthylamine will serve as an example of the usual method 
 of preparing amidoazo compounds. One molecule of /3 
 naphthylamine is dissolved in dilute hydrochloric acid by the 
 aid of heat, filtered from any impurity insoluble in acid, 
 very considerably diluted and cooled. One molecule of 
 aniline hydrochloride is dissolved in water, and a considerable 
 excess of hydrochloric acid added to prevent formation of 
 diazoamidobenzene on diazotisation, and one molecule of 
 sodium nitrite added slowly to the cooled liquid. This 
 solution of diazobenzene hydrochloride is filtered into the 
 J3 naphthylamine solution with constant stirring, and the 
 mixture allowed to stand for several hours to allow com- 
 bination to take place, when a red precipitate of benzene azo 
 /3 naphthylamine separates in accordance with the following 
 scheme : 
 
 C 6 H 5 N 2 C1 + C 10 H.NH 2 = C 6 H 5 N 2 C 10 H 6 NH 2 + HC1. 
 
 Substituting other amines or their sulpho acids for the 
 aniline and other amines, or phenols or their sulpho acids for 
 the naphthylamine, we may prepare other azo compounds. 
 The hydroxyazo compounds are almost invariably used as 
 sulpho acids, and this series of colours is perhaps the chief of all 
 those used in the manufacture of coal-tar lakes. Amongst 
 the amidoazo colours themselves only one is used to any 
 extent for assisting in the production of red lakes. This is 
 the w T ell-known dye chrysoidine, a more or less orange 
 colour, but which is used to give certain shades to other 
 well-defined red lakes. Chrysoidine is the hydrochloride 
 of diamidoazobenzene, C 6 H 5 N : NC 6 H 3 (NH 2 ) 2 HC1. Being a 
 strongly basic colour it can be used to advantage with 
 magenta, and in this combination it is known under the 
 name of cardinal, a name applied, however, to several other 
 colours. A scarlet is also sold which is a mixture of 
 
OEGANIC PIGMENTS. 253 
 
 safranine and chrysoidine. The lakes of these colours are 
 usually prepared as described under magenta and safranine. 
 
 The oxyazo colours rnjay be said to be now the most 
 important of all the coal-tar colours, and owe their existence 
 to the researches of the late Peter Greiss, who published 
 his investigations on these colours in 1878. Since that time 
 the chemistry of this group has advanced to an enormous 
 extent, and new colours are constantly being discovered. As 
 a general rule these colours are superior to the other earlier 
 known compounds, both in brilliancy and in permanence. 
 
 In the following short description of the more important 
 of the sulphonated azo colours, it must be remembered that 
 in actual practice the colours are not usually the pure com- 
 pounds here mentioned, but are composed of a mixture of 
 closely similar compounds. The usual initials used to desig- 
 nate the intensity of the shade (depending on the exact 
 degree of alkylisation, etc., of the parent compound) are added 
 where necessary; these are K (= roth, red) and G (= gelb, 
 yellow). 
 
 The following are the constitutions and technical names 
 of the principal colours : 
 
 Crocein. The enormous number of varieties of this 
 splendid colour, all of which may be employed according 
 to the shade desired, are all closely related compounds. 
 Typical amongst them is that known as Crocein 3BX. This 
 is the diazo combination of naphthionic acid combined with 
 one of the many /3 naphthol-sulphonic acids. Chemically, 
 its name is sodium naphthalene-sulphonate-azo /? naphthol 
 a sulphonate of sodium. In addition to this compound the 
 following croceins are well defined, all being similar com- 
 pounds in which the benzene, toluene and naphthalene groups 
 replace one another in various ways. Crocein scarlet 3E 
 ( = scarlet 4KB), crocein scarlet 7B ( = scarlet 6KB) and 
 brilliant crocein, are all diazo compounds of closely related 
 
254 CHEMISTRY OF PIGMENTS. 
 
 bodies in combination with one of the naphthol-sulphonic 
 acids. 
 
 Biebrich scarlet is one of the most useful compounds. It 
 is a combination of the diazo compound of amidoazoben- 
 zene-disulphonic acid and /3-naphthol. Xylidene red is also 
 much employed. This is the compound of the diazo deriva- 
 tive of xylidene and one of the naphthol-disulphonic acids. 
 
 The xylidene scarlets are such brilliant and permanent 
 colours that they are, to a considerable extent, displacing 
 the natural cochineal carmine. 
 
 In preparing the lakes of these hydroxy-sulphonic-azo 
 compounds, the best base for general use is alumina. The 
 shades produced by the use of this base are more brilliant 
 and clear than those made in any other manner. Most of 
 the metallic salts yield precipitates with these colours, but 
 they are, as a rule, soluble to a certain extent in large excess 
 of water ; therefore in their preparation a loss of colour is 
 often experienced. As a rule, the colour is largely diluted 
 with an inert material, such as sulphate of barium ; in the 
 preparation of the diluted colour, it is best to precipitate 
 the lake and the barium sulphate from a solution of alum 
 and barium chloride simultaneously, as the colour is then 
 intimately incorporated with the diluent. As a rule, the lakes 
 from this group of colours, as is the case with many others, 
 have a somewhat bluish shade when prepared from a single 
 compound. It is therefore usual to use a mixture of colours in 
 which there is sufficient orange to entirely overcome the blue 
 shade. 
 
 Although, as a class, these colours are fairly fast to light, 
 it has been observed that their permanence usually increases 
 with increase in molecular weight. 
 
 5. The Eosins. As has been mentioned earlier, phthalic 
 anhydride and the phenols possess the power of combina- 
 tion, with the formation of a group of bodies known as the 
 
ORGANIC PIGMENTS. 255 
 
 phthaleins. If, instead of using the monatomic phenols, one 
 employs the dihydroxy phenol, resorcinol (meta-dihydroxy- 
 benzene), a phthalein oi>great interest is obtained. The 
 reaction taking place is as follows : 
 
 I C / \Q 
 
 X CO X /I \C 6 H 3 OH / 
 
 C 6 H 4 ( \0 + 2C 6 H 4 (OH) 2 . C 6 H 4 / O 
 
 \co/ \ i 
 
 \ C = 
 
 + 2H.,0 
 
 The resulting compound is fluorescein, a yellowish-red 
 powder, which even in the most dilute solution shows an 
 intense greenish fluorescence. So intense is its colouring 
 power, that whole rivers may be coloured for miles by a 
 single pound or so of it. It has indeed been used to trace 
 the course of underground streams, and the existence of an 
 underground connection between the Danube and the Ach, 
 a small river running into the Lake of Constance, has been 
 proved by its use. 
 
 The eosins are derivatives of fluorescein, in which a certain 
 number of the hydrogen atoms are replaced by halogen 
 atoms, that is by chlorine, bromine or iodine, the last-named 
 being very expensive ; the usual commercial eosins are 
 bromine compounds. The iodine compounds are generally 
 termed Erythrosiris. The most important of these bodies 
 are the following : 
 
 Eosin (Eosin yellowish, Soluble Eosin. Eosin A, etc.) is 
 tetrabrom-fluorescein C 20 H 8 Br 4 O 5 . It comes into commerce 
 as its potassium salt, C 20 H 6 Br 4 5 K 2 + 6H 2 0. It is then 
 marked (in German commerce) Eosin J. It is a reddish 
 powder with a yellowish-green reflex. Its solutions are 
 intensely rose-coloured, with a very fine green fluorescence. 
 Its acid properties are very marked, its salts not being 
 decomposed by acetic acid. It combines with metallic 
 
256 CHEMISTRY OF PIGMENTS. 
 
 oxides, forming very insoluble lakes. Silver and lead salts 
 give red, aluminium and tin give red-yellow lakes. 
 
 Eosin orange, or Eosin 5 G, is a mixture of the tetrabromo 
 with the dibromo compound. 
 
 Erythrosin (Eosin blue shade, Pyrosin R, Dianthin B, 
 etc.) is tetraiodo-fluorescein. It closely resembles ordinary 
 eosin, but its solutions are not fluorescent. 
 
 Aureosin is a mixture of chlorinated fluoresceins. 
 
 Various bromnitro-fluoresceins are known in commerce ; 
 they are called saf rosin or Eosin BN. A mixture of bromnitro- 
 and of nitro-fluoresceins is also known as Lutecienne. A 
 nitrochlor-fluorescein is sold as Rubeosin. 
 
 Various methyl and ethyl derivatives of the eosins are also 
 occasionally met with. They are called spirit-soluble eosins, 
 and are sold under such names as Eosin BB, spirit primrose, 
 Rose JB (soluble in spirit). 
 
 Rose Bengale, a favourite colour, is the sodium salt of 
 tetraiodo-dichlor-fluorescein. 
 
 Phloxin (Phloxin TA) is the potassium salt of tetrabrom- 
 tetrachlor-fluorescein. 
 
 Cyanosin is the potassium salt of the methyl ether of 
 tetrabrom-dichlor-fluorescein. 
 
 These colours readily yield lakes with salts of lead, 
 aluminium, zinc, tin, etc., of great colouring and covering 
 power, but they are very fugitive. 
 
 Lead salts give the bluest shades, whilst tin and aluminium 
 lakes are of a much more yellow tint. The usual inert matter 
 used as a diluent is barium sulphate, but sometimes eosin 
 lakes are met with containing nothing but lead salts, both as 
 the precipitant for the lake and as the inert base. 
 
 The now very common " vermilionettes " are eosine lakes 
 with a lead base, mixed either with lead sulphate or with 
 barium sulphate. We have frequently met with vermilion,, 
 sold as pure, containing up to 50 per cent, of sulphate of lead 
 
OKGANIC PIGMENTS. 257 
 
 with a small quantity of a lead-eosin lake. The fugitive 
 nature of this colour renders such an adulteration very 
 pernicious. 
 
 Alizarin Compounds. 
 
 All that is necessary in connection with the alizarin lakes 
 for the present purpose has been said under madder lakes, to 
 which section the reader is referred. The close relationship of 
 the colouring matters of madder to the artificial colours ren- 
 ders it more convenient to deal with the two sets of colours 
 together. 
 
 Orange and Yellow Lakes. 
 
 The lakes of these colours need only be referred to shortly, 
 as the main principles of the chemistry of the groups of colours 
 to which they belong have been dealt with at sufficiently full 
 length in describing the red lakes. Nearly all the orange 
 colours employed for the preparation of lakes are sulphonic 
 acids of the azo colours, closely related to the azo reds. Types 
 of these are the following : 
 
 Mandarin (Orange II, Tropoeolin 000 No. 2) is benzene- 
 sulphonate of sodium-azo-yS-naphthol. 
 
 Mandarin GK (Orange T, Orange K) is different from this 
 only in the fact that the benzene is replaced by orthotoluene. 
 
 In all respects the principles governing the formation of 
 red lakes of this class apply to the orange lakes. An imita- 
 tion red lead is often met with, consisting of a lead lake of a 
 cheap orange, precipitated together with a large amount of 
 barium sulphate. The orange lakes are not very permanent. 
 Yellow lakes are not of very frequent occurrence, as the use 
 of chrome yellows is very satisfactory, and their production 
 is much cheaper than that of the yellow lakes. They are, 
 however, used to a certain extent to modify the shades of 
 
 green lakes. The principal colours used are the following : 
 
 17 
 
258 CHEMISTEY OF PIGMENTS. 
 
 The basic colour auramine (imido-tetramethyl-diparadi- 
 amidodiphenylmethane). It gives an excellent lake with 
 tannic acid and tartar emetic. 
 
 Thioflavine (dehydro - thiotoluidine trimethyl - chloride). 
 This also gives good results with tannic acid. 
 
 Amongst the acid yellows used for lakes are the follow- 
 ing : Tartrazine : this is the trisodium salt of tartrazinic 
 acid. Naphthol yellow. Quinoline yellow and metanil 
 yellow. These are often used as simple barium lakes, with 
 barium sulphate as a diluent. The colours are, how- 
 ever, very fugitive, and better results are obtained when 
 metanil yellow, which possesses acid and to a certain 
 extent basic properties, is used in the form of a tannic 
 acid and barium lake. 
 
 Green and Blue Lakes, 
 
 The majority of the green lakes usually met with are 
 made from basic colours of the triphenylmethane group (see 
 rosaniline), or from sulpho-acids of basic colours, in which 
 both the acid and the arnido groups have been neutralised in 
 the formation of the lake. A certain number are also made 
 from purely acid greens, such as certain sulpho-acids of azine 
 or azo-greens, and some alizarin derivatives. 
 
 Methyl green is the most important of the basic greens 
 from many points of view. It is the zinc chloride compound 
 of the hydrochloride of chlor-methyl-hexamethyl-pararosani- 
 line, of the formula C 19 H 12 (CH 3 ) 6 N 3 . CL CH 3 C1 4- ZnCl 2 + H 2 0- 
 It is readily soluble in water and alcohol, and also in amyl 
 alcohol. This last character distinguishes it from benzalde- 
 hyde green and its allies. By heat it splits up into methyl 
 chloride and methyl violet. Hence, by moistening a filter 
 paper with a solution of this colour and strongly drying it, 
 the colour turns to a fine violet. Strong hydrochloric acid 
 
ORGANIC PIGMENTS. 259 
 
 turns the colour yellow, and alkalies and reducing agents 
 decolourise the pigment. 
 
 Iodine green closely resembles the last described com- 
 pound. It was in former times manufactured by using 
 methyl iodide instead of methyl chloride, but the iodine 
 compound is seldom met with now, and much of the so- 
 called iodine green contains no iodine at all. 
 
 Malachite green (Victoria green, Benzaldehyde green) is 
 usually met with as the oxalate or the zinc chloride double 
 salt. The free base is tetramethyldiamidotriphenylcarbinol, 
 of the formula C(OH) (C 6 H 5 ) (C 6 H 4 N. (CH 8 ) 2 ) 2 . As is 
 usual with this group of colours, water is lost in the process 
 of salt formation, and the oxalate has the composition 
 2C, 8 H 24 N, + 3C 2 H 2 4 . 
 
 Ethyl green is the corresponding ethyl compound. 
 
 Acid green, SOF, is the sodium salt of diethyldibenzyl- 
 diamidotriphenylcarbinol trisulphonic acid. This body is 
 also known as diamond green and dragon green. 
 
 When the purely basic greens are used the acid used for 
 precipitation is arsenious acid, which gives by far the most 
 brilliant shade possible. The tannic acid and tartar emetic 
 lakes are dull, but at the same time useful for certain pur- 
 poses. 
 
 When such colours as diamond green are used, barium 
 chloride is a favourite precipitant, but the amido groups in 
 the colour should first be saturated with tannic acid or some 
 other acid. Sometimes an acid yellow is employed with 
 the acid greens to tint the resulting lake, and if picric acid 
 be used it also serves the purpose of saturating the amido 
 groups present. 
 
 Coerulein is a green colour made by heating gallein (the 
 phthalic anhydride compound of pyrogallol) with sulphuric 
 acid. Its constitution is not certain, but it is probably an 
 anthracene derivative of the formula 
 
260 CHEMISTRY OF PIGMENTS. 
 
 /C(C 6 H 5 K 
 
 ^<L > CA - 
 
 ^ UJrL /' 
 
 It gives very fast, but somewhat dull shades with most 
 metallic salts. With chromium salts it gives a splendid dull 
 olive green which is as fast to light as any of the alizarin 
 greens. 
 
 There are several varieties of alizarin green, of very 
 complicated constitution. The principal of these is alizarin 
 green G, the parent substance of which has the constitution 
 
 /co\ /CH = CH 
 
 CA(OH <co> (OH) < N ; 6n 
 
 The actual dye is a mixture of sulpho-acids of this body and 
 of tri- and penta-oxyanthraquinone quinoline. Various shades 
 are produced according to the degree to which the sulphona- 
 tion has gone, and also according to the number of OH 
 groups introduced. The others are closely related to this 
 body, and their lakes are formed in the same manner as the 
 alizarin reds, which have been described under the madder 
 lakes 
 
 There are not a great many blue lakes manufactured, as 
 they are, in general, rather fugitive, and the ultramarine and 
 Prussian blue colours are so permanent and cheap that they 
 are usually preferred to the coal-tar colour lakes. 
 
 The colours, however, from which blue lakes are made 
 (and also violet lakes, which are generally very closely related 
 to the blue colours) belong to the following series : (1) The 
 triphenyl-me thane compounds ; (2) the sulpho acids of those 
 compounds ; (3) the azines ; (4) the indulines. A few other 
 compounds are occasionally employed. 
 
 If the hydrogen atoms of the amido groups of rosaniline 
 or pararosaniline be replaced by organic radicles the colour 
 becomes violet or blue. The shade is bluer according as 
 there are more hydrogen atoms so replaced. The ethyl de- 
 
OBGANIC PIGMENTS. 261 
 
 rivatives are of a redder shade, the methyl and benzyl deriva- 
 tives less red, and the phenyl derivatives of the finest pure 
 blue colour. Of the purely basic blues and violets, the substi- 
 tuted magentas are perhaps amongst the best known. 
 
 Aniline blue (spirit soluble blue, gentian blue, opal blue) 
 is triphenyl-rosaniline, of the formula C 20 H 16 (C 6 H 5 ) 3 N 3 . The 
 commercial blue is a mixture of compounds of various degrees 
 of alkylisation, the more highly alkylised being of the bluest 
 shades ; it is sold in the form of its hydrochloride. 
 
 Spirit soluble diphenylamine blue, C 19 H 14 (C 6 H 5 ) 3 N, is 
 identical with the last described compound in chemical com- 
 position, except that it is triphenylated _p<mi-rosaniline. It 
 is not practicable to introduce more than three phenyl 
 groups into this series of compounds, but more ethyl and 
 methyl groups may be added, the resulting blues being very 
 intense. Both series of compounds may be sulphonated, 
 and the resulting so-called " soluble " blues are the most 
 generally useful for lake production. In addition to the 
 bodies included in the above series, the azine group is 
 represented by Nile blue, naphthylene blue and methylene 
 blue ; and the indulines by " neutral blue ". These will be 
 found referred to in the table at the end of the chapter. 
 
 Tartrate of antimony and tannic acid are generally used 
 as the precipitants of these blue colours. If hydroxy groups 
 are present in the colour base, they should be neutralised by 
 the addition of barium hydroxide. Sometimes zinc and 
 aluminum salts are used to a small extent. 
 
 Violet lakes in general are treated in the same manner 
 as blue lakes, but it is to be noted that the most brilliant 
 lakes are yielded by the basic violet colours precipitated by 
 means of phosphoric acid. 
 
 Gallein, the phthalein of pyrogallic acid, of the formula 
 C 20 H 10 7 , is largely employed for the manufacture of violet 
 lakes, with potassium bichromate and tartar emetic. It 
 
262 CHEMISTEY OF PIGMENTS. 
 
 yields lakes with a fine " bloom ". With lead acetate it 
 gives a fine grey-violet lake. The black lakes, which are 
 in reality an intensely blue black, are prepared from certain 
 acid azo colours. They are, however, usually mixed with 
 certain blacks to modify the shade, and are seldom employed 
 by themselves. 
 
 INDIGO, 
 
 The importance of this colour as a dyeing material can- 
 not be overestimated, but as a pigment, although it finds a 
 certain employment, it is equalled in permanence, without 
 losing at all in richness of colour, by some of the cheaper 
 blue pigments. Hence, and on account of its high price, it 
 is only employed to a limited extent for certain fine work. 
 Indigo was until quite recently the product only of certain 
 plants ; the artificial preparation of the colour, however, was 
 achieved some time ago, Prof. Baeyer, of Munich, taking 
 out a patent in 1880 for " the preparation of derivatives and 
 homologues of ortho-nitro-cinnamic acid, and their conversion 
 into indigo blue and allied dye stuffs ". This triumph in 
 chemical science was met with little more than amusement 
 by the indigo planters and traders, but within the last few 
 years synthetic indigo rather dearer, but purer than the 
 natural colour has become a commercial article, and it is 
 certain that before very long its price will be reduced as 
 easier processes are discovered, as they are sure to be. In 
 spite of this the indigo planters go on in the same way that 
 they have always done, without, except in rare cases, any 
 attempt at improvement in their methods. This has called 
 forth a very emphatic warning from Prof. Armstrong, and 
 there is little doubt that, unless every help that science 
 can afford is rapidly brought to bear on the natural pro- 
 duction of indigo, the experience of the madder industry will 
 be repeated, in which the production of synthetic alizarin in 
 
ORGANIC PIGMENTS. 263 
 
 time killed the natural madder production, and threw open 
 large tracts of cultivated land for the cultivation of other 
 crops. 
 
 The principal members of the leguminous genus, Indigo- 
 fera, producing indigo, are I. tinctoria (the most important), 
 and I. disperma, anil and argentea. Indigo does not exist 
 as such in the plants, but is produced by the action of a 
 ferment on a glucoside contained in them, called indican, 
 which may be extracted from them by means of cold alcohol. 
 
 Indigotin, or indigo blue, as it is often termed, was 
 formerly described as of the formula C 8 H 5 NO, but is now 
 well established as of the formula C 16 H 10 N 2 2 and the con- 
 stitution 
 
 C (\ / C \ 
 
 ^6^-4\ /C C \ /C 6 H 4 . 
 
 \NH/ \NH/ 
 
 Pure indigotin may be obtained from commercial indigo, 
 which contains from 20 to 90 per cent, of it, by mixing it 
 with plaster of Paris and water, spreading the mass on 
 an iron plate, and heating it cautiously to sublime the 
 indigotin, which may be removed from the surface by a fine 
 spatula. It is prepared by the oxidation of indigo-white 
 (see below), in a state of fair purity, but to obtain the finest 
 specimens of the colour the aid of synthetic methods must be 
 invoked. 
 
 Pure indigotin forms fine deep blue crystals with a 
 coppery sheen, subliming at about 290 C. It is insoluble in 
 water, cold alcohol, ether, and in essential oils, but soluble in 
 acetic acid, aniline, and nitrobenzene. It may be purified by 
 boiling it with aniline to saturation, filtering and allowing 
 the crystals to be deposited, and then washing them with 
 alcohol. It is a neutral body, and is not affected by dilute 
 acids or alkalies. As a dye it is largely employed for cloth, 
 but in the form of a pigment it has but a limited use, either 
 
264 CHEMISTKY OF PIGMENTS. 
 
 as an intense deep blue, or as a mixed colour with yellows, or 
 as a light blue diluted with a white. 
 
 Indigo-white is hydindigotin, or reduced indigo, of the 
 formula C 16 H 12 N 2 O._,. It is obtained by reducing indigotin 
 with any of the usual reducing agents. It is of interest only 
 to the dyeing industry, on account of the fact that it dissolves 
 easily in alkalies, and the weak compound thus formed, when 
 absorbed by the fibre, is decomposed by the latter, and the 
 indigo-white is fixed by some unknown constituent. On ex- 
 posure to weak oxidising agents (such as the atmosphere), 
 the indigo-white is re-oxidised to indigotin, and the fibres 
 assume the well-known blue colour. 
 
 Commercial indigo, made from the plants, consists chiefly 
 of the body indigotin (see below). To obtain the indigo, the 
 plants are chopped or rather those parts in which the 
 colour compounds are found, viz., the leaves and twigs and 
 immersed in water. After a certain time fermentation has 
 gone on to the proper degree, and the water is run off into 
 shallow vats, and is well agitated in order to expose it as 
 much as possible to the action of the air. The yellow liquid 
 assumes a greenish colour, and the indigo separates in a 
 pulpy state. The blue pulp is boiled with water in order 
 to prevent secondary fermentation setting in, which would 
 result in the formation of brown products. After a certain 
 time the liquid is filtered and the precipitate pressed, and 
 slowly dried in sheds from which the light is excluded as far 
 as possible. 
 
 The indigo thus obtained varies very greatly in quality, 
 both as far as its content in true indigotin and in the amount 
 of mineral impurity it contains. Apart from the plants of 
 the Indigoferce, several other species yield the colour, among 
 which the best known is the woad plant, Isatis tinctoria, and 
 several kinds of orchids also contain it in small quantities. 
 The chemistry of the group of compounds belonging to the 
 
OEGANIC PIGMENTS. 265 
 
 indigotin series is too extensive a subject to be adequately 
 dealt with in a work of this kind, and the reader is therefore 
 referred to text-books on organic chemistry for fuller details 
 than the short account which follows contains. 
 
 Indican, C 52 H 62 N 2 34 , is the glucoside from which the 
 indigotin is derived. It forms a brown syrup, from which 
 the last traces of water cannot be separated without great 
 trouble, if indeed it is possible at all to remove them. The 
 reaction by which the indigotin and glucose are formed is as 
 follows : 
 
 C 52 H 62 N 2 0, 4 + 4H 2 = C 16 H 10 N 2 2 + 6C 6 H 10 6 . 
 
 On treatment with strong sulphuric acid, indigotin yields 
 sulphonic acids. The bodies accompanying indigotin in 
 commercial indigo also yield such acids, and the resulting 
 mixture of sulpho acids is known as soluble indigo, or indigo 
 carmine. The exact properties of indigo carmine vary 
 according to the nature of the initial indigo and to the 
 details of manufacture ; with a moderate proportion of 
 acid, the principal body formed is a mono-sulphonic acid, 
 C 16 H 9 N 2 O 2 ,S0 3 H, which, as its sodium salt, is known as 
 indigo-purple. With excess of acid, a di-sulphonic acid, 
 C 16 H 8 N 2 2 (SO 3 H) 2 , known as sulphindigotic acid, is formed. 
 The indigo carmine of commerce is the sodium salt of the 
 ;sulphonated indigo. 
 
 A typical sample of commercial indigo analysed by 
 Giradin was found to be composed as follows : 
 
 Indigotin, C 16 H 10 N 2 O 2 61-4 
 
 Indigo red, G^gH^N,^ , 7 '2 
 
 Indigo brown . , 4 - 6 
 
 Indiglucin, C 6 H 10 6 1*5 
 
 Ash 19-6 
 
 Water 5-7 
 
 The preparation of synthetic indigo may be achieved in 
 several methods. For the historical details of the synthesis 
 Bichter's Organic Chemistry, vol. ii., may be consulted. The 
 
266 CHEMISTRY OF PIGMENTS. 
 
 commercial synthetic indigo now on the market, which is 
 claimed to contain 97 per cent, of pure indigotin, is prepared 
 in the following manner : Naphthalene, C 10 H S , is oxidised to 
 
 phthalic acid, C 6 H 4 / Q j|, and this is converted into 
 
 'CO 
 phthalimide, C 6 H 4 ^ n/ / NH. This is then converted into 
 
 anthranilic acid, C 6 H /^ H > and then into phenylglycine- 
 
 orthocarboxylic acid, C 6 H 4 <^HCH. COOH' and ^ "^ 
 indoxylcarboxylic acid, C 6 H 4 < N \CH. COOH, which is 
 finally converted into indigotin, 
 
 co\ /co\ 
 
 \NH/ 
 
 In analysing indigo it is important to determine the 
 amount of moisture and ash, and also the percentage of true 
 colouring matter. It depends on circumstances whether it 
 is necessary to determine the actual amount of indigotin 
 separately from the total amount of colouring matter. 
 
 The moisture in good commercial indigo varies from 
 about 3 to 9 per cent., and may be driven off in the usual 
 manner by drying at 100 C. 
 
 In good samples the ash falls as low as 2 per cent., but in 
 fair commercial samples of undoubted purity it may often 
 reach from 5 to 8 per cent. Some of the inferior kinds, such 
 as that from Madras, may contain as much as 25 per cent. 
 
 It has been proposed to determine the specific gravity of 
 the sample, but in the authors' experience this is without 
 any value in judging the quality of indigo. 
 
 Starch is said to be occasionally used as an adulterant of 
 indigo, but the authors have never met with it in any sample 
 they have examined. If it is thought necessary to look for 
 
OEGANIC PIGMENTS. 267 
 
 this body, the best plan is to boil the sample with water, and 
 after cooling to test the filtered liquid with a solution of 
 iodine, when the well-known blue colour will result. 
 
 According to A. H. Allen, a useful proximate analysis of 
 indigo may be effected in the following manner. The sample 
 is dried at 100 in order to determine the moisture, and the 
 dry residue is treated with hot water, and the residue dried 
 and weighed. This gives the amount of impurities soluble 
 in water. The residue is then treated with hydrochloric acid 
 and then with dilute alkali, the residues being weighed after 
 each treatment in order to determine the amount dissolved 
 by these solvents. It is then treated with alcohol, and the 
 amount dissolved determined. This very fairly represents 
 the amount of indigo red, which may be of importance to 
 determine, as it modifies the blue shade of the indigo. 
 
 The residue, after allowing for the ash it leaves on igni- 
 tion, very fairly represents the amount of indigotin. 
 
 C. T. Lee proposes to determine the amount of true 
 indigotin by observing the amount which can be obtained 
 by sublimation a method which is easy to carry out, and 
 which yields satisfactory results under certain conditions. A 
 more accurate method of determining the amount of true 
 indigotin is that based on the reduction of this body to indigo 
 white and its subsequent reoxidation by exposure to the air. 
 The process recommended by C. Kawson is as follows : One 
 gramme of the finely powdered sample is treated in a flask 
 with 2 grammes of crystallised ferrous sulphate and 5 gr. of 
 caustic soda in 1000 c.c. of water. The flask is closed by 
 a cork, which has three perforations, through one of which 
 passes a syphon, whilst the other two are used respectively 
 for the entrance and exit of a current of coal gas. The con- 
 tents of the flask are maintained for about two hours at a 
 temperature just below 100 C., and after removing the source 
 of heat the insoluble matter is allowed to subside ; 500 c.c. 
 
