
<£o -*'■? 
 
 STFRX1 N G 
 AND FRANCiNE 
 
 C1A1UC 
 ART INSTITUTE 
 L1BRART 
 
f 
 
ELEMENTS 
 
 OF 
 
 THE ART OF DYEING. 
 
 
Printed by Walker & Greig, 
 Edinburgh. 
 
ELEMENTS 
 
 OF THE 
 
 ART OF DYEING; 
 
 WITH A DESCRIPTION 
 
 OF THE 
 
 ART OF BLEACHING BY OXYMURIATIC ACID. 
 
 Scconlr iftitum. 
 
 Bv C: if as d A. B. BERTHOLLET. 
 
 TRANSLATED FROM THE FRENCH, 
 
 WITH NOTES AND ENGRAVINGS, ILLUSTRATIVE AND 
 SUPPLEMENTARY, 
 
 By ANDREW URE, M.D. F.R.S. 
 
 PROFESSOR OF THE ANDERSON1AN INSTITUTION, 
 GLASGOW. 
 
 IN TWO VOLUMES. 
 VOL. I. 
 
 LONDON : 
 
 PRINTED FOR THOMAS TECC, 73. CHEAPSIDE ; AND SIMPKIN & MARSHALL, 
 
 STATIONERS'-COURT : ALSO R. GRIFFIN & CO. GLASGOW ; 
 
 AND J. CUMMING, DUBLIN. 
 
 1824. 
 

TABLE 
 
 OF 
 
 CHAPTEES CONTAINED IN THE FIRST VOLUME. 
 
 Advertisement, Page 1 
 
 Historical Summary of the Art of Dyeing, 4 
 
 FIRST PART. 
 
 OF DYEING IN GENERAL. 
 
 SECTION I. 
 
 OF THE GENERAL PROPERTIES OF COLOURING 
 SUBSTANCES. 
 
 Chap. I. Of tlieTheory of Colours, and of the distinc- 
 tive Properties of Colouring Particles, 3 1 
 II. Of Mordants, 65 
 
 III. Of Astringents in general, and particularly 
 
 of the Gallic Acid and Tannin, . S6 
 
 IV. Of the Action of different Substances, par- 
 
 tiadarly of Air and Light, on Colours, 115 
 V. Recapitulation of the Theory laid down in 
 
 this Section, . . . . 141 
 
VI CONTENTS. 
 
 SECTION II. 
 
 OF THE DIFFERENCES WHICH DISTINGUISH WOOL, SILK, 
 COTTON, AND LINEN (FLAX), AND OF THE OPERATIONS 
 BY WHICH THESE SUBSTANCES ARE DISPOSED TO RE- 
 CEIVE DYES. 
 
 Chap. I. Considerations on the differences between 
 
 Animal and Vegetable Substances, 150 
 
 II. Of Wool, 154, 
 
 III. Of Silk, 163 
 
 IV. Of Cotton, 174- 
 
 V. Of Flax and Hemp, . . . 179 
 
 SECTION III. 
 
 of bleaching by the oxygenated muriatic acid. 
 
 Introduction, 186 
 
 Chap. I. Theory of Bleaching, . . . 190 
 
 II. Of the Preparation of the Oxygenated 
 
 Liquor, . . . . . 194* 
 
 III. Of Leys, 203 
 
 IV. Of the Immersions in the Oxygenated Mu- 
 
 riatic Acid, . . . . 219 
 V. Of the Washings, .... 224- 
 VI. Of the other Operations of Bleaching, 227 
 VII. Number and Order of the Operations, 233 
 VIII. Of the Different Preparations of the Oxy- 
 genated Liquor, . . . . 235 
 IX. Of the other Uses of the Oxygenated Mu- 
 riatic Acid, . . . . • 242 
 
 1. Preliminary Maceration of the Fibres, 256 
 
 2. Of the Leys and Immersions in Oxygen- 
 
 ated Muriatic Acid, . . 257 
 
CONTENTS. Vll 
 
 3. Bath of Sulphuric Acid, . . 259 
 
 4. Soaping, . . . ib. 
 
 5. To give Pliancy to Hemp-Cotton, 260 
 
 6. To give the Appearances of ordinary 
 
 Cotton to Hemp-Cotton, . ib. 
 
 SECTION IV. 
 
 OF DYEING OPERATIONS IN GENERAL. 
 
 Chap. I. Of Dyehouses and the Manipulations of 
 
 the Art of Dyeing, . . . 262 
 
 II. Of Fuel, 268 
 
 III. Of the Means of ascertaining the Goodness 
 
 of a Colour (Dye), . . . 282 
 Instructions concerning the Debouilli 
 (chemical trials) of Wool and Wool- 
 len Cloths, . . . . 28 9 
 
 SECTION V. 
 
 OF THE CHEMICAL AGENTS EMPLOYED IN DYEING. 
 
 Chap. 1. Of the Acids, 305 
 
 Art. 1. Of Sulphuric Acid, . . 310 
 
 2. Of Nitric or Nitrous Acid, 316 
 
 3. Of Muriatic Acid, . . 325 
 
 4. Of Aqua Begin, or Nitro-muria- 
 
 tic Acid, . . . 334 
 
 5. Of the Acidulous Tartrate of 
 
 Potash, and of some other 
 Acids, . . . . 341 
 II. Of Alum, or the Sulphate of Alumina, 348 
 
 III. Of the Sulphate, and some other Combina- 
 tions of Iron, . . . . 363 
 
Vlll 
 
 CONTENTS. 
 
 Chap. IV. Of Sulphate of Copper, 
 
 • • • 
 
 371 
 
 V. Of Verdigris, or the Acetate of Copper, 
 
 ,375 
 
 VI. Of the Acetate of Lead, 
 
 or S«/lf q/Saturfi, 
 
 380 
 
 VII. Of the Fixed Alkalies, 
 
 . 
 
 384. 
 
 Art. 1. Of Potash, 
 
 • • • 
 
 ib. 
 
 2. Of Soda, 
 
 • • • 
 
 392 
 
 VIII. Of Soap, 
 
 • • • 
 
 396 
 
 IX. Of Sulphur, 
 
 • • • 
 
 401 
 
 X. Of Waters, . 
 
 . 
 
 405 
 
EXPLANATION OF THE PLATES. 
 
 Plate I. Apparatus for Bleaching by Oxymuriatic 
 
 Acid. 
 
 Fig* 1. Horizontal projection according to the line 
 
 A' B', and section of one of the furnaces according to 
 
 CD. 
 
 A, Tub of Immersion. 
 
 B, Receiver. 
 
 M, M, M, M, M, Plates which close exactly the space 
 between the upper shallow tub, And the sides of the re- 
 ceiver. Only the side looking >.j the furnace is left open. 
 
 Q, Pipe into which the syphon for running the acid 
 into the immersion tub is introduced. 
 
 O, O, Gross pieces which support the shallow tubs, 
 and are fixed into the extremities N, N, N, N, of four 
 uprights. 
 
 K, Circular groove cut out in the plate, which closes 
 the space between the second shallow tub, and the side 
 of the receiver, for the passage of the conductor tubes, 
 one of which is traced in the figure* 
 
 C, C, Partition which separates the receiver from the 
 furnaces. 
 
 D, Plan of a furnace, of the boiler E, serving for a 
 sand bath, and of the matrass F, which communicates 
 by the tube G with the intermediate bottle H, enclosed 
 in its double box I : in the furnace, round the sand bath, 
 
X EXPLANATION OF 
 
 and opposite each angle, channels have been cut, which 
 serve as chimnies and registers. A section of the second 
 furnace D is made at the height of the fire-place, that the 
 grate d may be perceived, and the plate of iron d', which 
 separate the fire-place from the ash-pit. 
 
 Fig. 2. Vertical section of the receiver, and of the mi 
 mersion tub, according to the lines A B and C D. 
 
 L, L, L, Shallow tubs, separated from each other by 
 the cross pieces O, fixed on the uprights N. The space 
 between them and the sides of the receiver is closed by 
 the plates M, M, M, so as to leave a free space, but on 
 sides alternately opposite ; that is to say, from the side of 
 the furnaces to the inferior shallow tub, as also to the 
 superior, and on the side of the immersion tub, to the 
 middle shallow tub. 
 
 P, P, P, Tubes which allow the gas to pass from one 
 shallow tub to its superior, when it contains a stratum 
 of it, equal to the length of these tubes. The tube of the 
 upper shallow tub is made long enough, as is shewn, to 
 disperse the gas, which being undissolved in the water, 
 would be diffused in the air, and annoy the workmen. 
 
 K, Conductor tube, which proceeds from the interme- 
 diate bottle, and terminates under the lower shallow tub. 
 
 Q, Pipe which communicates down to the bottom of 
 the apparatus, in order that the syphon R may conduct 
 the most concentrated acid (aqueous chlorine) into the 
 immersion tub. 
 
 S, Tube of safety. 
 
 D, Elevation of the furnace provided with all its dis- 
 tillatory apparatus. 
 
 Fig. 3. Vertical projection of the two distillatory ap- 
 paratuses, according to the line D D. The letters indicate 
 the same objects as in the two preceding figures. 
 
 Fig. 4. Vertical section of a fui-nace, and of one of the 
 boxes, with a view of shewing its internal form, and the 
 position of the sand bath. 
 
 \ 
 
 
THE PLATES. XI 
 
 Fig. 5. Plan of a furnace without a sand bath. 
 
 Fig. 6. Plan and elevation of the boiler serving as a 
 sand bath. 
 
 Fig. 7. F, matrass ; T, cork of the matrass. 
 
 Fig. 8. V, small syphon to draw out the air from be- 
 neath the shallow tubs. 
 
 Fig. 9. I, box, with two square cells, serving to con- 
 tain the intermediate bottles, drawn on a double scale. 
 Y, small box, which encloses the bottle held in one of 
 the cells, by the corners X, X, X, X. 
 
 Fig. 10. Elevation of the same box, furnished with its 
 two bottles. 
 
 Plan and elevation of the small boxes, Y. 
 
 Plate II. Fig. 1, 2, 3, 4-. Apparatus for the running off 
 leys. The same letters serve for the same objects in 
 these different figures. 
 
 Fig. 1 . Vertical section of the apparatus. 
 
 A, tub. 
 
 B, boiler, the bottom of which is concave, and pro- 
 vided with a stopcock T. On the pipe to which this 
 stopcock is attached, a socket is soldered, into which 
 the glass tube, V, enters, that communicates by another 
 kneed socket with one of the wooden pipes F, which 
 afford passage to the steam. This tube serves to shew 
 what height the liquor rises to in the boiler. The bottom 
 of this is sustained on the edges of the interior masonry 
 of the furnace, except in the part corresponding to the 
 aperture S, through which the smoke passes off. Its 
 edges are turned back on the masonry for receiving the 
 tub, they are then raised round it, in order that the 
 vapour and the liquid may not find an outlet between 
 the tub and the boiler. 
 
 H, Grating of deal, the ribs of which rest at their 
 ends on the edges of the masonry of the furnace, and 
 which are supported by two bars, I I, connected with 
 
Xll EXPLANATION OF 
 
 the grating by four copper straps, which bear upon the 
 corners. 
 
 D, Body of the pump. It has at its lower part an in- 
 verted cup, pierced with small holes, to prevent in the 
 aspiration (sucking), the introduction of bodies, which 
 might hinder the valves from shutting, or might scratch 
 the body of the pump. It is prolonged by a thin copper 
 pipe, C, which, at the upper part of the tub, carries a 
 copper heel, on which the cylinder of copper, K, rests. 
 This cylinder stands on four casters. It carries four 
 sockets, to each of which an arm, X, X, is adjusted, of a 
 length equal to the diameter of the tub, and pierced with 
 holes, like the bulb of a watering pot. In order that the 
 ley raised by the pump may be diffused, the pipe of the 
 pump is perforated in like manner with small holes in 
 the whole portion which corresponds to the copper cylin- 
 der ; and in order that the ley may not run off by the 
 bottom of this cylinder, it presses exactly at this part on 
 the pipe of the pump. The arms X are fitted on like 
 the bayonet to the muzzle of a musket ; they are taken 
 off, for the introduction and removal of the cloths. 
 