268 CHEMISTKY OF PIGMENTS. 
 
 (representing 0'5 gr. of the sample) of the liquid, which is 
 made up to 1000 c.c. exactly, after cooling, with well boiled 
 distilled w r ater, unless it is preferred to make an allowance 
 for the quantity of water lost during the heating of the liquid, 
 is then syphoned off and the reduced indigo is oxidised by 
 allowing a current of air to pass through the liquid. To com- 
 plete the precipitation, the liquid is acidified and the precipi- 
 tate of indigotin, together with the indigo-red and the indigo- 
 brown, is allowed to subside. The supernatant liquid is 
 passed through a tared filter, and the precipitate washed 
 several times with hot water by decantation, and then boiled 
 with alcohol to dissolve the red and brown colouring matter. 
 The alcoholic liquid is then allowed to cool in order to ensure 
 the deposition of any traces of dissolved indigotin, and the 
 residue then collected on the filter and dried and weighed 
 after washing with absolute alcohol. 
 
 There are many other methods for an accurate assay of 
 indigo, but for the purpose of the present work it is unneces- 
 sary to deal further with the subject. For fuller details of 
 the numerous processes, the reader is referred to Allen's 
 Commercial Organic Analysis, vol. iii., part i., in which a very 
 full account of the subject will be found. 
 
 VARIOUS UNCLASSIFIED PIGMENTS. 
 Dragon's Blood, 
 
 The ordinary dragon's blood of commerce, which is im- 
 ported in the form of sticks or lumps, is a resinous product 
 of the fruit of several different plants, of which the chief 
 appears to be Damonodrops Draco. This product is known 
 as palm dragon's blood, and is imported from Southern 
 Asia. A very similar, but less esteemed product, is the 
 Socotra dragon's blood obtained from the fruits of Draccena 
 Cinnabari. Other products are also used. 
 
OEGANIC PIGMENTS. 269 
 
 The crude resinous product is of a deep red colour, vary- 
 ing much in quality, and when powdered forms an intensely 
 red powder, which is not -used in medicine, but is largely 
 employed for colouring varnishes and polishes. It forms the 
 basis of the majority of the so-called mahogany stains. As a- 
 pigment it finds only a limited employment. 
 
 According to Dieterich, the resinous product consists of 
 the following compounds : dracoalban, a white amorphous- 
 powder, softening at 192, and probably of the composition 
 C 20 H 40 O 4 ; this body occurs to the extent of about 2*5 per cent. ; 
 dracoresene, a bright yellow amorphous resin, melting at 14 r 
 occurring to the extent of about 14 per cent. ; red resin, the 
 true colouring matter, about 55 to 60 per cent. This body 
 consists mainly of the benzoate and the benzoyl-aceta'te of a 
 complex alcohol, dracoresinotannol, C 8 H 9 0. OH. Of these 
 esters the former largely preponderates. 
 
 There are in addition small quantities of other resinous 
 bodies, and in most samples certain .quantities of woody fibre 
 and other vegetable matter, and about 8 per cent, of mineral 
 matter. 
 
 The powdered resin is of a somewhat high value, and 
 is therefore liable to considerable adulteration. The chief 
 substances used for the purpose of sophistication are oxide of 
 iron, powdered bole, common colophony, and finely powdered 
 red Sanders wood. The grosser adulterations, such as iron 
 oxide or powdered bole, etc., will be left as a residue when 
 the resin is treated with solvents, such as alcohol and ether. 
 The microscope will reveal the presence of any appreciable 
 quantity of woody fibres, and the iron oxide will be found in 
 the ash and can be estimated in the usual manner. 
 
 According to Hirschsohn, the saponification number 
 (number of millegrams required to saponify one gram of the 
 resin) is about 150. 
 
270 
 
 CHEMISTRY OF PIGMENTS. 
 
 Gamboge (Gamboge). 
 
 This pigment is a gum- resin yielded by several trees 
 growing in various parts of the Malay Peninsula, and 
 in Ceylon. It comes into commerce, as a rule, in the 
 form of cylindrical rolls, which are prepared by run- 
 ning the exuded juice into hollow bamboo canes. 
 When broken the mass of gamboge exhibits a conchoid al 
 or vitreous fracture, and is of a fine yellow red colour. 
 When powdered the colour is of a very fine yellow. The 
 finest qualities of gamboge are very brittle, and are nearly 
 odourless ; it has little taste at first, but after a time it 
 causes a sensation of acridity in the throat. By the 
 successive action of ether and water it is almost entirely 
 dissolved. When in the powdered form it is often adulter- 
 ated, either with starch or with mineral matter. The former 
 adulterant is best tested for by the usual reaction for 
 starch. A decoction of the gamboge when cooled does not 
 become green when a little solution of iodine is added to 
 it, but merely of a tawny colour. Inferior varieties of the 
 mass gum-resin often contain appreciable quantities of woody 
 fibre, etc., and on grinding this is naturally found in the 
 powder. The ash of pure gamboge is usually about 0'5 per 
 cent., or even less, and should certainly not exceed 1 per 
 cent. If it does the presence of added mineral matter may 
 be inferred, and the ash should be carefully examined. A 
 number of samples were examined by Christison many years 
 ago (Companion to the Botanical Magazine, ii., 233), and he gives 
 the following results : 
 
 
 Siam Gamboge. 
 
 
 
 
 Ceylon Gamboge. 
 
 
 
 
 
 Pipe. 
 
 Lump. 
 
 Coarse. 
 
 
 Resin 
 
 71-674-2 
 
 64-365-0 
 
 35 _61-4 
 
 68-872-9 
 
 Soluble gum 
 
 21-824-0 
 
 19-720-7 
 
 14-217-2 
 
 18-820-7 
 
 Woody fibre 
 
 Traces 
 
 4-4_ 6-2 
 
 7-819-0 
 
 4-3 6-8 
 
 Starchy matter 
 
 
 
 5-0 6-2 
 
 7-822-0 
 
 
 
 Moisture 
 
 4-8 
 
 4-0 4-2 
 
 7-210-6 
 
 Not determined 
 
ORGANIC PIGMENTS. 271 
 
 Those samples containing starch are obviously adulterated. 
 
 A solution of gamboge is acid in reaction, owing to the 
 presence of a peculiar resija acid called cambogic acid. The 
 approximate composition of normal gamboge may be regarded 
 as follows : Moisture, from 1 to 4 per cent. ; resins, chiefly of 
 an acid nature, 65 to 70 per cent. ; gum, from 15 to 25 per 
 cent. ; wax, under 5 per cent. ; mineral matter, under 1 per 
 cent. The gum resin contains no essential oil. Although 
 starch and mineral matter may be regarded as the most 
 usual adulterants, samples have been found mixed with 
 common resin and with dextrin. 
 
 The quantitative action of caustic alkalies on gamboge 
 is a useful criterion of its purity. Several chemists have 
 examined the gum-resin from this point of view. According 
 to Williams the acid number (number of millegrams of 
 caustic potash, KOH, used to neutralise the free acids) of a 
 genuine sample was 80'6 ; the ester number 67*2, and the 
 total saponification number 147*8. Kremel gives lOO'O for the 
 acid, and 56 '1 for the ester numbers. Beckurts and Briiche 
 give for four samples the following figures ': Acid numbers, 
 89, 81, 69 and 71 ; for the ester numbers, 61, 50, 43 and 44. 
 
 Gamboge is partly soluble in alcohol, ether and ammonia. 
 The ammoniacal solution gives a red precipitate with barium 
 salts, yellow with zinc salts, red-yellow with lead salts, and 
 brownish-yellow with silver salts. 
 
 Buchner has examined the resin acids of gamboge, and 
 although the chemistry of these bodies is but poorly under- 
 stood, there is good evidence that the formula for the chief 
 of these acids, which is termed cambogic or gambogic acid, is 
 
 Gamboge is, in painting work, chiefly employed as a 
 water colour, as a bright yellow, or in admixture with blues, 
 to form dull greens. It is very useful as a glazing colour, 
 but is not permanent in sunlight. 
 
272 CHEMISTRY OF PIGMENTS. 
 
 Sepia. 
 
 This dark brown ink-like pigment is contained in the ink 
 bag, a defensive weapon, of the ordinary cuttle fish, Sepia 
 officinalis, of Sepia loligo, and other cephalopods, the "shells " 
 of which are often thrown up on our sea-beaches. 
 
 The ink obtained from this source, and which the animal 
 has the power of ejecting at will, in order either to effect 
 its escape in the clouded water, or for offensive purposes, 
 was known to the ancients. Horace in his Fourth Satire 
 speaks of nigra succus loliginis. Aristotle also mentions the 
 sepia, but rather as a table delicacy than as a pigment 
 bearer. 
 
 The juice, or ink, should be taken from the animal soon 
 after capture, as it is liable to putrefaction, and when dried 
 forms a black mass which, according to Prout, whose analysis 
 is the only one we have seen, consists of 
 
 Black pigment (melanin) ...... 78'00 
 
 Calcium carbonate 1O40 
 
 Magnesium carbonate 7*00 
 
 Alkaline sulphates and chlorides .... 2-16 
 
 Mucus . 0-84 
 
 98-40 
 
 The black pigment is isolated by boiling the dried mass 
 with water, hydrochloric acid and ammonium carbonate suc- 
 cessively. These menstrua presumably remove the mineral 
 matter and mucus, and leave the colour as an insoluble 
 residue. 
 
 Sepia is insoluble in water, alcohol and ether, but remains 
 suspended in water for a time, hence its use as an ink. Its- 
 deposition is accelerated by acids or ammonium chloride. 
 It forms a dark-brown solution with caustic potash, and is 
 separated by hydrochloric or sulphuric acids, but not by nitric 
 acid. It dissolves in ammonia, but not in alkaline carbonates. 
 
 Sepia is prepared in commerce by saturating the dried 
 
OEGANIC PIGMENTS. 273 
 
 cuttlefish ink with caustic alkali solution, adding more alkali, 
 boiling for half an hour, filtering and precipitating with an 
 acid, washing and drying at-a gentle heat. It is a fine dark 
 brown, used principally in water, and for monochrome work. 
 
 Warm Sepia is prepared by the addition of a redder brown, 
 as one of the ferric oxide colours. 
 
 Roman Sepia is sepia mixed with a yellow-brown. 
 
 Indian Yellow. 
 
 Indian yellow (Purree, Piuri, Pioury) is a peculiar pig- 
 ment of animal origin, used by the natives of India, and to 
 some extent by artists. It is a fairly bright yellow, but not 
 so fine a colour as gamboge, and is found in commerce as 
 round balls weighing a few ounces. Externally it is of a 
 brown or dirty green colour, but bright yellow inside, and 
 with a characteristic urinous smell, which is easily accounted 
 for. 
 
 Indian yellow is obtained by collecting the urine of cows 
 fed on the leaf of the mango plant (Mangifera indica), and 
 inspissating it until the yellow separates, when it is collected, 
 partially dried over a charcoal fire, and then in the air. The 
 cows are trained only to micturate when the labia majors 
 are stroked, and by this means about 3*5 litres of urine per 
 cow are collected daily. This amount yields about 50 grams 
 of purree. 
 
 Purree consists principally of the magnesium and calcium 
 salts of euxanthic acid, C 19 H 18 OH. 
 
 Graebe, who did a good deal of work on this pigment, 
 gives the composition of a fine sample examined by him as 
 
 Euxanthic acid 51 '0 
 
 Silicic acid and alumina 1'5 
 
 Magnesium 4-2 
 
 Calcium . . . 3-4 
 
 Water and volatile matter 39 - 
 
 99-1 
 18 
 
274 CHEMISTKY OF PIGMENTS. 
 
 The value of this pigment appears to depend on the pro- 
 portion of euxanthic acid present. Some samples contain 
 a considerable amount of euxanthone, C 13 H 8 4 , which is a 
 pale yellow substance, whereas the acid and its salts are of 
 a bright yellow colour. 
 
 The composition of five samples, apparently from MM. 
 Lefranc et Cie, of Paris, is given in Thorpe's Dictionary of 
 Applied Chemistry : 
 
 Euxanthic acid 
 
 72-3 
 
 70-96 
 
 4-35 
 
 9-3 
 
 33-34 
 
 Euxanthone 
 
 6-0 
 
 1-12 
 
 2-80 
 
 7-4 
 
 34-00 
 
 Mg . . . 
 
 5-35 
 
 4-88 
 
 4-85 
 
 4-60 
 
 3-70 
 
 Ca . 
 
 1-75 
 
 2-43 
 
 2-61 
 
 3-33 
 
 3-70 
 
 As the quality goes down the proportion of magnesium 
 euxanthate steadily decreases, and the euxanthone increases. 
 
 On treating Indian yellow with dilute hydrochloric acid, 
 and then removing the bases with ammonium carbonate, a 
 solution of ammonium euxanthate is obtained, from which 
 hydrochloric acid precipitates crystalline euxanthic acid. 
 Melting-point, 156 to 158 (with decomposition). On de- 
 composition by boiling with dilute acids, ^e;rro-glucuronic 
 acid and euxanthone are formed : 
 
 c i9 H i 8 Oii = C 13 H 8 4 + C 6 H 10 O 7 . 
 
 Deo^ro-glucuronic acid is CHO(CHOH) 4 *C0 2 H, and accord- 
 ing to Graebe euxanthone is represented by the formula 
 
 OH 
 
 co- 
 
 OH. 
 
 Euxanthic acid would appear to be a glucoside-like com- 
 pound of euxanthone. Against this constitution the fact 
 that euxanthic acid forms two series of salts, C 1V H 17 O 11 M / 
 and CuHuQuM'g, would appear to militate. 
 
 The magnesium salt, which is the principal constituent 
 of purree, is C ]9 H 16 O n Mg, 5H 2 0. 
 
ORGANIC PIGMENTS. 275 
 
 Indian yellow was formerly believed by some (Stenhouse, 
 for example) to be of vegetable origin, but this view is evi- 
 dently erroneous, as its pla*ce of manufacture, Monghyr, in 
 Bengal Province, is known. We believe that the peculiar 
 feeding which results in the formation of this colour is not 
 for the benefit of the cows used, and that they do not survive 
 the treatment for long, unless occasionally put off the mango 
 feed. 
 
 Indian yellow is only used for water colour. 
 
 Bitumen, Asphaltum, Mummy. 
 
 Asphaltum or bitumen was originally obtained from the 
 neighbourhood of the Dead Sea, and is a kind of pitch similar 
 to that now obtained in great quantity from the great pitch 
 lake, Trinidad. From its nature it can only be used in oil 
 painting. It is a blackish-brown which both darkens in colour 
 and cracks on the painted surface. It is, therefore, though 
 once used to a considerable extent, an unsuitable pigment for 
 permanent work. Much of the pitch used for black tar, 
 varnishes and japans is now obtained from coal tar, being 
 the residue left in the retort after the distillation of this sub- 
 stance. According to the extent to which the distillation is 
 carried it is known as " hard " or " soft " pitch, and for pro- 
 tective work is usually dissolved in light oils which soon 
 evaporate and leave a black glossy surface. 
 
 Mummy is a bituminous product associated with animal 
 remains and derives its rather gruesome name from its source, 
 the bituminous matter having been used in the process of em- 
 balming, and probably altered somewhat in character through 
 lapse of time. It is used in oil by artists and is less liable to 
 change than asphaltum. It has probably, in keeping so long, 
 reached its limits of change. 
 
INDEX. 
 
 ABNEY'S, Sir W., experiments, 27, 
 
 31. 
 Alizarin, 16, 207, 211, 212. 
 
 - lakes, 211. 
 Alkannin, 235. 
 Amplitude of waves, 2. 
 Anchusic acid, 234. 
 Anthrapurpurin, 213. 
 Arsenic greens, 157. 
 
 - sulphides, 179. 
 
 - yellows, 179. 
 Asphaltum, 275. 
 Aureolin, 28, 153. 
 Aureosin, 256. 
 Azines, 248. 
 
 Azo compounds, 250. 
 Azorubine, 15. 
 
 B. 
 
 BARIUM sulphate, 99. 
 Barytes, 99. 
 Bistre, 176. 
 Bitumen, 275. 
 Black, ivory, 45, 174. 
 
 - lamp, 175. 
 Blanc fixe, 99. 
 Blue, alizarin, 216. 
 
 aniline, 261. 
 
 Antwerp, 32. 
 
 - Celestial, 44, 45, 192. 
 
 - Chinese, 45. 
 
 - copper, 163. 
 
 diphenylamine, 261. 
 
 indigo, 262. 
 
 - Prussian, 28, 32, 144, 182. 
 
 - ultramarine, 164. 
 Brazilein, 232. 
 Brazilin, 232. 
 Brown, Cappagh, 140. 
 
 Prussian, 144. 
 
 Brown, purple, 141. 
 - Vandyck, 32, 44, 180. 
 
 C. 
 
 CARBON pigments, 173. 
 Cardinal, 252. 
 Carmine, 28, 32. 
 
 lake, 32, 197, 210. 
 Chocolate, 141. 
 Chromates, 116. 
 
 - analysis of, 123. 
 Chrome yellow, 32. 
 Chromium oxide, 32, 113. 
 Chrysoidine, 252. 
 Cobalt, 32. 
 
 - brown, 149. 
 
 - colours, 147. 
 
 oxide, 148. 
 
 - pink, 149. 
 
 - silicates, 151. 
 Coerulein, 259. 
 Coeruleum, 349. 
 Coloured bodies, 1, 9. 
 Colours, oil, 61. 
 
 - primary and complementary, 8. 
 
 water, 53. 
 Copper pigments, 153. 
 Crimson lakes, 28, 32, 203. 
 Crocein, 253. 
 
 D. 
 
 DlCHROISM, 11. 
 
 Diorcellinic acid, 238. 
 Dispersion, irrationality of, 6. 
 
 E. 
 
 ENAMELS, 68, 71. 
 Encaustic painting, 60. 
 Eosin, 16, 254. 
 Erythrin, 237, 238. 
 
278 
 
 INDEX. 
 
 Erythrol, 237. 
 Erythrosin, 256. 
 Eurhodines, 249. 
 Euxanthic acid, 274. 
 Euxanthone, 274. 
 
 F. 
 
 FACTORY Act, as applied to white 
 
 lead, 82. 
 
 Flavopurpurin, 214. 
 Frauenhofer's lines, 3, 4. 
 Fresco painting, 56. 
 Fuchsia, 249. 
 Fuchsine, 13. 
 
 GK 
 
 GALLEIN, 261. 
 
 Gamboge, 28, 270. 
 
 Garancin, 206. 
 
 Giallolino, 177. 
 
 Glass, stained and painted, 72. 
 
 Green, acid, 16, 259. 
 
 arsenical, 157. 
 
 - bice, 154. 
 
 - Bremen, 155. 
 
 - Brunswick, 45, 126, 162. 
 
 - copper, 153. 
 
 emerald, 32, 157. 
 
 - ethyl, 259. 
 
 - Guignet's, 114. 
 
 - iodine, 259. 
 
 malachite, 259. 
 
 - methyl, 258. 
 
 Mittler's, 114. 
 
 - mountain, 154. 
 
 - Paris, 157. 
 
 - sap, 231. 
 
 Scheele's, 157. 
 
 - Schweinfurt, 157. 
 
 - verdigris, 160. 
 Grenadin, 245. 
 
 HJSMATIN, 219. 
 Hsematoxylin, 217. 
 
 I. 
 
 INDIAN red, 28, 32, 44, 133. 
 Indican, 265. 
 
 Indigo, 17, 32, 262. 
 
 - purple, 265. 
 
 - white, 264. 
 Indigotin, 263. 
 
 Iron oxide pigments, 128. 
 - analysis of, 145. 
 Isorubin, 244. 
 
 K. 
 
 KERAMIC art, 66. 
 
 LACCAINIC acid, 205. 
 Lakes, alizarin, 211. 257. 
 
 - alkanet, 210, 234. 
 
 - archil, 210, 237. 
 
 artificial, 242. 
 
 - azine, 248. 
 azo, 250. 
 
 i blue, 258. 
 
 Brazil wood, 209, 232. 
 
 - Campeachy, 210, 217. 
 
 - carmine, 32, 197, 210. 
 
 coal tar, 239. 
 
 - cochineal, 196. 
 
 - crimson, 28, 32, 203. 
 
 - eosin, 254. 
 
 - eurhodine, 249. 
 
 - green, 256. 
 
 lac dye, 205. 
 
 - logwood, 210, 217. 
 
 - madder, 32, 206. 
 
 - magenta^ 245. 
 
 natural, 194. 
 
 orange, 257. 
 
 - orchil, 210, 237. 
 
 - quercitron, 221. 
 
 - red, 242. 
 
 - rhamnus, 225. 
 
 - rhodamine, 246. 
 
 - safranine, 248. 
 
 - scarlet, 32, 206. 
 
 - Venice, 210. 
 
 - violet, 261. 
 
 - yellow, 257. 
 
 Laurie, A. P., on white lead, 78. 
 
 Laws of refraction, 9. 
 
 Lead chromates, 116, 117, 119. 
 
 - orange, 40, 43, 119. 
 
 red, 40, 43, 100. 
 
 white, 41, 43, 77. 
 
INDEX. 
 
 279 
 
 Light, diffused, 10. 
 
 - nature of, 1. 
 
 - synthesis of, 7. 
 
 - white, 2. 
 Litharge, 102. 
 Lithopone, 41, 43. 
 Lokao, 231. 
 
 M. 
 
 MAGENTA, 243. . 
 
 - new, 244. 
 Malachite, 154. 
 Mandarin, 157. 
 Maroon, 245. 
 Mars colours, 143. 
 Massicot, 102. 
 Mercuric chromate, 123. 
 
 - iodide, 112. 
 Methyl green, 258. 
 Minium, 100. 
 Mosaic, 76. 
 Mummy, 275. 
 
 N. 
 NAPLES yellow, 176. 
 
 0. 
 
 OCHRES, 128. 
 
 - red, 132. 
 
 - yellow, 32, 129. 
 Opaque bodies, 9. 
 Orange eosin, 256. 
 
 - lead, 40, 43, 119. 
 Orcellinic acid, 238. 
 Orcinol, 238. 
 Orpiment, 179. 
 
 P. 
 
 PAINTS, antifouling, 37. 
 Pastels, crayon, 49, 50. 
 Persian berries, 226, 230. 
 Phloxin, 256. 
 Picroerythrin, 238. 
 Pigments, application of, 18, 49. 
 
 - artistic uses of, 18 et seq. 
 
 - decorative uses of, 34 et seq. 
 
 - protective uses of, 36 et seq. 
 Powders, coloured, 12. 
 Purple, French, 239. 
 
 - indigo, 265. 
 
 Purple, oxide, 141. 
 Purpurin, 213. 
 Purree, 273. 
 
 Q. 
 
 QUERCETIN, 223, 226, 227, 228 229 
 Quercitrin, 222. 
 
 R. 
 
 RAYS, chemical, 5 
 
 - heat, 5. 
 
 light, 5. 
 
 - transmitted, 11. 
 Realgar, 179. 
 
 Red, Indian, 28, 32, 44, 133 
 
 - light, 139. 
 
 Magdala, 249. 
 
 oxide, 141. 
 
 - scarlet, 40, 43. 
 
 - Venetian, 28, 32, 133. 
 fthaminose, 226. 
 fthamnazin, 227, 229. 
 3-hamnegin, 227. 
 ilhamnetin, 227, 229. 
 ilhamnose, 230. 
 Ihodamine, 243, 246. 
 losaniline, 230. 
 
 Russell, Dr. (see Abney). 
 
 SAFRANINES, 248. 
 antaline, 209. 
 ap green, 231. 
 carlet, Biebrich, 254. 
 
 - naphthalene, 249. 
 
 - R., 15. 
 
 - royal, 112. 
 epia, 28, 272. 
 iennas, 134. 
 
 - burnt, 32, 46, 136. 
 
 - raw, 32, 135. 
 ilver chromate, 122. 
 maltine, 151. 
 
 mith, H., experiments on paints, 
 
 38. 
 
 pectra absorption, 14. 
 ^ectral colours, simple nature 
 
 of, 7. 
 pectrum, 2, 6. 
 
 - invisible, 4. 
 normal, 5, 6. 
 
280 
 
 INDEX. 
 
 T. 
 
 TARTRAZINE, 16, 258. 
 Tempera painting, 55. 
 Terra verte, 32, 143. 
 Thioflavine, 258. 
 Transparent bodies, 9. 
 Triphenyl - methane derivatives, 
 243. 
 
 U. 
 
 ULTRAMARINE, 32, 46, 164. 
 Umbers, 134. 
 
 burnt, 32, 138. 
 
 - raw, 137. 
 
 - Turkey, 45, 137. 
 
 V. 
 
 VANDYCK brown, 32, 180. 
 Varnishes, asphaltic, 37. 
 
 oil, 37. 
 
 Venetian red, 28, 32, 133. 
 Verdigris, 160. 
 
 Vermilion, 28, 32, 103. 
 Vermilionette, 40, 43, 108, 112. 
 Violet, methyl, 17. 
 Vividian, 114. 
 
 W. 
 
 WATER colours, action of light 
 
 27, 31. 
 
 Wave length, 2. 
 White, enamel, 99. 
 Whitening, 99. 
 
 XANTHORHAMNIN, 228. 
 Y. 
 
 YELLOW, cadmium, 180. 
 
 Indian, 273. 
 
 Naples, 176. 
 
 ochre, 32, 129. 
 - royal, 179. 
 
 Turner's, 177. 
 
 THE ABERDEEN UNIVERSITY PRESS LIMITED. 
 
SEPTEMBER, 1901. 
 This Catalogue cancels all former editions. 
 
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 By AN EXPERT OIL REFINER. 100pp. 1898. DemySvo. Price 7s. 6d. ; 
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 IV., Perfumes. V., Water as a Soap Material. VI., Soap Machinery. VII., Tech- 
 nology of Soap = making. VIII., Glycerine in Soap Lyes. IX., Laying out a Soap 
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 ANIMAL PATS AND OILS: Their Practical Production, 
 Purification and Uses for a great Variety of Purposes. Their Pro- 
 perties, Falsification and Examination. A Handbook for Manufacturers 
 of Oil and Fat Products, Soap and Candle Makers, Agriculturists, 
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 Contents. 
 
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 Preparation of Animal Fats and Oils. Machinery. Tallow-melting Plant. Extraction Plant. 
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 VEGETABLE FATS AND OILS : Their Practical Prepara- 
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 ties, Adulteration and Examination. A Handbook for Oil Manufacturers 
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 CORROSIVE PAINTS. By Louis EDGAR ANDES. 62 Illus- 
 trations. 275pp. Translated from the German. DemySvo. 1900. Price 
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 Ironrust and its Formation Protection from Rusting by Paint Grounding the Iron with 
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 THE MANUFACTURE OF ALUM AND THE SUL- 
 PHATES AND OTHER SALTS OF ALUMINA AND 
 IRON. Their Uses and Applications as Mordants in Dyeing 
 and Calico Printing, and their other Applications in the Arts, Manufac- 
 tures, Sanitary Engineering, Agriculture and Horticulture. Translated 
 from the French of LUCIEN GESCHWIND. 195 Illustrations. Nearly 
 400 pp. Royal 8vo. 1901. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; 
 Other Countries, 15s. ; strictly net. 
 
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 Aluminium Sulphate and Alums Application to Wool and Silk Preparing and using Aluminium 
 Acetates Employment of Aluminium Sulphate in Carbonising Wool The Manufacture of 
 Lake Pigments Manufacture of Prussian Blue Hide and Leather Industry Paper Making 
 Hardening Plaster Lime Washes Preparation of Non-inflammable Wood, etc. Purifica- 
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 Analytical Characteristics of Iron Salts Analysis of Pyritic Lignite Ferrous and Ferric 
 Sulphates Rouil Mordant Index. 
 
 MANUAL OF AGRICULTURAL CHEMISTRY. By 
 
 HERBERT INGLE, F.I.C., Lecturer on Agricultural Chemistry, the 
 Yorkshire College; Lecturer in the Victoria University. [In the press. 
 Contents. 
 
 Chapters I., Introduction. II., The Atmosphere. III., The Soil. IV., The Reactions 
 occurring in Soils. V., The Analysis of Soils. VI., Manures, Natural. VII., Manures (con- 
 tinued). VIII., The Analysis of Manures. IX., The Constituents of Plants. X., The Plant. 
 XL, Crops. XII., The Animal. 
 
 LUBRICATING OILS, PATS AND GREASES: Their 
 
 Origin, Preparation, Properties, Uses and Analyses. A Handbook for 
 Oil Manufacturers, Refiners and Merchants, and the Oil and Fat 
 Industry in General. By GEORGE H. HURST, F.C.S. Second Edition. 
 Sixty-five Illustrations. 313 pp. Demy 8vo. 1901. Price 10s. 6d. ; 
 India and Colonies, lls. ; Other Countries, 12s. ; strictly net. 
 Contents. 
 
 i Chapters I., Introductory. Oils and Fats, Fatty Oils and Fats, Hydrocarbon Oils, Uses 
 of Oils. II., Hydrocarbon Oils. Distillation, Simple Distillation, Destructive Distillation, 
 Products of Distillation, Hydrocarbons, Paraffins, Olefins, Napthenes. III., Scotch Shale 
 Oils. Scotch Shales, Distillation of Scotch Oils, Shale Retorts, Products of Distilling Shales 
 
Separating Products, Treating Crude Shale Oil, Refining Shale Oil, Shale Oil Stills, Shale 
 Naphtha Burning Oils, Lubricating Oils, Wax. IV., Petroleum. Occurrence, Geology, Origin, 
 Composition, Extraction, Refining, Petroleum Stills, Petroleum Products, Cylinder Oils, 
 Russian Petroleum, Deblooming Mineral Oils. V., Vegetable and Animal Oils. Intro- 
 duction, Chemical Composition of Oils and Fats, Fatty Acids, Glycerine, Extraction of Animal 
 and Vegetable Fats and Oils, Animal Oils, Vegetable Oils, Rendering, Pressing, Refining, 
 Bleaching, Tallow, Tallow Oil, Lard Oil, Ne"atsfoot Oil, Palm Oil, Palm Nut Oil, Cocoanut 
 Oil, Castor Oil, Olive Oil, Rape and Colza Oils, Arachis Oil, Niger Seed Oil, Sperm Oils, 
 Whale Oil, Seal Oil, Brown Oils, Lardine, Thickened Rape Oil. VI., Testing and Adultera- 
 tion Of Oils. Specific Gravity, Alkali Tests, Sulphuric Acid Tests, Free Acids in Oils, Vis- 
 cosity Tests, Flash and Fire Tests, Evaporation Tests, Iodine and Bromide Tests, Elaidin 
 Test, Melting Point of Fat, Testing Machines. VII., Lubricating Greases. Rosin Oil, 
 Anthracene Oil, Making Greases, Testing and Analysis of Greases. VIII., Lubrication. 
 Friction and Lubrication, Lubricant, Lubrication of Ordinary Machinery, Spontaneous Com- 
 bustion of Oils, Stainless Oils, Lubrication of Engine Cylinders, Cylinder Oils. Appendices. 
 A. Table of Baume's Hydrometer B. Table of Thermometric Degrees C. Table of Specific 
 Gravities of Oils Index. 
 
 Press Opinions. 
 
 " The book is well printed, and is a credit alike to author, printer and publisher." Textile 
 Mercury. 
 
 " It will be a valuable addition to the technical library of every steam user's establishment." 
 Machinery Market. 
 
 " Mr. Hurst has in this work supplied a practical treatise which should prove of especial 
 value to oil dealers, and also, though in a less degree, to oil users." Textile Manufacturer. 
 
 " This is a clear and concise treatment of the method of manufacturing and refining lubri- 
 cating oils. . . . The book is one which is well worthy the attention of readers who are users 
 of oil." Textile Recorder. 
 
 " We have no hesitation in saying that in our opinion this book ought to be very useful to 
 all those who are interested in oils, whether as manufacturers or users of lubricants, or to 
 those chemists or engineers whose duty it may be to report upon the suitability of the same 
 for any particular class of work." Engineer. 
 
 " The author is widely known and highly respected as an authority on the chemistry of oils 
 and the technics of lubrication, and it is safe to say that no work of similar interest or equal 
 value to the general oil-selling and consuming public has heretofore appeared in the English 
 language." Drugs, Oils and Paints, U.S.A. 
 
 41 This valuable and useful work, which is both scientific and practical, has been written 
 with a view of supplying those who deal in and use oils, etc., for the purpose of lubrication, 
 with some information respecting the special properties of the various products which cause 
 these various oils to be of value as lubricants." Industries and Iron. 
 
 " A mere glance at the table of contents is sufficient to show how various are the conditions 
 to which these materials have to be applied, how much knowledge is required for the selection 
 of the right kind for each particular purpose, and how by processes of mixture or manufacture 
 the requisite qualities are obtained in each case." Manchester Guardian. 
 
 AMMONIA AND ITS COMPOUNDS : Their Manufacture 
 and Uses. By CAMILLE VINCENT, Professor at the Central School of 
 Arts and Manufactures, Paris. Translated from the French by M. J. 
 SALTER. Royal 8vo. 113pp. 1901. Thirty-two Illustrations. Price 
 5s. ; India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Chapters I., General Considerations: Sections 1. Various Sources of Ammoniacal 
 Products; 2. Human Urine as a Source of Ammonia. II., Extraction of Ammoniacal 
 Products from Sewage: Sections 1. Preliminary Treatment of Excreta in the Settling 
 Tanks The Lencauchez Process, The Bilange Process, The Kuentz Process ; 2. Treatment of 
 the Clarified Liquors for the Manufacture of Ammonium Sulphate The Figuera Process and 
 Apparatus, Apparatus of Margueritte and Sourdeval, The Lair Apparatus, Apparatus of Sintier 
 and Muh, Apparatus of Bilange, The Kuentz Process, Process and Apparatus of Hennebutte 
 and De Vaureal; 3. Treatment of Entire Sewage Chevalet's Apparatus, Paul Mallet's 
 Apparatus, Lencauchez's Apparatus. III., Extraction of Ammonia from Gas Liquor: 
 Sections 1. Clarification of Gas Liquor; 2. Manufacture of Ammonium Sulphate A. Mallet's 
 Apparatus, A. Mallet's Modified Apparatus, Paul Mallet's Apparatus, Chevalet's Apparatus, 
 Griineberg's Apparatus ; 3. Concentration of Gas Liquor Solvay's Apparatus, Kuentz's 
 Apparatus, Griineberg's Apparatus. IV., Manufacture of Ammoniacal Compounds from 
 Bones, Nitrogenous Waste, Beetroot Wash and Peat: Sections 1. Ammonia from Bones; 
 2. Ammonia from Nitrogenous Waste Materials; 3. Ammonia from Beetroot Wash (Vinasse); 
 4. Ammonia from Peat Treatment of the Ammoniacal Liquors. V., Manufacture of 
 Caustic Ammonia, and Ammonium Chloride, Phosphate and Carbonate: Sections 1. 
 Manufacture of Caustic Ammonia; 2. Manufacture of Ammonium Chloride From Fermented 
 Urine, Process of the Lesage Company, Kuentz's Process ; From Gas Liquor, English Process, 
 Kuentz's Process; From the Dry Distillation of Animal Matter; From Ammonium Sulphate, 
 Sublimation ; 3. Ammonium Phosphates; 4. Carbonates of Ammonium Sesquicarbonate from 
 Animal Matter, English Process, Uses. VI., Recovery of Ammonia from the Ammonia- 
 Soda Mother Liquors : Sections 1. General Considerations; 2. Apparatus of Schloesing and 
 Holland ; 3. Apparatus of the Societd Anonyme de 1'Est. Index. 
 
6 
 
 THE MANUFACTURE OF VARNISHES, OIL RE- 
 FINING AND BOILING, AND KINDRED INDUS- 
 TRIES. Describing the Manufacture of Spirit Varnishes 
 and Oil Varnishes ; Raw Materials : Resins, Solvents and Colouring 
 Principles ; Drying Oils : their Properties, Applications and Prepara- 
 tion by both Hot and Cold Processes ; Manufacture, Employment and 
 Testing of Different Varnishes. Translated from the French of ACH. 
 LIVACHE, Ingenieur Civil des Mines. Greatly Extended and Adapted 
 to English Practice, with numerous Original Recipes. By JOHN 
 GEDDES MC!NTOSH, Lecturer on Oils, Colours and Varnishes, Regent 
 Street Polytechnic. Twenty-seven Illustrations. 400 pp. Demy 8vo. 
 1899. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other Countries, 
 15s.; strictly net. 
 
 Contents. 
 
 I. Resins : Gum Resins, Oleo Resins and Balsams, Commercial Varieties, Source, Collec- 
 tion, Characteristics, Chemical Properties, Physical Properties, Hardness, Adulterations. 
 Appropriate Solvents, Special Treatment, Special Use. II. Solvents: Natural, Artificial, 
 Manufacture, Storage, Special Use. III. Colouring : Principles, (1) Vegetable, (2) Coal Tar, 
 (3) Coloured Resinates, (4) Coloured Oleates and Linoleates. Gum Running : (Furnace*, 
 Bridges, Flues, Chimney Shafts, Melting Pots, Condensers, Boiling or Mixing Pans, Copper 
 Vessels, Iron Vessels (Cast), Iron Vessels (Wrought), Iron Vessels (Silvered), Iron Vessels 
 Enamelled), Steam Superheated Plant, Hot-air Plant. Spirit Varnish Manufacture: Cold 
 Solution Plant, Mechanical Agitators, Hot Solution Plant, Jacketted Pans, Mechanical 
 \gitators, Clarification and Filtration, Bleaching Plant, Storage Plant. Manufacture, Char- 
 acteristics and Uses of the Spirit Varnishes yielded by : Amber, Copal, Dammar, Shellac, 
 Mastic, Sandarac, Rosin, Asphalt, India Rubber, Gutta Percha, Collodion, Celluloid, Resin- 
 ates, Oleates. Manufacture of Varnish Stains. Manufacture of Lacquers. Manufacture of 
 Spirit Enamels. Analysis of Spirit Varnishes. Physical and Chemical Constants of Resins. 
 Table of Solubility of Resins in different Menstrua. Systematic qualitative Analysis of 
 Resins, Hirschop's tables. Drying Oils : Oil Crushing Plant, Oil Extraction Plant, Individual 
 Oils, Special Treatment of Linseed Oil, Poppyseed Oil, Walnut Oil, Hempseed Oil, Llamantia 
 Oil, Japanese Wood Oil, Gurjun Balsam, Climatic Influence on Seed and Oil. Oil Refining : 
 Processes, Thenard's, Liebig's, Filtration, Storage, Old Tanked Oil. Oil Boiling : Fire Boil- 
 ng Plant, Steam Boiling Plant, Hot-Air Plant, Air Pumps, Mechanical Agitators, Vincent's 
 Process, Hadfield's Patent, Storer's Patent, Walton's Processes, Continental Processes, Pale 
 Boiled Oil, Double Boiled Oil, Hartley and Blenkinsop's Process. Driers : Manufacture, 
 Special Individual Use of (1) Litharge, (2) Sugar of Lead, (3) Red Lead, (4) Lead Borate, 
 (S) Lead Linoleate, (6) Lead Resinate, (7) Black Oxide of Manganese, (8) Manganese Acetate, 
 (9) Manganese Borate, (10) Manganese Resinate, (11) Manganese Linoleate, Mixed Resinates 
 and Linoleates, Manganese and Lead, Zinc Sulphate, Terebine, Liquid Driers. Solidified 
 Boiled Oil. Manufacture of Linoleum. Manufacture of India Rubber Substitutes. Printing 
 Ink Manufacture Lithographic Ink Manufacture. Manufacture of Oil Varnishes. Running 
 and Special Treatment of Amber, Copal, Kauri, Manilla. Addition of Oil to Resin. Addition 
 of Resin to Oil. Mixed Processes. Solution in Cold of previously Fused Resin. Dissolving 
 Resins in Oil, etc., under pressure. Filtration. Clarification. Storage. Ageing. Coach- 
 makers' Varnishes and Japans. Oak Varnishes. Japanners' Stoving Varnishes. Japanners' 
 Gold Size. Brunswick Black. Various Oil Varnishes. Oil-Varnish Stains. Varnishes for 
 " Enamels ". India Rubber Varnishes. Varnishes Analysis : Processes, Matching. Faults in 
 Varnishes: Cause, Prevention. Experiments and Exercises. 
 
 Press Opinions. 
 
 " There is no question that this is a useful book." Chemist and Druggist. 
 'The different formulae which are quoted appear to be fap more 'practical' than such as 
 
 the 
 
 are usually to be found in text-books ; and assuming that the original was published two or 
 three years ago, and was only slightly behindhand in its information, the present volume gives 
 a fair insight into the position of the varnish industry." The Ironmonger. 
 
 
 
 Letter from the Teacher of a Technical Class. 
 
 "As a teacher I have often been consulted as to the best work on Varnish Manufacture 
 and kindred industries, and have been at a loss in recommending a really practical one. It is 
 therefore with pleasure that I can now testify as to the merits of the book on these subjects 
 by A. Livache and J. G. Mclntosh recently published by Messrs. Scott, Greenwood & Co. In 
 my opinion no varnish maker ought to be without it ; moreover, it is the best text-book that 
 could be put into the hands of trade students or beginners. It has also the merits of being 
 thoroughly up-to-date and of possessing a remarkably comprehensive index. I can conscien- 
 tiously recommend it to my students and trade friends." CHARLES HARRISON, Lecturer on 
 the Manufacture of Painters' Oils, Colours and Varnishes, Borough Polytechnic, Borough 
 Road, S.E. 
 
 "Bird May. 1899" 
 
THE MANUFACTURE OF LAKE PIGMENTS FROM 
 ARTIFICIAL COLOURS. By FRANCIS H. JENNISON, 
 F.I.C., F.C.S. Sixteen Coloured Plates, showing Specimens of 
 Eighty-nine Colours, specially prepared from the Recipes given 
 in the Book. 136 pp. Demy 8vo. 1900. Price 7s. 6d. ; India and 
 Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Chapters I., Introduction. II., The Groups of the Artificial Colouring Matters. III., The 
 Nature and Manipulation of Artificial Colours. IV., Lake-forming Bodies for Acid Colours. 
 V., Lake-forming Bodies' Basic Colours. VI., Lake Bases. VII., The Principles of Lake 
 Formation. VIII., Red Lakes. IX., Orange, Yellow, Green, Blue, Violet and Black Lakes. 
 X., The Production of Insoluble Azo Colours in the Form of Pigments. XL, The General 
 Properties of Lakes Produced from Artificial Colours. XII., Washing, Filtering and Fin- 
 ishing. XIII, , Matching and Testing Lake Pigments. Index. 
 
 Press Opinions. 
 
 " It is evidently the result of prolonged research, and cannot but prove a valuable con- 
 sulting work to those engaged in the industry." Derby Mercury. 
 
 " The practical portion of the volume is the one which will especially commend itself, as 
 that is the part of the subject which most readers would buy the book for." Chemist and 
 Druggist. 
 
 "This work just issued is a very valuable treatise on the manufacture of lake pigments of 
 the coal-tar series principally. The plan adopted by the author in writing up the subject 
 enables the manufacture to be very readily understood. . . . The general properties of lakes 
 produced from artificial colours, washing, filtering and finishing, and matching and testing 
 lake pigments are well and exhaustively described, so that no manufacturer or user of lake 
 pigments can well afford to be without this work." Chemical Trade Journal. 
 
 "This is undoubtedly a book which will occupy a very high place amongst technical works, 
 and will prove of exceptional value to all whom it immediately concerns. We have no 
 hesitation in reeommending it as one of the best works of its class we have ever read. Mr. 
 Jennison has set about his task with a lucid style, and with a complete mastery of his subject. 
 . . We do not think students of the technical side of the paint and colour industry can 
 possibly spend 7s. 6d. in a more profitable way than by buying this publication." Eastern 
 Morning News. 
 
 THE TESTING AND VALUATION OF RAW MATE- 
 RIALS USED IN PAINT AND COLOUR MANU- 
 FACTURE. By M. W. JONES, F.C.S. A Book lor the 
 Laboratories of Colour Works. 88 pp. Crown 8vo. 1900. Price 5s. ; 
 India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Aluminium Compounds. China Clay. Iron Compounds. Potassium Compounds. Sodium 
 Compounds. Ammonium Hydrate. Acids. Chromium Compounds. Tin Compounds. Cop- 
 per Compounds. Lead Compounds. Zinc Compounds. Manganese Compounds. Arsenic 
 Compounds. Antimony Compounds. Calcium Compounds. Barium Compounds. Cadmium 
 Compounds. Mercury Compounds. Ultramarine. Cobalt and Carbon Compounds. Oils 
 Index. 
 
 Press Opinions. 
 
 "Though this excellent little work can appeal only to a limited class, the chemists in colour 
 works, yet it will appeal to them very strongly indeed, for it will put them on the track of 
 short, rapid, and yet approximately, accurate methods of testing the comparative value of 
 competing samples of raw material used in paint and colour manufacture." North British 
 Daily Mail. 
 
 "This little text-book is intended to supplement the larger and more comprehensive works 
 on the subject, and it embodies the result of Mr. Jones' experiments and experiences, extend- 
 ng over a long period. It gives, under separate headings, the principal ingredients and im- 
 purities found in the raw materials, and is a handy work of reference for ascertaining what is 
 valuable or detrimental in the sample under examination." Blackburn Times. 
 
 "There is no attempt at literary adornment nor straining after literary effect, but the 
 lessons are imparted in simple and concise language. This is just what a text-book should 
 be. ... The treatise is certainly most useful, and bears internal evidence of being the results 
 of actual work in a busy manufactory and not of ephemeral cramming in a technical school. 
 The chapter arrangement is good, the index satisfactory, and the book is altogether one which 
 the practical chemist should keep as accessible to his crucibles and filter paper." Manchester 
 Courier. 
 
 C 
 
8 
 
 THE CHEMISTRY OF ESSENTIAL OILS AND ARTI- 
 FICIAL PERFUMES. By ERNEST J. PARRY, B.Sc. 
 (Lond.), F.I.C., F.C.S. Illustrated with Twenty Engravings. 400 pp. 
 1899. Demy 8vo. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other 
 Countries, 15s. ; strictly net. 
 
 Contents. 
 
 Chapters I., The General Properties of Essential Oils. II., Compounds occurring 
 in Essential Oils. III., The Preparation of Essential Oils. IV., The Analysis of 
 Essential Oils. V., Systematic Study of the Essential Oils. VI.. Terpeneless Oils. 
 VII., The Chemistry of Artificial Perfumes. Appendix : Table of Constants. 
 Press Opinions. 
 
 "There can be no doubt that the publication will take a high place in the list of scientific 
 text-books." London Argus 
 
 "We can heartily recommend this volume to all interested in the subject of essential oils 
 from the scientific or the commercial standpoint." British and Colonial Druggist, 
 
 " Mr. Parry has done good service in carefully collecting and marshalling the results of the 
 numerous researches published in various parts of the world." Pharmaceutical Journal. 
 
 " At various times monographs have been printed by individual workers, but it may safely 
 be said that Mr. Parry is the first in these latter days to deal with the subject in an adequate 
 manner. His book is well conceived and well written. . . . He is known to have sound practi- 
 cal experience in analytical methods, and he has apparently taken pains to make himself aufait 
 with the commercial aspects of the subject." Chemist and Druggist, 
 
 " Mr. Parry's reputation as a scientist is fully established, and we can therefore accept any 
 work emanating from his pen as being of the greatest practical value. We have perused the 
 work before us with much care, and are convinced that the contents will be found most service- 
 able and its publication most opportune. . . . He avoids unnecessary details, but includes 
 everything that is essential to systematic treatment, while he attempts no more ' than to give 
 an outline of the principles involved '. . . . We congratulate Mr. Parry on the scientific value 
 of his work, and hope that if the progress of the colonies in the manufacture of essential oils 
 and perfumes equals what we are justified in expecting, it will become an Australian hand-book, 
 everywhere appreciated." The Australian B reivers' Journal. 
 
 DRYING OILS, BOILED OIL AND SOLID AND 
 LIQUID DRIERS. By L. E. ANDES. A Practical Work 
 for Manufacturers of Oils, Varnishes, Printing Inks, Oilcloth and Lino- 
 leum, Oilcakes, Paints, etc. Expressly Written for this Series of Special 
 Technical Books, and the Publishers hold the Copyright for English and 
 Foreign Editions. Forty-two Illustrations. 360pp. 1901. Demy 8vo. 
 Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other Countries, 15s. ; 
 strictly net. 
 
 Contents. 
 
 Chapters I., General Chemical and Physical Properties of the Drying Oils ; Cause of the 
 Drying Property; Absorption of Oxygen; Behaviour towards Metallic Oxides, etc. II., The 
 Properties of and Methods for obtaining the Drying Oils. III., Production of the Drying Oils 
 by Expression and Extraction ; Refining and Bleaching ; Oil Cakes and Meal ; The Refining 
 and Bleaching of the Drying Oils; The Bleaching of Linseed Oil. IV., The Manufacture of 
 Boiled Oil ; The Preparation of Drying Oils for Use in the Grinding of Paints and Artists' 
 Colours and in the Manufacture of Varnishes by Heating over a Fire or by Steam, by the Cold 
 Process, by the Action of Air, and by Means of the Electric Current; The Driers used in 
 Boiling Linseed Oil; The Manufacture of Boiled Oil and the Apparatus therefor ; Livache's 
 Process for Preparing a Good Drying Oil and its Practical Application. V., The Preparation 
 of Varnishes for Letterpress, Lithographic and Copperplate Printing, for Oilcloth and Water- 
 proof Fabrics : The Manufacture of Thickened Linseed Oil, Burnt Oil, Stand Oil by Fire Heat, 
 Superheated Steam, and by a Current of Air. VI., Behaviour of the Drying Oils and Boiled 
 Oils towards Atmospheric Influences, Water, Acids and Alkalies. VII., Boiled Oil Substitutes. 
 VIII., The Manufacture of Solid and Liquid Driers from Linseed Oil and Rosin; Linolic 
 Acid Compounds of the Driers. IX., The Adulteration and Examination of the Drying Oils 
 and Boiled Oil. 
 
 REISSUE OF CHEMICAL ESSAYS OF C. W. 
 SCHEELE. First Published in English in 1786. Trans- 
 lated from the Academy of Sciences at Stockholm, with Additions. 300 
 pp. Demy 8vo. 1901. Price 5s. ; India and Colonies, 5s. 6d. ; Other 
 Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Memoir: C. W. Scheele and his work (written for this edition). Chapters I., On Fluor 
 Mineral and its Acid. II., On Fluor Mineral. III., Chemical Investigation of Fluor Acid, 
 with a View to the Earth which it Yields, by Mr. Wiegler. IV., Additional Information 
 Concerning Fluor Minerals. V., On Manganese, Magnesium, or Magnesia Vitrariorum. 
 VI., On Arsenic and its Acid. VII., Remarks upon Salts of Benzoin VIII., On Silex, 
 Clay and Alum. IX., Analysis of the Calculus Vesical. X., Method of Preparing Mercurius 
 
Dulcis Via Humida. XI., Cheaper and more Convenient Method of Preparing Pulvis 
 Algarothi. XII., Experiments upon Molybdaena. XIII., Experiments on Plumbago. XIV., 
 Method of Preparing a New Green Colour. XV., Of the Decomposition of Neutral Salts by 
 Unslaked Lime and Iron. XVI., On the Quantity of Pure Air which is Daily Present in our 
 Atmosphere. XVII., On Milk and its Acid. XVIII., On the Acid of Saccharum Lactis. 
 XIX., On the Constituent Parts of Lapis Ponderosus or Tungsten. XX., Experiments and 
 Observations on Ether. 
 
 GLUE AND GLUE TESTING. By SAMUEL RIDEAL, D.Sc. 
 Lond., F.I.C. Fourteen Engravings. 144pp. Demy 8vo. 1900. Price 
 10s. 6d. ; India and Colonies, 11s. ; Other Countries, 12s.; strictly net. 
 Contents. 
 
 Chapters I., Constitution and Properties: Definitions and Sources, Gelatine, Chondrin 
 and Allied Bodies, Physical and Chemical Properties, Classification, Grades and Commercial 
 
 Varieties. II., Raw Materials and Manufacture : Glue Stock, Lining, Extraction, Washing 
 and Clarifying, Filter Presses, Water Supply, Use of Alkalies, Action of Bacteria and of 
 Antiseptics, Various Processes, Cleansing, Forming, Drying, Crushing, etc., Secondary Pro- 
 
 , , , , , , ., - 
 
 ducts. III., Uses of Glue : Selection and Preparation for Use, Carpentry, Veneering, 
 Paper-Making, Bookbinding, Printing Rollers, Hectographs, Match Manufacture, Sandpaper, 
 etc., Substitutes for other Materials, Artificial Leather and Caoutchouc. IV., Gelatine : 
 General Characters, Liquid Gelatine, Photographic Uses, Size, Tanno-, Chrome and Formo- 
 Gelatine, Artificial Silk, Cements, Pneumatic Tyres, Culinary, Meat Extracts, Isinglass, Medi- 
 cinal and other Uses, Bacteriology. V., Glue Testing: Review of Processes, Chemical 
 Examination, Adulteration, Physical Tests, Valuation of Raw Materials. VI., Commercial 
 Aspects. 
 
 Press Opinions. 
 
 " This work is of the highest technical character, and gives not only a full and practical ac- 
 count of the raw materials and manufacture of glues, gelatines and similar substances, but 
 gives many hints and information on the use of such substances in veneering, carpentry and 
 many other purposes. Many tests are given for glue in different stages of the progress of its 
 manufacture, and the commercial value of a commodity so much in general use is exemplified 
 by statistics and figures. It is certainly a valuable treatise upon an article for which very 
 little literature in any form has previously been obtainable." Carpenter and Builder. 
 
 " Books on the art of glue making are more than usually scarce, and users of that article, 
 as well as those who may be tempted to embark in the industry, should therefore welcome 
 this book by Dr. Samuel Rideal, a Fellow of the Institute of Chemistry, and a leading authority. 
 In this book he has collected the more important facts connected with the manufacture of glue 
 and allied products, and stated the experience he has gained in examining various commercial 
 samples during the past ten years. . . . Dr. Rideal's book must be regarded as a valuable con- 
 tribution to other technical literature, which manufacturers, merchants and users may study 
 with profit." British Trade Journal. 
 
 "This volume is the latest addition to the excellent series of special technical works for 
 manufacturers and professional and commercial men issued by the well-known publishers of 
 The Oil and Colourman's Journal. The volume in every way fully maintains the high standard 
 of excellence of the whole series, and deals with the subject of glue making and glue testing in 
 a thoroughly exhaustive manner. Chapters are given on the constitution and properties, and 
 raw material and manufacture, and of the uses of glue, and in this latter respect it will doubtless 
 be information to many readers to learn to what extent glue enters into the manufacture of 
 many commercial products not apparently associated with glue. Exhaustive chapters on the 
 processes and methods of glue testing, and on its commercial aspects, complete this useful and 
 most carefully prepared volume." Carriage Builders' Journal. 
 
 TECHNOLOGY OF PETROLEUM : Oil Fields of the 
 World Their History, Geography and Geology Annual Production 
 and Development Oil-well Drilling Transport. By HENRY NEU- 
 BERGER and HENRY NOALHAT. Translated from the French by J. G. 
 MclNTOSH. 550pp. 153 Illustrations. 26 Plates. RoyalSvo. 1901. Price 
 21s. ; India and Colonies, 22s. ; Other Countries, 23s. 6d. ; strictly net. 
 Contents. 
 
 Part I., Study of (the Petroliferous Strata Chapters I., Petroleum Definition. II., 
 The Genesis or Origin of Petroleum. III., The Oil Fields of Galicia, their History. IV., 
 Physical Geography and Geology of the Galician Oil Fields. V., Practical Notes on Galician 
 Land Law Economic Hints on Working, etc. VI., Roumania History, Geography, Geology. 
 VII., Petroleum in Russia History. VIII., Russian Petroleum (continued) Geography and 
 Geology of the Caucasian Oil Fields. IX., Russian Petroleum (continued). -X., The Secondary 
 Oil Fields of Europe, Northern Germany, Alsace, Italy, etc. XL, Petroleum in France. XII., 
 Petroleum in Asia Transcaspian and Turkestan Territory Turkestan Persia British 
 India and Burmah British Burmah or Lower Burmah China Chinese Thibet Japan, 
 Formosa and Saghalien. XIII., Petroleum in Oceania Sumatra, Java, Borneo Isle of 
 Timor Philippine Isles New Zealand. XIV., The United States of America History. 
 XV., Physical Geology and Geography of the United States Oil Fields. XVI., Canadian and 
 other North American Oil Fields. XVII., Economic Data of Work in North America. 
 XVIIL, Petroleum in the West Indies and South America. XIX., Petroleum in the French 
 Colonies. 
 
10 
 
 Part II., Excavations. Chapter XX., Hand Excavation or Hand Digging of Oil Wells. 
 
 Part III., Methods Of Boring. Chapters XXI., Methods of Oil-well Drilling or Boring. 
 XXII., Boring Oil Wells with the Rope. XXIII.. Drilling with Rigid Rods and a Free-fall- 
 Fabian System. XXI V., Free-fall Drilling by Steam Power. XXV., Oil-well Drilling by the 
 Canadian System. XXVI., Drilling Oil Wells on the Combined System. XXVII., Com- 
 parison between the Combined Fauck System and the Canadian. XXVIII., The American 
 System of Drilling with the Rope. XXIX., Hydraulic Boring with the Drill by Hand and 
 Steam Power. XXX., Rotary Drilling of Oil Wells, Bits, Steel-crowned Tools, Diamond 
 Tools Hand Power and Steam Power Hydraulic Sand-pumping. XXXI., Improvements 
 in and different Systems of Drilling Oil Wells. 
 
 Part IV., Accidents. Chapters XXXII., Boring Accidents Methods of preventing them 
 Methods of remedying them. XXXIII., Explosives and the use of the "Torpedo" Leviga- 
 tion. XXXIV., Storing and Transport of Petroleum. XXXV., General Advice Prospecting, 
 Management and carrying on of Petroleum Boring Operations. 
 
 Part V., General Data. Customary Formulae. Memento. Practical Part. General 
 Data bearing on Petroleum. Glossary of Technical Terms used in the Petroleum Industry. 
 Copious Index. 
 