 The cylinder is terminated by a ratchet wheel L, the 
 number of whose teeth should be a prime number, in 
 order that having no exact divisor, the arms may not be 
 periodically brought back to the same positions. The 
 ratchet L is set in motion by a rod a, hooked to one of 
 the pieces of wood that form the frame-work, on which 
 the balance-beam d of the pump rests, and fixed very 
 freely by a pin to a horizontal rod b. This rod is fixed 
 in like manner, by its other extremity, to one of the 
 branches of a bell movement M, whose other branch 
 communicates, by the rod c, with the balance-beam. 
 Hence, on turning the handle e, every movement of the 
 balance-beam is communicated to the rods, and onwards 
 to the ratchet, which, for each stroke of the piston, per- 
 curs the space of one tooth. 
 
THE PLATES. Xlll 
 
 The body of the pump D and the pipe C, are joined 
 by two straps and screws. Under these straps passes an 
 iron collar, traversed by six bolts, whose screwed ends 
 are fixed with nuts to a copper platform placed on the 
 grating. By this means the pump rests on the grating, 
 and bears no weight on the bottom of the boiler. The 
 pipe C is also held fast at its upper end by an iron strap, 
 adapted to, and fixed on the cross barf. 
 
 G represents the copper funnel, by which are intro- 
 duced the solution of potash, and the waters necessary 
 for the lixivium. It terminates in one of the tubes F, to 
 prevent the solution of potash spouting out on the adjoin- 
 ing pieces. 
 
 P indicates the form of the fire-place, the grate being 
 at R, and the ash-pit at Q. The smoke issues by the 
 aperture S, of which only half the altitude is seen here ; 
 it circulates by the flue U round the boiler, entering then 
 into the tube of the chimney, which rises vertically. 
 
 Fig. 2. Horizontal section of the tub taken above the 
 platform of copper I, on which are fixed by nuts the six 
 bolts which support the body of the pump. 
 
 ?», Furnace door. 
 
 The dotted lines n n, indicate the separation, formed 
 by fire bricks, in the flue which runs round the boiler, 
 and which determines the entrance of the smoke into 
 this passage, as well as its issue into the vertical pipe p. 
 
 Fig. 3. Vertical projection of the apparatus taken in 
 another direction. 
 
 h, Register, with which the chimney p ought to be 
 furnished. 
 
 q, Rim of the boiler turned up on the outside of the 
 tub. 
 
 Fig. 4. Horizontal projection of the apparatus, accord- 
 ing to the line T" G'", 
 
 Fig. 2. V, Horizontal projection of the body of the 
 
XIV EXPLANATION OF 
 
 pump, in which the details of the adjustment of the piston 
 are represented. 
 
 D, Vertical section of the body of the pump; R, clack 
 valve. S, piston ; T, cup attached by a strap to the 
 lower extremity of the body of the pump. 
 
 Fig. 4. Horizontal projection, and vertical, section of 
 the cylinder K, which bears the sockets to which the arms 
 X X are adjusted. 
 
 C, copper pipe to which is soldered the heel x. y, y, 
 brass casters which rest on the heel x, and which support 
 the cylinder K. 
 
 u, u, u, sockets having an opening for receiving the 
 knob soldered to the extremity of the arms. L, ratchet 
 wheel fixed to the upper part of the cylinder K. It con- 
 tains in the figure 17 teeth. 
 
 These two figures have been made on a double scale, 
 in order that the details might be better understood. 
 
 The apparatus for the oxygenated muriatic acid, and 
 for the running off of leys, are on the same scales. 
 
 N. B. — To avoid embarrassing the figures, a small 
 plank is not represented here, which, when the appa- 
 ratus is constructed on as large dimensions as the present, 
 should be placed at about two metres (yards) from the 
 ground, for throwing the goods upon, and from which a 
 child can hand them to the workman, who arranges 
 them in the tub. 
 
 Fig. 5. Vessels for the testing of potashes. 
 
 1. Small measure; it is filled by plunging the bulb 
 into the liquid, and stopping the tube with the finger 
 whenever it is full. It may then be carried without fear 
 of losing what it contains. To make it flow, the finger 
 has only to be lifted. 
 
 2. Tube containing up to the mark 50 times the small 
 measure. 
 
 3. Goblet or jar in which the mixture cf the test acid 
 is made and the solution of potash. 
 
THE PLATES. XV 
 
 4. Tube employed for stirring, and making the traces 
 on stained paper. 
 
 For the trial of the oxygenated muriatic acid, the 
 small measure is filled with the solution of indigo, which 
 is poured into a glass jar of the same form as the above, 
 or into a glass tumbler ; then the number of measures is 
 introduced that are required for discharging its colour. 
 
 Fig. 6. Ordinary distribution (arrangement) of the 
 mode of running off leys. 
 
 1. Tub on whose bottom a wooden grating is placed, 
 or some simple pieces of wood, which prevent the cloths, 
 when heaped, from choking up the aperture of the pipe 
 3, by which the ley falls back into the boiler. 
 
 2. Boiler, here represented cut vertically through its 
 diameter, in order to see its form. Those usually em- 
 ployed are different, and do not possess the advantage 
 which the present one does, of directing the liquid, 
 which spouts up, when the ebullition is brisk, towards the 
 middle of the boiler. It has been, moreover, represented 
 as mounted on a furnace different from those which the 
 bleachers usually construct. Its construction is nearly 
 the same as that of the furnace of 
 
 Fig. 1. The form of this boiler and of its furnace is 
 adopted in a great many dyehouses. When their dimen- 
 sions are good, there is much economy of fuel, and con- 
 venience of manipulation. Those of the figure have been 
 copied from well constructed furnaces. If pit coal be 
 burned, the height of the fire-place should be diminished 
 a little, and if turf, a little increased. 
 
 Instead of sinking the furnace into the ground, its bottom 
 may, however, be put nearly on a level with that of the 
 tub, and the ley made to fall back from the tub into the 
 boiler by a kneed pipe, which, reaching to near the bot- 
 tom of the tub, and opening above the boiler, does the 
 office of a syphon, and reconveys to it the leys wh'ch 
 had gone through the whole thickness of the goods. 
 
% 
 
 
EXPLANATION 
 
 OF THE 
 
 PLATES FURNISHED BY THE TRANSLATOR. 
 
 Plates I. and II. represent the padding machine, for 
 applying mordants to cotton cloth, or, generally speaking, 
 for passing cloth through any chemical solution. It con- 
 sists of a frame in which are placed two rollers, either of 
 wood with an axis of iron, or of cast-iron covered with 
 copper. The upper roller is pressed, by means of levers, 
 against the under one, which revolves horizontally in a 
 box, containing the mordant that is to be put on the 
 cloth. 
 
 The bevelled wheel and shaft that convey the power 
 to the padding machine, are represented in Plate II. as 
 inclined; a circumstance not essential, but accidentally 
 required in the particular machine from which this draw- 
 ing was taken. 
 
 Plates III. and IV. represent the wash or dash wheel. 
 The pieces of cloth are put into the quadrantal compart- 
 ments of the wheel, into which a stream of pure water 
 flows through a circular slit in its posterior surface. By 
 the rotation of the wheel, the cloth is dashed back- 
 wards and forwards between the quadrantal partitions. 
 Twenty-five revolutions per minute is the proper speed 
 
 VOL. i. b 
 
XV111 EXPLANATION OF 
 
 of a wash wheel six feet in diameter. Some persons 
 suppose them to perform better with twenty-six or twenty- 
 seven revolutions. But any considerable deviation from 
 this velocity either impairs the utility of the machine, or 
 destroys its functions altogether. In these and the other 
 plates, the parts are so distinctly delineated by the artist, 
 as to supersede the necessity of letters of reference and 
 minute explanations. 
 
 Plate V. A bucking boiler, exhibiting the fire-place, 
 the iron boiler, surmounted by the wooden crib, with its 
 grated bottom and central iron pipe. Whenever the 
 water or alkaline ley boils briskly, its vapour, confined by 
 the goods in the crib, presses on the surface of the liquid, 
 and forces this to issue in a sudden stream from the top 
 of the pipe, whence it is spread over the surface of the 
 goods, and gradually percolates down through them. 
 The liquid in its descent becomes slightly cooled; but 
 after a little while, accumulating and becoming hot again 
 in the boiler, a new eruption of boiling liquid takes place. 
 A more complex, though, I believe, not more effective 
 form of bucking apparatus, is described in the Edinburgh 
 Encyclopedia — Article Bleaching. 
 
 Plates VI. and VII. Cylinder printing machine. 
 
 A. The engraved copper roller. 
 
 B. The mandril on which the roller is fixed. 
 
 C. The back roller covered with soft materials. It 
 presses the piece of cloth to be printed against the cop- 
 per roller. 
 
 D. Situation for a second copper roller, when two 
 colours are to be applied at once. In this case, the back 
 roller is pressed against it by means of the screws E. 
 
 F. The colour-box. 
 
 G. Steel doctor for scraping off the colour from those 
 parts of the roller which are not engraved. 
 
THE PLATES. 
 
 XIX 
 
 H. Wheel which gives a horizontal motion to the 
 doctor. 
 
 I. A long piece of thick woollen cloth, sewed end to 
 end, which passes under the back roller, along with the 
 piece of cloth to be printed. 
 
 K. Beam on which the pieces of cloth are rolled be- 
 fore being printed. 
 
TO 
 
 M. CLEMENT, 
 
 PROFESSOR OF PRACTICAL CHEMISTRY 
 
 IN THE 
 
 CONSERVATORY OF ARTS, PARIS, 
 
 IN TESTIMONY OF THE ESTEEM ENTERTAINED FOR, HIS 
 SCIENCE AND FRIENDSHIP, 
 
 TRANSLATOR. 
 
TRANSLATOR'S PREFACE. 
 
 Among the academicians of France, who figured in 
 the antiphlogistic revolution of chemistry, M. Berthollet, 
 if not entitled to the first place, yields precedence to 
 Lavoisier alone. His early discovery of the composition 
 of ammonia, was of capital importance. It threw light 
 on many obscure chemical phenomena, and furnished an 
 excellent mirror of gaseous research. 
 
 But undoubtedly M. Berthollet's peculiar merit con- 
 sisted in applying scientific results to the common business 
 of life. Scheele's happy genius, while examining an ore 
 of manganese, revealed to the world that singularly ener- 
 getic element, chlorine, called by him dephlogisticated 
 marine acid. Its power of destroying colour was no- 
 ticed by the Swedish chemist, merely as it affected the 
 cork of his phial. This cursory remark suggested to 
 Berthollet's active mind a new art, that of bleaching 
 without exposure to sunshine and air. This art, which 
 has been of incalculable benefit to the manufactures of 
 linen and cotton, was expounded by him with much sa- 
 gacity and address, in a treatise, which forms a part of 
 the present publication. Though important improve- 
 ments in the mode of preparing and applying this blanch- 
 ing power have been made, and particularly by British 
 manufacturers, since Berthollet's time, it must be admit- 
 ted, that his principles, as far as practice is concerned, 
 
xxiv translator's preface. 
 
 have recently received little further elucidation. The 
 theoretical modifications, occasioned by Sir H. Davy's 
 admirable researches on chlorine, with an account of the 
 actual processes adopted by our bleachers, have been 
 briefly stated in the notes of the translator. 
 
 M. Berthollet's success in the bleaching department 
 naturally led the government of France to select him as 
 a fit successor to M. Macquer, in superintending the 
 dyeing establishments of that kingdom. This honour- 
 able appointment, previously held by very eminent che- 
 mists, turned Berthollet's attention to the art of dyeing, 
 the operations of which he seems to have studied with 
 great assiduity. His elements of this art must undoubted- 
 ly be regarded as constituting the first truly philosophi- 
 cal treatise on the subject ; nor has any work appeared 
 since, which can bear a comparison with it for precision 
 of detail, and perspicuity of explication. The various 
 essays on dyeing, and dye-stuffs, which have within these 
 few years been multiplied in our Encyclopedias, &c. are, 
 in a great measure, extracts from Berthollet. 
 yTt is more than probable, indeed, that these elements 
 will henceforth be accounted his principal performance ; 
 for notwithstanding the air of profound speculation which 
 pervades his Chemical Statics, and the valuable re- 
 marks scattered through that elaborate work, the hypo- 
 thesis of indefinite combination which forms its basis, has 
 greatly lessened its estimation among chemists, since the 
 theory of definite and multiple combination has been 
 satisfactorily established. Berzelius, in his essay on che- 
 mical proportions, has endeavoured, with some ingenuity, 
 to reconcile Berthollet's statical doctrines to the atomic 
 theory, but apparently with little success.^ 
 
 The first edition of the Elements of Dyeing was very 
 ably translated into English by Dr Hamilton ; and had 
 not the French philosopher published a second edition 
 containing important modifications and additions, the 
 
translator's PREFACE. XXV 
 
 labour of the present translator would have been altoge- 
 ther superfluous. It is hoped that the copious notes now 
 appended, will be found a useful supplement to the origi- 
 nal work. They contain details of the most remarkable 
 chemical researches connected with dyeing and dye- 
 stuffs which have recently appeared in scientific journals, 
 as also extracts from the valuable work of Vitalis,* on 
 the Adrianople madder red, and on calico printing, 
 along with some observations not hitherto laid before 
 the public. 
 