 A DICTIONARY OF CHEMICALS AND RAW PRO- 
 DUCTS USED IN THE MANUFACTURE OF 
 PAINTS, COLOURS, VARNISHES AND ALLIED 
 PREPARATIONS. By GEORGE H. HURST, F.C.S. Demy 
 8vo. 380 pp. 1901. Price 7s. 6d. ; India and Colonies, 8s.; Other 
 Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 The names of the Chemicals and Raw Products are arranged in alphabetical order, and 
 the description of each varies in length from half to eight pages. The following are some of 
 the articles described and explained : Acetates Acetic Acid Acidimetry Alcohol Alum 
 Ammonia Amber Animi Arsenic Beeswax Benzol Bichromates of Potash and Soda 
 Bleaching Powder Bone Black Boric Acid Brunswick Green Cadmium Yellow Car- 
 bonatesCarmine Carnauba Wax Caustic Potash and Soda Chrome Colours Clay Coal 
 Tar Colours Copal Dammar Drying Oils Emerald Green Gamboge Glue Glycerine 
 Gums Gypsum Indian Red Japanese Lacquer Lac Lakes Lamp Black Lead Com- 
 pounds Linseed Oil Magnesia Manganese Compounds Mica Nitric Acid Ochres 
 Orange Lead Orr's White Paraffin Prussian Blue Rosin Oil Sepia Sienna Smalts 
 Sodium Carbonate Sublimed White Lead Sulphuric Acid Terra Verte Testing Pigments 
 Turpentine Ultramarine Umbers Vermilionettes White Lead Whiting Zinc Com- 
 pounds. Appendix: Comparison of Baume Hydrometer and Specific Gravity for Liquids 
 Lighter than Water Hydrometer Table for Liquids Heavier than Water Comparison of 
 Temperature Degrees Tables for Converting French Metric Weights and Measures into 
 English Table of the Elements etc., etc. Copious Index. 
 
 Press Opinions. 
 
 " This treatise will be welcomed by those interested in this industry who have not secured 
 the full advantage of a course of scientific training." Chemical Trade Journal. 
 
 " In concise and lucid terms almost every ingredient used in paint and colour manufacture 
 is described, together with the methods of testing their intrinsic and chemical value." 
 Pontefract Express. 
 
 " Such a book of reference for paint, colour and varnish manufacturers has long been 
 needed, and in Mr. Hurst the publishers have secured a compiler who is not only a well-known 
 authority and expert, but who has the gift of communicating his knowledge in a concise and 
 lucid form." Manchester Courier. 
 
 PURE AIR, OZONE AND WATER. A Practical Treatise 
 
 of their Utilisation and Value in Oil, Grease, Soap, Paint, Glue and 
 
 other Industries. By W. B. COWELL. Twelve Illustrations. 1900. 
 
 Price 5s. ; India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Chapters I., Atmospheric Air; Lifting of Liquids; Suction Process; Preparing Blown Oils; 
 Preparing Siccative Drying Oils. II., Compressed Air; Whitewash. III., Liquid Air; Retro- 
 cession. IV., Purification of Water; Water Hardness. V., Fleshings and Bones. VI., Ozon- 
 ised Air in the Bleaching and Deodorising of Fats, Glues, etc. ; Bleaching Textile Fibres. 
 Appendix : Air and Gases ; Pressure of Air at Various Temperatures ; Fuel ; Table of Com- 
 bustibles; Saving of Fuel by Heating Feed Water; Table of Solubilities of Scale Making 
 Minerals; British Thermal Units Tables; Volume of the Flow of Steam into the Atmosphere; 
 Temperature of Steam. Index. 
 
 Press Opinions. 
 
 "This is a valuable work in little space. ... In arrangement it is a commendable work, 
 and its value is increased by the index which brings the little volume to a close." Newcastle 
 Daily Journal. 
 
 "The book is written solely for manufacturers, who, without doubt, will find it exceedingly 
 practical and useful. The volume contains an" appendix wherein is given a great many tables, 
 etc., which'manufacturers in the trades referred to will find of inestimable valuo " R'nrkhurtt 
 Times. 
 
11 
 
 THE MANUFACTURE OF MINERAL AND LAKE 
 PIGMENTS. Containing Directions for the Manufacture 
 of all Artificial, Artists and Painters' Colours, Enamel, Soot and Me- 
 tallic Pigments. A Text-book for Manufacturers, Merchants, Artists 
 and Painters. By Dr. JOSEF BERSCH. Translated from the Second 
 Revised Edition by ARTHUR C. WRIGHT, M.A. (Oxon.), B.Sc. (Lond.), 
 formerly Assistant Lecturer and Demonstrator in Chemistry at the 
 Yorkshire College, Leeds. Forty-three Illustrations. 476 pp., demy 
 8vo. 1901. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other 
 Countries, 15s. ; strictly net. 
 
 Contents. 
 
 Chapters I., Introduction. II., Physico-chemical Behaviour of Pigments. III., Raw 
 Materials Employed in the Manufacture of Pigments. IV., Assistant Materials. V., Metallic 
 Compounds. VI., The Manufacture of Mineral Pigments. VII., The Manufacture of White 
 Lead. VIII., Enamel White. IX., Washing Apparatus. X., Zinc White. XI., Yellow 
 Mineral Pigments. XII., Chrome Yellow. XIII., Lead Oxide Pigments. XIV., Other 
 Yellow Pigments. XV., Mosaic Gold. XVI., Red Mineral Pigments. XVII., The Manu- 
 facture of Vermilion. XVIII., Antimony Vermilion. XIX., Ferric Oxide Pigments. XX., 
 Other Red Mineral Pigments. XXI , Purple of Cassius. XXII., Blue Mineral Pigments. 
 XXIII., Ultramarine. XXIV., Manufacture of Ultramarine. XXV., Blue Copper Pigments. 
 XXVI., Blue Cobalt Pigments. XXVII., Smalts. XXVIII., Green Mineral Pigments. 
 XXIX., Emerald Green. XXX., Verdigris. XXXI., Chromium Oxide. XXXII., Other 
 Green Chromium Pigments. XXXIII., Green Cobalt Pigments. XXXIV., Green Man- 
 ganese Pigments. XXXV., Compounded Green Pigments. XXXVI., Violet Mineral Pig- 
 ments. XXXVII. , Brown Mineral Pigments. XXXVIII., Brown Decomposition Products. 
 XXXIX., Black Pigments. XL., Manufacture of Soot Pigments. XLI., Manufacture of 
 Lamp Black. XLII., The Manufacture of Soot Black without Chambers. XLIII., Indian 
 Ink. XLIV., Enamel Colours. XLV., Metallic Pigments. XLVI., Bronze Pigments 
 XLVIL, Vegetable Bronze Pigments. 
 
 PIGMENTS OF ORGANIC ORIGIN. Chapters XLVIIL, Lakes. XLIX., Yellow Lakes. L., 
 Red Lakes. LI., Manufacture of Carmine. LII., The Colouring Matter of Lac. LIII., Saf- 
 flower or Carthamine Red. LIV., Madder and its Colouring Matters. LV., Madder Lakes. 
 LVI., Manjit (Indian Madder). LVI I., Lichen Colouring Matters. LVI 1 1., Red Wood Lakes. 
 LIX., The Colouring Matters of Sandal Wood and Other Dye Woods. LX., Blue Lakes. 
 LXI., Indigo Carmine. LXI I., The Colouring Matter of Log Wood. LXIII., Green Lakes. 
 LXIV., Brown Organic Pigments. LXV., Sap Colours. LXVI., Water Colours. LXVII., 
 Crayons. LXVIII., Confectionery Colours. LXIX., The Preparation of Pigments for 
 Painting. LXX., The Examination of Pigments. LXXI., Examination of Lakes. LXXII., 
 The Testing of Dye- Woods. LXXI 1 1., The Design of a Colour Works. LXXI V. Commercial 
 Names of Pigments. Appendix : Conversion of Metric to English Weights and Measures. 
 Centigrade and Fahrenheit Thermometer Scales. Index. 
 
 BONE PRODUCTS AND MANURES : An Account of the 
 most recent Improvements in the Manufacture of Fat, Glue, Animal 
 Charcoal, Size, Gelatine and Manures. By THOMAS LAMBERT, Techni- 
 cal and Consulting Chemist. Illustrated by Twenty-one Plans and 
 Diagrams. 162 pp., demy 8vo. 1901. Price 7s. 6d. ; India and 
 Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Chapters I., Chemical Composition of Bones Arrangement of Factory Crushing of Bones 
 Treatment with Benzene Benzene in Crude Fat Analyses of Clarified Fats Mechanical 
 Cleansing of Bones Animal Charcoal Tar and Ammoniacal Liquor, Char and Gases, from 
 good quality Bones Method of Retorting the Bones Analyses of Chars "Spent" Chars 
 Cooling of Tar and Ammoniacal Vapours Value of Nitrogen for Cyanide of Potash Bone 
 Oil Marrow Bones Composition of Marrow Fat Premier Juice Buttons. II., Properties 
 of Glue Glutin and Chondrin Skin Glue Liming of Skins Washing Boiling of Skins- 
 Clarification of Glue Liquors Acid Steeping of Bones Water System of Boiling Bones-*- 
 Steam Method of Treating Bones Nitrogen in the Treated Bones Glue-Boiling and Clarify- 
 ing-House Plan showing Arrangement of Clarifying Vats Plan showing Position of Evapora- 
 tors Description of Evaporators Sulphurous Acid Generator Clarification of Liquors- 
 Section of Drying-House Specification of a Glue Size Uses and Preparation and Composi- 
 tion of Size Concentrated Size. III., Properties of Gelatine Preparation of Skin Gelatine 
 Washing Bleaching Boiling Clarification Evaporation Drying Bone Gelatine Se- 
 lecting Bones Crushing Dissolving Bleaching Boiling Properties of Glutin and Chondrin 
 Testing of Glues and Gelatines. IV., The Uses of Glue, Gelatine and Size in Various 
 Trades Soluble and Liquid Glues Steam and Waterproof Glues. V., Manures Importation 
 of Foodstuffs Soils Germination Plant Life. VI., Natural Manures Water and Nitrogen 
 in Farmyard Manure Full Analysis of Farmyard Manure Action on Crops Water-Closet 
 
12 
 
 System Sewage Manure Green Manures. VII., Artificial Manures Bones Boiled and 
 Steamed Bones Mineral Phosphates English Coprolites French and Spanish Phosphorites 
 German and Belgian Phosphates Basic Slag Guanos Proper Guano Phosphates. VIII., 
 Mineral Manures Common Salt Potash Salts Calcareous Manures Prepared Nitrogenous 
 Manures Ammoniacal Compounds Sodium Nitrate Potassium Nitrate Organic Nitro- 
 genous Matters Shoddy Hoofs and Horns Leather Waste Dried Meat Dried Blood 
 Superphosphates Composition Manufactuie Section of Manure-Shed First and Ground 
 Floor Plans of Manure-Shed Quality of Acid Used Mixings Special Manures Potato 
 Manure Dissolved Bones Dissolved Bone Compound Enriched Peruvian Guano Special 
 Manure for Garden Stuffs, etc. Special Manure for Grass Lands Special Tobacco Manures 
 Sugar-Cane Manure Compounding of Manures Valuation of Manures. IX., Analyses of 
 Raw and Finished Products Common Raw Bones Degreased Bones Crude Fat Refined 
 Fat Degelatinised Bones Animal Charcoal Bone Superphosphates Guanos Dried Animal 
 Products Potash Compounds Sulphate of Ammonia Extraction in Vacuo Description of a 
 Vacuum Pan French and British Gelatines compared. Index. 
 
 Press Opinion. 
 
 " We can with confidence recommend the perusal of the book to all persons interested in 
 the manufacture of artificial manures, and also to the large number of farmers and others who 
 are desirous of working their holdings on the most up-to-date methods, and obtaining the best 
 possible results, which scientific research has placed within thei 1 * reach." Wigan Observer. 
 
 ANALYSIS OF RESINS AND BALSAMS. Demy 8vo. 
 340 pp. 1901. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 
 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Part I., Definition of Resins in General Definition of Balsams, and especially the Gum 
 Resins External and Superficial Characteristics of Resinous Bodies Distinction between 
 Resinous Bodies and Fats and Oils Origin, Occurrence and Collection of Resinous Sub- 
 stances Classification Chemical Constituents of Resinous Substances Resinols Resinot 
 Annols Behaviour of Resin Constituents towards the Cholesterine Reactions Uses and 
 Identification of Resins Melting-point Solvents Acid Value Saponification Value Resin 
 Value Ester and Ether Values Acetyl and Corbonyl Value Methyl Value Resin Acid 
 Systematic Resume of the Performance of the Acid and Saponification Value Tests. 
 
 Part II., Balsams Introduction Definitions Canada Balsam Copaiba Balsam Angos- 
 tura Copaiba Balsam Babia Copaiba Balsam Carthagena Copaiba Balsam Maracaibo 
 Copaiba Balsam Maturin Copaiba Balsam Gurjum Copaiba Balsam Para Copaiba Balsam 
 Surinam Copaiba Balsam West African Copaiba Balsam Mecca Balsam Peruvian 
 Balsam Tolu Balsam Acaroid Resin Amine Amber African and West Indian Kino 
 Bengal Kino Labdanum Mastic Pine Resin Sandarach Scammonium Shellac Storax 
 Adulteration of Styrax Liquidus Crudus Purified Storax Styrax Crudus Colatus Taca- 
 mahac Thapsia Resin Turpentine Chios Turpentine Strassburg Turpentine Turpeth 
 Turpentine. Gum Resins Ammoniacum Bdellium Euphorbium Galbanum Gamboge 
 Lactucarium Myrrh Opopanax Sagapenum Olibanum or Incense Acaroid Resin 
 Amber Thapsia Resin. Index. 
 
 MANUFACTURE OF PAINT. A Practical Handbook for 
 Paint Manufacturers, Merchants and Painters. By J. CRUICKSHANK 
 SMITH, B.Sc. Demy 8vo. 1901. 200pp. 60 Illustrations and 1 Large 
 Diagram. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 
 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Part I., Chapters I., Preparation of Raw Material. II., Storing of Raw Material. III., 
 Testing and Valuation of Raw iMaterial Paint Plant and Machinery. 
 
 Part II., Chapters V., The Grinding of White Lead. VI., Grinding of White Zinc. VII., 
 Grinding of other White Pigments. VIII., Grinding of Oxide Paints. IX., Grinding of Stain- 
 ing Colours. X., Grinding of Black Paints. XI., Grinding of Chemical Colours Yellows. 
 XII., Grinding of Chemical Colours Blues. XIII., Grinding Greens. XIV., Grinding Reds. 
 XV., Grinding Lakes. XVI., Grinding Colours in Water. XVII., Grinding Colours in 
 Turpentine. 
 
 Part III., Chapters XVIII., The Uses of Paint. XIX., Testing and Matching Paints. 
 XX., Economic Considerations. Index. 
 
 THE CHEMISTRY OF PIGMENTS. By ERNEST J. PARRY, 
 B.Sc., F.I.C., F.C.S., and J. H. COSTE, F.I.C., F.C.S. [In the press. 
 
 Contents. 
 
 Chapters I., Introductory Composition of White Light Theory of Colour, etc. II., The 
 Application of Pigments Artistic, Decorative, Protective Methods of Applying Pigments. 
 III., White Pigments. IV., Inorganic Coloured Pigments. V., Organic Pigments. 
 
13 
 
 NOTES ON LEAD ORES : Their Distribution and Properties. 
 By JAS. FAIRIE, F.G.S. Crown 8vo. 1901. 64 pages. Price 2s. 6d. ; 
 Abroad, 3s. ; strictly net. * 
 
 Contents. 
 
 Chapters I., Definitions Properties^-Occurrence. II., Galena Johnstonite Cerussite 
 CeVuse (White Lead) Minium Red Lead. III., Pyromorphite Mimetene Hediphane 
 Crocoise Wulfenite. Vanadinite IV., Bleiglatte Anglesite Caledonite Linarite Lanark- 
 ite Leadhillite Susannite Clausthalite Cotunnite. V., Mendipite Matlockite Crom- 
 fordite Nagyagite Altaite Melanochroite Vauguelinite Scheeletine. VI., Plattncrite 
 Tilkcrodite Raphanosmite Deckenite Descloezite Dufrenaysite Bleinierite Moffrasite 
 Geocronite Kilbrechenite Schulzite Boulangcrite Heterpmorphite Meneghinite 
 Jamesonite Plagionite Zinkenite. VII., Kobellite Bournonite Selenkupferblei Nus- 
 sierite Percylite Wolchite Polysphracrite Miesite. Index. 
 
 THE RISKS AND DANGERS OF VARIOUS OCCUPA- 
 TIONS AND THEIR PREVENTION. By LEONARD 
 A. PARRY, M.D., B.S. (Lond.). 196 pp., demy 8vo. 1900. Price 7s. 6d. ; 
 India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Chapters I., Occupations which are Accompanied by the Generation and Scattering of 
 Abnormal Quantities of Dust. II., Trades in which there is Danger of Metallic Poisoning. 
 III., Certain Chemical Trades. IV., Some Miscellaneous Occupations. V., Trades in which 
 Various Poisonous Vapours are Inhaled. VI., General Hygienic Considerations. Index. 
 
 This book contains valuable information for the following trades Aerated Water Manu- 
 facture, Alkali Manufacture, Aniline Manufacture, Barometer Making, Brass Founders, Bromine 
 Manufacture, Bronze Moulders, Brush Making, Builders, Cabinet Makers, Calico Printing, 
 Chloride of Lime Manufacture, Coal Miners, Cocoa-nut Fibre Making, Colour Grinders, 
 Copper Miners, Cotton Goods Manufacture, Cotton Yarn Dyeing, Cutlery Trades, Dry Clean- 
 ing, Electricity Generating, Electroplaters, Explosives Manufacture, File Making, Flint 
 Milling, Floor Cloth Makers, Furriers, Fustian Clothing Making, Galvanised Iron Manufacture, 
 Gassing Process, Gilders, Glass Making, Glass Paper Making, Glass Polishing and Cutting, 
 Grinding Processes, Gunpowder Manufacturing, Gutta-percha Manufacture, Hat Makers, 
 Hemp Manufacture, Horn Goods Making, Horse-hair Making, Hydrochloric Acid Manufacture, 
 India-rubber Manufacture, Iodine Manufacture, Ivory Goods Making, Jewellers, Jute Manu- 
 facture, Knife Grinders, Knife Handle Makers, Lace Makers, Lacquering, Lead Melters, Lead 
 Miners, Leather Making, Linen Manufacture. Linoleum Making, Lithographic Printing and 
 Bronzing, Lithographing, Masons, Match Manufacture, Melanite Making, Mirror Making, 
 Needle Grinders, Needle Making, Nitro-benzole Making, Nitro-glycerine Making, Paint 
 Makers, Paper Making, Philosophical Instrument Makers, Photographers, Picric Acid Making, 
 Portland Cement Making, Pottery Manufacture, Printers, Quicksilver Mining, Rag Pickers, 
 Razor Grinders, Red Lead Making, Rope Making, Sand Paper Making, Saw Grinders, Scissors 
 Grinders, Shoddy Manufacture, Shot Making, Silk Making, Silver Mining, Skinners, Slag, Wood 
 Manufacture, Steel Makers, Steel Pen Making, Stereotypers, Stone Masons, Straw Hat Makers, 
 Sulphuric Acid Manufacture, Sweeps, Table-knife Grinders, Tanners, Telegraphists, Textile 
 Industries, Tin Miners, Turners, Type Founders, Umbrella Makers, Wall Paper Making, 
 White Lead Making, Wood Working, Woollen Manufacture, Wool Sorters, Zinc Oxide 
 Manufacture, Zinc Working, etc., etc. 
 
 Press Opinions. 
 
 "The language used is quite simple, and can be understood by any intelligent person en- 
 gaged in the trades dealt with." The Clarion. 
 
 "This is an appalling book. It shows that there is scarcely a trade or occupation that has 
 not a risk or a danger attached to it-" Local Government Journal. 
 
 " Dr. Parry has not only pointed out the ' risks and dangers of various occupations ' ; he has 
 suggested means for their prevention. The work is primarily a practical one." Colliery 
 Manager. 
 
 "This is a most useful book which should be in the hands of all employers of labour, 
 foremen, and intelligent workmen, and is one of great utility to sanitary inspectors, and even 
 on occasion to medical men." Health. 
 
 "The writer has succeeded in collecting a large amount of information, and though one 
 could wish he had presented it in a rather more attractive style, he has certainly condensed it 
 into a very small space." Physician and Surgeon. 
 
 "The little book before us is one which will be found exceedingly useful to manufacturers 
 and even factory inspectors. . . . No attempt is made to show how diseases when originated 
 are to be cured, but, acting on the sound principle that prevention is better than cure, means 
 are stated how to avoid the harm." Bristol Mercury. 
 
 " The author has endeavoured to treat the question in simple rather than in technical lan- 
 guage, and he has lucidly catalogued the most dangerous trades and their symptoms, and in 
 each case specified the best methods of dealing with them. ... To those for whom the volume 
 is specially designed, Dr. Parry's treatise should be a useful handbook." Sheffield Independent. 
 
14 
 
 "A very useful manual for employers of labour, foremen, intelligent workmen, and, in spite 
 t)f the author's modesty, for medical men. We have the peculiar risks and dangers of all the 
 dangerous trades carefully described ; the mode of action of various chemicals, etc., used in 
 different industries given, with full directions how to minimise unavoidable risks." Leeds 
 Mercury. 
 
 "Most of the trades in the country are alluded to, and upon those that are dangerous the 
 necessary attention is bestowed, and means are recommended whereby danger may be pre- 
 vented or lessened. The author has evidently studied his subject with care, and has made full 
 use of the experience of others who have had a larger insight into the industries of the country." 
 ^-British Medical Journal. 
 
 "The work is well written and printed, and its verbiage such as to be comprehensible to the 
 workman no less than to the master. The careful and general perusal of a work of this nature 
 cannot but be attended by beneficial results of a far-reaching nature, and we therefore heartily 
 recommend the book to our readers. Medical Officers of Health and Sanitary Inspectors 
 especially should find the work of great interest." Sanitary Record. 
 
 " It is written in simple language, and its instructions can be easily followed. . . . There 
 are some employers, at any rate, who are more ignorant of, than indifferent to, the slow murder 
 of their workpeople, and if the facts so succinctly set forth in this book were brought to their 
 notice, and if the Trade Unions made it their business to insist on the observance of the better 
 conditions Dr. Parry described, much might be done to lessen the workman's peril." Weekly 
 Times and Echo. 
 
 PRACTICAL X RAY WORK. By FRANK T. ADDYMAN, 
 B.Sc. (Lond.), F.I.C., Member of the Roentgen Society of London ; 
 Radiographer to St. George's Hospital; Demonstrator of Physics and 
 Chemistry, and Teacher of Radiography in St. George's Hospital 
 Medical School. Demy 8vo. 12 Plates from Photographs of X Ray 
 Work. 52 Illustrations. 200 pp. 1901. Price 10s. 6d. ; India and 
 Colonies, 11s.; Other Countries, 12s.; strictly net. 
 
 Contents. 
 
 Part I., Historical Chapters I., Introduction. II., Work leading up to the Discovery of 
 the X Rays. 111., The Discovery. 
 
 Part II., Apparatus and its Management Chapters I., Electrical Terms. II., Sources 
 of Electricity. III., Induction Coils. IV., Electrostatic Machines. V., Tubes. VI., Air 
 Pumps. VII., Tube Holders and Stereoscopic Apparatus. VIII., Fluorescent Screens. 
 
 Part III., Practical X Ray Work Chapters I., Installations. II., Radioscopy. III., 
 Radiography. IV., X Rays in Dentistry. V., X Rays in Chemistry. VI., X Rays in War. 
 Index. 
 
 List of Plates. 
 
 Frontispiece Congenital Dislocation of Hip-Joint. I., Needle in Finger. II., Needle in 
 Foot. III., Revolver Bullet in Calf and Leg. IV., A Method of Localisation. V., Stellate 
 Fracture of Patella showing shadow of "Strapping". VI., Sarcoma. VII., Six-weeks'-old 
 Injury to Elbow showing new Growth of Bone. VIII., Old Fracture of Tibia and Fibula 
 badly set. IX., Heart Shadow. X., Fractured Femur showing Grain of Splint. XI., Bar- 
 rell's Method of Localisation. 
 
 DRYING BY MEANS OF AIR AND STEAM. Explana- 
 tions, Formulae, and Tables for Use in Practice. Translated from the 
 German of E. HAUSBRAND. Two Diagrams and Thirteen Tables. Demy 
 8vo. 1901. 72 pp. Price 5s.; India and Colonies, 5s. 6d. ; Other 
 Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Preface. British and Metric Systems Compared Centigrade and Fahr. Thermometers. 
 Chapters I., Introduction. II., Estimation of the iMaximum Weight of Saturated Aqueous 
 Vapour which can be contained in 1 kilo, of Air at Different Pressure and Tempera- 
 tures. III., Calculation of the Necessary Weight and Volume of Air, and of the Least 
 Expenditure of Heat, per Drying Apparatus with Heated Air, at the Atmospheric Pressure : 
 A, With the Assumption that the Air is Completely Saturated with Vapour both before Entry 
 and after Exit from the Apparatus. B, When the Atmospheric Air is Completely Saturated 
 before entry, but at its exit is only |, J or | Saturated. C, When the Atmospheric Air is not 
 Saturated with iMoisture before Entering the Drying Apparatus. IV., Drying Apparatus, in 
 which, in the Drying Chamber, a Pressure is Artificially Created, Higher or Lower than that 
 of the Atmosphere. V., Drying by Means of Superheated Steam, without Air. VI., Heating 
 Surface, Velocity of the Air Current. Dimensions of the Drying Room, Surface of the Drying 
 Material, Losses of Heat. Index. 
 
15 
 
 Leather Trades. 
 
 THE LEATHER WORKER'S MANUAL. Being a Com- 
 pendium of Practical Recipes and Working Formulae for Curriers, 
 Bootmakers, Leather Dressers, Blacking Manufacturers, Saddlers, 
 Fancy Leather Workers, and all Persons engaged in the Manipulation 
 of Leather. By H. C. STANDAGE. 165 pp. 1900. Price 7s. 6d. ; 
 India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Chapters I., Blackings, Polishes, Glosses, Dressings, Renovators, etc., for Boot and Shoe 
 Leather. II., Harness Blackings, Dressings, Greases, Compositions, Soaps, and Boot-top 
 Powders and Liquids, etc., etc. III., Leather Grinders' Sundries. IV., Currier's Seasonings, 
 Blacking Compounds, Dressings, Finishes, Glosses, etc. V., Dyes and Stains tor Leather. 
 VI., Miscellaneous Information. VII., Chrome Tannage. Index. 
 
 Press Opinions. 
 
 "The book being absolutely unique, is likely to be of exceptional value to all whom it con- 
 cerns, as it meets a long-felt want." Birmingham Gazette. 
 
 "This is a valuable collection of practical receipts and working formulae for the use of those 
 engaged in the manipulation of leather. We have no hesitation in recommending it as one of 
 the best books of its kind, an opinion which will be endorsed by those to whom it appeals." 
 Liverpool Mercury. 
 
 "We think we may venture to state, so far as the opinion of the leather trade under the 
 Southern Cross is concerned, that it will be one of approval. As practical men, having a long 
 and wide experience of the leather trade in Australia, we are certain that there are many 
 tanners and curriers carrying on business in remote townships of the colonies to whom such a 
 manual of practical recipes will be invaluable. . . . This manual is not a mere collection of re- 
 cipes for the various purposes to which they may be applied, but it is also replete with instruc- 
 tions concerning the nature of the materials recommended to be used in making up the recipes. 
 . . . We think every intelligent leather man should avail himself of the manual. It is un- 
 doubtedly a valuable contribution to the technology of the leather trade." Australian Leather 
 Journal and Boot and Shoe Recorder. 
 
 PRACTICAL TREATISE ON THE LEATHER IN- 
 DUSTRY. By A. M. VILLON. A Translation of Villon's 
 "Traite Pratique de la Fabrication des cuirs et du Travail des Peaux ". 
 By FRANK T. ADDYMAN, B.Sc. (Lond.), F.I.C., F.C.S. ; and Corrected 
 by an Eminent Member of the Trade. 500 pp., royal 8vo. 1901. 123 
 Illustrations. Price 21s. ; India and Colonies, 22s. ; Other Countries, 
 23s. 6d. ; strictly net. 
 
 Contents. 
 
 Preface Translator's Preface List of Illustrations. 
 
 Part I., Materials used in Tanning Chapter I., Skins: I., Skin and its Structure; II., 
 Skins used in Tanning; III., Various Skins and their Uses Chapter II., Tannin and Tanning 
 Substances: I., Tannin; II., Barks (Oak); III., Barks other than Oak; IV., Tanning 
 Woods; V., Tannin-bearing Leaves; VI., Excrescences; VII., Tan-bearing Fruits; VIII., 
 Tan-bearing Roots and Bulbs; IX., Tanning Juices ; X., Tanning Substances used in Various 
 Countries; XI., Tannin Extracts; XII., Estimation of Tannin and Tannin Principles. 
 
 Part II., Tanning Chapter I., The Installation of a Tannary: I., Tan Furnaces; II., 
 Chimneys, Boilers, etc.; III., Steam Engines Chapter II., Grinding and Trituration of 
 Tanning Substances: I., Cutting up Bark; II., Grinding Bark; III., The Grinding of Tan 
 Woods; IV., Powdering Fruit, Galls and Grains; V., Notes on the Grinding of Bark Chap- 
 
 ter III., Manufacture of Sole Leather: I., Soaking; II., Sweating and Unhairing; III., 
 Plumping and Colouring; IV., Handling; V., Tanning; VI., Tanning Elephants' Hides; 
 VII., Drying; VIII., Striking or Pinning Chapter IV., Manufacture of Dressing Leather: 
 I., Soaking; II., Depilation ; III., New Processes for the Depilation of Skins; IV., Tanning; 
 V., Cow Hides; VI., Horse Hides; VII., Goat Skins; Manufacture of Split Hides Chap 
 ter V., On Various Methods of Tanning: I., Mechanical Methods; II., Physical Methods; 
 III., Chemical Methods; IV., Tanning with Extracts Chapter VI., Quantity and Quality: 
 I., Quantity; II., Net Cost; III., Quality of Leather Chapter VII., Various Manipulations 
 of Tanned Leather: I., Second Tanning; II., Grease Stains; III., Bleaching Leather; IV., 
 Waterproofing Leather; V., Weighting Tanned Leather; VI., Preservation of Leather- 
 Chapter VIII., Tanning Various Skins. 
 