 The Plates furnished by the translator, represent some 
 of the most useful machines at present employed in our 
 best dyeing establishments. 
 
 At the end, tables will be found for converting the 
 French hydrometric degrees into the numbers denoting 
 specific gravity, and the French weights and measures 
 into those of this country. 
 
 The following obituary notice of Berthollet was pub- 
 lished by M. J. J. Virey, in the Journal de Pharmacie 
 for December 1822. It may probably prove acceptable 
 to some readers : — 
 
 " M. Claude-Louis Berthollet, Member of the Royal 
 Academy of Sciences of the Institute, and of several 
 other academies, Count and Peer of France, &c, was 
 born in 1 749 at Talloire in Savoy. He received the 
 degree of Doctor in Medicine, became attached to the 
 house of Orleans, and entered the Academy of Sciences 
 in 1780. In 1794; he received the appointment of Pro- 
 fessor of Chemistry in the Normal school, and subse- 
 quently in the Polytechnic school. He was nominated 
 a member of the Institute at its formation. His probity 
 caused him to be appointed to collect the objects of art 
 conquered in our triumphs in Italy. He soon afterwards 
 joined the memorable expedition to Egypt, and returned 
 
 * Cours Elementaire de Teinture. Paris, 1823. 
 
xxvi translator's preface. 
 
 in 1799 with the extraordinary man who raised him to 
 the rank of senator along with his colleague, Monge, 
 who appreciated the value of his genius. Nominated to 
 the Chamber of Peers by his Majesty, in 1814, he con- 
 tinued a member of it till his death, which happened on 
 the 6th November 1822, at the age of 73 years and a 
 few months. 
 
 " His splendid career was marked by important dis- 
 coveries, although his hands were deficient in address, 
 his style and elocution in perspicuity.* A friend of the 
 great and unfortunate founder of pneumatic chemistry, 
 Lavoisier, he co-operated with him, with Guyton de 
 Morveau, Fourcroy, &c. in reforming the nomenclature 
 of this science. His analysis of ammonia, — his disco- 
 veries on fulminating silver, — the manufacture of the de- 
 tonating powder of chlorate of potash, — the bleaching 
 of goods by chlorine, — his researches on prussic acid, in 
 which hydrogen acts the (acidifying) part of oxygen, — 
 his valuable labours on dyeing, which first illustrated 
 the principles of this art, — his profound observations on 
 sulphuretted hydrogen, whose acidifying properties he 
 pointed out, — above all, his capital work Chemical Statics, 
 of which he had conceived the basis amidst the burning 
 sands of Egypt, and while braving the murderous steel 
 of the Arabs — the foundation of the Chemical Society of 
 Arcueil, in that celebrated retirement of his old age, 
 where he delighted to assemble round him young men 
 eager to collect the fruits of his experience, in order to 
 perpetuate his labours and his renown — such are the titles 
 of Berthollet to immortality, if this award can be at all 
 promised to men. 
 
 * This want of clearness in the author's mode of expression has been 
 experienced by his translator on several occasions, and may possibly have 
 caused some mistakes. 
 
 
translator's preface. xxvii 
 
 " If we penetrate into the privacy of his life, we shall 
 see him, under a modest exterior, and a robust frame, 
 concealing a sensible heart; we shall contemplate this 
 soul, too exalted not to be simple in its greatness, pos- 
 sessed of that intrepid firmness which yielded neither to 
 the accidents of fortune, to dangers, nor to power. Never 
 would his candour make a compromise with error or 
 falsehood, or prefer wealth to self-esteem. Even in the 
 bosom of those political tempests which held nothing 
 sacred, he retained his imperturbable strength of mind. 
 Such lofty virtues were venerated by all parties, zealous 
 to contribute to the illustration of a glory become in some 
 measure European. 
 
 " His tomb has received the sincere tears of his friends, 
 Laplace, Chaptal, of his pupils erewhile, but now his 
 honourable competitors, Gay Lussac, Thenard, and 
 many other associates of labours, always subservient to 
 the love of his country and of science." 
 
 Glasgow, July 2. 1824. 
 
 
DIRECTIONS TO BINDER. 
 
 The Plates copied from the original work are to be 
 placed at the end of the First Volume. The Plates fur- 
 nished by the Translator at the end of the Second. 
 
ADVERTISEMENT. 
 
 The chief object of the author of these Elements, 
 was to apply the theories, which had recently 
 diffused so vivid a light on chemistry, to the phe- 
 nomena presented by the art of dyeing, and to its 
 ordinary processes, of which he gave the descrip- 
 tion. 
 
 The arts can make but a limited progress, when 
 they are directed merely by a blind practice. 
 Thus, they have remained for several centuries 
 in nearly the same state in China and in India. 
 But if artisans be guided by the knowledge of 
 those properties which have been investigated by 
 physics, and its complement, chemistry, there are 
 no boundaries to the perfection which they may 
 reach. How many advantages has that nation, 
 so powerful by its industry, derived from Watt, 
 Wedgewood, Henry, and some other philoso- 
 phers ! 
 
 In this respect a happy revolution has been 
 effected among ourselves. Our manufactories 
 are no longer intrusted to ignorant workmen. 
 In the greater part of them are to be found very 
 
 VOL. I. a 
 
2 ADVERTISEMENT. 
 
 enlightened individuals, well informed philoso- 
 phers, to whom indeed we must have recourse, if 
 we wish to excite the progress of the useful arts, 
 and remove the obstacles which stand in their 
 way. 
 
 By such considerations the author of this Work 
 has been actuated. He has been less occupied 
 with the collection of recipes, than in explaining 
 the properties on which those effects depend 
 which we wish to produce. He has endeavour- 
 ed, however, to introduce great precision into the 
 description of the processes, selecting those which 
 deserve most confidence. 
 
 Some persons imagine, that physical theories 
 are merely systems, to which we wish to accom- 
 modate nature, without regard to the practice of 
 the workshops. Yet these theories are themselves 
 only the result of analytical experiments. To 
 observation they always appeal ; and, in seeking 
 to direct it, they fix attention on the very facts, 
 whose relations cannot as yet be established with 
 those already classed. They indicate, moreover, 
 their application, which they also try to circum- 
 scribe within just limits. 
 
 The theory of the art of dyeing is connected 
 on one side with the most delicate speculations of 
 natural philosophy; on the other, with the practice 
 of many different arts. It is not to be regarded 
 as a portion of knowledge, which can be carried 
 to perfection by itself. Its improvements must 
 follow the advancement of the physical sciences, 
 and of several other arts. 
 
ADVERTISEMENT. 
 
 O 
 
 The author of these Elements, whose sole pre- 
 tensions in this second edition were to render his 
 work less defective, and to introduce recent dis- 
 coveries, has associated with himself a fellow- 
 labourer,* who, directing from his youth peculiar 
 attention to this object, may eventually conduct 
 it to greater perfection. 
 
 * This fond parental anticipation does not seem to have 
 been realized. M. Berthollet, junior, died a considerable 
 time before his father. 
 
HISTORICAL SUMMARY 
 
 OF 
 
 THE ART OF DYEING. 
 
 The desire of attracting public admiration may 
 be observed even in the least civilized state of 
 society. Among the means of distinction which 
 are eagerly laid hold of, the glare of colours is 
 one of the most obvious. Savages assume an im- 
 posing aspect, by staining their skins, or wearing 
 feathers, stones, and shells, with gaudy colours. 
 The Gaulish women gave themselves, on festivals, 
 an olive-brown complexion, by means of woad ; 
 and those of high rank were no doubt jealous of 
 this distinction. 
 
 The art of dyeing, therefore, has unquestion- 
 ably a very ancient origin ; for when nature af- 
 forded colouring substances of easy application, 
 there might arise among people but slightly civi- 
 lized, methods of dyeing which have been sought 
 after by polished nations. Thus the Gauls pre- 
 pared some dyes which were not disdained by the 
 Romans. But for its enlargement and perfec- 
 
HISTORICAL SUMMARY. 5 
 
 tion, the art required to follow the progress of 
 manufactures and luxury. 
 
 The Egyptians, according to Pliny,* had dis- 
 covered a mode of dyeing analogous to that of 
 our printed calicoes. Cloths, impregnated pro- 
 bably with different mordants, were plunged in a 
 bath, in which they assumed different colours. 
 He alludes to the employment of these mordants 
 in the following passage : Candida vela postquam 
 attrivere, illinuntur non coloribus, sed colorem sor- 
 bentibus medicamentis. It may, however, be pre- 
 sumed, that manufactures possessed little activity 
 among a people where the authority of the priest- 
 hood prohibited by law every change in even the 
 most indifferent customs. 
 
 It is to Greece that our attention turns, when 
 we wish to ascertain the progress which the hu- 
 man mind had made in antiquity. Here, how- 
 ever, we find a vast difference between the fine 
 arts,t and the useful arts, or the arts of luxury ; 
 a difference of which the cause is obvious. Public 
 opinion set these arts at an immense distance 
 from each other : glory was associated with the 
 former, but the latter were confounded with ser- 
 vile labours. 
 
 This distinction was, in some measure, well 
 founded. The painter, the statuary, the architect, 
 stamped their genius on their productions. Their 
 arts did not each require a long series of efforts for 
 
 * Hist. Natur. lib. xxxv. cap. 2. 
 
 f Poetical arts would be here a juster expression ; for sta- 
 tuary is surely an art of luxury T. 
 
6 HISTORICAL SUMMARY. 
 
 its advancement ; nor did it enrich itself slowly 
 by the casualties and experiments of ages. Ima- 
 gination could suddenly overleap the boundaries 
 of time ; and the masterpieces which appeared 
 in rapid succession among the Greeks, were des- 
 tined to become the admiration of posterity. 
 
 Yet this people, so ingenious, so sensitive, and 
 so fertile in great men, suffered themselves to be 
 seduced in the distribution of their esteem by 
 tastes often frivolous. He who Won a victory in 
 wrestling, pugilism, or the race, obtained crowns, 
 and enjoyed the greatest honours ; but the useful 
 arts were degraded even in the eyes of their phi- 
 losophers. 
 
 Here we perceive one of the most striking 
 characters which distinguish the ancients from 
 the moderns. The Greek philosophers, occupied 
 especially in speculations which might ensure to 
 them the homage of a people so prone to enthu- 
 siasm, regarded the useful arts as unworthy of 
 their attention. This contempt was inherited 
 by the Romans. Pliny, in speaking of dyeing, 
 avowedly neglects to describe operations which 
 do not belong to a liberal art. Nee tingendi ra- 
 tionem omisissemus, si unquam ea liberalium artium 
 fuisset. 
 
 Ever since philosophy has taken observation 
 for a guide, and, abandoning the illusions of 
 systems, has adhered to the study of the pheno- 
 mena of nature, and of the real properties to 
 which they owe their origin, it has followed the 
 chain of the numerous wonders which it has 
 
HISTORICAL SUMMARY. 7 
 
 analyzed, in subserviency to the welfare of society. 
 It has recognized in manufacturing industry, as 
 well as in commerce, the source of the prosperity 
 of the nation, the germ of a great population, the 
 principal support of agriculture. But it was the 
 Academy of Sciences of Paris which first sought 
 to spread the light of science over all the arts, 
 which first formed the project of publishing their 
 description, and which, in the midst of prohibi- 
 tory ordinances, arrived at this truth, That national 
 industry was to be augmented and enlightened by 
 a free communication of the processes which it 
 employed ; and that the sacrifices which it might 
 make by this publicity, are well recompensed by 
 the advantages thence derived. This project was 
 extended to all the objects of our studies, by the 
 Encyclopedia, the mightiest monument which 
 philosophy and reason have ever raised. 
 
 The art of dyeing must have felt feebly, we 
 perceive, the influence of learning among the 
 Greeks. Yet the activity of genius has some- 
 thing sympathetic, and industry multiplies her 
 trials when solicited by luxury. Let us observe, 
 then, to what point refinement had raised it in 
 the prosperous days of Greece ; let us consult 
 the picture of it traced by Barthelemy. 
 