 Part III., Currying Chapter I., Waxed Calf: I., Preparation; II., Shaving; III., 
 Stretching or Slicking; IV., Oiling the Grain ; V., Oiling the Flesh Side; VI., Whitening and 
 Graining; VII., Waxing; VIII., Finishing; IX., Dry Finishing; X., Finishing in Colour; 
 XL, Cost Chapter II., White Calf: I., Finishing in White Chapter III., Cow Hide for 
 Upper Leathers: I., Black Cow Hide; II., White Cow Hide; III., Coloured Cow Hide. 
 Chapter IV., Smooth Cow Hide Chapter V., Black Leather Chapter VI., Miscellaneous 
 Hides: I., Horse; II., Goat; III., Waxed Goat Skin; IV., Matt Goat Skin Chapter VII., 
 Russia Leather: I., Russia Leather; II.. Artificial Russia Leather. 
 
16 
 
 Part IV., Enamelled, Hungary and Chamoy Leather, Morocco, Parchment, Purs 
 and Artificial Leather Chapter I., Enamelled Leather: I., Varnish Manufacture; II., 
 Application of the Enamel; III., Enamelling in Colour Chapter II., Hungary Leather: I., 
 Preliminary; II., Wet Work or Preparation; III., Aluming; IV., Dressing or Loft Work; 
 V., Tallowing; VI., Hungary Leather from Various Hides Chapter III., Tawing: I., Pre- 
 paratory Operations; II., Dressing; III., Dyeing Tawed Skins; IV., Rugs Chapter IV., 
 Chamoy Leather Chapter V., Morocco : I., Preliminary Operations; II., Morocco Tanning; 
 III., Mordants used in Morocco Manufacture; IV., Natural Colours used in Morocco 
 Dyeing; V., Artificial Colours ; VI. Different Methods of Dyeing; VII., Dyeing with Natural 
 Colours; VIII., Dyeing with Aniline Colours; IX., Dyeing with Metallic Salts; X., Leather 
 Printing; XL, Finishing Morocco; XII., Shagreen; XIII., Bronzed Leather Chapter VI., 
 Gilding and Silvering: I., Gilding; II., Silvering; III., Nickel and Cobalt Chapter VII., 
 Parchment Chapter VIII., Furs and Furriery: I., Preliminary Remarks?; II., Indigenous 
 Furs; III., Foreign Furs from Hot Countries; IV. Foreign Furs from Cold Countries; V., 
 Furs from Birds' Skins; VI., Preparation of Furs; VII., Dressing; VIII., Colouring; IX., 
 Preparation of Birds' Skins; X., Preservation of Furs Chapter IX., Artificial Leather: I., 
 Leather made from Scraps; II., Compressed Leather; III., American Cloth; IV., Papier 
 Max:he; V., Linoleum; VI., Artificial Leather. 
 
 Part V., Leather Testing and the Theory of Tanning Chapter I., Testing and Analysis 
 of Leather: I., Physical Testing of Tanned Leather; II., Chemical Analysis Chapter II., 
 The Theory of Tanning and the other Operations of the Leather and Skin Industry: I., 
 Theory of Soaking; II., Theory of Unhairing; III., Theory of Swelling; IV., Theory of 
 Handling; V. Theory of Tanning; VI., Theory of the Action of Tannin on the Skin; VII., 
 Theory of Hungary Leather Making; VIII., Theory of Tawing; IX., Theory of Chamoy 
 Leather Making ; X., Theory of Mineral Tanning. 
 
 Part VI., Uses of Leather Chapter I., Machine Belts: I., Manufacture of Belting; II., 
 Leather Chain Belts; III., Various Belts, IV., Use of Belts Chapter II., Boot and Shoe- 
 making: I., Boots and Shoes; II., Laces Chapter III., Saddlery: I., Composition of a 
 Saddle; II., Construction of a Saddle Chapter IV., Harness: I., The Pack Saddle; II., 
 Harness Chapter V., Military Equipment Chapter VI., Glove Making Chapter VII., 
 Carriage Building Chapter VIII., Mechanical Uses. 
 
 Appendix, The World's Commerce in Leather I., Europe; II., America; III., Asia; 
 IV., Africa ; Australasia Index. 
 
 Press Opinions. 
 
 "The book is well and lucidly written. The writer is evidently a practical man, who also 
 has taken the trouble to make himself acquainted with the scientific and technical side of his 
 trade. . . . French methods differ largely from our own; sometimes we think our ways the 
 best, but not always. The practical man may pick up many useful hints which may help him 
 to improve his methods." Shoe Manufacturers' Monthly Journal. 
 
 "This book cannot fail to be of great value to all engaged in the leather trades. . . . The 
 British may believe that the French can teach them nothing in the work of leather tanning 
 generally, but a comparison of the methods of the two countries will certainly yield a few 
 wrinkles which may lead to advantageous results. Only a man understanding the science and 
 technique of the trade could have written the book, and it is well done." Midland Free Press. 
 
 "Gives much useful and interesting information concerning the various processes by which 
 the skins of animals are converted into leather. Written by a French Cnemist after five 
 years of constant study and application ; it shows all that detail of analysis which we are 
 accustomed to find in scientists, and which the practical tanner is too much in the habit of 
 ignoring, sometimes to his own loss." Leeds Mercury. 
 
 "Nor can there be much doubt that this expectation will be fully justified by the result. 
 Thanks to the conspicuous painstaking with which Mr. Addyman has discharged his duty, and 
 the 123 illustrations by which the text is elucidated, the volume can hardly fail to prove a very 
 valuable standard work of its class. It can thus be confidently recommended to all who are 
 more or less practically interested in the technology of a very important subject." Leicester 
 Post. 
 
 " This is, in every respect, an altogether admirable, practical, clear and lucid treatise on 
 the various and numerous branches of the great leather industry, of which it deals in an ex- 
 haustive, highly intelligent, workmanlike and scientific manner. . . . It is- a handsome addition 
 to every man's knowledge of his trade, whether he be a leading director of a large public com- 
 pany, or an industrious employee in the works, wishing to improve his services by the addition 
 of his brains to his work." Shoe and Leather Trader. 
 
 " M. Villon writes as one having a very full knowledge of all branches of the subject, and in 
 days when foreign competition has enforced on English manufacturers the importance of no 
 longer being content with rule-of-thumb methods which have come down to them from their 
 forefathers it certainly should be worth the while of English tanners to see what lessons they 
 can learn from French practice, and French practice, we should imagine, could hardly have a 
 better exponent than the author of this large volume." Western Daily Press and Bristol Times. 
 
 "At a time when all or nearly all our British industries are to a greater or less extent 
 hampered by the pressure of continental and American competition, any hints that can be 
 obtained as to the methods pursued by competitors must necessarily be of value. . . . That it 
 will be of interest and value, not merely to English tanners, but to those associated with many 
 kindred industrial branches, goes without saying. . . . As a work of reference the volume will 
 be extremely useful in the trade, and where leisure affords sufficient opportunity a careful 
 perusal and study of it would afford ample reward." KMering Guardian. 
 
 "This is a very handsomely got up and elaborate work just issued by this well-known 
 technical book-publishing firm. . . . When we say that the work consists of over 500 large 
 pages with about 120 illustrations, and almost innumerable tables, it will be seen at once that 
 
17 
 
 we cannot attempt anything like an exhaustive resume of its contents, and even if we did the 
 details would be of little interest to our general readers, while those who are engaged in the 
 leather industry will probably obtain the book for themselves at least they would do well to 
 do so. ... Altogether the 'Treatise' has evidently been very carefully prepared, and by a man 
 who thoroughly knows the subject, and hence it \vill be a very valuable technical book for 
 English firms and workers.' Walsall Qbserver. 
 
 Books on Pottery, Bricks, 
 Tiles, Glass, etc. 
 
 THE MANUAL OF PRACTICAL POTTING. Revised 
 
 and Enlarged. Third Edition. 200 pp. 1901. Price 17s. 6d.; India 
 and Colonies, 18s. 6d. ; Other Countries, 20s. ; strictly net. 
 Contents. 
 
 Introduction. The Rise and Progress of the Potter's Art. Chapters I., Bodies. China 
 and Porcelain Bodies, Parian Bodies, Semi-porcelain and Vitreous Bodies, Mortar Bodies, 
 Earthenwares Granite and C.C. Bodies, Miscellaneous Bodies, Sagger and Crucible Clays, 
 Coloured Bodies, Jasper Bodies, Coloured Bodies for Mosaic Painting, Encaustic Tile Bodies, 
 Body Stains, Coloured Dips. II., Glazes. China Glazes, Ironstone Glazes, Earthenware 
 Glazes, Glazes without Lead, Miscellaneous Glazes, Coloured Glazes, Majolica Colours. III., 
 Gold and Cold Colours. Gold, Purple of Cassius, Marone and Ruby, Enamel Coloured 
 Bases, Enamel Colour Fluxes, Enamel Colours, Mixed Enamel Colours, Antique and Vellum 
 Enamel Colours, Underglaze Colours, Underglaze Colour Fluxes, Mixed Underglaze Colours, 
 Flow Powders, Oils and Varnishes. IV., Means and Methods. Reclamation of Waste 
 Gold, The Use of Cobalt, Notes on Enamel Colours, Liquid or Bright Gold. V., Classification 
 and Analysis. Classification of Clay Ware, Lord Playfair's Analysis of Clays, The Markets 
 of the World, Time and Scale of Firing, Weights of Potter's Material, Decorated Goods 
 Count. VI., Comparative Loss of Weight of Clays. VII., Ground Felspar Calculations. 
 VIII., The Conversion of Slop Body Recipes into Dry Weight. IX., The Cost of Prepared 
 Earthenware Clay. X., Forms and Tables. Articles of Apprenticeship, Manufacturer's 
 Guide to Stocktaking, Table of Relative Values of Potter's Materials, Hourly Wages Table. 
 Workman's Settling Table, Comparative Guide for Earthenware and China Manufacturers in 
 the use of Slop Flint and Slop Stone, Foreign Terms applied to Earthenware and China 
 Goods, Table for the Conversion of Metrical Weights and Measures on the Continent of South 
 America. Index. 
 
 CERAMIC TECHNOLOGY : Being some Aspects of Tech- 
 nical Science as Applied to Pottery Manufacture. Edited by CHARLES 
 F. BINNS. 100 pp. 1897. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; 
 Other Countries, 15s. ; strictly net. 
 
 Contents. 
 
 Preface. Introduction. Chapters I., The Chemistry of Pottery. II., Analysis and Syn- 
 thesis. III., Clays and their Components. IV., The Biscuit Oven. V., Pyrometry. VI., 
 Glazes and their Composition. VII., Colours and Colour-making. Index. 
 
 RECIPES FOR FLINT GLASS MAKING. By a British 
 Glass Master and Mixer. Sixty Recipes. Being Leaves from the 
 Mixing Book of several experts in the Flint Glass Trade, containing 
 up-to-date recipes and valuable information as to Crystal, Demi-crystal 
 and Coloured Glass in its many varieties. It contains the recipes for 
 cheap metal suited to pressing, blowing, etc., as well as the most costly 
 crystal and ruby. British manufacturers have kept up the quality of 
 this glass from the arrivals of the Venetians to Hungry Hill, Stour- 
 bridge, up to the present time. The book also contains remarks as 
 to the result of the metal as it left the pots by the respective metal 
 mixers, taken from their own memoranda upon the originals. 1900. 
 Price for United Kingdom, 10s. 6d. ; Abroad. 15s. ; United States, $4 ; 
 strictly net. 
 
 Contents. 
 
 Ruby Ruby from Copper Flint for using with the Ruby for Coating A German Metal- 
 Cornelian, or Alabaster Sapphire Blue Crysophis Opal Turquoise Blue Gold Colour- 
 Dark Green Green (common) Green for Malachite Blue for Malachite Black for Mela- 
 chite Black Common Canary Batch Canary White Opaque Glass Sealing-wax Red- 
 Flint Flint Glass (Crystal and Demi) Achromatic Glass Paste Glass White Enamel 
 Firestone Dead White (for moons) White Agate Canary Canary Enamel Index. 
 
18 
 
 COLOURING AND DECORATION OF CERAMIC 
 WARE. By ALEX. BRONGXIART. With Notes and Additions 
 by ALPHONSE SALVETAT. Translated from the French. 200 pp. 1898. 
 Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
 strictly net. 
 
 Contents. 
 
 The Pastes, Bodies or Ceramic Articles Capable of being Decorated by Verifiable Colours 
 The Chemical Preparation of Vitrifiable Colours Composition and Preparation of Verifiable 
 Colours The Oxides Preparation of Oxides Preparation of Chromates Preparation of 
 other Colours Composition and Preparation of Fluxes Muffle Colours Recipes for Colours 
 Use of Metals Lustres Preparation and Application of Colours Composition of Coloured 
 Pastes Underglaze Colours Colours in the Glaze Overglaze Colours Painting in Vitri- 
 fiable Colours Gilding Burnishing Printing Enlarging and Reducing Gelatine Prints 
 Muffle Kilns for Vitrifiable Colours Influence of the Material on the Colour Changes Re- 
 sulting from the Actions of the Fire Alterations Resulting from the Colours Alterations in 
 Firing. 
 
 HOW TO ANALYSE CLAY. Practical Methods for Prac- 
 tical Men. By HOLDEN M. ASHBY, Professor of Organic Chemistry, 
 Harvey Medical College, U.S.A. Twenty Illustrations. 1898. Price 
 2s. 6d. ; Abroad, 3s. ; strictly net. 
 
 Contents. 
 
 List of Apparatus List of Atomic Weights Use of Balance, and Burette, Sand Bath, and 
 Water Bath Dessicator Drying Oven Filtering Fusion Determination of Water, Organic 
 Matter, Iron, Calcium, Alkalies, Limestone, Silica, Alumina, Magnesium, etc. Mechanical 
 Analysis Rational Analysis Standard Solutions Volumetric Analysis Standards for Clay 
 Analysis Sampling. 
 
 ARCHITECTURAL POTTERY. Bricks, Tiles, Pipes, Ena- 
 melled Terra-cottas, Ordinary and Incrusted Quarries, Stoneware 
 Mosaics, Faiences and Architectural Stoneware. By LEON LEFEVRE. 
 With Five Plates. 950 Illustrations in the Text, and numerous estimates. 
 500 pp., royal 8vo. 1900. Translated from the French by K. H. BIRD, 
 M.A., and W. MOORE BINNS. Price 15s.; India and Colonies, 16s.; 
 Other Countries, 17s. 6d. ; strictly net. 
 Contents. 
 
 Part I. Plain Undecorated Pottery. Chapter I., Clays: 1, Classification, General Geo- 
 logical Remarks. Classification, Origin, Locality ; 2, General Properties and Composition : 
 Physical Properties, Contraction, Analysis, Influence of Various Substances on the Properties 
 of Clays ; 3, Working of Clay-Pits I. Open Pits : Extraction, Transport, Cost II. Under- 
 ground Pits Mining Laws. Chapter II., Preparation of the Clay : Weathering, Mixing, 
 Cleaning, Crushing and Pulverising Crushing Cylinders and Mills, Pounding Machines 
 Damping : Damping Machines Soaking, Shortening, Pugging : Horse and Steam Pug-Mills, 
 Rolling Cylinders Particulars of the Above Machines. Chapter III., Bricks : 1, Manufacture 
 (1) Hand and Machine Moulding. I. Machines Working by Compression : on Soft Clay, on 
 Semi-Firm Clay, on Firm Clay, on Dry Clay. II. Expression Machines: with Cylindrical Pro- 
 pellers, with Screw Propellers Dies Cutting-tables Particulars of the Above Machines 
 General Remarks on the Choice of Machines Types of Installations Estimates Plenishing, 
 Hand and Steam Presses, Particulars (2) Drying, by Exposure to Air, Without Shelter, and 
 Under Sheds Drying-rooms in Tiers, Closed Drying-rooms, in Tunnels, in Galleries De- 
 tailed Estimates of the Various Drying-rooms, Comparison of Prices Transport from 
 the Machines to the Drying-rooms, Barrows, Trucks, Plain or with Shelves, Lifts -(3) Firing 
 I. In Clamps II. In Intermittent Kilns. A, Open: a, using Wood ; b Coal; b', in Clamps ; 
 b", Flame B, Closed: c, Direct Flame; c', Rectangular; c", Round; d, Reverberatory III. 
 Continuous Kilns: C, with Solid Fuel: Round Kiln, Rectangular Kiln, Chimneys (Plans and 
 Estimates) D, With Gas Fuel, Fillard Kiln (Plans and Estimates), Schneider Kiln (Plans and 
 Estimates), Water-gas Kiln Heat Production of the Kilns ; 2, Dimensions, Shapes, Colours, 
 Decoration, and Quality of Bricks Hollow Bricks, Dimensions and Prices of Bricks, Various 
 Shapes, Qualities Various Hollow Bricks, Dimensions, Resistance, Qualities ; 3, Applications 
 History Asia, Africa, America, Europe : Greek, Roman, Byzantine, Turkish, Romanesque, 
 Gothic, Renaissance, Architecture Architecture of the Nineteenth Century: in Germany, 
 England, Belgium, Spain, Holland, France, America Use of Bricks Walls, Arches, Pavements, 
 Flues, Cornices Facing with Coloured Bricks Balustrades. Chapter IV., Tiles: $ 1, His- 
 tory; 2, Manufacture (1) Moulding, by Hand, by Machinery: Preparation of the Clay, Soft 
 Paste, Firm Paste, Hard Paste Preparation of the Slabs, Transformation into Flat Tiles, into 
 Jointed Tiles Screw, Cam and Revolver Presses Particulars of Tile-presses (2) Drying 
 Planchettes, Shelves, Drying-barrows and Trucks (3) Firing Divided Kilns Installation of 
 Mechanical Tileworks Estimates ; 3, Shapes, Dimensions and Uses of the Principal Types 
 of Tile Ancient Tiles: Flat, Round, Roman, Flemish Modern Tiles With Vertical Inter- 
 rupted Join : Gilardoni's, Martin's ; Hooked, Boulet's Villa ; with Vertical Continuous Join : 
 Muller's, Alsace, Pantile Foreign Tiles Special Tiles Ridge Tiles, Coping Tiles, Border 
 Tiles, Frontons, Gutters, Antefixes, Membron, Angular Roofing Accessories : Chimney-pots, 
 
19 
 
 Mitrons, Lanterns, Chimneys Qualities of Tiles Black Tiles Stoneware Tiles Particulars 
 of Tiles. Chapter V., Pipes: I. Conduit Pipes Manufacture Moulding : Horizontal 
 Machines, Vertical Machines, Worked by Hand and Steam Particulars of these Machines 
 Drying Firing II. Chimney Flues Ventiducts and " Bpisseaux," " Waggons " Particulars 
 of these Products. Chapter VI., Quarries: 1, Plain Quarries of Ordinary Clay; 2, of Cleaned 
 Clay Machines, Cutting, Mixing, Polishing Drying and Firing Applications Particulars of 
 Quarries. Chapter VII., Terra-cotta : History Manufacture Application : Balustrades, 
 Columns, Pilasters, Capitals, Friezes, Frontons, Medallions, Panels, Rose-windows, Ceilings 
 Appendix : Official Methods of Testing Terra-cottas. 
 
 Part II. Made = up or Decorated Pottery. Chapter I., General Remarks on the Deco- 
 ration of Pottery : Dips Glazes : Composition, Colouring, Preparation, Harmony with 
 Pastes Special Processes of Decoration Enamels, Opaque, Transparent, Colours, Under- 
 glaze, Over-glaze Other Processes : Crackling, Mottled, Flashing, Metallic Iridescence, 
 Lustres. Chapter II., Glazed and Enamelled Bricks History: Glazing Enamelling Appli- 
 cations : Ordinary Enamelled Bricks, Glazed Stoneware, Enamelled Stoneware Enamelled 
 Tiles. Chapter III., Decorated Quarries: I. Paving Quarries 1, Decorated with Dips 2, 
 Stoneware: A, Fired to Stoneware; a, of Slag Base Applications; b, of Melting Clay 
 Applications B, Plain or Incrusted Stoneware; a, of Special Clay (Stoke-on-Trent) Manu- 
 facture Application b, of Felspar Base Colouring, Manufacture, Moulding, Drying, Firing 
 Applications. II. Facing Quarries 1, in Faience A, of Limestone Paste B, of Silicious 
 Paste C, of Felspar Paste Manufacture, Firing 2, of Glazed Stoneware 3, of Porcelain 
 Applications of Facing Quarries. III. Stove Quarries Preparation of the Pastes, Moulding, 
 Firing, Enamelling, Decoration Applications Faiences for Fireplaces. Chapter IV., Archi- 
 tectural Decorated Pottery: 1, Faiences; 2, Stoneware; 3, Porcelain. Chapter V., 
 Sanitary Pottery: Stoneware Pipes : Manufacture, Firing Applications Sinks Applications 
 Urinals, Seats and Pans Applications Drinking-fountains, Washstands. Index. 
 
 A TREATISE ON THE CERAMIC INDUSTRIES. A 
 
 Complete Manual for Pottery, Tile and Brick Works. By EMILE 
 BOURRY, Ingenieur des Arts et Manufactures. Translated from the 
 French by WILTON P. Rix, Examiner in Pottery and Porcelain to the 
 City and Guilds of London Technical Institute, Pottery Instructor to 
 the Hanley School Board. Royal 8vo. 1901. Over 700 pp. Price 
 21s. ; India and Colonies, 22s. ; Other Countries, 23s. 6d. ; strictly net. 
 Contents. 
 
 Part I., General Pottery Methods. Chapters I., Definition and History. Definitions 
 .and Classification of Ceramic Products Historic Summary of the Ceramic Art. II., Raw 
 Materials of Bodies. Clays : Pure Clay and Natural Clays Various Raw Materials : Analogous 
 to Clay Agglomerative and Agglutinative Opening Fusible Refractory Trials of Raw 
 Materials. III., Plastic Bodies. Properties and Composition Preparation of Raw Materials: 
 Disaggregation Purification Preparation of Bodies : By Plastic Method By Dry Method 
 By Liquid Method. IV., Formation. Processes of Formation : Throwing Expression 
 Moulding by Hand, on the Jolley, by Compression, by Slip Casting Slapping Slipping. V., 
 Drying. Drying of Bodies Processes of Drying : By Evaporation By Aeration By 
 Heating By Ventilation By Absorption. VI., Glazes. Composition and Properties Raw 
 Materials Manufacture and Application. VII., Firing. Properties of the Bodies and Glazes 
 during Firing Description of the Kilns Working of the Kilns. VIII., Decoration. Colouring 
 Materials Processes of Decoration. 
 
 Part II., Special Pottery Methods. Chapters IX., Terra Cottas. Classification: 
 Plain Ordinary, Hollow, Ornamental, Vitrified, and Light Bricks Ordinary and Black Tiles 
 Paving Tiles Pipes Architectural Terra Cottas Vases, Statues and Decorative Objects 
 Common Pottery Pottery for Water and Filters Tobacco Pipes Lustre Ware Properties 
 and Tests for Terra Cottas. X., Fireclay Goods. Classification : Argillaceous, Aluminous, 
 Carboniferous, Silicious and Basic Fireclay Goods Fireclay Mortar (Pug) Tests for Fireclay 
 Goods. XL, Faiences. Varnished Faiences Enamelled Faiences Silicious Faiences Pipe- 
 clay Faiences Pebble Work Feldspathic Faiences Composition, Processes of Manufacture 
 ^nd General Arrangements of Faience Potteries. XII., Stoneware. Stoneware Properly So- 
 called : Paving Tiles Pipes Sanitary Ware Stoneware for Food Purposes and Chemical 
 Productions Architectural Stoneware Vases, Statues and other Decorative Objects Fine 
 Stoneware. XIII., Porcelain. Hard Porcelain for Table Ware and Decoration, for the Fire, 
 for Electrical Conduits, for Mechanical Purposes; Architectural Porcelain, and Dull or Biscuit 
 Porcelain Soft Phosphated or English Porcelain Soft Vitreous Porcelain, French and New 
 Sevres Argillaceous Soft or Seger's Porcelain Dull Soft or Parian Porcelain Dull Felds- 
 pathic Soft Porcelain. Index. 
 
 THE ART OF RIVETING GLASS, CHINA AND 
 EARTHENWARE. By J. HOWARTH. Second Edition. 
 1900. Price Is. net; by post, home or abroad, Is. Id. 
 
 Tools and Materials Required Wire Used for Rivets Soldering Solution Preparation 
 for Drilling Commencement of Drilling Cementing Preliminaries to Riveting Rivets to 
 Make To Fix the Rivets Through-and-through Rivets Soldering Tinning a Soldering-iron 
 Perforated Plates, Handles, etc. Handles of Ewers, etc. Vases and Comports Marble 
 and Alabaster Ware Decorating How to Loosen Fast Decanter Stoppers China Cements. 
 
20 
 
 NOTES OF POTTERY CLAYS. Their Distribution, Pro- 
 perties, Uses and Analyses of Ball Clays, China Clays and China 
 Stone. By JAS. FAIRIE, F.G.S. 1901. 132 pp. Crown Svo. Price 
 3s. 6d. ; India and Colonies, 4s. ; Other Countries, 4s. 6d. ; strictly net. 
 Contents. 
 
 Definitions Occurrence Brick Clays Fire Clays Analyses of Fire Clays. Ball Clays 
 Properties Analyses Occurrence Pipe Clay Black Clay Brown Clay Blue Clay Dor- 
 setshire and Devonshire Clays. China Clay or Kaolin Occurrence Chinese Kaolin Cornish 
 Clays Hensbarrow Granite Properties, Analyses and Composition of China Clays 
 Method of Obtaining China Clay Experiments with Chinese Kaolin Analyses of Chinese 
 and Japanese Clays and Bodies Irish Clays. Chinese Stone Composition Occurrence 
 Analyses. Index. 
 
 PAINTING ON GLASS AND PORCELAIN AND 
 ENAMEL PAINTING. A Complete Introduction to the 
 Preparation of all the Colours and Fluxes used for Painting on Porce- 
 lain, Enamel, Faience and Stoneware, the Coloured Pastes and Col- 
 oured Glasses, together with a Minute Description of the Firing of 
 Colours and Enamels. On the Basis of Personal Practical Experience 
 of the Condition of the Art up to Date. By FELIX HERMANN, Technical 
 Chemist. With Eighteen Illustrations. 300 pp. Translated from the 
 German second and enlarged Edition. 1897. Price 10s. 6d. ; India 
 and Colonies, 11s.; Other Countries, 12s.; strictly net. 
 Contents. 
 
 History of Glass Painting. Chapters I., The Articles to be Painted : Glass, Porcelain, 
 Enamel, Stoneware, Faience. II., Pigments: 1, Metallic Pigments: Antimony Oxide, Naples 
 Yellow, Barium Chromate, Lead Chromate, Silver Chloride, Chromic Oxide. III., Fluxes: 
 Fluxes, Felspar, Quartz, Purifying Quartz, Sedimentation, Quenching, Borax, Boracic Acid r 
 Potassium and Sodium Carbonates, Rocaille Flux. IV., Preparation of the Colours for Glass 
 Painting. V., The Colour Pastes. VI., The Coloured Glasses. VII., Composition of the 
 Porcelain Colours. VIII., The Enamel Colours: Enamels for Artistic Work. IX., Metallic 
 Ornamentation: Porcelain Gilding, Glass Gilding. X., Firing the Colours: 1, Remarks on 
 Firing: Firing Colours on Glass, Firing Colours on Porcelain; 2, The Muffle. XI., Accident* 
 occasionally Supervening during the Process of Firing. XII., Remarks on the Different 
 Methods of Painting on Glass, Porcelain, etc. Appendix: Cleaning Old Glass Paintings. 
 
 Press Opinions. 
 
 " Mr. Hermann, by a careful division of his subject, avoids much repetition, yet makes 
 sufficiently clear what is necessary to be known in each art. He gives very many formulae ; 
 and his hints on the various applications of metals and metallic lustres to glass and porcelains 
 will be found of much interest to the amateur." Art Amateur, New York. 
 
 " For the unskilled and amateurs the name of the publishers will be sufficient guarantee for 
 the utility and excellence of Mr. Hermann's work, even if they are already unacquainted with 
 the author. . . . The whole cannot fail to be both of service and interest to glass workers and 
 to potters generally, especially those employed upon high-class work." Staffordshire Sentinel. 
 
 " In Painting on Glass and Porcelain the author has dealt very exhaustively with the 
 technical as distinguished from the artistic side of his subject, the work being entirely devoted 
 to the preparation of the colours, their application and firing. For manufacturers and students 
 it will be a valuable work, and the recipes which appear on almost every page form a very 
 valuable feature. The author has gained much of his experience in the celebrated Sevres 
 manufactory, a fact which adds a good deal of authority to the work." Builders Journal. 
 