 " A great proportion of the citizens of Athens 
 passed their time in the different tribunals, and 
 received a salary of three oboli, that is, fourpence- 
 halfpenny a-day. The average price of the 
 seller (twelve bushels of Paris) of corn, whose 
 value is the least uncertain standard of compari- 
 
8 HISTORICAL SUMMARY. 
 
 son, was thirteen French livres, (10s. lOd. Eng- 
 lish), that is, a little more than the half of the 
 medium price with us. A citizen of Athens 
 could thus, with the daily pay annexed to the 
 most important functions of the republic, pur- 
 chase a measure of corn, which would at present 
 cost sevenpence-halfpenny English. In order to 
 form an idea, therefore, not indeed of the public 
 magnificence, nor of that of some individuals, but 
 of the ease and luxury of the ordinary class of 
 citizens, we must represent to ourselves what they 
 would be at Paris, if the salary of the public 
 functionaries was fifteen sous a-day. 
 
 " Many of them (the Athenians) went bare- 
 footed. The common people were clad in cloth 
 which had received no dye, and which could 
 therefore be re-whitened. The rich preferred 
 coloured clothes : * they held in considerable 
 estimation those which had been dyed scarlet, 
 by means of small reddish grains, and in still 
 higher those of a purple dye." 
 
 Silk, which is subjected to the most varied pro- 
 cesses of dyeing, comes originally from China. 
 It was, say the Chinese annals, the wife of the 
 emperor Hoang-ti who first engaged in spinning 
 the cocoons which are naturally found on trees. 
 Silk was carried thereafter into Hindostan, and 
 thence into Persia, Greece, and Rome. But it 
 arrived here at a very late period. Some have 
 concluded, from a verse in the Georgics of Vir- 
 
 '&* 
 
 * Voyage de Jeune Anacharsis. 
 
\ 
 
 HISTORICAL SUMMARY. 9 
 
 gil,* that its use was known at Rome in the time 
 of Augustus. We find less doubtful indications 
 in Pliny. Silk bore still so high a price in the 
 time of the emperor Justinian, that it was sold 
 for its weight of gold, t Lastly, some monks 
 brought from India to Constantinople eggs of 
 the silk-worm, and established there the method 
 of rearing them, and of spinning the down of 
 their cocoons, t 
 
 It appears to have been in the time of the 
 Crusades that silk-worms were introduced into 
 Italy. 
 
 The art of dyeing webs seems to have been 
 unknown in Greece before Alexander's invasion 
 of India. Pliny relates, that the sails of his ves- 
 sels were there dyed of different colours. Hence 
 the Greeks possibly borrowed this art from the 
 Indians. 
 
 India is indeed the nursery of that knowledge 
 and those arts which were subsequently diffused 
 and improved among other nations. Fortunate 
 accidents might be readily multiplied in a country 
 rich in natural productions ; which requires little 
 labour to supply the subsistence of its inhabitants ; 
 and whose population was promoted by the pro- 
 fusion of nature, and the simplicity of manners, 
 ere the tyranny of conquerors had exercised their 
 ravages; but religious prejudices, and the unal- 
 
 * Velleraque utfoliis depectant tennia Seres. 
 f Voltaire, Essai sur les Mceurs, &c. 
 % Procop. lib. iv. cap. 17. De bello Gothico. Georg. 
 lib. ii. 
 
10 HISTORICAL SUMMARY. 
 
 terable division of castes, soon shackled industry. 
 The arts have been thenceforward stationary in 
 India; and it would appear, that in the time of 
 Alexander dyeing had attained nearly the same 
 state as at present, in regard to cotton goods ; 
 for silk was still unknown there, or at least very 
 scarce. 
 
 The beautiful colours which we observe on the 
 Indian goods, to which the name of Perses was 
 originally given, because it was through the trade 
 of Persia that it first reached us, might lead to 
 the belief that the art of dyeing was there pushed 
 to a great degree of perfection. But we learn 
 from the description which Beaulieu gave, at the 
 request of Dufay, of operations performed in 
 his presence,* that the processes of the Indians 
 are so complicated, tedious, and imperfect, that 
 they would be . impracticable elsewhere, from the 
 difference in the price of labour. European ma- 
 nufactures soon surpassed them in correctness of 
 design, variety of shade, and simplicity of manipu- 
 lation. If they have not yet rivalled the vivacity 
 of two or three of their colours, this must be as- 
 cribed merely to the superiority of some colouring 
 substances, or perhaps to the very length and 
 multiplicity of the operations. 
 
 We may therefore conclude, that the art of 
 dyeing was less extended and less improved 
 
 * Traite sur les Toiles Feintes, in which we observe the 
 manner of fabricating printed calicoes in India and in Europe. 
 The opinion given in the text is confirmed by the more exact 
 details found in Bancroft on Permanent Colours. 
 
V 
 
 \ 
 \ 
 
 HISTORICAL SUMMARY. 11 f 
 
 among the ancients than among the moderns; but ( 
 
 the former possessed a dye which has been lost 
 
 or neglected, and which was the most eagerly 
 
 desired object of luxury, — this was purple. Its V 
 
 processes have, however, been better preserved 
 
 in historical monuments, than those of any other 
 
 colours. j 
 
 We shall not dwell on the tales with which it I 
 
 has been attempted to embellish the origin of the j 
 
 purple dye. There is a great probability of the 
 discovery having been made at Tyre, and that it 
 contributed much to the opulence of this cele- 
 brated city. 
 
 The liquor which was employed to dye the 
 purple, was derived from two principal species of 
 shells. The larger bore the name of the purple; 
 and the other was a species of whelk. Both were V 
 
 subdivided into several varieties. They were fur- 
 ther distinguished by the greater or less beauty of 
 colour which they could afford, and according to 
 the coasts where the fishing was carried on. 
 
 The colouring juice of the purples is contained 
 in a vessel which is found in the throat. Only 
 one drop of liquid was obtained from each shell- 
 fish. The whelks were bruised : These contain- 
 ed a very small quantity of a red liquor, verging 
 on black. (Nigricantis Rosce. — Plin.) 
 
 When they had collected a certain quantity of 
 the colouring liquor, they added to it a propor- 
 tion of sea-salt. They then macerated for three 
 days ; after which five times as much water was 
 added. This mixture was kept at a moderate 
 
12 HISTORICAL SUMMARY. 
 
 heat, separating from time to time the animal 
 matters which rose to the surface. These opera- 
 tions lasted ten days. They now tried, with a 
 little white wool, if the liquid had taken the 
 proper hue. The stuff was subjected to different 
 preparations before it was dyed. Some passed it 
 through lime water ; others prepared it with a 
 species of Jucus, which served, like some of our 
 astringents, to render the colour more durable. 
 We do not know precisely the marine plant to 
 which the ancients gave the name of fucus; but 
 it was of such extensive use in their dye-works, 
 that the word became a generic name for all kinds 
 of colouring substances, (dye-stuffs.) Pileur 
 d'Apligny conjectures, that it might be a spe- 
 cies of archil or rocella, which is found on the 
 coasts of Candia ;* others, again, prepared the 
 cloth with alkanet. 
 
 The juice of the whelk did not yield of itself a 
 permanent colour j but it increased the brilliancy 
 of the colour of the other shell-fish. The purple 
 of Tyre was made in two operations. They 
 commenced by dyeing with the juice of the pur- 
 pura; after this they gave it a second dye with 
 the juice of the whelk, whence Pliny calls it 
 purpura dibapha. In other processes, the liquors 
 of two species of shell-fish were mingled ; thus, 
 for 50 kilogrammes of wool, 200 kilogrammes of 
 the liquor of the whelk and 100 kilogrammes of 
 
 * Essai sur les Moyens de perfectionner l'Art de la Tein- 
 lure. 
 
HISTORICAL SUMMARY. 13 
 
 that of the purpura were taken. An amethyst 
 colour was thereby obtained. Sometimes a body 
 or basis was given with the coccus, which is our 
 kermes, and after that the dye was completed 
 with the juice of the purpura. Finally, they 
 combined some of the preceding methods, and 
 thereby obtained a great variety of purple hues, 
 which were distinguished by different names. 
 That of Tyre possessed, according to Pliny, .the 
 colour of coagulated blood ; the amethyst purple 
 had that of the stone so called ; another species 
 resembled violet, &c. * 
 
 It seems that some kinds of purple preserved 
 their colour a very long time : Plutarch relates, 
 in the Life of Alexander, that the Greeks found 
 in the treasury of the king of Persia a great 
 quantity of purple, of which the beauty was not 
 affected though it was 190 years old. 
 
 The very small quantity of liquor which was 
 extracted from each shell, and the length of the 
 dyeing process, gave to the purple so high a 
 price, that, in the time of Augustus, a pound 
 of wool dyed in Tyrian purple, could not be had 
 for less than 1000 denarii, about 700 French 
 livres, (L. 28 sterling.) 
 
 * Those who wish to acquire more extensive information 
 on the purple ofthe ancients, may consult among the mo- 
 derns the following works : — Fabii Colomni lynccei purpura ; 
 G. Gottl. Richter, Progr. de purpuras antiquo et novo pig- 
 mento; Reaumur, Mem. de l'Academie, 1711 ; and especially 
 a learned work of M. Bischoff, entitled, Versucke einer 
 geschichte der faberkunst, 8$c. 1788. 
 
) 
 
 r 
 
 / 
 
 ; 
 
 14 HISTORICAL SUMMARY. 
 
 The priests, who sought always to take ad- 
 vantage of what might make an impression on 
 the people, attributed, in early times, a sacred 
 character to the purple. It was a colour pleas- 
 ing to the Deity, and which must be reserved 
 for his worship. Although the true purple has 
 
 been lost for a long time, the pride of the name 
 
 { has been preserved in our sacerdotal hierarchy. 
 
 i Purple was almost every-where an attribute of 
 
 exalted birth, and of dignities. It served as a 
 
 / decoration to the first magistrates of Rome. But 
 
 the luxury which was afterwards carried to excess 
 
 ( in this capital of the world, rendered the use of 
 
 it common to opulent individuals, until the em- 
 perors reserved to themselves the privilege of 
 wearing it. It soon became the symbol of their 
 inauguration. They appointed officers who were 
 charged with the superintendence of this dye in 
 the manufactories, where it was prepared for them 
 alone, principally in Phoenicia. The punishment 
 of death was decreed against all those who might 
 have the audacity to wear purple, even should 
 they cover it with another dye. 
 
 The penalty annexed to this whimsical kind of 
 high treason, was undoubtedly the cause which 
 made the art of dyeing purple disappear, first in 
 the West, and much later in the East, where this 
 art still existed in vigour in the --eleventh cen- 
 tury. 
 
 There was extracted from coccus, now known 
 under the name of kermes, (an account of which 
 may be seen Sect. iii. Part 2.), a dye, which was 
 
HISTORICAL SUMMARY. 15 
 
 hardly less esteemed than the purple, and which 
 was sometimes associated with it, as we have al- 
 ready mentioned. Pliny relates, that it was em- 
 ployed for the robes of emperors. The name of 
 scarlet was usually given to it ; but it was some- 
 times confounded with purple. 
 
 It was only in the age of Alexander and his 
 successors, according to Pliny, that the Greeks 
 sought to give some perfection to black, blue, 
 yellow, and green (dyes). 
 
 Among the Romans, newly married women 
 wore in the early times a yellow veil. This colour 
 was appropriated to matrons. 
 
 In the games of the circus, four parties were 
 distinguished by their colours : green, color pra- 
 sinus ; orange, rufatus ; ash-colour, venetus; and 
 white. 
 
 We may judge of the qualities of these colours 
 by the substances which they employed. As 
 BischofF has made very extensive researches on 
 this subject, I shall give, after him, an enumera- 
 tion of the ingredients which entered into the art 
 of dyeing in those times, independently of the 
 coccus and the purple shell-fish. 
 
 1. Alum ; but we may see in the first part of 
 this work, (Sect, v.) that very probably the an- 
 cients were not acquainted with our alum in a 
 state of purity. 
 
 2. Alkanet. Suidas relates, that this substance 
 served likewise as a pigment for women. 
 
 3. The blood of birds, which was employed by 
 the Jews. 
 
( 
 
 I 
 
 16 HISTORICAL SUMMARY. 
 
 
 j 4, The fucus. That of Crete was preferred. 
 
 I It was usually employed to give a basis or ground 
 
 / to good colours. 
 
 I 5. Broom. 
 
 j 6. Violet. The Gauls prepared from it a co- 
 
 \ lour which resembled one species of purple. 
 
 / 7' Lotus medicago arborea. Snail trefoil, (Lu- 
 
 zerne en arbre). The bark served for dyeing 
 skins, and the root was employed in dyeing 
 I wool. 
 
 / 8, The bark of the walnut tree, and the rind 
 
 of the nut. 
 
 9. Madder. It is not known whether the mad- 
 der of the ancients be the same plant as ours, or 
 some other root of the same family. 
 
 10. Woad. (Glastum.) This plant was cer- 
 tainly employed by the ancients j but it is doubt- 
 ful if they gave it the same preparation as we do. 
 
 They made use of the sulphate of iron, and of 
 that of copper, for dyeing black, especially skins. 
 Nut-galls, of which the most valued came from 
 Comagena, served as the astringent. They used, 
 as a substitute for it, the seeds contained in the 
 pods of an acacia peculiar to Egypt. They also 
 employed the bark of pomegranate and of some 
 other astringents.* 
 
 Although the ancients may have used some 
 substances of which no memorial is preserved, it 
 is easy to see that the acquisitions which we have 
 made, especially since the discovery of America, 
 
 * Ameilhon, Mem. de l'lnstit. Litter, et Beaux Arts, torn. iii« 
 
 I 
 
HISTORICAL SUMMARY. 17 
 
 give us a great superiority with regard to several 
 colours. But is the regret frequently expressed 
 for the loss of the purple, well founded ? Are we 
 not able to rival the beauty of this highly famed 
 colour ? 
 
 The shell-fish which furnished the colouring 
 liquor of the purple, exist probably in as great 
 abundance as formerly. They have been suffi- 
 ciently characterized to enable us to recognize 
 them. In fact, Thomas Gage relates that there 
 was found near Nicoya, a small Spanish town 
 of South America, shell-fish possessed of all the 
 properties described by Pliny and the other an- 
 cient writers. It appears, even, that some use 
 was made of these shell-fish for dyeing cotton 
 on the coasts of Guayaquil and of Guatimala.* 
 Cole discovered some of them in 1686 on the 
 English coasts j Plumier found a species of them 
 at the Antilles ; Reaumur made several experi- 
 ments on the buccinum which he found on the 
 coasts of Peru ; Duhamel made also several on 
 the colouring juice of the shell-fish which bears 
 the name of purpura, which he found in abun- 
 dance on the coasts of Provence. He observed 
 that this juice assumes a purple colour only by 
 the action of light, as Reaumur had already re- 
 marked respecting the colouring juice of the 
 buccinum ; that this juice, at first white, assumes 
 a yellowish-green colour, which deepens, verging 
 on blue ; that, finally, it is seen to redden, and 
 
 * Histoire Philosophique et Politique du Commerce des 
 Indes, liv. vii. 
 
 VOL. I. B 
 
18 HISTORICAL SUMMARY. 
 
 in less than five minutes to become of a very 
 vivid deep purple colour.* Now, the purple of 
 the ancients possessed these characters. 
 
 Moreover, we have a very detailed description 
 of the manner in which the fishing was conduct- 
 ed of the shell-fish which served for purple, in a 
 work of an eye-witness, Eudocia Macrembolitissa, 
 daughter of the emperor Constantine VIII. who 
 lived in the eleventh century, t 
 
 Our indifference, therefore, in procuring the 
 purple, and in profiting by the researches which 
 some moderns have successfully made, probably 
 proceeds from our having acquired more beautiful 
 and less costly colours. Many learned men are 
 of this opinion, t 
 
 In fact, the kermes afforded a colour which 
 was esteemed by the ancients as almost equal to 
 the purple (purpura), and which contributed to 
 that distinguished by the name of color hysginus. 
 Now, we understand the management of the 
 kermes in probably a more advantageous manner 
 than the ancients did, because we possess a pure 
 alum, which disposes the stuff to receive a finer 
 and more permanent colour ; and yet our dyers 
 
 * Mem. del' A cad. 1736. 
 
 f Eudocia Macrembolitissa was married to a Constantine, 
 and after his death to Romanus III., who was elected empe- 
 ror in 1068. Her work is to be found in a collection pub- 
 lished by M. d'Anse de Villoison, under the title of Anecdota 
 Grceca e regid Parisiensi et e Venetd S. Marci bibliothecis de- 
 prompta, T. i. 178 1. 
 
 J Bischoff, Versuche, &c. Goguet de l'Origine des Lois, 
 Arts, et des Sciences, 2 partie, liv. ii. 
 
HISTORICAL SUMMARY. 19 
 
 have been obliged to renounce its use almost en- 
 tirely, notwithstanding the solidity of its colour, 
 because it cannot, in point of beauty, bear a com- 
 parison with the colours now produced from co- 
 chineal. 
 
 Supposing the slight difference which may exist 
 between the colour of the kermes, and that of 
 the purple of Tyre, to be compensated by the 
 advantage which we derive from our alum, we 
 might regard this purple, which was so precious 
 that the Caesars reserved it to themselves under 
 penalty of death, to be similar to that blood-red 
 which we observe in ancient tapestries, for the 
 production of which kermes was employed. 
 
 The supposition, that the colour which we de- 
 rive from kermes is preferable to that which the 
 ancients obtained from it, can be supported by the 
 testimony even of Pliny ; for he insinuates that it 
 had little permanence ; but the colour which is 
 now given by means of kermes, to wool prepared 
 with alum, is of the greatest durability. 
 
 Soap, the discovery of which is ascribed to the 
 Gauls, appears to have had no other use among 
 the ancients than that of a pomade forcleansing the 
 hair, or for staining it with any colours which they 
 chose to mix with it. This substance is, however, 
 of such utility, that it must give us a superiority 
 in bleaching, and in some parts of dyeing. They 
 supplied its use, in the scouring of wool and whit- 
 ening of cloth, by a plant which Pliny calls ra- 
 dicular which was termed struthion by the Greeks, 
 and which some consider as our saponaria; as 
 also by another plant, which Pliny designates as 
 
20 HISTORICAL SUMMARY. 
 
 a species of poppy. Homer paints the princess 
 Nausica and her waiting-maids treading their 
 dresses with their feet in ditches, in order to bleach 
 them. From other evidence we learn that wood 
 ashes were mingled with them ; and also, that 
 some earthy boles were employed. 
 
 We have acquired from the New World several 
 dye-stuffs, cochineal, brazil wood, logwood, an- 
 notta. We owe the superiority of our dyes 
 especially to the preparation of alum and to the 
 solution of tin, which lends such lustre to several 
 colouring substances. Silk, which has become so 
 common with us, and which takes such lively and 
 brilliant dyes; the rapid movements of commerce, 
 which place the productions of China and the 
 Indies within the enjoyment of even the common 
 people ; an active and enlightened industry, sti- 
 mulated by the rivalship of the different nations 
 of Europe, who endeavour to counterbalance their 
 instruments of power ; all these circumstances set 
 an immense interval between the luxuries most 
 familiar to us, and those of the most opulent indi- 
 viduals among the ancients. Europe, however, 
 before acquiring this superiority, experienced all 
 the devastations of barbarism. 
 
 In the fifth century the arts became extinct in 
 the West ; soon thereafter, almost every trace of 
 intelligence, reason, humanity and industry, dis- 
 appeared. A few decayed arts, indeed, were 
 preserved merely in Italy. Muratori quotes a 
 
 manuscript of the eighth century,* in which we 
 
 # 
 * Diss, de Textrina et Vestibus saeculor. rudium Antiq. Ital. 
 vol. xi. 
 
HISTORICAL SUMMARY. 21 
 
 find some descriptions of dyes, chiefly for skins, 
 and some processes of the other arts ; but the 
 Latin, which is almost unintelligible, and some 
 chasms in the writing, prevent us from forming a 
 just idea of these processes.* 
 
 The arts were better preserved in the East, 
 whence were derived, till the twelfth century, the 
 objects of luxury which a few of the great were 
 able to procure. During the Crusades, the Ve- 
 netians reared their power on the frenzy of the 
 age : their fleets took charge of the victualling 
 of our fatal emigrations ; their commerce became 
 enriched ; the arts were established among them, 
 enlightened by the manufactures of the Greeks ; 
 and from this city they were propagated into the 
 other parts of Italy. In 1338, 200 manufacturers 
 were employed in Florence, who fabricated, it 
 was said, from 70,000 to 80,000 pieces of cloth, 
 forming an object of- commerce worth 1,200,000 
 golden crowns. 
 
 The discovery of rocella was accidentally made 
 by a merchant of Florence about the year 1300. 
 Having remarked that urine gave a fine colour 
 to a species of moss, he made experiments, and 
 learned to prepare archil. He kept this disco- 
 very secret for a long time. His descendants, of 
 whom a branch still remains, according to the 
 
 * I shall quote literally a description of alum, which seems 
 to prove, that only aluminous stalactites, or a volcanic earth 
 impregnated with alum, was used. De Alumen. Acumen 
 antem metallum, est terra Jioriens de eritarin. Eritarin terra 
 est alba,Jacilis ad pisandum. 
 
22 HISTORICAL SUMMARY. 
 
 report of Dominique Manni, have retained the 
 name of JRuccelai, from the Spanish word oreiglia, 
 which that species of moss bore. 
 
 The arts long continued to be cultivated in 
 Italy with increasing success. In 1429 appeared 
 at Venice the first collection of processes employed 
 in dyeing, under the name of Mariegola delV Arte 
 de Tentori. A second edition of it, much enlarged, 
 was given in 1510. One Giovan Ventura Rosetti 
 formed the project of giving more extent and 
 utility to this description. He travelled into the 
 different parts of Italy and the neighbouring 
 countries, where the arts had begun to revive, to 
 learn the processes which were there pursued j 
 and he published, under the name of Plictho, a 
 collection, which, according to BischofF, is the first 
 wherein the different processes were assembled, 
 and which must be regarded as the primary 
 impulse towards that perfection which the art of 
 dyeing has since reached.* 
 
 It is to be remarked, that in the work of Plictho 
 there is no mention made of either cochineal 
 or indigo ; so that in 1<548 these two colouring 
 substances were probably not yet employed in 
 
 * Plictho dell' Arte de Tentori, che insegna tenger panni, tele 
 banbasi e sede, si per Varte magiore, come per la comune. Venezia, 
 1548. This work has been translated into French under the 
 title of Suite du Tenturier parfait, on Vart de teindre les laines, 
 soies,Jils, peaux, poils, plumes, fyc. comme il se pratique h Venise, 
 Genes, Florence, et dans tout le Levant, et la maniere de passer 
 en chamois toute sorte de peaux; traduite de Vltalien, Paris, 
 1716. 
 
HISTORICAL SUMMARY. 2,3 
 
 Italy. Pliny indeed speaks of a substance which 
 came from India, and to which the name of In- 
 dicum was given j but no use was made of it 
 except for painting. It is, however, very pro- 
 bable, that the Indians used it in dyeing ; it 
 appears, even, that the first which was employed 
 in Europe was brought from the East Indies by 
 the Dutch. The cultivation of it was first esta- 
 blished in Mexico, and thence in the other parts 
 of America, where it has acquired qualities supe- 
 rior to what comes to us from India.* 
 
 For a long time Italy, and particularly Venice, 
 possessed almost exclusively the art of dyeing, 
 which contributed to the prosperity of their ma- 
 nufactures and their commerce ; but by degrees 
 this art was introduced into France. Giles Gobe- 
 lin made an establishment in the place which bears 
 his name. This enterprise was regarded as so rash, 
 that the name of Gobelin's Folly was given to the 
 establishment ; and the success which it obtained 
 so astonished our ancestors, that they believed 
 Gobelin had entered into a compact with the 
 devil. 
 
 The discovery of the scarlet dye may be re- 
 garded as the most remarkable era in the art of 
 dyeing, not only by the lustre which distinguishes 
 it, but also by the brilliancy which we can impart, 
 by means of the same process, to several other 
 colours. We have seen that the ancients gave 
 
 * The indigo imported into Great Britain from Calcutta 
 now, is in general superior to the South American. — T. 
 
24 HISTORICAL SUMMARY. 
 
 the name of scarlet to the colour w&ich they 
 obtained from kermes, and which was very infe- 
 rior in beauty to what we designate by the same 
 appellation. 
 