 "The compiler displays that painstaking research characteristic of his nation, and goes at 
 length into the question of the chemical constitution of the pigments and fluxes to be used in- 
 glass-painting, proceeding afterwards to a description of the methods of producing coloured 
 glass of all tints and shades. . . . Very careful instructions are given for the chemical and 
 mechanical preparation of the colours used in glass-staining and porcelain-painting; indeed, 
 to the china painter such a book as this should be of permanent value, as the author claims t& 
 have tested and verified every recipe he includes, and the volume also comprises a section de- 
 voted to enamels both opaque and translucent, and another treating of the firing of porcelain, 
 and the accidents that occasionally supervene in the furnace." Daily Chronicle. 
 
 A Reissue of 
 
 THE HISTORY OF THE STAFFORDSHIRE POTTER- 
 IES ; AND THE RISE AND PROGRESS OF THE 
 MANUFACTURE OF POTTERY AND PORCELAIN. 
 
 With References to Genuine Specimens, and Notices of Eminent Pot- 
 ters. By SIMEON SHAW. (Originally Published in 1829.) 265 pp. 
 1900. Demy Svo. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
 Countries, 8s. 6d. ; strictly net. 
 
21 
 Contents. 
 
 Introductory Chapter showing the position of the Pottery Trade at the present time 
 1899). Chapters I., Preliminary Remarks. II., The Potteries, comprising Tunstall, 
 Brownhills, Greenfield and New Field, Golden Hill, Latebrook, Green Lane, Burslem, Long- 
 port and Dale Hall, Hot Lane and Cohjidge, Hanley and Shelton, Etruria, Stoke, Penkhull, 
 Fenton, Lane Delph, Foley, Lane End. III., On the Origin of the Art, and its Practice 
 among the early Nations. IV., Manufacture of Pottery, prior to 1700. V., The Introduc 
 don of Red Porcelain by Messrs. Elers, of Bradwell, 1690. VI., Progress of the Manu 
 acture from 1700 to Mr. Wedgwood's commencement in 1760. VII. Introduction of Fluid 
 Glaze. Extension of the Manufacture of Cream Colour. Mr. Wedgwood's Queen's Ware. 
 Jasper, and Appointment of Potter to Her Majesty. Black Printing. VIII., Introduction 
 Of Porcelain. Mr. W. Littler's Porcelain. Mr. Cookworthy's Discovery of Kaolin and 
 Petuntse, and Patent. Sold to Mr. Champion resold to the New Hall Com. Extension of 
 Term. IX., Blue Printed Pottery. Mr. Turner, Mr. Spode (1), Mr. Baddeley, Mr. Spode 
 (2), Messrs. Turner, Mr. Wood, Mr. Wilson, Mr. Minton. Great Change in Patterns of Blue 
 Printed. X., Introduction of Lustre Pottery. Improvements in Pottery and Porcelain 
 subsequent to 1800. 
 
 Press Opinions. 
 
 " There is much curious and useful information in the work, and the publishers have rendered 
 the public a service in reissuing it." Burton Mail, 
 
 "Copies of the original work are now of considerable value, and the facsimile reprint now 
 issued cannot but prove of considerable interest to all interested in the great industry." Derby 
 Mercury. 
 
 " The book will be especially welcomed at a time when interest in the art of pottery manu- 
 facture commands a more widespread and general interest than at any previous time." 
 Wolverhampton Chronicle. 
 
 "This work is all the more valuable because it gives one an idea of the condition of affairs 
 existing in the north of Staffordshire before the great increase in work and population due to 
 modern developments." Western Morning News. 
 
 . . The History gives a graphic picture of North Staffordshire at the end of the last and 
 the beginning of the present century, and states that in 1829 there was 'a busy and enterprising 
 community ' in the Potteries of fifty thousand persons. . . . We commend it to our readers as 
 a most entertaining and instructive publication." Staffordshire Sentinel. 
 
 A Reissue of 
 
 THE CHEMISTRY OF THE SEVERAL NATURAL 
 AND ARTIFICIAL HETEROGENEOUS COM- 
 POUNDS USED IN MANUFACTURING POR- 
 CELAIN, GLASS AND POTTERY. By SIMEON SHAW. 
 (Originally published in 1837.) 750 pp. 1900. Royal 8vo. Price 14s. ; 
 India and Colonies, 15s. ; Other Countries, 16s. 6d. ; strictly net. 
 
 Contents. 
 
 PART I., ANALYSIS AND MATERIALS. Chapters I., Introduction : Laboratory and 
 Apparatus; Elements: Combinative Potencies, Manipulative Processes for Analysis and 
 Reagents, Pulverisation, Blow-pipe Analysis, Humid Analysis, Preparatory Manipulations, 
 General Analytic Processes, Compounds Soluble in Water, Compounds Soluble only in Acids, 
 Compounds (Mixed) Soluble in Water, Compounds (Mixed) Soluble in Acids, Compounds 
 Mixed) Insoluble, Particular Analytic Processes. II., Temperature: Coal, Steam Heat for 
 Printers' Stoves. III., Acids and Alkalies : Boracic Acid, Muriatic Acid, Nitric Acid, Sul- 
 phuric Acid, Potash, Soda, Lithia, Calculation of Chemical Separations. IV., The Earths : 
 Alumine, Clays, Silica, Flint, Lime, Plaster of Paris, Magnesia, Barytes, Felspar, Grauen (or 
 China Stone), China Clay, Chert. V., Metals : Reciprocal Combinative Potencies of the Metals, 
 Antimony, Arsenic, Chromium, Green Oxide, Cobalt, Chromic Acid, Humid Separation of 
 Nickel from Cobalt, Arsenite of Cobalt, Copper, Gold, Iron, Lead, Manganese, Platinum, Silver, 
 Tin, Zinc. 
 
 PART II., SYNTHESIS AND COMPOUNDS. Chapters I., Sketch of the Origin and 
 Progress of the Art. II., Science of Mixing : Scientific Principles of the Manufacture, Com- 
 binative Potencies of the Earths. III., Bodies : Porcelain Hard, Porcelain Fritted Bodies, 
 Porcelain Raw Bodies, Porcelain Soft, Fritted Bodies, Raw Bodies, Stone Bodies, Ironstone, 
 Dry Bodies, Chemical Utensils, Fritted Jasper, Fritted Pearl, Fritted Drab, Raw Chemical 
 Utensils, Raw Stone, Raw Jasper, Raw Pearl, Raw Mortar, Raw Drab, Raw Brown, Raw Fawn, 
 Raw Cane, Raw Red Porous, Raw Egyptian, Earthenware, Queen's Ware, Cream Colour, Blue 
 and Fancy Printed, Dipped and Mocha, Chalky, Rings, Stilts, etc. IV., Glazes : Porcelain- 
 Hard Fritted, Porcelain Soft Fritted, Porcelain Soft Raw, Cream Colour Porcelain, Blue 
 Printed Porcelain, Fritted Glazes, Analysis of Fritt, Analysis of Glaze, Coloured Glazes, Dips, 
 Smears and Washes; Glasses: Flint Glass, Coloured Glasses, Artificial Garnet, Artificial 
 Emerald, Artificial Amethyst, Artificial Sapphire, Artificial Opal, Plate Glass, Crown Glass, 
 Broad Glass, Bottle Glass, Phosphoric Glass, British Steel Glass, Glass-Staining and Painting, 
 Engraving on Glass, Dr. Faraday's Experiments. V., Colours: Colour Making, Fluxes or 
 Solvents, Components of the Colours; Reds, etc., from Gold, Carmine or Rose Colour, 
 Purple, Reds, etc., from Iron, Blues, Yellows, Greens, Blacks, White, Silver for Burnishing, 
 Gold for Burnishing, Printer's Oil, Lustres. 
 
22 
 
 PART III., TABLES OF THE CHARACTERISTICS OF CHEMICAL SUB- 
 STANCES. Preliminary Remarks, Oxygen (Tables), Sulphur and its Compounds, Nitrogen 
 ditto, Chlorine. ditto, Bromine ditto, Iodine ditto, Fluorine ditto, Phosphorous ditto, Boron ditto, 
 Carbon ditto, Hydrogen ditto, Observations, Ammonium and its Compounds (Tables), Thorium 
 ditto, Zirconium ditto, Aluminium ditto, Yttrium ditto, Glucinum ditto, Magnesium ditto, 
 Calcium ditto, Strontium ditto, Barium ditto, Lithium ditto, Sodium and its' Compounds 
 Potassium ditto, Observations, Selenium and its Compounds (Tables), Arsenic ditto, Chromium 
 ditto, Vanadium ditto, Molybdenum ditto, Tungsten ditto, Antimony ditto, Tellurium ditto, 
 Tantalum ditto, Titanium ditto, Silicium ditto, Osmium ditto, Gold ditto, Iridium ditto, Rhodium 
 ditto, Platinum ditto, Palladium ditto, Mercury ditto, Silver ditto, Copper ditto, Uranium ditto, 
 Bismuth and its Compounds, Tin ditto, Lead ditto, Cerium ditto, Cobalt ditto, Nickel ditto, 
 Iron ditto, Cadmium ditto, Zinc ditto, Manganese ditto, Observations, Isomorphous Groups, 
 Isomeric ditto, Metameric ditto, Polymeric ditto, Index. 
 
 Press Opinions. 
 
 "This interesting volume has been kept from the pencil of the modern editor and reprinted 
 in its entirety by the enterprising publishers of The Pottery Gazette and other trade journals. 
 . . . There is an excellent historical sketch of the origin and progress of the art of pottery 
 which shows the intimate knowledge of classical as well as (the then) modern scientific litera- 
 ture possessed by the late Dr. Shaw; even the etymology of many of the Staffordshire place- 
 names is given." Glasgow Herald. 
 
 "The historical sketch of the origin and progress of pottery is very interesting and instruc- 
 tive. The science of mixing is a problem of great importance, and the query how the natural 
 products, alumina and silica can be compounded to form the best wares may be solved by the 
 aid of chemistry instead of by guesses, as was formerly the case. This portion of the book may 
 be most suggestive to the manufacturer, as also the chapters devoted to the subject of glazes, 
 glasses and colours." Birmingham Post. 
 
 " Messrs. Scott, Greenwood & Co. are doing their best to place before the pottery trades 
 some really good books, likely to aid the Staffordshire manufacturers, and their spirited enter- 
 prise is worthy of encouragement, for the utility of technical literature bearing upon the 
 I ractical side of potting goes without saying. . . . They are to be congratulated on ther 
 enterprise in republishing it, and we can only hope that they will meet with the support they 
 deserve. It seems to be a volume that is worth looking through by both manufacturers and 
 operatives alike, and all local institutions, at any rate, should secure copies." Staffordshire 
 Sentinel. 
 
 Paper Making. 
 
 THE DYEING OF PAPER PULP. A Practical Treatise for 
 the use of Papermakers, Paperstainers, Students and others. By 
 JULIUS ERFURT, Manager of a Paper Mill. Translated into English 
 and Edited with Additions by JULIUS HUBNER, F.C.S., Lecturer on 
 Papermaking at the Manchester Municipal Technical School. With 
 Illustrations and 157 patterns of paper dyed in the pulp. Royal 
 8vo, 180 pp. 1901. Price 15s.; India and Colonies, 16s.; Other 
 Countries, 20s. ; strictly net. Limited edition. 
 
 Contents. 
 
 1., Behaviour of the Paper Fibres during the Process of Dyeing, Theory of the 
 Mordant Cotton; Flax and Hemp; Esparto; Jute; Straw Cellulose; Chemical and Mechani- 
 cal Wood Pulp; Mixed Fibres; Theory of Dyeing. II., Colour Fixing Mediums (Mordants) 
 Alum; Aluminium Sulphate; Aluminium Acetate; Tin Crystals (Stannous Chloride); Cop- 
 peras (Ferrous Sulphate); Nitrate of Iron (Ferric Sulphate); Pyrolignite of Iron (Acetate of 
 Iron); Action of Tannic Acid; Importance of Materials containing Tannin; Treatment with 
 Tannic Acid of Paper Pulp intended for dyeing ; Blue Stone (Copper Sulphate) ; Potassium 
 Bichromate; Sodium Bichromate; Chalk (Calcium Carbonate); Soda Crystals (Sodium Car- 
 bonate) ; Antimony Potassium Tartrate (Tartar Emetic). III., Influence of the Quality of 
 the Water Used. IV., Inorganic Colours 1. Artificial Mineral Colours: Iron Buff; Man- 
 ganese Bronze; Chrome Yellow (Chromate of Lead); Chrome Orange (Basic Chromate of 
 Lead) ; Red Lead ; Chrome Green ; Blue with Yellow Prussiate ; Prussian Blue ; Method for 
 Producing Prussian Blue free from Acid; Ultramarine 2. Natural Mineral Colours (Earth 
 Colours): Yellow Earth Colours; Red Earth Colours; Brown Earth Colours; Green, Grey and 
 Black Earth Colours; White Earth Colours; White Clay (China Clay): White Gypsum; 
 Baryta; Magnesium Carbonate; Talc, Soapstone. V., Organic Colours 1. Colours of 
 Vegetable and Animal Origin : (a) Substantive (Direct Dyeing) Colouring Matters : Annatto ; 
 Turmeric ; Safflower ; (b) Adjective (Indirect Dyeing) Colouring Matters : Redwood ; Cochineal ; 
 Weld ; Persian Berries ; Fustic Extract ; Quercitron ; Catechu (Cutch) ; Logwood Extract 2. 
 Artificial Organic (Coal Tar) Colours: Acid Colours; Basic Colours; Substantive (Direct 
 Dyeing) Colours; Dissolving of the Coal Tar Colours; Auramine 00 ; Naphthol Yellow S; 
 
 euinoline Yellow ; Metanil Yellow ; Paper Yellow ; Azoflavine RS, S; Cotton Yellow 
 xx and Rxx ; Orange 11; Chrysoidine A 00 , RL; Vesuvine Extra 00 ; Vesuvine BC; Fast 
 
23 
 
 Brown,Naphthylamine Brown ; Water Blue IN ; Water Blue TB ; Victoria Blue B Methy- 
 lene Blue MD; Nile Blue R; New Blue S; Indoine Blue BB; Eosine442 NX; Phloxine 
 BBN ; Rhodamine B; Rhodamine 6G; Naphthylamine Red G ; Fast Red A; Cotton 
 Scarlet ; Erythrine RR ; Erythrine X; Erythrine P; Ponceau 2 R; Fast Ponceau G and 
 B; Paper Scarlet P ; Saffranine PP* 1 ; Magenta Powder A 00 ; Acetate of Magenta 00 ; 
 Cerise D 10; Methyl Violet BB ; Crystal Violet 00 ; Acid Violet 3 BN, 4 R; Diamond 
 Green B; Nigrosine WL; Coal Black 00 ; Brilliant Black B. VI., Practical Application 
 of the Coal Tar Colours according to their Properties and their Behaviour towards 
 the Different Paper Fibres Coal Tar Colours, which rank foremost, as far as their fastness 
 to light is concerned ; Colour Combinations with which colourless or nearly colourless Back- 
 water is obtained ; Colours which do not bleed into White Fibres, for Blotting and Copying 
 Paper Pulp ; Colours which produce the best results on Mechanical Wood and on Unbleached 
 Sulphite Wood; Dyeing of Cotton, Jute and Wool Half-stuff for Mottling White or Light 
 Coloured Papers; Colours suitable for Cotton; Colours specially suitable for Jute Dyeing; 
 Colours suitable for Wool Fibres. VII., Dyed Patterns on Various Pulp Mixtures- 
 Placard and Wrapping Papers ; Black Wrapping and Cartridge Papers ; Blotting Papers ; 
 Mottled and Marbled Papers made with Coloured Linen, Cotton and Union Rags, or with 
 Cotton, Jute, Wool and Sulphite Wood Fibres, dyed specially for this purpose; Mottling with 
 Dark Blue Linen ; Mottling with Dark Blue Linen and Dark Blue Cotton ; Mottling with Dark 
 Blue Cotton; Mottling with Dark Blue and Red Cotton; Mottling with Dark Red Cotton; 
 Mottling of Bleached Stuff, with 3 to 4 per cent, of Dyed Cotton Fibres ; Mottling with Dark 
 Blue Union (Linen and Wool or Cotton Warp with Wool Weft); Mottling with Blue Striped 
 Red Union ; Mottling of Bleached Stuff with 3 to 4 per cent, of Dyed Wool Fibres; Mottling 
 of Bleached Stuff with 3 to 4 per cent, of Dyed Jute Fibres ; Mottling of Bleached Stuff with 
 3 to 4 per cent, of Dyed Sulphite Wood Fibres; Wall Papers; Packing Papers. VIII., 
 Dyeing to Shade Index. 
 
 Press Opinions. 
 
 " The book is one that is of value to every one connected with the colouring of paper." 
 Paper Trade Journal. 
 
 "The great feature of the volume is undoubtedly the series of actual patterns of dyed 
 papers, 157 in all twelve of which, made in England, have been added to the original German 
 series. Detailed formulae are given for the preparation of the pulp for each, and the tints of 
 the samples practically form a key, by means of which the accuracy of the student's or 
 practitioner's experiments can be tested. . . . On the whole the publication is one of distinct 
 importance to the trade, and will no doubt speedily become a standard work of reference 
 amongst papermakers, both in the 'lab. 1 and the office, as well as being an excellent text-book 
 for the use of students in the increasing number of technical institutes in which papermaking 
 is taught." World's Paper Trade Review, 
 
 Enamelling on Metal. 
 
 ENAMELS AND ENAMELLING. An Introduction to the 
 Preparation and Application of all Kinds of Enamels for Technical and 
 Artistic Purposes. For Enamel Makers, Workers in Gold and Silver, 
 and Manufacturers of Objects of Art. By PAUL RANDAU. Translated 
 from the German. With Sixteen Illustrations. 180 pp. 1900. Price 
 10s. 6d. ; India and Colonies, lls. ; Other Countries, 12s. ; strictly net. 
 Contents. 
 
 I., Introduction. II., Composition and Properties of Glass. III., Raw Materials for the 
 Manufacture of Enamels. IV., Substances Added to Produce Opacity. V., Fluxes. VI., Pig- 
 ments. VII., Decolorising Agents. VIII., Testing the Raw Materials with the Blow-pipe 
 Flame. IX., Subsidiary Materials. X., Preparing the Materials for Enamel Making. XL, 
 Mixing the Materials. XII., The Preparation of Technical Enamels, The Enamel Mass. 
 XIII., Appliances for Smelting the Enamel Mass. XIV., Smelting the Charge. XV., Com- 
 position of Enamel Masses. XVI., Composition of Masses for Ground Enamels. XVII. 
 
 epairmg 
 
 Articles of Sheet Metal. XXIV., Decorating Enamelled Ware. XXV., Specialities in Ena- 
 melling. XXVI., Dial-plate Enamelling. XXVII., Enamels for Artistic Purposes, Recipes 
 for Enamels of Various Colours. Index. 
 
 Press Opinions. 
 
 " Should prove of great service to all who are either engaged in or interested in the art or 
 enamelling." -Jewellers and Watchmakers' Trade Advertiser. 
 
 " I must inform you that this is the best book ever I have come across on enamels, and it is 
 worth double its cost." J. MINCHIN, Jr., Porto, Portugal, 22nd July, 1900. 
 
 "This is a very useful and thoroughly practical treatise, and deals with every branch of the 
 enameller's art. The manufacture of enamels of various colours and the methods of their 
 application are described in detail. Besides the commoner enamelling processes, some of the 
 more important special branches of the business, such as cloisonne work are dealt with. The 
 work is well got up, and the illustrations of apparatus are well executed. The translator is 
 evidently a man well acquainted both with the German language and the subject-matter of the 
 book. ' ' Invention. 
 
24 
 
 " This is a most welcome volume, and one for which we have long waited in this country. 
 For years we have been teaching design applied to enamelling as well as to several other 
 crafts, but we have not risen to the scientific side of the question. Here is a handbook dealing 
 with the composition and making of enamels for application to metals for the most part, but 
 also for other allied purposes. It is written in a thoroughly practical way, and its author 
 Paul Randau has made its subject a very particular study. The result, like almost all things 
 which come from the German chemical expert, is a model of good workmanship and arrange- 
 ment, and no one who is in search of a handbook to enamelling, no matter whether he is a 
 craftsman producing his beautiful translucent colours on gold, silver and copper, or the hollow- 
 ware manufacturer making enamelled saucepans and kettles, can wish for a more useful 
 practical manual." Birmingham Gazette. 
 
 THE ART OF ENAMELLING ON METAL. By W. 
 
 NORMAN BROWN. Twenty-eight Illustrations. Crown 8vo. 60 pp. 
 1900. Price 2s. 6d. ; Abroad, 3s. ; strictly net. 
 Contents. 
 
 Chapters I., History Cloisonne Champs Leve Translucent Enamel Surface Painted 
 Enamels. II., Cloisonne Champs Leves Translucent Painted. III., Painted Enamel 
 Apparatus Furnaces and Muffles for Firing. IV., The Copper Base or Plate Planishing 
 Cloisons Champ Leve Plates. V., Enamels Trituration Washing Coating a Plate with 
 Enamel Firing Ordinary Plaques for Painting Designing Squaring off. VI., Designs for 
 Cloisonne Designs for Painted Enamels Technical Processes Brushes, etc., Colours 
 Grisaille Full-coloured Designs. 
 
 Press Opinion. 
 
 "The information conveyed in The Art of Enamelling on Metal is as complete as can be ex- 
 pected in a manual of ordinary length, and is quite ample in all respects to start students in a 
 most interesting branch of decorative art. All necessary requisites are fully described and 
 illustrated, and the work is one, indeed, which any one may pursue with interest, for those who 
 are interested artistically in enamels are a numerous body." Hardware Metals and Machinery. 
 
 Books on Textile and Dyeing 
 Subjects. 
 
 THE TECHNICAL TESTING OF YARNS AND TEX- 
 TILE FABRICS. With Reference to Official Specifica- 
 tions. Translated from the German of Dr. J. HERZFELD. Second 
 Edition. Sixty-nine Illustrations. 200 pp. Demy 8vo. 1901. Price 
 10s. 6d. ; India and Colonies, 11s. ; Other Countries, 12s. ; strictly net. 
 
 Contents. 
 
 Yarn Testing. III., Determining the Yarn Number. IV., Testing the Length of 
 Yarns. V., Examination of the External Appearance of Yarn. VI., Determining the 
 Twist of Yarn and Twist. VII., Determination of Tensile Strength and Elasticity. 
 VIII., Estimating the Percentage of Fat in Yarn. IX., Determination of Moisture 
 
 (Conditioning). Appendix. 
 
 Press Opinions. 
 
 " It would be well if our English manufacturers would avail themselves of this important 
 addition to the extensive list of German publications which, by the spread of technical infor- 
 mation, contribute in no small degree to the success, and sometimes to the supremacy, of 
 Germany in almost every branch of textile manufacture." Manchester Courier. 
 
 "This is probably the most exhaustive book published in English on the subject dealt with. 
 . We have great confidence in recommending the purchase of this book by all manu- 
 facturers of textile goods of whatever kind, and are convinced that the concise and direct way 
 in which it is written, which has been admirably conserved by the translator, renders it 
 peculiarly adapted for the use of English readers." Textile Recorder. 
 
 " A careful study of this book enables one to say with certainty that it is a standard work on 
 the subject. Its importance is enhanced greatly by the probability that we have here, for the 
 first time in our own language, in one volume, a full, accurate, and detailed account, by a prac- 
 tical expert, of the best technical methods for the testing of textile materials, whether in the 
 raw state or in the more or less finished product." Glasgow Herald. 
 
 "The author has endeavoured to collect and arrange in systematic form for the first time 
 all the data relating to both physical and chemical tests as used throughout the whole of the 
 textile industry, so that not only the commercial and textile chemist, who has frequently to 
 reply to questions on these matters, but also the practical manufacturer of textiles and his 
 subordinates, whether in spinning, weaving, dyeing, and finishing, are catered for. . . . The 
 book is profusely illustrated, and the subjects of these illustrations are clearly described." 
 Textile Manufacturer. 
 
25 
 DECORATIVE AND FANCY TEXTILE FABRICS. 
 
 With Designs and Illustrations. By R. T. LORD. A Valuable Book for 
 Manufacturers and Designers of Carpets, Damask, Dress and all Textile 
 Fabrics. 200pp. 1898. DemySvo. 132 Designs and Illustrations. Price 
 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Chapters I., A Few Hints on Designing Ornamental Textile Fabrics. II., A Few Hints on 
 Designing Ornamental Textile Fabrics (continued). III., A Few Hints on Designing Orna- 
 mental Textile Fabrics (continued). IV., A Few Hints on Designing Ornamental Textile 
 Fabrics (continued). V., Hints for Ruled-paper Draughtsmen. VI., The Jacquard Machine. 
 VII., Brussels and Wilton Carpets. VIII., Tapestry Carpets. IX., Ingrain Carpets. X., 
 Axminster Carpets. XI., Damask and Tapestry Fabrics. XII., Scarf Silks and Ribbons. 
 XIII., Silk Handkerchiefs. XIV., Dress Fabrics. XV., Mantle Cloths. XVI., Figured Plush. 
 XVII., Bed Quilts. XVIII., Calico Printing. 
 
 Press Opinions. 
 
 "The book can be strongly recommended to students and practical men." Textile Coloutist* 
 
 "Those engaged in the designing of dress, mantle tapestry, carpet and other ornamental 
 textiles will find this volume a useful work of reference." Leeds Mercury. 
 
 "The bosk is to be commended as a model manual, appearing at an opportune time, since 
 every day is making known a growing desire for development in British industrial art." 
 Dundee Advertiser. 
 
 " Designers especially, who desire to make progress in their calling, will do well to take the 
 hints thrown out in the first four chapters on ' Designing Ornamental Textile Fabrics '." 
 Nottingham Daily Guardian. 
 
 POWER-LOOM WEAVING AND YARN NUMBERING, 
 
 According to Various Systems, with Conversion Tables. An Auxiliary 
 and Text-book for Pupils of Weaving Schools, as well as for Self- 
 Instruction and for General Use by those engaged in the Weaving 
 Industry. Translated from the German of ANTHON GRUNER. With 
 Twenty-six Diagrams in Colours. 150 pp. 1900. Crown 8vo. Price 
 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 I., Power=Loom Weaving in General. Various Systems of Looms. II., Mounting 
 and Starting the Power=Loom. English Looms. Tappet or Treadle Looms. Dobbies. 
 III., General Remarks on the Numbering, Reeling and Packing of Yarn. Appendix. 
 Useful Hints. Calculating Warps. Weft Calculations. Calculations of Cost Price in Hanks. 
 
 Press Opinions. 
 
 " A long-felt want in the weaving industry has been suppliedjby the issue of a cheap volume 
 dealing with the subject." Belfast Evening Telegraph. 
 
 "The work has been clearly translated from the German and published with suitable 
 illustrations. . . . The author has dealt very practically with the subject." Bradford Daily 
 Telegraph. 
 
 "The book, which contains a number of useful coloured diagrams, should prove invaluable 
 to the student, and its handy form will enable it to become a companion more than some cum- 
 brous work." Cotton Factory Times. 
 
 " The book has been prepared with great care, and is most usefully illustrated. It is a capital 
 text-book for use in the weaving schools or for self-instruction, while all engaged in the weaving 
 industry will find its suggestions helpful." Northern Daily Telegraph. 
 
 " The various systems are treated in a careful manner; also the different looms and their 
 manufacture, as well as the whole processes of the work. Yarn numbering according to various 
 systems, with conversion tables and numerous coloured diagrams, materially assist to a clear 
 comprehension of the subject." Northern Whig. 
 
 "The ' inside ' managers of our textile mills in which the work is complex or greatly varied, 
 and where yarns of different materials are in use, will find this work convenient for reference in 
 case of novelty or difficulty. We may also say the same in relation to the textile student. Its 
 description of the parts of the loom and their functions will be of use to the latter, being of the 
 most elementary kind." Textile Mercury. 
 
 " The author attempts to fill a gap in weaving literature caused by the neglect of many 
 obscure points connected with the industry. A short review is given of the power-loom as a 
 whole, followed by a description of the different parts of the machinery with their advantages 
 and defects. . . . The book is severely technical, but must on that account be very valuable to 
 the pupil who is determined to master this industrial art.'" Cheshire County News. 
 
 " It is clear and concise, and gives just that knowledge in quality and amount which any 
 
 student of the weaving industry ought to consider as a minimum necessary for his thorough 
 
 comprehension of his future profession. The handiness and variety of the information com- 
 
 nrised in Section III., dealing with the numbering and reeling of yarns employed in the various. 
 
 terns in different countries, struck us as particularly useful " North British Daily Mail. 
 
26 
 
 "This work brings before weavers who are actually engaged in the various branches of 
 fabrics, as well as the technical student, the different parts of the general run of power looms in 
 such a manner that the parts of the loom and their bearing to each other can be readily under- 
 stood. . . . The work should prove of much value, as it is in every sense practical, and is put 
 before the reader in such a clear manner that it can be easily understood." Textile Industries. 
 
 "The book under notice is intended as an instructor to those engaged in power-loom weaving, 
 and, judging by its compilation, the author is a thorough master of the craft. It is not over- 
 loaded with details, and he manages to compress in a book of some 150 pages all that one can 
 possibly wish to know about the different parts of the machinery, whether of English or foreign 
 make, and for whatever kind of cloth required. A comprehensive summary is also included of 
 the various yarns and methods of numbering them, as well as a few useful hints and a number 
 of coloured diagrams For mandarin weavings. The book is printed in bold, legible type, on 
 good paper, has a copious index, and is well and strongly bound." Ashtou-under-Lyne Herald. 
 