 Some Spaniards having observed that the in- 
 habitants of Mexico made use of cochineal for 
 colouring their houses and dyeing their cottons, 
 informed the ministry of the beauty of this co- 
 lour j and Cortes received, in 1523, an order to 
 promote the multiplication of the precious insect 
 which produced it. The colour which cochineal 
 gives naturally is, however, a pretty dull crim- 
 son. 
 
 A little while after the cochineal became known 
 in Europe, the scarlet process, by means of the 
 solution of tin, was discovered. It is stated, that 
 about 1630 Cornelius Drebbel observed, by an 
 accidental mixture, the brilliancy which the solu- 
 tion of tin gave to the infusion of cochineal. He 
 communicated his observation to his son-in-law, 
 KufTelar, who was a dyer at Leyden. He soon 
 improved the process, kept it secret in his work- 
 shop, and brought into vogue the colour which 
 bore his name.* 
 
 Soon thereafter, a German chemist, called 
 Kuster, Kuffier, or Kepjler, found out also the 
 scarlet process by means of the solution of tin. 
 He carried his secret to London in 1643. A 
 Flemish painter named Kloeck or Jean Glucq, 
 
 * Grundriss der farbekunst. Sigismond. Friedrich Herm-> 
 stadt. m 
 
HISTORICAL SUMMARY. 25 
 
 procured the knowledge of it, and entered into 
 partnership with a family of the name of Jul- 
 lienne, the last of whom died in 1767.* This 
 process was subsequently diffused over Europe. 
 Kloeck travelled in the East, which, since the 
 time of the Greeks, had preserved a remnant of 
 manufactures ; and he naturalized in Flanders the 
 art of dyeing on wool and silk, which flourished 
 there for a long time. M. Francheville fixes the 
 death of this man, who was so useful to his coun- 
 try, towards the year 1550.t 
 
 The employment of indigo, which has been 
 likewise a great acquisition to the art of dyeing, 
 experienced more difficulty in its establishment 
 than that of cochineal. It was severely prohibit- 
 ed in England under the reign of Elizabeth, as 
 well as logwood, which was ordered to be burned 
 whenever it was found in a manufactory. This 
 prohibition was removed only in the reign of 
 Charles II. 
 
 The use of indigo was equally proscribed in 
 Saxony. It was treated in the ordinance issued 
 against it (which reminds one of the decree 
 against tartar emetic), as a corrosive colour, and 
 food for the Devil. Fressende TeufelsX 
 
 This is a grand example of the abuses into 
 which an unenlightened administration, easily 
 misled by the suggestions of personal interests, 
 
 * Notice sur la manufacture nationale de Tapisserie des 
 Gobelins, par Guillaumeau. 
 f Mem. de Berlin, 1767- 
 % Bischoff, Veituche, &c. 
 

 26 HISTORICAL SUMMARY. 
 
 may fall. The blue dyers, who were in posses- 
 sion of the process with pastil and woad, repre- 
 sented, that indigo would ruin the commerce of 
 these two substances, which were native >r*n uc- 
 tions. This motive, which would be still spe- 
 cious in the eyes of several persons, readily de- 
 termined the issuing a prohibition, which was 
 soon to be eluded, at the expense of paying a 
 tribute to the industry of other nations. The 
 prejudice against indigo was also communicated 
 to France ; and in the Instructions of Colbert 
 it is forbidden to put above a certain proportion 
 of it into the woad vats. 
 
 Colbert gave to French manufactures, which 
 had remained languishing under the stormy ad- 
 ministrations of Richelieu and Mazarin, an impulse 
 which soon advanced them beyond the progress 
 of other nations. He called forth the most expert 
 artists j he recompensed every alent ; he esta- 
 blished several manufactories ; and it may be re- 
 marked, that those of Vaurobais and Sedan were 
 designated, in the letters-patent which were grant- 
 ed them, under the name of fine cloths of Dutch 
 / and English fabric. He published, in 1672, a 
 
 code of instruction for dyers, which merits atten- 
 tion.* 
 
 * Instruction generate pour la teinture des laities et manu- 
 factures de laines de toutes nuances, et pour la culture des 
 drogues ou ingredients qu'on emploie. This work was reprinted 
 in 1708, under the following title: — Le Teinturier parfait, ou 
 instruction nouvelle et generate pour la teinture des laines et 
 manufacture de laine de toutes couleurs, ct pour la culture des 
 ^drogues ou ingredients qu'on y emploie. 
 
 J 
 
 
HISTORICAL SUMMARY. 27 
 
 There are presented in this, first the motives 
 which give importance to the object under con- 
 sideration : — " If the manufactures of silk, wool, 
 and thread, are those which serve principally to 
 sustain and give value to commerce, dyeing, 
 which communicates to them that beautiful va- 
 riety of colours which makes them agreeable, 
 imitating whatever is most lovely in nature, 
 forms the soul, without which the body would 
 have but a feeble existence. 
 
 " Wool and silk, which, in their natural co- 
 lours, shew rather the rudeness of the age, than 
 the genius of man, and the refinement of our 
 days, would command but a moderate trade, if 
 dyeing did not impart to them that elegance 
 which makes them be sought after and desired 
 even by the most barbarous nations. 
 
 " All visible objects are distinguished or ren- 
 dered desirable by their colours, which must 
 be not only beautiful to give commercial cur- 
 rency to the stuffs, but also good, that their 
 durability be equal to that of the fabrics to which 
 they are applied.'* 
 
 In placing alongside of several salutary regula- 
 tions, instructions for cultivators and artists, Col- 
 bert did homage to that feudal spirit, which mul- 
 tiplying with fiscal views the shackles of com- 
 merce, manufactures, and agriculture, had im- 
 pressed throughout nearly the whole of Europe 
 the idea of regarding these bonds as indispensable. 
 Instead of restricting himself to measures which 
 should serve to guarantee the fidelity of the 
 
 I 
 
28 
 
 HISTORICAL SUMMARY. 
 
 fabrics and the goodness of the colours, — instead 
 of developing the germ of that honour which 
 belongs to commerce, and which promotes its 
 interest, he pushed the prohibitory regulation to 
 the point of requiring, that the dyeing of black 
 cloth should be begun by the dyers in the grand 
 tint, and finished by the dyers of the little tint. 
 — ( Teinturiers en grand teint, et en petit teint.J 
 The former were allowed to have in their posses- 
 sion only a certain number of ingredients, while 
 the latter were also restricted to a certain num- 
 ber. Neither the one nor the other were per- 
 mitted to have brazil wood, &c. It is true, in- 
 deed, that the sad effects of these prohibitions 
 were tempered by the facility of evasion, as well 
 as by the premiums awarded to those who made 
 some advancement in their art, and whose dis- 
 coveries being subsequently communicated to the 
 public, produced modifications in the regulations. 
 French manufactures lost their pre-eminence by 
 the revocation of the edict of Nantes, which scat- 
 tered them over the rest of Europe, leaving deso- 
 lation in our factories. 
 
 Since this period, the department of adminis- 
 tration charged with the superintendence of our 
 arts and manufactures, has been constantly oc- 
 cupied with the means of repairing our losses, 
 and of making our industry flourish. It has 
 employed that plan in particular, which, with a 
 judicious liberty, is the most efficacious of all, viz. 
 the diffusion of instruction and scientific know-, 
 ledge. 
 
 i 
 
HISTORICAL SUMMARY. 
 
 29 
 
 Dufay, Hellot, Macquer, were, in succession, 
 charged with the duty of presiding over the art 
 of dyeing ; and to their labours we owe precious 
 improvements. Dufay was the first who formed 
 sound, though incomplete ideas, on the nature 
 of the colouring particles, and on the forces by 
 which they adhered to cloth. He examined some 
 processes with sagacity, and established the surest 
 tests which could at that time be formed, for de- 
 termining in a ready and practical manner the 
 goodness of a colour. Hellot published a metho- 
 dical description of the processes which are prac- 
 tised in the dyeing of wool, which forms still the 
 best treatise we possess on this subject. Macquer 
 gave an exact description of the processes exe- 
 cuted on silk : he made known the combinations 
 of the colouring principle of Prussian blue ; he 
 tried to apply its use to dyeing ; and he furnished 
 a process for imparting to silk brilliant colours 
 by means of cochineal. 
 
 The solicitude of administration has had, in the 
 judgment of foreigners, the success which it de- 
 served. Anderson ascribes to the perfection of 
 our dyes the superiority which some French 
 manufactures have preserved over those of the 
 nations which possess the finest wools ; * and 
 Home (Lord Karnes) thus explains himself: — 
 " It is to the Academy of Sciences that the French 
 owe the superiority which they enjoy in several 
 arts, and especially in that of dyeing." t Several 
 
 * History of Commerce. 
 
 •f- Essay on the Bleaching of Cloth. 
 
 \ 
 
 : ;f 
 
 u 
 
■ 
 
 1 
 
 30 HISTORICAL SUMMARY. 
 
 distinguished philosophers, indeed, have followed 
 with equal success the example set by the Aca- 
 demy of Sciences. 
 
 Macquer had undertaken to publish a general 
 treatise on dyes, of which he gave the prospectus 
 in 1781 ; but the languor which for a long time 
 announced his dissolution, prevented him from 
 executing it. He who replaced Macquer in the 
 administration of commerce, endeavoured, in the 
 first edition of these Elements, to connect the 
 theory of the phenomena presented by the art of 
 dyeing, with the great discoveries which had ef- 
 fected at that period a revolution in chemistry ; 
 to make the application of it to the practice of 
 this art 5 and to pave the way for a new career of 
 advancement, by a more exact analysis of the pro- 
 perties of the substances which serve as agents 
 in dyeing, or which have relations with the qua- 
 lities of colours. 
 
 
ELEMENTS 
 
 OF 
 
 THE ART OF DYEING. 
 
 PART I. 
 
 OF DYEING IN GENERAL. 
 
 SECTION I. 
 
 OF THE GENERAL PROPERTIES OF COLOURING 
 
 SUBSTANCES. 
 
 CHAPTER I. 
 
 Of the Theory of Colours, and of the distinctive Properties 
 of Colouring Particles. 
 
 The physical theory of colours may appear fo- 
 reign to a work, in which we are to consider 
 only the properties which distinguish them, in 
 reference to the agents which are employed in 
 their application to the stuffs which receive them, 
 and to the circumstances which produce in them 
 changes or modifications. It may however be in- 
 teresting, and possibly useful to the discussions 
 
 L_ 
 
S C Z OF DYEING 
 
 / on which we are about to enter, to establish a* 
 
 7 connexion between the phenomena which the 
 
 / colouring substances produce, and those which 
 
 ) the great Newton has analyzed in his Optics. 
 
 j We shall begin, then, by examining if the 
 
 J theory of Newton, concerning the colours assumed 
 
 by transparent liquid or solid bodies, such as air, 
 water, glass, according to the difference of tenuity 
 of the plates which they form, and according to 
 their respective density, can be applied to bodies 
 constantly coloured, such as the colouring sub- 
 stances which are the objects of dyeing. 
 
 In order to represent the ideas of Newton, and 
 the consequences to be drawn from his observa- 
 tions, we shall enjoy the advantage of being guided 
 by the treatise of Haiiy, where physical know- 
 ledge is concentrated with equal elegance, clear- 
 ness, and precision.* 
 
 " In proportion as the transparent parts of 
 bodies vary in size," says Newton, " they reflect 
 the rays of one colour, and transmit the rays of 
 another colour, for the same reason that thin 
 plates and bubbles reflect the light, or transmit 
 these rays ; now, this is the principle of the uni- 
 form colours of all bodies. "t 
 
 Newton, however, supported this induction 
 merely by the experiments which he made on 
 colourless substances. Delaval endeavoured to 
 discover proofs of it in the operations which che- 
 
 * Traits Elementaire de Physique, tome xi. 
 f Optic, lib. ii. part. 3. prop. 5. 
 
IN GENERAL. 33 
 
 mistry causes bodies to undergo, and in those of 
 the art of dyeing.* Some doubts had been offered 
 about this application of the theory of Newton, 
 in the first edition of this work ; since which time 
 Bancroft has opposed to it a great number of 
 facts.t We shall avail ourselves of these several 
 observations in the discussion which we are about 
 to undertake, solely in the view of recalling to 
 this interesting object the attention of those who 
 can follow the traces of Newton. We must be- 
 gin by forming an exact idea of the opinion which 
 it is proposed to examine. 
 
 " In every body the particles are separated 
 from each other by small interstices, which we 
 call pores, and which contain different subtile 
 fluids. These particles having a determinate 
 thickness, repel the rays, which, in penetrating 
 them, are found in a fit (retour) of easy reflection, 
 and the body thus assumes the colour, either sim- 
 ple or mixed, analogous to that of the reflected 
 rays, and which depends on the degree of tenuity 
 of the particles. 
 
 " In fact we have seen, that coloured rings are 
 produced in the plates of solid bodies, as well as 
 in those of liquids or fluids ; and since every little 
 
 * Experimental Inquiries on the cause of the changes of 
 colours in opaque and naturally coloured bodies. Letter to 
 the Earl of 'Morton, on the relation between the specific gra- 
 vity of several metals and their colours. This last work was 
 honoured, in 1765, with a medal by the Royal Society. 
 
 f Exper. Researches concerning the philosophy of perma- 
 nent colours. 
 
 VOL. I. C 
 
34) OF DYEING 
 
 space comprised in one of these plates reflects or 
 refracts the light* it follows, that if this plate were 
 divided into a multitude of small fragments, each 
 of these would still produce the same effect as 
 when it was in continuity with the others. Now, 
 as the particles of a body may be likened to the 
 separated fragments of a plate, whatever may be 
 said of this plate is exactly applicable to them 
 also. 
 
 " In speaking of the particles of bodies, it is 
 not meant to designate their smallest molecules, 
 or those which we call integrant molecules. In 
 order to conceive what ought to be understood 
 by the particles which reflect the light, we may 
 suppose, with Newton, that the integrant mole- 
 cules, already separated from one another by the 
 pores, form, by means of the union of a certain 
 number of them, other molecules of the second 
 order, separated by more extensive pores ; that 
 these, in their turn, compose molecules of the 
 third order, with interstices always more consider- 
 able ; and thus in succession. Now the particles 
 which reflect the light in the ordinary state of a 
 body, have a certain thickness, whence result se- 
 parations to a certain extent between them : these 
 particles are then considered as insulated, rela- 
 tively to the adjoining ones. The media which 
 intercept them, namely, the subtile fluids which 
 occupy their pores, and the air which surrounds 
 their outer surface, perform the function of two 
 glasses, between which the plate of air in the ex- 
 periment of Newton is comprised ; for example, 
 
IN GENERAL. 35 
 
 in a plate of mica of a perceptible thickness, there 
 are particles of a certain order, which possess the 
 property of reflecting the rays of a yellowish- 
 white, and these exist naturally at sufficient rela- 
 tive distances for the light to act upon them, as 
 if they existed alone. If we divide this leaf into 
 leaflets, to a certain degree of tenuity, we insulate 
 the particles of another order, which will reflect 
 other colours, as is confirmed by observation. 
 
 " We have spoken, under the article divisibility, 
 of a plate detached from a piece of mica, whose 
 degree of thinness was such, that its primitive 
 colour, which was yellowish-white, had passed to 
 the most intense blue." — Haw/. 
 
 Yet, whatever tenuity be given to carmine or 
 indigo, by bruising, as Bancroft observes, the co- 
 lour peculiar to each is not affected. We merely 
 brighten it, by multiplying, according to Monge, 
 the surfaces which reflect the white. 
 
 It may, indeed, be replied, that these substances 
 are composed of homogeneous particles, which, 
 notwithstanding the greatest division at which 
 we can arrive, produce the same effect as when 
 they formed a continuity, whilst the mica has 
 particles of a certain order, which possess the 
 property of reflecting the rays of a yellowish- 
 white -, while on dividing a plate into thin folia 
 to a certain degree of tenuity, we insulate the 
 particles of another order, which reflect the blue. 
 
 We shall here venture to offer some observa- 
 tions. — 
 
36 OF DYEING 
 
 1. This manner of supposing mechanical ar- 
 rangements, in order to employ them in the ex- 
 planations of physical properties, without directly 
 proving them, may easily serve to prop hypotheses 
 otherwise entirely destitute of probability. 
 
 2. This supposition of particles of different or- 
 ders, which may reflect different colours in a ho- 
 mogeneous body, does not accord with the opinion 
 of Newton, who ascribed all the colours obtained 
 from plates of Muscovy talc, which is merely a 
 mica, to the thickness which he mechanically gave 
 to these plates ; and who compares these colours 
 to those produced by soap bubbles, according to 
 the very variable thickness which they assume. 
 By this opinion, indigo and carmine ought cer- 
 tainly to afford different colours, according to the 
 tenuity of their parts ; but we shall presently ob- 
 serve a circumstance, where it is difficult to sup- 
 pose that the particles of indigo preserve, along 
 with their colour, the same dimensions and the 
 same density. 
 
 . It is admitted, that a solvent must intervene in 
 the dimensions of the molecules which reflect the 
 colours ; and this effect is employed to explain 
 some changes of colours produced by acids and 
 alkalies. " We may easily explain, on the prin- 
 ciples laid down, the colours produced in certain 
 liquors which are colourless, by the mixture of 
 one of these liquors with the other, or the changes 
 of colour which a liquor naturally coloured suffers 
 in the same case. Thus, nitric acid dropped into 
 alcohol, in which an infusion of roses has been 
 
IN GENERAL. 37 
 
 made too feeble to communicate any hue, 
 developes instantly a colour similar to that of the 
 roses before infusion. The same acid, mingled 
 with tincture of litmus, changes the blue into a 
 lively red. Syrup of violets becomes green by 
 the addition of an alkali. In all these mixtures, 
 the union of the molecules of the two liquids 
 forms mixed molecules, whose thickness is differ- 
 ent from that of the component molecules, and 
 occasions the reflection of the colour analogous 
 to this thickness." 
 
 Newton specifies more particularly the cause 
 of the changes of colour produced by acids and 
 alkalies. " It is known," says he, " that saline 
 menstrua are very proper for dissolving certain 
 substances, and it is also known, that some of them 
 precipitate what others dissolve ; and as it is the 
 nature of acids to attenuate and dissolve, and 
 that of alkalies to thicken and precipitate, if the 
 colour of the syrup of violets were of the second 
 order, an acid liquid attenuating its particles 
 would change this colour into a red of the second 
 order." 
 
 Delaval has also tried to explain the action of 
 acids and alkalies, by ascribing to the first the 
 property of attenuating, and to the second that of 
 inspissating. Let us examine, therefore, if the 
 properties of acids and alkalies, and those of the 
 solutions which they effect, authorize these ex- 
 planations. 
 
 If, in the effect which they produce, the union 
 of the two liquids forms mixed molecules, whose 
 
38 OF DYEING 
 
 thickness is different from that of the component 
 molecules, and determines the reflection of the 
 colour analogous to this thickness, there must be 
 a remarkable difference in this respect between 
 barytes, which has a great specific gravity and a 
 great fixity, and ammonia, which is, on the con- 
 trary, specifically very light and of an elastic 
 disposition : there ought to be found a similarity of 
 effect between some acids and some alkalies j yet 
 barytes and ammonia produce the very same 
 change. Sulphuric or phosphoric acid does not 
 act differently from carbonic acid, on the substan- 
 ces whose colour they can alter. 
 
 The supposition advanced by Newton, that 
 alkalies augment the thickness of the molecules, 
 and that acids attenuate, will not appear well 
 founded to those who direct their attention to 
 the properties of the solutions of colouring sub- 
 stances in acids or alkalies : the solution by 
 alkalies properly presents, in the greater number 
 of cases, more decided characters of attenuation 
 than that which is due to acids, and it is for this 
 reason that they destroy, in dissolving them, the 
 greater part of the colours which have been fixed 
 upon stuffs. It is only, therefore, for explaining 
 certain changes of colour, that to alkalies is 
 assigned a property which cannot be reconciled 
 with observation. 
 
 We are now to examine a circumstance, where, 
 notwithstanding a great difference introduced 
 into the density, and a great attenuation of the 
 colouring substance, this preserves unchangeably 
 
IN GENERAL. 39 
 
 its colour. We shall confine ourselves to one 
 example, although we could adduce many of the 
 same kind. It is from indigo that we shall take 
 it. If we dissolve indigo in sulphuric acid, we 
 may dilute the solution by successive additions of 
 water, so that it requires at least, according to the 
 observation of Bergmann, 20 pounds of water in 
 a cylindric vessel of glass, 7 inches diameter, to 
 destroy the effect of the smallest drop of the solution. 
 
 The molecules which always reflect the blue, 
 ought however to pass through all the dimensions 
 which exist between that of the solution of indigo, 
 possessing much specific gravity, and that of 
 water ; they ought to suffer a greater and greater 
 attenuation. Further, we may substitute the 
 acetic acid for the sulphuric, by precipitating the 
 latter with acetate of lead. A portion of the 
 indigo falls with the sulphate of lead. This pre- 
 cipitate, which ought to have molecules much 
 thicker, as well as the liquid which holds the 
 indigo in solution merely by means of the acetic 
 acid, possess equally the same blue colour. 
 
 Newton concluded from his observations, that 
 the corpuscles which produce blade, must be smaller 
 than any of those which produce other colours. — 
 His theory appears to us to lead even here to 
 a result, which proves that a false application 
 has been made of it. In fact, ink consists of 
 molecules, which are a metallic compound in a 
 state of precipitation, and which of consequence, 
 according to the very idea of Newton, are placed 
 in circumstances that announce the greatest com- 
 
 w 
 
40 OF DYEING 
 
 pactness. If we dilute it with much water, the 
 black passes to blue or violet. When the solu- 
 tion of indigo in sulphuric acid is much condens- 
 ed, it appears absolutely black ; by dilution with 
 water it becomes blue ; that is to say, by diminish* 
 ing its condensation, or by doing the contrary 
 of what the theory requires. 
 
 Hitherto we have discussed the opinion on the 
 supposition that the colouring molecules act, by 
 virtue of the form which belongs to them, in the 
 liquids in which they are in solution, as we see 
 it stated in the following passage of Haiiy. 
 " With regard to transparent and even coloured 
 bodies, they seem to offer a middle term between 
 limpid and opaque bodies. Their molecules 
 reflect the rays of the colour under which they 
 are presented to the eye, and at the same time 
 these bodies transmit, throughout all their extent, 
 other rays, which usually have the same colour as 
 the reflected rays. Thus the molecules situated 
 at the surface reflect one part of the rays which 
 arrive at this surface, and transmit the rest; 
 other molecules situated a little lower, reflect one 
 part of the rays which have escaped the first 
 reflection, then transmit the others j and thus in 
 succession, to the last surface, where there still 
 arrive a sufficiently great number of rays passing 
 into the air, to give the body placed between the 
 eye and the light a very sensible transparency. 
 It thence results, that the greater thickness the 
 medium has, the deeper is its colour, which 
 agrees with observation. 
 
IN GENERAL. 41 
 
 " This supposition will not accord with the 
 opinion which we must form of chemical combi- 
 nations possessing liquidity, and in which all the 
 properties become common among all the parts 
 by their reciprocal action, whilst the equilibrium 
 of the action is not disturbed. The figure which 
 belongs to the different molecules allows no 
 influence to be perceived till they approach the 
 term where they must pass to the solid state : It 
 is then, for example, that water, which tends to 
 congeal, acquires an expansion due to the effort 
 which it makes, in order that its molecules, in 
 losing their liquidity, may assume an arrangement 
 determined by their surfaces. 
 
 " Experiments made by Delaval appear to prove, 
 that the effects attributed to the distinct parts of 
 the colouring substances in solution, do not de- 
 pend on their individual reflection. He filled a 
 flask, of a square form, with a coloured liquid, 
 after having covered three of its sides and the 
 bottom with a black paint ; and he observed, on 
 looking to the liquid by the free face, which 
 formed a right angle with his window, to prevent 
 the reflection from the posterior surface, that the 
 above liquid appeared black, whatever might be 
 its proper colour. Glasses having the same form, 
 and differently coloured, equally appeared black 
 when they were covered with a black cloth, with 
 the exception of one face which was left free, to 
 admit the incident light. If their mass be con^ 
 siderable, they thus also appeared black j but 
 
42 OF DYEING 
 
 their fragments, applied to a white ground, ex- 
 hibited the colour peculiar to them." * 
 
 He thence concludes, that coloured liquids and 
 glasses are seen in their proper colours only by 
 rays reflected from their posterior surfaces ; so 
 that it is the rays which have traversed the colour- 
 ed liquid or glass, which give the sensation of 
 colour by transmission or reflection. 
 