 " In dealing with the complicated parts of various classes of power-looms, the writer, who is 
 -one of the professors at the Royal Weaving School of Asch, brings to the work a thorough 
 knowledge of the subject, and, what is of great value, he has the gift of communicating his 
 knowledge in a way which is easily understood. The smallest details of loom-setting are 
 entered into, and a full explanation of problems, which are a source of anxiety to many en- 
 gaged in overlooking, is given. Students will find the work an admirable text-book, and all 
 who are interested in weaving will see in it a valuable addition to the literature on this subject. 
 . . The book is in small compass, and is crowded with valuable information." Bradford 
 Observer. 
 
 COLOUR: A HANDBOOK OP THE THEORY OP 
 COLOUR. By GEORGE H. HURST, F.C.S. With Ten 
 Coloured Plates and Seventy-two Illustrations. 160 pp. Demy Svo. 
 1900. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
 strictly net. 
 
 Contents. 
 
 Chapters I., Colour and Its Production. Light, Colour, Dispersion of White Light 
 Methods of Producing the Spectrum, Glass Prism and Diffraction Grating Spectroscopes, The 
 Spectrum, Wave Motion of Light, Recomposition of White Light, Hue, Luminosity, Purity 
 of Colours, The Polariscope, Phosphorescence, Fluorescence, Interference. II., Cause of 
 Colour in Coloured Bodies. Transmitted Colours, Absorption Spectra of Colouring 
 Matters. III., Colour Phenomena and Theories. Mixing Colours, White Light from 
 Coloured Lights, Effect of Coloured Light on Colours, Complementary Colours, Young- 
 Helmholtz Theory, Brewster Theory, Supplementary Colours, Maxwell's Theory, Colour 
 Photography. IV., The Physiology of Light. Structure of the Eye, Persistence of Vision, 
 Subjective Colour Phenomena, Colour Blindness. V., Contrast. Contrast, Simultaneous 
 Contrast, Successive Contrast, Contrast of Tone.. Contrast of Colours, Modification of Colours 
 by Contrast, Colour Contrast in Decorative Design. VI., Colour in Decoration and 
 Design. Colour Harmonies, Colour Equivalents, Illumination and Colour, Colour and 
 Textile Fabrics, Surface Structure and Colour. VII., Measurement of Colour. Colour 
 Patch Method, The Tintometer, Chromometer. 
 
 Press Opinions. 
 
 " This useful little book possesses considerable merit, and will be of great utility to those for 
 whom it is primarily intended." Birmingham Post. 
 
 " It will be found to be of direct service to the majority of dyers, calico printers and colour 
 mixers, to whom we confidently recommend it." Chemical Trade Journal. 
 
 " It is thoroughly practical, and gives in simple language the why and wherefore of the many 
 colour phenomena which perplex the dyer and the colourist." Dyer and Calico Printer. 
 
 " We have found the book very interesting, and can recommend it to all who wish to master 
 the different aspects of colour theory, with a view to a practical application of the knowledge so 
 gained." Chemist and Druggist. 
 
 " Mr. Hurst's Handbook on the Theory of Colour will be found extremely useful, not only to 
 the art student, but also to the craftsman, whose business it is to manipulate pigments and 
 dyes." Nottingham Daily Guardian. 
 
 TEXTILE RAW MATERIALS AND THEIR CON- 
 VERSION INTO YARNS. (The Study of the Raw 
 Materials and the Technology of the Spinning Process.) Text-book for 
 Textile, Trade and Higher Technical Schools. By JULIUS ZIPSER. 
 Translated from German by CHARLES SALTER. 302 Illustrations. 
 480pp. Demy Svo. 1901. Price 10s. 6d. ; India and Colonies, 11s.; 
 Other Countries, 12s. ; strictly net. 
 
 Contents. 
 
 Raw Materials: Cotton Wool Flax Hemp Jute Hair Shearing Sheep Goat 
 Wool Silk Detection and Estimation of Textile Raw Materials in Yarns and Fabrics Tests. 
 The Technology of Spinning. Cotton Spinning : Bale Breakers Carding Combing 
 Roving Mule Frames Yarn Testing Humidifiers. Flax Spinning : Tow Spinning 
 String Spinning Carded Woollen Yarn Belt Condenser Fine Spinning Yarn Numbering. 
 Manufacture of True Worsted Yarn : Semi-Worsted Yarns. Artificial Wool or 
 Shoddy Spinning: Spinning Shoddy. Index. 
 
27 
 THE COLOUR PRINTING OP CARPET YARNS. A 
 
 Useful Manual for Colour Chemists and Textile Printers. By DAVID 
 PATERSON, F.C.S. Seventeen Illustrations. 132pp. Demy 8vo. 1900. 
 Price 7s. 6d. ; India and Colonies, 8s. Other Countries, 8s. 6d. ; strictly 
 net. Contents. 
 
 Chapters I., Structure and Constitution of Wool Fibre. II., Yarn Scouring. III., Scouring 
 Materials. IV., Water for Scouring. V., Bleaching Carpet Yarns. VI., Colour Making for 
 Yarn Printing. VII., Colour Printing Pastes. VIII., Colour Recipes for Yarn Printing. 
 IX., Science of Colour Mixing. X., Matching of Colours. XL, "Hank" Printing. XII., 
 Printing Tapestry Carpet Yarns. XIII., Yarn Printing. XIV., Steaming Printed Yarns. 
 XV., Washing of Steamed Yarns. XVI., Aniline Colours Suitable for Yarn Printing. XVII., 
 Glossary of Dyes and Dye-wares used in Wood Yarn Printing. Appendix. 
 
 Press Opinions. 
 
 ' The book is worthy the attention of the trade." Worcester Herald. 
 
 " The treatise is arranged with great care, and follows the processes described in a manner 
 at once clear and convincing." Glasgoiv Record. 
 
 " A most useful manual dealing in an intelligible and interesting manner with the colour 
 printing of carpet yarns." Kidderminster Times. 
 
 " An eminent expert himself, the author has evidently strained every effort in order to make 
 his work the standard guide of its class." Leicester Post. 
 
 " The book, which is admirably printed and illustrated, should fulfil the need of a practical 
 guide in the colour printing of carpet yarns. Nottingham Express. 
 
 "The subject is very exhaustively treated in all its branches. . . . The work, which is very 
 well illustrated with designs, machines, and wool fibres, will be a useful addition to our textile 
 literature." Northern Whig. 
 
 " It gives an account of its subject which is both valuable and instructive in itself, and likely 
 to be all the more welcome because books dealing with textile fabrics usually have little or 
 nothing to say about this way of decorating them." Scotsman. 
 
 "The work shows a thorough grasp of the leading characteristics as well as the minutse of 
 the industry, and gives a lucid description of its chief departments. . . . As a text-book in 
 technical schools where this branch of industrial education is taught.jthe book is valuable, or 
 it may be perused with pleasure as well as profit by any one having an interest in textile in- 
 dustries." Dundee Courier. 
 
 "The book bears every mark of an extensive practical knowledge of the subject in all its 
 bearings, and supplies a real want in technical literature. Chapters IX. and X., on the science 
 of colour mixing and colour matching respectively, are especially good, and we do not remem- 
 ber to have seen the bearing of various kinds of light, and of the changes from one kind of light 
 to another on the work of the colourist, so well treated elsewhere." Dyer and Calico Printer* 
 
 " It is thoroughly practical, and contains much information which has not hitherto appeared 
 in book form. It is pleasing to note that the practical part is not crowded out with purely 
 ' practical recipes '. A few typical examples are given, and the rest is left to the common sense 
 and judgment of the printer or works' chemist. Another pleasing feature is the accounts given 
 here and there of the author's own researches on the subject. The work will be of interest to 
 printers of wool generally, and to those engaged in the dyeing of this fibre." Journal of the 
 Society of Dyers and Colourists. 
 
 A PRACTICAL TREATISE ON THE BLEACHING OF 
 LINEN AND COTTON YARN AND FABRICS. By 
 
 L. TAILFER, Chemical and Mechanical Engineer. Translated from the 
 French by JOHN GEDDES MC!NTOSH, Lecturer on Chemical Technology, 
 London. Demy 8vo. 1901. Price 12s. 6d. ; India and Colonies, 13s. 6d ; 
 Other Countries, 15s. ; strictly net. 
 
 Contents. 
 
 Chapter I. General Considerations on Bleaching. Chapter II. Steeping. Chapter III 
 Washing : Its End and Importance Roller Washing Machines Wash Wheel (Dash Wheel) 
 Stocks or Wash Mill Squeezing. Chapter IV. Lye Boiling Lye Boiling with Milk of Lime 
 Lye Boiling with Soda Lyes Description of Lye Boiling Keirs Operations of Lye Boiling 
 Concentration of Lyes. Chapter V. Mather and Platt's Keir Description of the Keir 
 Saturation of the Fabrics Alkali used in Lye Boiling Examples of Processes. Chapter VI. 
 Soap Action of Soap in Bleaching Quality and Quantity of Soaps to use in the Lye Soap 
 Lyes or Scalds Soap Scouring Stocks. Chapter VII. Bleaching on Grass or on the Bleach- 
 ing Green or Lawn. Chapter VIII. Chemicking Remarks on Chlorides and their De- 
 colourising Action Chemicking Cisterns Chemicking Strengths, etc. Chapter IX. Sours 
 Properties of the Acids Effects Produced by Acids Souring Cisterns. Chapter X. 
 Drying Drying by Steam Drying by Hot Air Drying by Air. Chapter XI. Damages to 
 Fabrics in Bleaching Yarn Mildew Fermentation Iron Rust Spots Spots from Contact 
 with Wood Spots incurred on the Bleaching Green Damages arising from the Machines. 
 Chapter XII. Examples of Methods used in Bleaching Linen Cotton. Chapter XIII. The 
 Valuation of Caustic and Carbonated Alkali (Soda) and General Information Regarding these 
 Bodies Object of Alkalimetry Titration of Carbonate of Soda Comparative Table of 
 Different Degrees of Alkalimetrical Strength Five Problems relative to Carbonate of Soda 
 Caustic Soda, its Properties and Uses Mixtures of Carbonated and Caustic Alkali Note 
 on a Process of Manufacturing Caustic Soda and Mixtures of Caustic and Carbonated Alkali 
 iBoda). Chapter XIV. Chlorometry Titration Wagner's Chlorometric Method Prepara- 
 
28 
 
 tion of Standard Solutions Apparatus for Chlorine Valuation Alkali in Excess in De- 
 colourising Chlorides. Chapter XV. Chlorine and Decolourising Chlorides Synopsis 
 Chlorine Chloride of Lime Hypochlorite of Soda Brochoki's Chlorozone Various De- 
 colourising Hypochlorites Comparison of Chloride of Lime and Hypochlorite of Soda. 
 Chapter XVI. Water Qualities of Water Hardness Dervaux's Purifier Testing the 
 Purified Water Different Plant for Purification Filters. Chapter XVII. Bleaching of 
 Yarn Weight of Yarn Lye Boiling Chemicking Washing Bleaching of Cotton Yarn. 
 Chapter XVIII. The Installation of a Bleach Works Water Supply Steam Boilers Steam 
 Distribution Pipes Engines Keirs Washing Machines Stocks Wash Wheels Chemick- 
 ing and Souring Cisterns Various Buildings. Chapter XIX. Addenda Energy of De- 
 colourising Chlorides and Bleaching by Electricity and Ozone Energy of Decolourising 
 Chlorides Chlorides Production of Chlorine and Hypochlorites by Electrolysis Lunge's 
 Process for increasing the intensity of the Bleaching Power of Chloride of Lime Trilfer's 
 Process for Removing the Excess of Lime or Soda from Decolourising Chlorides Bleaching 
 by Ozone. 
 
 THE SCIENCE OF COLOUR MIXING. A Manual in- 
 tended for the use of Dyers, Calico Printers and Colour Chemists. By 
 DAVID PATERSON, F.C.S. Forty-one Illustrations, Five Coloured Plates, 
 and Four Plates showing: Eleven Dyed Specimens of Fabrics. 132 
 
 pp. Demy 8vo. 1900. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
 Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Chapters I., Colour a Sensation; Colours of Illuminated Bodies; Colours of Opaque and 
 Transparent Bodies; Surface Colour. II., Analysis of Light; Spectrum; Homogeneous 
 Colours; Ready Method of Obtaining a Spectrum. III., Examination of Solar Spectrum; 
 The Spectroscope and Its Construction ; Colourists' Use of the Spectroscope. IV.. Colour by 
 Absorption ; Solutions and Dyed Fabrics; Dichroic Coloured Fabrics in Gaslight. V., Colour 
 Primaries of the Scientist versus the Dyer and Artist ; Colour Mixing by Rotation and Lye 
 Dyeing; Hue, Purity, Brightness; Tints; Shades, Scales, Tones, Sad and Sombre Colours. 
 VI., Colour Mixing; Pure and Impure Greens, Orange and Violets; Large Variety of Shades 
 from few Colours; Consideration of the Practical Primaries: Red, Yellow and Blue. VII., 
 Secondary Colours ; Nomenclature of Violet and Purple Group; Tints and Shades of Violet; 
 Changes in Artificial Light. VIII., Tertiary Shades; Broken Hues; Absorption Spectra of 
 Tertiary Shades. Appendix: Four Plates with Dyed Specimens Illustrating Text. Index. 
 
 Press Opinions. 
 
 "The work has evidently been prepared with great care, and, as far as we can judge, should 
 be very useful to the dyer and colourist." Halifax Courier. 
 
 "The volume, which is clearly and popularly written, should prove of the utmost service to 
 all who are concerned with the practical use of colours, whether as dyers or painters." 
 Scotsman. 
 
 "To the practical colourist, and also to technical students, Mr. Paterson's new work will be 
 very welcome We are often asked to recommend books on different subjects, and have no 
 hesitation in advising the purchase of the present volume by dyers and calico printers, as con- 
 taining a mass of most useful information at a nominal price." Irish Textile Journal. 
 
 "Mr. Paterson's work not only clearly deals with the theory of colour, but supplies lucid 
 ^directions for the practical application of the theory. His work will be found exceedingly 
 helpful, not only to the practical colourist, but also to students in our textile colleges, by 
 forming a useful complement to their class lectures. There are several exquisitely coloured 
 plates and a large number of other illustrations of theory and practice in colour blending, and 
 also a series of plates with specimens of dyed fabrics attached, in explication of the author's 
 views." Wakefield Express. 
 
 " Mr. Paterson has little to say upon the experimental aspect or on its aesthetics, but much 
 upon the theory of colour, especially as it bears upon the question an all-important one to 
 dyers, calico printers and artists, who have to produce such a variety of shades and tints of 
 the admixture of one colour upon another. . . . The author is a dyer, and in his concluding 
 chapters keeps well before him the special wants and requirements of dyers. He writes 
 pleasantly and lucidly, and there is no difficulty in following him, although here and there a 
 lapse into ambiguousness occurs. The book is well printed, generously supplied with coloured 
 plates, very nicely if not brightly got up ; and the dyed patterns at the end enhance the value 
 of the book to the dyer." Textile Mercury. 
 
 " For some time the proprietors of The Oil and Colour-man's Journal have been engaged in 
 the publication of a series of practical handbooks intended for the use of those interested in 
 certain branches of technology, and the present volume is the latest addition to their list. 
 The feature which the works have in common and it is an all-important one in treatises of 
 this sort is their eminently practical character. The primary aim of the publishers is to 
 provide scientific text-books which will be helpful to those who are either actively engaged in 
 the practice of the arts in question, or who are studying with that immediate end in view. . . . 
 Mr. Paterson speaks with that assured knowledge of an expert, and in the present volume, as 
 in that which he has already contributed to the same series, he sets forth the true foundation 
 of the art of colouring in a manner at once comprehensive and judicious. . . . For dyers, 
 calico printers and colourists in general, whose desire it is to work with accuracy in their 
 respective branches, the treatise will prove an invaluable guide-book, provided the principles 
 and methods it describes are studied with intelligence and care. To this end, every encourage- 
 ment has been given that well-chosen examples, carefully executed plates and diagrams, and 
 an exhaustive index can supply." Glasgow Herald. 
 
29 
 
 COLOUR MATCHING ON TEXTILES. A Manual in- 
 tended for the use of Students of Colour Chemistry, Dyeing and 
 Textile Printing. By DAVID PATERSON, F.C.S. Coloured Frontis- 
 piece. Twenty-nine Illustrations and Fourteen Specimens of Dyed 
 Fabrics Illustrating Text. Demy 8vo. 132 pp. 1901. Price 7s. 6d. ; 
 India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Chapters I., Colour Vision and Structure of the Eye Perception of Colour Primary 
 and Complementary Colour Sensations. II., Daylight for Colour Matching Selection of a 
 Good Pure Light Diffused Daylight, Direct Sunlight, Blue Skylight, Variability of Daylight, 
 etc., etc. III., Matching of Hues Purity and Luminosity of Colours Matching Bright Hues 
 Aid of Tinted Films Matching Difficulties Arising from Contrast. IV., Examination of 
 Colours by Reflected and Transmitted Lights Effect of Lustre and Transparency of Fibres 
 in Colour Matching. V., Matching of Colours on Velvet Pile Optical Properties of Dye- 
 stuffs, Dichroism, Fluorescence. VI., Use of Tinted Mediums Orange Film Defects of the 
 EyeYellowing of the Lens Colour Blindness, etc. VII., Matching of Dyed Silk Trimmings 
 and Linings and Bindings Its Difficulties Behaviour of Shades in Artificial Light Colour 
 Matching of Old Fabrics, etc. VIII., Examination of Dyed Colours under the Artificial Lights 
 Electric Arc, Magnesium and Dufton, Gardner Lights, Welsbach, Acetylene, etc. Testing 
 Qualities of an Illuminant. IX., Influence of the Absorption Spectrum in Changes of Hue 
 under the Artificial Lights Study of the Causes of Abnormal Modifications of Hue, etc. 
 
 Reissue of 
 THE ART OP DYEING WOOL, SILK AND COTTON. 
 
 Translated from the French of M. HELLOT, M. MACQUER and M. LE 
 PILEUR D'APLIGNY. First Published in English in 1789. Six Plates. 
 Demy 8vo. 446 pp. 1901. Price 5s. ; India and Colonies, 5s. 6d. ; 
 Other Countries, 6s. ; strictly net. 
 
 Contents. 
 
 Part I., The Art of Dyeing Wool and Woollen Cloth, Stuffs, Yarn, Worsted, etc. : 
 Introduction. Chapters I., Of the Vessels and Utensils used in Dyeing. II., Of the Fixed 
 ind Fugitive, commonly called Great and Little Dye. III., Of Colours in Grain. Dyeing 
 Wool : IV., Of Blue. V., Of the Pastel Vat Directions for the Proper Management of the 
 Vat Indications when the Vat has Suffered by too much or too little Lime, the two extremes 
 which ought carefully to be avoided The Preparations of Indigo for the Pastel Vat. VI., 
 Of the Woad Vat. VII., Of the Indigo Vat. VIII., Of the Cold Indigo Vat with Urine A 
 Hot Indigo Vat with Urine To Reheat a Urine Vat. IX., A Cold Indigo Vat without Urine. 
 X., Of the Method of Dyeing Blue. XI., Of Red. XII., Of Scarlet in Grain, or Venetian 
 Scarlet. XIII., Of Fire Scarlet. XIV., Of Crimson XV., Of Gum Lac Scarlet. XVI., Of 
 the Coccus polonicus, a Colouring Insect. XVII., Of Madder Red. XVIII., Of Yellow. XIX., 
 Of Brown or Fawn Colour. XX., Of Black. XXI., Of the Colours obtained from a Mixture of 
 Blue and Red. XXII., Of the Mixture of Blue and Yellow. XXIII., Of the Mixture of Blue 
 and Fawn Colour. XXIV., Of the Mixture of Blue and Black. XXV., Of the Mixture of Red 
 and Yellow. XXVI., Of the Mixture of Red and Fawn. XXVII., Of the Mixture of Red and 
 Black. XXVIII., Of the Mixture of Yellow and Fawn Colours. XXIX., Of the Mixture of 
 Yellow and Black. XXX., Of the Mixture of Fawn Colour and Black. XXXI., Of the Prin- 
 cipal Mixtures of the Primitive Colours by Three and Three. XXXII., The Method of Blending 
 Wool of Different Colours for mixed Cloth or Stuffs. XXXIII., The Method of Preparing 
 Felts for Trial. XXXIV., The Method of Dyeing Woollens False Colours. XXXV., Of Flock 
 or Goats' Hair. XXXVI., Of Archil, and the Method of Using It. XXXVII., Of Logwood. 
 XXXVIII., Of Brazil Wood. XXXIX., Of Fustic. XL., Roucou. XLL, Of French Berries. 
 XLII., Of Turmeric. XLII I., Instructions for the Proof Liquor for Wool and Woollen 
 Stuffs. 
 
 Pa 
 
 Silks I 
 
 ing. Sulphuring. Observations on Whitening and Sulphuring. Of Aluming. Remarks on 
 Aluming. Of Blue. Remarks on the Blue of Indigo. Of Yellow. Remarks on Yellow. 
 Aurora, Orange, Mordore, Gold Colour and Chamois. Red and Crimson. Remarks on 
 Crimson. Of False Crimson or the Red of Brazil. Remarks on the Red, or Crimson of Brazil 
 Wood. Of Scarlet, Orange, Red and Cherry Colour. Preparation of the Carthamus or 
 Bastard Saffron. Remarks on the Dye of Carthamus or Bastard Saffron. Of the False 
 Poppy or Fire Colour Produced with Brazil Wood. False Rose Colour. Of Green. 
 Remarks. Of Olives. Remarks. Of Violet. Of Fine Violet, or Violet in Grain. Of False 
 or Common Violets or Lilac. Of the Violet of Logwood. Remarks. Violet of Logwood and 
 Verdigris. Violets of Brazil and Logwood. Remarks. Violets from Brazil Wood and Archil. 
 Of Purple, Gillyflower, and of Fine Cochineal or Purple. Of False Purple. Of Maroons, 
 Cinnamons and White Lees. Remarks. Of Nut Greys, Thorn Greys, Black and Iron Greys 
 and others of the same Species. Of Black. Softening of Black. Black in the Raw. Remarks 
 on Black. Particular Process Communicated by M. Hellot. Genoa Crimson, a Process 
 Proved in May, 1743. Violet Crimson of Italy. Half Violet. Genoa Black for Velvets. 
 
 Part III., The Art of Dyeing Cotton and Linen Thread, together with the Method 
 Of Stamping Silks, Cottons, etc. : Of Dyeing in General. Inquiry concerning Wool, Silk, 
 Cotton and Flax. Of Wool. Of Silk. Of Cotton. Of Flax. Conclusion from the Examina- 
 
30 
 
 tion of Substances Commonly Dyed. Of Bleaching. Preparation for Stuffs to be Dyed. 
 Astringents. Theory of Dyeing Stuffs Prepared with Alum. Of Colouring Substances. 
 Of Cochineal and Colouring Insects. Of Madder. Of Vegetables Furnishing a Yellow Dye. 
 Of the Colouring Drugs Used in Dyeing without Astringents. Of Indigo. Of Substances 
 Used in Dyeing Fawn and Root Colour. Of Carthamus, Roucou, etc. Of Black. Of Dyeing 
 of Cotton Thread : Of Cleansing. Of the Colours Employed for the Dyeing of Cotton 
 Thread. Of Blue. Of Red. Adrianople Red. Observations on this Dye. Of Yellow. Of 
 Green. Of Violet. Of Red Cinnamon. Of Black. Black for Linen and Cotton Thread by a 
 Combination of Colours. Of Grey. Of More Durable Greys. Of Musk Colour. Olive and 
 Duck Greens. Of Browns, Maroons, Coffee Colours, etc. Of Silk Stuffs Dyed of Several 
 Colours. The Manner of Stamping Silk, etc., in Europe. Of a Linen with a Blue Ground 
 and White Pattern. Of Saxon Blue. Observations on this Dye. Indexes. 
 
 THE DYEING OP COTTON FABRICS: A Practical 
 Handbook for the Dyer and Student. By FRANKLIN BEECH, Practical 
 Colourist and Chemist. 272 pp. Forty-four Illustrations of Bleaching 
 and Dyeing Machinery. Demy 8vo. 1901. Price 7s. 6d. ; India 
 and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Chapters I., Structure and Chemistry of the Cotton Fibre. II., Scouring and Bleaching of 
 Cotton. III., Dyeing Machinery and Dyeing Manipulations. IV., Principals and Practice of 
 Cotton Dyeing 1, Direct Dyeing; 2, Direct Dyeing followed by Fixation with Metallic Salts; 
 3, Direct Dyeing followed by Fixation with Developers; 4, Direct Dyeing followed by Fixation 
 with Couplers ; 5, Dyeing on Tannic Mordant ; 6, Dyeing on Metallic Mordant ; 7, Production 
 of Colour Direct upon Cotton Fibres; 8, Dyeing Cotton by Impregnation with Dye-stuff Solu- 
 tion. V., Dyeing Union (Mixed Cotton and Wool) Fabrics. VI., Dyeing Half Silk (Cotton- 
 Silk, Satin) Fabrics. VII., Operations following Dyeing Washing, Soaping, Drying. VIII., 
 Testing of the Colour of Dyed Fabrics. IX., Experimental Dyeing and Comparative Dye 
 Testing. Index. 
 
 The book contains numerous recipes for the production on Cotton Fabrics of all kinds of a 
 great range of colours, thus making it of great service in the Dyehouse, while to the Student it 
 is of value in that the scientific principles which underlie the operations of dyeing are clearly 
 laid down. 
 
 COTTON SPINNING (First Year). By THOMAS THORNLEY, 
 Spinning Master, Bolton Technical School. 160 pp. 84 Illustrations. 
 Crown 8vo. 1901. Price 3s. ; Abroad, 3s. 6d. ; strictly net. 
 Contents. 
 
 Syllabus and Examination Papers of the City and Guilds of London Institute. Chapters 
 I., Cultivation, Classification, Ginning, Baling and Mixing of the Raw Cotton. II., Bale- 
 Breakers, Mixing Lattices and Hopper Feeders III., Opening and Scutching. IV., Carding. 
 Index to Illustrations. General Index. 
 
 COTTON SPINNING (Intermediate, or Second Year). By 
 THOMAS THORNLEY. 180 pp. 70 Illustrations. Crown 8vo. 1901. 
 Price 5s. ; India and British Colonies, 5s. 6d. ; Other Countries, 6s. ; 
 strictly net. 
 
 Contents. 
 
 Syllabuses and Examination Papers of the City and Guilds of London Institute. Chapters 
 I., The Combing Process. II., The Drawing Frame. III., Bobbin and Fly Frames. IV., Mule 
 Spinning. V., Ring Spinning. Index to Illustrations. General Index. 
 
 COTTON SPINNING (Honours, or Third Year). By THOMAS 
 THORNLEY. 216 pp. 74 Illustrations. Crown 8vo. 1901. Price 5s. ; 
 India and British Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 
 Contents. 
 
 Syllabuses and Examination Papers of the City and Guilds of London Institute. Chapters 
 I., Cotton. II., The Practical Manipulation of Cotton Spinning Machinery. III., Doubling 
 and Winding. IV., Reeling. V., Warping. VI., Production and Costs. VII., Main Driving. 
 VIII., Arrangement of Machinery and Mill Planning. IX., Waste and Waste Spinning. 
 Index to Illustrations. General Index. 
 
 Books for Mining Engineers 
 and Steam Users. 
 
 RECOVERY WORK AFTER PIT FIRES. A Description 
 of the Principal Methods Pursued, especially in Fiery Mines, and of 
 the Various Appliances Employed, such as Respiratory and Rescue 
 Apparatus, Dams, etc. By ROBERT LAMPRECHT, Mining Engineer and 
 
31 
 
 Manager. Translated from the German. Illustrated by Six large 
 Plates, containing Seventy-six Illustrations. 175 pp., demy 8vo. 190L 
 Price 10s. 6d. ; India and Colonies, 11s.; Other Countries, 12s.; 
 strictly net. Contents. 
 
 Preface. I., Causes of Pit Fires: 1, Fires Resulting from the Spontaneous Ignition of 
 Coal; 2, Fires Caused by Burning Timber; 3, Fires Caused by Fire-damp Explosions. II., 
 Preventive Regulations: 1, The Outbreak and Rapid Extension of a Shaft Fire can be 
 most reliably prevented by Employing little or no Combustible Material in the Construction of 
 the Shaft ; 2, Precautions for Rapidly Localising an Outbreak of Fire in the Shaft ; 3, Pre- 
 cautions to be Adopted in case those under 1 and 2 Fail or Prove Inefficient Precautions 
 against Spontaneous Ignition of Coal. Precautions for Preventing Explosions of Fire-damp 
 and Coal Dust. Employment of Electricity in Mining, particularly in Fiery Pits. Experiments 
 on the Ignition of Fire-damp Mixtures and Clouds of Coal Dust by Electricity. III., Indica- 
 tions of an Existing or Incipient Fire. IV., Appliances for Working in Irrespirable 
 Gases : 1, Respiratory Apparatus ; 2, Apparatus with Air Supply Pipes, (a) The Bremen Smoke 
 Helmet, (b) The Miiller Smoke Helmet, (c) The Stolz Rescue Mask; 3, Reservoir Apparatus; 
 4, Oxygen Apparatus. The Schwann Respiratory Apparatus. The Fleuss Respiratory Ap- 
 paratus. The Improved Walcher-Gartner Pneumatophor, (a) The Single Bottle Apparatus, 
 Instructions for Using the Pneumatophor, Taking to Pieces and Resetting the Apparatus 
 ready for Use ; (b) Two Bottle Apparatus (Shamrock Type). The Neupert Rescue Apparatus 
 (The Mayer-Pilar System). V. Extinguishing Pit Fires : (a) Chemical Means ; (b) Extinction 
 with Water. Dragging down the Burning Masses and Packing with Clay ; (c ) Insulating the 
 Seat of the Fire by Dams. Dam Building. Dam Work in the Fiery Pits of Southern Hungary : 
 (a) Cross-dams of Clay ; (b) Masonry Dams, Gallery Linings. Wagner's Portable Safety Dam. 
 Analyses of Fire Gases. Isolating the Seat of a Fire with Dams : Working in Irrespirable 
 Gases ("Gas-diving ") : 1, Air-Lock Work (Horizontal Advance) on the Mayer System as Pur- 
 sued at Karwin in 1894 ; 2, Air-Lock Work (Horizontal Advance) by the Mauerhofer Modified 
 System. Vertical Advance. Mayer System. Complete Isolation of the Pit. Flooding a 
 Burning Section isolated by means of Dams. Wooden Dams : () Upright Balk Dams ; (b) 
 Horizontal Balk Dams ; (c) Wedge Dams, Masonry Dams. Examples of Cylindrical and Dome- 
 haped Dams. Dam Doors: Flooding the Whole Pit. VI., Rescue Stations: (a) Stations 
 bove Ground; (b) Underground Rescue Stations. VII., Spontaneous Ignition of Coal in 
 Bulk. Index. 
 
 Illustrations. 
 
 Sheet I., Respiratory and Rescue Appliances Precautions against Fire. Figs. 1, 
 Smoke Helmet; 2, Mialler's Smoke Helmet; 3, Low-pressure Respiration Apparatus; 4, High- 
 pressure Respiration Apparatus; 5, The Stolz Mask for Rescue Work; 6, Precautions against 
 Fire. Sheet II., Respiratory and Rescue Apparatus. Figs. 1, Recovery Work with 
 Miiller's Smoke Helmet after a Fire ; 2-8, The Fleuss Respiration Apparatus ; 9, The Walcher- 
 Gartner Pneumatophor: 10-12, Pneumatophor (Shamrock Type). Sheet III., Respiratory 
 and Rescue Apparatus Stretchers. Figs. 1-8, Rescue Apparatus manufactured by O. 
 Neupert's Successor (Mayer-Pilar System) ; 1, Front View; 2, Section through Bag and Mask ; 
 3, Rear View ; 4, Apparatus and Mask laid out Flat (view from above) ; 5, Apparatus and Mask 
 laid out Flat (view from below) ; 6, Locking Device for Closing Bag ; 7, Apparatus Complete, 
 Mounted for Rescue Work; 8, Improved Valve in the Respiration Tubes; 9-12, Stretchers. 
 Fig. 9, Stretcher Covered with Brown Canvas ; 10, Stretcher Covered with Brown Canvas, 
 fitted with Adjustable Head-rest; 11, Folding Stretcher Covered with Brown Canvas; 12, 
 Rupprecht's Stretcher Covered with Brown Canvas ; 13, Dr. Riihlmann's Stretcher. Sheet 
 IV., Dams. Figs. 1-7, R. Wagner's Portable Safety Dam. Sheet V., Signalling Appliances 
 Dam Construction Cable Laying. Figs. 1-3, Signalling Appliances; 1, Small Induction 
 Apparatus for Pit Work; 2, Bell Signal for Pit Work; 3, Pit Telephone; 4-18, Dam Con- 
 struction ; 4, 5, Upright Timber Dam ; 6, 7, Timber Dam with Wooden Door ; 8, 9, Dome- 
 shaped Dams; 10, 11, Dome-shaped Dam with Iron Door; 12, 13, The Wenker and Berninghaus 
 Locking Device for Dam Doors ; 14-17, Dam Construction ; 18, Damming a Gallery Lined with 
 Iron ; 19, Support for Cable. Sheet VI., Working with Diving Gear in Irrespirable Gases 
 Gallery Work. Figs. 1-4, Air-Lock Work (Mayer System); 5-7, Air-Lock (Mauerhofer's 
 Modification of the Mayer System); 8-11, Construction of Dams at the Pluto Shaft. Sheet 
 VII., Working with Diving Gear in Irrespirable Gases (Mayer System) Appliances in 
 the Shaft. Figs. 1, 2, Sections of Shaft and Air Apparatus ; 3, Salzmann Reducing Valve for 
 Reserve Air Supply ; 4, 5, L. v. Bremen's Respiration Apparatus with Karwin Reserve Ap- 
 pliance ; 6, Cross Section of the Franziska Shaft ; 7, Method of Supplying Air to Main Pipe 
 and Winding same on Drum ; 8, Clamp. 
 
 Press Opinions. 
 
 " A work of this extremely valuable character deserves to be made widely known amongst 
 colliery managers and mining engineers at home and abroad." Coal and Iron. 
 
 "This book is, in a manner, unique. The literature of mining accidents is fairly extensive, 
 but it consists largely of departmental Blue Books." Sheffield Daily Telegraph. 
 
 "A concise and lucid description of the principal methods pursued, especially in fiery 
 mines, and of the various appliances employed, such as respiratory and rescue apparatus, 
 dams, etc." Staffs Advertiser. 
 
 "The prevention of spontaneous combustion in collieries and the extinction of underground 
 fires are duties that fall heavily on many colliery managers. They should, therefore, welcome 
 this translation of Mr. Lamprecht's German treatise." Ironmonger, 
 
 "The book under notice supplies the needed full description, drawings, and mode of using 
 these new appliances in actual fires, and should be studied by every colliery manager, seeing 
 that even our best managed collieries have not been free from fires, more or less disastrous 
 to life and property. Colliery Manager. 
 
32 
 
 THE PREVENTION OF SMOKE. Combined with the 
 Economical Combustion of Fuel. By W. C. POPPLEWELL, M.Sc., 
 A.M.Inst., C.E., Consulting Engineer. 46 Illustrations. 190 pp. 
 1901. Demy 8vo. Price 7s. 6d. ; India and Colonies, 8s.; Other 
 Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Introductory. Chapters I., Fuel and Combustion. II., Hand Firing in Boiler Furnaces. 
 III., Stoking by Mechanical Means. IV., Powdered Fuel. V., Gaseous Fuel. VI., Efficiency 
 and Smoke Tests of Boilers. VII., Some Standard Smoke Trials. VIII., The Legal Aspect 
 of the Smoke Question. IX., The Best Means to be adopted for the Prevention of Smoke. 
 Index. 
 
 GAS AND COAL DUST FIRING. A Critical Review of 
 the Various Appliances Patented in Germany for this purpose since 
 1885. By ALBERT PUTSCH. 130 pp. Demy 8vo. 1901. Translated 
 from the German. With 103 Illustrations. Price 7s. 6d. ; India and 
 Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Generators Generators Employing Steam Stirring and Feed Regulating Appliances 
 Direct Generators Burners Regenerators and Recuperators Glass Smelting Furnaces 
 Metallurgical Furnaces Pottery Furnace Coal Dust Firing. Index. 
 
 Press Opinions. 
 
 " The work is worthy of perusal by all consumers of fuel. It is exceedingly well printed 
 and illustrated." Chemical Trade Journal. 
 
 "The book will appeal with force to the manufacturer as well as to the technical student, 
 whilst it is also of far more than average interest to the general reader." Halifax Guardian. 
 
 "The importance that gas and coal dust firing have attained of recent years, and especially 
 the great interest attaching of late to the question of coal dust firing, makes the appearance 
 of the present volume most opportune." Iron and Coal Trades Review'. 
 
 "The German author has long followed the development of various systems of gas firing, 
 and in the present treatise he discusses the merits of appliances patented since 1885. His text 
 and the numerous illustrations indispensable to it will be found useful by all who are engaged 
 in practical work in the same field." North British Daily Mail. 
 
 Books on Plumbing, Decorating, 
 Metal Work, etc., etc. 
 
 EXTERNAL PLUMBING WORK. A Treatise on Lead 
 Work for Roofs. By JOHN W. HART, R.P.C. 180 Illustrations. 270 
 pp. Demy 8vo. 1896. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
 Countries, 8s. 6d. ; strictly net. 
 
 Contents. 
 
 Chapters I., Cast Sheet Lead. II., Milled Sheet Lead. III., Roof Cesspools. IV., Socket 
 Pipes. V., Drips. VI., Gutters. VII., Gutters (continued). VIII., Breaks. IX., Circular 
 Breaks X., Flats. XI., Flats (continued). XII., Rolls on Flats. XIII., Roll Ends. XIV., 
 Roll Intersections. XV., Seam Rolls. XVI., Seam Rolls (continued). XVII., Tack Fixings. 
 XVIII., Step Flashings. XIX., Step Flashings (continued). XX., Secret Gutters. XXI., 
 Soakers. XXII., Hip and Valley Soakers. XXIII., Dormer Windows. XXIV., Dormer 
 Windows (continued). XXV., Dormer Tops. XXVI., Internal Dormers. XXVII., Skylights. 
 XXVIII., Hips and Ridging. XXIX., Hips and Ridging (continued). XXX., Fixings for 
 Hips and Ridging. XXXI., Ornamental Ridging. XXXII., Ornamental Curb Rolls. XXXIII., 
 Curb Rolls. XXXIV., Cornices. XXXV., Towers and Finials. XXXVI., Towers and Finials 
 (continued). XXXVI I. .Towers and Finials (continued). XXXVIII., Domes. XXXIX., Domes 
 (continued). XL., Ornamental Lead Work. XLL, Rain Water Heads. XLII., Rain Water 
 Heads (continued). XLIIL, Rain Water Heads (continued). 
 
 Press Opinions. 
 
 "This is an eminently practical and well-illustrated volume on the management of external 
 ead work." Birmingham Daily Post. 
 
 11 It is thoroughly practical, containing many valuable hints, and cannot fail to be of great 
 benefit to those who have not had large experience." Sanitary Journal. 
 
 "Works on sanitary plumbing are by no means rare, but treatises dealing with external 
 plumbing work are sufficiently scarce to ensure for Mr. Hart's new publication a hearty recep- 
 tion." The Ironmonger. 
 
 "With Mr. Hart's treatise in his hands the young plumber need not be afraid of tackling 
 outside work. He would do well to study its pages at leisure, so that he may be ready for it 
 when called upon." Ironmongery. 
 
33 
 
 HINTS TO PLUMBERS ON JOINT WIPING, PIPE 
 BENDING AND LEAD BURNING. Third Edition, 
 Revised and Corrected. By JOHN W. HART, R.P.C. 184 Illustrations. 
 313 pp. Demy 8vo. 1901. Price 7s. 6d. ; India and Colonies, 8s.; 
 Other Countries, 8s. 6d. ; strictly net. 
 Contents. 
 
 Introduction. Chapters I., Pipe Bending. II., Pipe Bending (continued). III., Pipe 
 Bending (continued). IV., Square Pipe Bendings. V., Half-circular Elbows. VI., Curved 
 Bends on Square Pipe. VII., Bossed Bends. VIII., Curved Plinth Bends. IX., Rain-water 
 Shoes on Square Pipe. X., Curved and Angle Bends. XL, Square Pipe Fixings. XII., Joint- 
 wiping. XIII., Substitutes for Wiped Joints. XIV., Preparin 
 
 iping. XIII., Substitutes for Wiped Joints. XIV., Preparing Wiped Joints. XV., Joint 
 Fixings. XVI., Plumbing Irons. XVII., Joint Fixings. XVIII., Use of "Touch" in Solder- 
 ing. XIX., Underhand Joints. XX., Blown and Copper Bit Joints. XXL, Branch Joints. 
 XXII. , Branch Joints (continued). XXIII. , Block Joints. XXIV., Block Joints (continued). 
 XXV., Block Fixings. XXVL, Astragal Joints Pipe Fixings. XXVI L, Large Branch 
 Joints. XXVIII. , Large Underhand Joints. XXIX., Solders. XXX., Autogenous Soldering 
 or Lead Burning. Index. 
 
 Press Opinions. 
 
 " Rich in useful diagrams as well as in hints." Liverpool Mercury. 
 
 " The papers are eminently practical, and go much farther into the mysteries they describe 
 than the title ' Hints' properly suggests." Scotsman. 
 
 " The articles are apparently written by a thoroughly practical man. As a practical guide 
 the book will doubtless be of much service." Glasgow Herald. 
 
 " So far as the practical hints in this work are concerned, it will be useful to apprentices and 
 students in technical schools, as it deals mainly with the most important or difficult branches 
 of the plumber's craft, viz., joint wiping, pipe bending and lead burning. ... ' Hints ' are the 
 most useful things to an apprentice, and there are many in this work which are not to be found 
 in some of the text-books." English Mechanic. 
 
 "22 PRYME STREET, HULL, 24th November, 1894. 
 
 " Gentlemen, Your books to hand for which accept my best thanks, also for circulars. I 
 myself got one of J. W. Hart's books on Plumbing from your traveller, and having looked 
 through the same I can safely recommend it as being the best book I have seen. Mr. J. W. 
 Hart treats exhaustively upon soldering and pipe bending, which are two of the most essential 
 branches in the plumbing trade.' 
 
 THE PRINCIPLES AND PRACTICE OF DIPPING, 
 BURNISHING, LACQUERING AND BRONZING 
 BRASS WARE. By W. NORMAN BROWN. 35 pp. Crown 
 8vo. 1900. Price 2s. ; Abroad, 2s. 6d. ; strictly net. 
 Contents. 
 
 Chapters L, Cleansing and Dipping; Boiling up and Cleansing; Dipping. II., Scratch- 
 brushing and Burnishing; Polishing; Burnishing. III., Lacquering; Tools; Lacquers. 
 IV., Bronzing ; Black Bronzing ; Florentine Red Bronzing ; Green Bronzing. Index. 
 
 Press Opinions. 
 
 " Mr. Brown is clearly a master of his craft, and has also the immense advantage of being 
 able to convey his instructions in a manner at once clear and concise." Leicester Post. 
 
 "A thoroughly practical little treatise on the subject in all its branches, and one which 
 should be in the hands of every tradesman or amateur who has lacquering to do." Irish Builder. 
 
 WORKSHOP WRINKLES for Decorators, Painters, Paper- 
 hangers and Others. By W. N. BROWN. Crown 8vo. 128 pp. 1901. 
 Price 2s. 6d. ; Abroad, 3s. ; strictly net. 
 Contents. 
 
 Parts L, Decorating. II., Painting. III., Paper-hanging. IV., Miscellaneous. 
 Arranged in alphabetical order. 
 
 HOUSE DECORATING AND PAINTING. By W. 
 
 NORMAN BROWN. Eighty-eight Illustrations. 150 pp. Crown 8vo. 
 1900. Price 3s. 6d. ; India and Colonies, 4s. ; Other Countries, 4s. 6d. . 
 strictly net. Contents. 
 
 Chapters L, Tools and Appliances. II., Colours and Their Harmony. III., Pigments and 
 Media. IV., Pigments and Media. V., Pigments and Media. VI., Pigments and Media. 
 VII., Preparation of Work, etc. VIII., Application of Ordinary Colour. IX., Graining. 
 X., Graining. XL, Graining. XII., Gilding. XIII., Writing and Lettering. XIV., Sign 
 Painting. XV., Internal Decoration. Index. 
 
 Press Opinion. 
 
 "The author is evidently very thoroughly at home in regard to the technical subjects he has 
 set himself to elucidate, from the mechanical rather than the artistic point of view, although 
 the matter of correctness of taste is by no means ignored. Mr. Brown's style is directness 
 itself, and there is no tyro in the painting trade, however mentally ungifted, who could fail tc 
 carry away a clearer grasp of the details of the subject after going over the performance." 
 Building Industries. 
 
34 
 
 A HISTORY OF DECORATIVE ART. By W. NORMAN 
 BROWN. Thirty-nine Illustrations. 96 pp. Crown 8vo. 1900. Price 
 2s. 6d. ; Abroad, 3s. ; strictly net. 
 
 Contents. 
 
 Chapters I., Primitive and Prenistoric Art. II., Egyptian Art. III., Assyrian Art. IV., 
 The Art of Asia Minor. V., Etruscan Art. VI., Greek Art. VII., Roman Art. VIII., 
 Byzantine Art. IX., Lombard or Romanesque Art. X., Gothic Art. XI., Renaissance Art. 
 XII., The Victorian Period. Index. 
 
 Press Opinion. 
 
 " In the course of a hundred pages with some forty illustrations Mr. Brown gives a very 
 interesting and comprehensive survey of the progress and development of decorative art. It 
 cannot, of course, be pretended that in the limited space named the subject is treated ex- 
 haustively and in full detail, but it is sufficiently complete to satisfy any ordinary reader : 
 indeed, for general purposes, it is, perhaps, more acceptable than a more elaborate treatise." 
 Midland Counties Herald* 
 
 A HANDBOOK ON JAPANNING AND ENAMELLING 
 FOR CYCLES, BEDSTEADS, TINWARE, ETC. By 
 
 WILLIAM NORMAN BROWN. Price 2s. net. [Ready. 
 
 Contents. 
 
 A Few Words on Enamelling Appliances and Apparatus Japans or Enamels To Test 
 Enamel for Lead Japanning or Enamelling Metals Japanning Tin, such as Tea Trays, and 
 similar Goods Enamelling Old Work Enamel for Cast Iron Enamel for Copper Cooking 
 Utensils The Enamelling Stove Enamelling Bedsteads, Frames and similar large pieces- 
 Paints and Varnishes for Metallic Surfaces Varnishes for Ironwork Blacking for Iron 
 Processes for Tin Plating Galvanising Metal Polishes Colours for Polished Brass A 
 Golden Varnish for Metal Painting on Zinc Carriage Varnish Japanese Varnish and its 
 Application. Index. 
 
 THE PRINCIPLES OF HOT WATER SUPPLY.- 7 By 
 
 JOHN W. HART, R.P.C. With 129 Illustrations. 1900. 177 pp.', demy 
 8vo. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
 strictly net. 
 
 Contents. 
 
 Chapters I., Water Circulation. IL, The Tank System. III., Pipes and Joints. IV., The 
 Cylinder System. V., Boilers for the Cylinder System. VI., The Cylinder System. VII., The 
 Combined Tank and Cylinder System. VIII., Combined Independent and Kitchen Boiler. 
 IX., Combined Cylinder and Tank System with Duplicate Boilers. X., Indirect Heating and 
 Boiler Explosions. XL, Pipe Boilers. XII., Safety Valves. XIII., Safety Valves. XIV., The 
 American System. XV., Heating Water by Steam. XVI., Steam Kettles and Jets. XVII., 
 Heating Power of Steam. XVIIL, Covering for Hot Water Pipes. Index. 
 
 Press Opinion. 
 
 " If all plumbers were to read this book, and if they followed the instructions given, there 
 would, we are sure, be fewer accidents from household boiler explosions, and many lives might 
 be saved. No doubt the majority of householders know or care little about the subject, but 
 any one who wishes to adopt the most up-to-date system of supplying hot water throughout 
 his house will be able to do so if he reads Mr. Hart's book and follows the instruction given. 
 It is a work that all who have charge of domestic water supply should study. It is a practical 
 and profitable book." Wigan Observer. 
 
 Brewing and Botanical. 
 
 HOPS IN THEIR BOTANICAL, AGRICULTURAL 
 AND TECHNICAL ASPECT, AND AS AN ARTICLE 
 OF COMMERCE. By EMMANUEL GROSS, Professor at 
 the Higher Agricultural College, Tetschen-Liebwerd. Translated 
 from the German. Seventy-eight Illustrations. 1900. 340 pp. Demy 
 8vo. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other Countries, 
 15s. ; strictly net. 
 
 Contents. 
 
 PART L, HISTORY OF THE HOP. 
 
 PART II., THE HOP PLANT. Introductory. The Roots. The Stem and Leaves. 
 Inflorescence and Flower: Inflorescence and Flower of the Male Hop; Inflorescence and 
 Flower of the Female Hop. The Fruit and its Glandular Structure : The Fruit and Seed. 
 Propagation and Selection of the Hop. Varieties of the Hop: (a) Red Hops; (b) Green Hops; 
 (c) Pale Green Hops. Classification according to the Period of Ripening: 1. Early August 
 Hops; 2. Medium Early Hops; 3. Late Hops. Injuries to Growth : Malformations; Diseases 
 Produced by Conditions of Soil and Climate: 1. Leaves Turning Yellow, 2. Summer or Sun- 
 brand, 3. Cones Dropping Off, 4. Honey Dew, 5. Damage from Wind, Hail and Rain ; Vegetable: 
 Enemies of the Hop : Animal Enemies of the Hop. Beneficial Insects on Ho?" 
 
35 
 
 PART III., CULTIVATION, The Requirements of the Hop in Respect of Climate, Soil 
 and Situation : Climate; Soil; Situation. Selection of Variety and Cuttings. Planting a Hop 
 Garden : Drainage ; Preparing the Ground ; Marking-out for Planting ; Planting ; Cultivation 
 and Cropping of the Hop Garden in the First Year. Work to be Performed Annually in the 
 Hop Garden : Working the Ground ; Cutting ; The Non-cutting System ; The Proper Per- 
 formance of the Operation of Cutting : I. Method of Cutting : Close Cutting, Ordinary Cutting, 
 The Long Cut, The Topping Cut; II. Proper Season for Cutting: Autumn Cutting, Spring 
 Cutting; Manuring; Training the Hop Plant: Poled Gardens, Frame Training; Principal 
 Types of Frames ; Pruning, Cropping, Topping, and Leaf Stripping the Hop Plant ; Picking, 
 Drying and Bagging. Principal and Subsidiary Utilisation of Hops and Hop Gardens. Life 
 of a Hop Garden ; Subsequent Cropping. Cost of Production, Yield and Selling Prices. 
 
 PART IV. Preservation and Storage. Physical and Chemical Structure of the Hop Cone. 
 Judging the Value of Hops. 
 
 PART V. Statistics of Production. The Hop Trade. Index. 
 
 Press Opinions. 
 
 " The subject is dealt with fully in every little detail ; consequently, even the veriest tyro can 
 take away some useful information from its pages." Irish Farming World. 
 
 " Farmers are but little given to reading ; but nowadays brewers have to study their trade 
 and keep abreast of its every aspect, and as far as regards our trade, to them this book 
 especially appeals, and will be especially useful." Licensed Victuallers' Gazette. 
 
 " Like an oasis in the desert comes a volume upon the above subject, by the Professor at 
 the Higher Agricultural College, Tetschen-Liebwerd, Germany, who has been fortunate 
 enough to obtain an excellent translator from the German in the person of Mr. Charles 
 Salter. The paucity of works upon the history and cultivation of hops is surprising con- 
 sidering the scope it gives for an interesting and useful work." Hereford Times. 
 
 " We can safely say that this book deals more comprehensively and thoroughly with the 
 subject of hops than any work previously published in this country. . . . No one interested in 
 the hop industry can fail to extract a large amount of information from Professor Gross's 
 pages, which, although primarily intended for Continental readers, yet bear very closely on 
 what may be termed the cosmopolitan aspects of the science of hop production." South 
 Eastern Gazette. 
 
 " This is, in our opinion, the most scholarly and exhaustive treatise on the subject of hops, 
 their culture and preservation, etc., that has been published, and to the hop grower especially 
 will its information and recommendations prove valuable. Brewers, too, will find the chapter 
 devoted to ' Judging the Value of Hops ' full of useful hints, while the whole scope and tenor of 
 the book bear testimony to the studious and careful manner in which its contents have been 
 elaborated." brewers Journal. 
 
 " Considering the extent to which this country draws its hop supplies from abroad, this 
 translation of Professor Gross's volume will prove an interesting and instructive addition to 
 the library of any brewer or brewers' chemist, the more so as the work of translation has been 
 admirably carried out in simple and vigorous English. . . . The volume is one of a valuable 
 series of special technical works for trades and professions the publishers are issuing, and is 
 the first so far dealing with the brewing industry." Burton Mail. 
 
 " A work upon the above subject must be welcomed if for no other reason than the dearth 
 of books dealing with so interesting a theme, but fortunately apart from this the book will 
 afford excellent reading to all interested in hops and their culture. Professor Gross takes one 
 over the whole field, by commencing with the earliest history of the plant so far back as the 
 days of ancient Greece and from both practical, theoretical and scientific standpoints, deals 
 with the cultivation, classification and formation of the hop. ... In speaking of the produc- 
 tion of new varieties sound information is given, and should be of value to those who are 
 always in search of improvements." Hereford Journal. 
 
 " This work is, without doubt, the most thorough and extensive compilation on hops ever 
 yet offered to the public, and for this reason should be warmly welcomed and appreciated by 
 men interested in the subject. Although primarily written for those engaged in the industry 
 abroad, and mainly Continental in theory and practice, it nevertheless appeals to those con- 
 nected with the hop growing and brewing business in England, not only by way of a com- 
 parison, but also as an instruction. The volume is at once practical and scientific, is well 
 got up, and teems with illustrations and statistics. In a word, it is a book that should find 
 its way into the hands of all who are occupied in hop production and distribution at home ; 
 and it also contains valuable information and suggestions for the brewers themselves." 
 Brewers' Guardian. 
 
 Public Libraries. 
 
 BRITISH LIBRARY YEAR BOOK, 1900-1901. A Record 
 of Library Progress and Work. 54 Illustrations. Crown 8vo, 345 pp. 
 1900. Edited by THOMAS GREENWOOD. Price 3s. ; abroad, 3s. 6d. ; 
 strictly net. 
 
 Contents. 
 
 Notes for Library Committees. Contributed Articles : The Library Rajre. Some Points in 
 Library Planning Mr. Burgoyne. Library Classification Mr. Jast. Developments in Lib- 
 rary Cataloguing Mr. Quinn. Children and Public Libraries Mr. Ballinger. Fire Prevention 
 and Insurance Mr. Davis. The Educational Work of the Library Association Mr. Roberts. 
 The Library Assistants' Association Mr. Chambers. British Municipal Libraries established 
 under the various Public Libraries or Special Acts, and those supported out of Municipal Funds 
 
36 
 
 giving particulars of Establishment, Organisation, Staff, Methods and Librarians. Table 
 showing the Rate, Income, Work and Hours of the Rate-supported Libraries. Statistical 
 Abstracts. British non-Municipal Libraries, Endowed, Collegiate, Proprietary and others, 
 showing date of Establishment, number of Volumes, Particulars of Administration, and Lib- 
 rarians. Library Associations and Kindred Societies. 
 
 Press Opinions. 
 
 "This is a handbook which tells the reader everything about public libraries, great and 
 small, in the United Kingdom. . . . The book is decidedly one of the best arranged volumes ever 
 published, and there is no doubt that the editor has been at great pains to obtain the latest 
 and most accurate information from all places. County, district and parish councils, 
 ministers of religion, and schoolmasters everywhere should make themselves acquainted with 
 its contents. Its perusal cannot fail to serve the ends of the library movement. The illustra- 
 tions, of which there is a large number, are very good." Western (Cardiff) Mail. 
 
 WORKS IN PREPARATION. 
 
 PRINCIPLES OF SIDEROLOGY (The Science of Iron). 
 
 Translated from the German of HANNS FREIHERR v. ZUPTNER. 
 STAINED GLASS (Ancient and Modern) and FRET LEAD 
 
 GLAZING. By E. R SUPPLING. 
 
 TREATISE ON CLOTH FINISHING. By ROBERT 
 BEAUMONT, of Yorkshire College, Leeds. 
 
 INDIA-RUBBER; GUTTA PERCHA. 
 
 EVAPORATION, CONDENSATION AND COOLING. 
 
 Calculations of Dimensions of Apparatus. By E. HAUSBRAND. 
 Tables. For Chemists, Chemical and Mechanical Engineers. 
 
 THE CHEMICAL TECHNOLOGY OF TEXTILE 
 FIBRES. Spinning, Washing, Bleaching, Dyeing, Printing 
 and Finishing. By Dr. G. VON GEORGIEVICS. [In the Press. 
 
 WEAVING MACHINERY. Three Vols. By HARRY NISBET. 
 
 COLOUR TERMS : THEIR PROPER USE AND 
 MEANING. By DAVID PATERSON. 
 
 LEAD AND ITS COMPOUNDS. By THOS. LAMBERT. 
 
 COTTON COMBERS AND THE COMBING PROCESS. 
 
 By THOS. THORN LEY. [In the Press. 
 
 TIMBER. Its Physical and Chemical Properties, Description, 
 Distribution throughout the World, Forests, Preservation of Timber, 
 and Applications. From the French of Paul Charpentier. 179 Illus- 
 trations. About 500 pp. 
 
 USE OF WATER IN THE INDUSTRIAL ARTS. Com- 
 
 position Influences Residual Water Purification Analysis. From 
 the French of H. de la Coux. 135 Illustrations. About 500 pp. 
 
 DYERS' MATERIALS : An Introduction to the Examination, 
 Evaluation and Application of the Most Important Substances Used 
 in Dyeing, Printing, Bleaching and Finishing. By PAUL HEERMANN, 
 Ph.D. Translated by ARTHUR C. WRIGHT, M.A. (Oxon.), B.Sc. 
 (Lond.). [In the Press. 
 
 HANDY GUIDES TO THE CHOICE OF BOOKS. 
 
 Vol. I. PROSE FICTION. 
 
 Vol. II. TECHNICAL, TRADE AND COMMERCIAL 
 BOOKS. 
 
 Others to follow. [In Preparation* 
 
 The Publishers will advise when any of the above books are 
 ready to firms sending their addresses. 
 
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