 He makes a remark, whose application is found 
 in this place. " If a small quantity of colouring 
 substance is mixed with a medium which has no 
 colour, the mass appears dyed with the colouring 
 substance. But if we add a great quantity of this 
 colouring matter, the mass appears black ; conse- 
 quently, in ascribing to the colouring substance 
 the power of reflection, we advance a contradic- 
 tory and inexplicable proposition ; for we affirm, 
 that the more of the substance, having the power 
 of reflection, the incident light encounters, the 
 less light is reflected; so that if the colouring 
 substance be very abundant, there is no longer 
 any colour but a black." 
 
 In order to extend this theory to opaque 
 coloured bodies, Delaval supposes that they are 
 always composed of two substances, one of which 
 is white, and the other, which is coloured, possesses 
 transparency, so that the rays of a certain colour 
 which traverse it, are reflected by the white sur- 
 faces that they meet. When white molecules do 
 not separate those which are coloured, it is enough 
 
 * Mem. of the Liter, and Philos. Soc. of Manchester, vol. ii. 
 
IN GENERAL. 43 
 
 if there be present any medium whatever possess- 
 ed of a different density ; as Newton has shewn 
 that two transparent substances, of a widely dif- 
 ferent density, produce an opaque body. Delaval 
 thus explains the colour of gold and metallic 
 oxides. 
 
 i This explanation is very specious, and satisfies 
 the greater numb er of observations. Nevertheless 
 its application appears to us too general, because 
 it requires us to suppose, between the coloured 
 molecules of the metals, the existence of a medium, 
 which the other properties do not indicate, and 
 because other causes may produce the effect here 
 ascribed to it. 
 
 In recapitulating what has been said, we find, 
 that in order to explain the different phenomena 
 presented by coloured bodies, 1st, we consider, 
 in a general manner, the colouring molecules of a 
 body as insulated, relatively to those which adjoin 
 them, and the media which are interposed ; viz. 
 the subtile fluids which occupy their pores, and the 
 air surrounding their exterior surface, as two 
 glasses, between which is comprised the plate of 
 air, as in the experiment of Newton. 
 
 2. It is admitted, however, that in the solutions 
 which experience changes of colour by the action 
 of acids and alkalies, the union of the molecules 
 of the two liquids forms mixed molecules, whose 
 thickness is different from that of the component 
 molecules, without explaining the uniformity of 
 effect of those acids and alkalies which differ most v 
 
 in their specific gravity, fixity, and volatility. 
 
44 OP DYEING 
 
 3. It is presumed, on the contrary, that in the 
 solutions, combinations, and precipitations, where 
 the substances preserve the same colour, there 
 occurs no alteration in their dimensions, apply- 
 ing to the colouring parts the theory of No. 1., 
 although the state in which they exist be equally 
 the effect of a reciprocal action, and although 
 there be equally a combination. 
 
 In all the cases of transparency, the colouring 
 molecules are supposed to act individually on the 
 rays of light ; and experiment seems to prove, that 
 the reflection of bodies which are not opaque, 
 takes place only at their anterior and posterior 
 faces. 
 
 The effects observed in the solution of water 
 in air, and in its precipitation, appear to us capa- 
 ble of illustrating the properties of solutions 
 relatively to light. 
 
 When damp air has been compressed in a 
 globe, according to the experiment of Kratzein- 
 stein related by Saussure,* and when we restore 
 the freedom of communication, this air, which, 
 placed between the eye and the light, exhibited 
 at first only a pure transparency, causes vapours 
 to be perceived, which have the colours of the 
 rainbow at the moment when the compression is 
 removed ; and it resumes its transparency by a 
 new compression. 
 
 This phenomenon is not difficult to analyze. 
 When the air, saturated with humidity in a state of 
 
 * Essai sur l'Hygrom. § 209. 
 
IN GENERAL. 45 
 
 compression, is suddenly liberated, it produces by 
 its dilatation a degree of cold, which causes the 
 precipitation of a part of the water which it held 
 in solution. Compression produces a contrary 
 effect, by the heat which accompanies it.* 
 Saussure remarks, that the phenomenon due to 
 the vapours lasts only an instant, because the 
 temperature becoming fixed, the state of solution 
 becomes equally so. 
 
 Light then experiences no peculiar reflection 
 or refraction from the water or air while the 
 solution exists ; and it is only when these two 
 elements acquire a peculiar existence that this 
 effect begins. Is it not natural to ascribe to other 
 solutions what is here observed in that of water ? 
 On the other hand, can we compare the constant 
 properties of coloured substances, with the varia- 
 ble and transient effects owing to the refraction 
 and reflection of the molecules in simple juxta- 
 position ? 
 
 Delaval made a great many experiments to 
 prove, " that the more considerable the densi- 
 ty of constantly coloured bodies is, the greater 
 also is their power of reflection (everything else 
 being equal) for reflecting the least refrangible 
 rays ; that, on the contrary, when they have less 
 density, they can proportionally reflect only the 
 less refrangible rays ; and consequently they must 
 exhibit different colours, according to the order 
 of their density." 
 
 * Stat. Chim. torn. i. p. 163. 
 
 \ 
 
46 OF DYEING 
 
 He makes choice particularly of metallic bodies 
 to prove, " that they differ as to colour, exactly 
 in the same gradation as in density ; the densest 
 body being red, that which is immediately of a 
 less density being orange-yellow," &c. 
 
 A little attention, however, is sufficient to con- 
 vince us, that there is no relation between the 
 specific gravity of metals, or of glasses coloured 
 by their oxides, and their colours. Delaval re- 
 garded, with Newton, the solution of metals as 
 a simple division of their molecules, without re- 
 gard to their oxidation, the theory of which was 
 then unknown, and on which principally depend 
 the changes of colours in their solutions and 
 oxides. To establish his opinion, and to make 
 the peculiar colour of every metal coincide with 
 its specific gravity, he selected that state of solu- 
 tion and oxidation which best suited his views. 
 "We refer to the treatise of Bancroft for a detail 
 of the facts hostile to the opinion of Delaval. 
 
 Newton ascribed the colour of white metals 
 " to their excessive density, by virtue of which 
 they seem to reflect almost all the incident light, 
 unless, when dissolved in suitable menstrua, they 
 be thereby reduced into very small parcels (par- 
 ticles), when they become transparent."* 
 
 If, from the density, we judge of the effect which 
 silver ought to produce on light, its solution in 
 nitric acid, which can take up a great quantity of 
 
 * The brilliant white of potassium and sodium, bodies of 
 little density, seems adverse to this idea of Newton. — T. 
 
IN GENERAL. 47 
 
 it, and can be diluted with water as much as we 
 please without decomposition, ought, in passing 
 through different densities, to acquire the pro- 
 perty of reflecting different colours. It remains, 
 however, colourless and transparent, although, 
 according to the observation of Wollaston, the 
 refracting quality of the metallic solutions varies 
 with their different degrees of concentration.* It 
 ought to tally with the density and attenuation 
 of the solutions or precipitates of cobalt, nickel, 
 and manganese, which, like silver, void of colour 
 in the metallic state, acquire it very intensely and 
 very variously in their oxidation and precipita- 
 tion. 
 
 The considerations now presented lead us to 
 believe, that we ought not to confound the fugi- 
 tive colours produced by the reflection of plates, 
 which follow the laws described by Newton, with 
 the colours which continue, notwithstanding the 
 changes of density and thickness. These appear 
 to depend on properties, in which the peculiar 
 affinity for the different rays of light has an in- 
 fluence which resists that of the dimensions and 
 the density. On examining the facts, we per- 
 ceive that condensed oxygen exercises a great 
 power in this species of affinity. A variable pro- 
 portion of it, affecting in an insensible manner 
 the specific gravity of the metallic oxides, pro- 
 duces in them great changes of colour. In like 
 manner, a little oxygen, conveyed by muriatic 
 
 * Phil. Trans. 1802. Ann. de Chim. tom. xlvi. 
 
 8 
 
 f 
 
 \ 
 
48 OF DYEING 
 
 acid to colouring substances, either makes their 
 colours disappear, or produces in them consider- 
 able alterations ; whilst other combinations, for 
 example that of alumina, which precipitates the 
 greater number of colouring substances in the 
 form of lakes, and which, according to the ideas 
 of Newton and Delaval, ought to give consider- 
 able density to these substances, preserves mean- 
 while their proper colour, merely concentrating it 
 by the condensation which the earth occasions. 
 
 The very experiments of Newton prove, that 
 the peculiar affinity of different substances has a 
 great influence on their relations to the rays of 
 light, since, according to him, their refractive 
 power is proportional, not merely to their den- 
 sity, but also to their inflammable disposition. 
 This proposition ought not to be taken with too 
 great latitude. For phosphorus, which is very 
 inflammable, has no great refrangency. It follows 
 however, from the very observations on which 
 the doctrine rests, that there is a great difference 
 of action, according to the affinity of the bodies 
 for the rays of light. 
 
 The interesting experiments of Dr Blair like- 
 wise prove the peculiar power of the affinity : — 
 When light passes from any medium whatever into 
 a vacuum, the red rays are the least refrangible, 
 and the violet are at the other extreme ; but if 
 light passes from one medium into another, he 
 shews, that it is the quality or particular nature of 
 these media that determines which of these rays 
 shall be the most refrangible, or if they shall be 
 
IN GENERAL. 49 
 
 equally so. The green rays occupy the middle 
 of the spectrum in the dispersion occasioned by 
 crown glass ; they are found among the least 
 refrangible by the dispersive action of flint glass ; 
 but in muriatic acid these rays are found, on the 
 contrary, on the side of the violet or the most 
 refrangible. It thence happens, that the order of 
 the colours is reversed in the secondary spectrum, 
 formed by a combination of crown glass with the 
 liquid. 
 
 If we depart, in these considerations, from the 
 consequences to which physical observations have 
 led; if we believe that we must resist, in this 
 particular, the authority of Newton, and that of 
 his illustrious interpreter, it is with regret ; for 
 we feel how important it is to connect all the 
 effects due to the reciprocal action of bodies, and 
 we hope that future experiments will fill up the 
 space which here seems still to separate natural 
 philosophy and chemistry. Meanwhile, we shall 
 confine ourselves to the results of this last part 
 of the science, which treats of the properties of 
 bodies. 
 
 In the metallic oxides, and in several mineral 
 substances, all the parts are equally coloured ; 
 but this is not the case with vegetable or animal 
 substances. The colour in the latter is usually 
 owing merely to particles, which are mixed or 
 combined with those constituting the bodies 
 themselves ; and vegetables contain sometimes 
 different colouring molecules at different periods 
 of their growth, or in their different parts. 
 
 VOL. I. D 
 
 
50 OF DYEING 
 
 The colouring molecules of vegetable and ani- 
 mal substances are almost the only ones employ- 
 ed for the purpose of dyeing ; but they are often 
 modified by the use of intermedia. Such are the 
 substances designated in this treatise by the name 
 of colouring particles, (parties colorantes.J 
 
 These colouring particles do not exhibit, in 
 their composition, the simplicity of mineral sub- 
 stances, nor does oxygen affect their colours in 
 the same way. We shall examine, in one of the 
 following chapters, in what manner this principle 
 acts upon them so as to alter their nature. 
 
 Some chemists have regarded iron as the cause 
 of all vegetable and animal colours ; and Adol- 
 phus Becker employed, in support of this opinion, 
 considerations derived from the property which 
 this generally diffused metal possesses, of assum- 
 ing a great number of colours in the states of 
 oxide, solution, and vitrification.* 
 
 Iron, in fact, appears to be contained in all 
 vegetable and animal substances, but in extreme- 
 ly small quantity. Oak, one of the vegetable 
 substances which ought to yield the largest re- 
 siduum, leaves in its combustion only l-200th of 
 its weight of ashes ; and these ashes do not con- 
 tain l-200th of iron. Can the rich and splendid 
 colours, with which vegetables are enamelled, be 
 explained by so minute a proportion ? Is there 
 in reality any relation between the changeable- 
 
 * Specimen sistens experiraenta circa mutationem colorum 
 quorundam vegetabilium a corporibus salibus, cum corollariis ; 
 auctore J. F. Adolpho Becker, 1779. 
 
IN GENERAL. 51 
 
 ness of some of these colours, by acids, alkalies, 
 and air, and the uniform succession of colours 
 which iron assumes according to its degree of 
 oxidation ? 
 
 The opinion which we are combating might 
 indeed be supported by the suffrage of Bergmann, 
 who supposed he had proved that indigo owes its 
 colour to the iron which it contains j* but we 
 may be permitted to reply, that it is easy to shew 
 how this great chemist had deceived himself on 
 this subject. By means of the alkaline prussiate, 
 he obtained, from the ashes of an ounce of indigo, 
 from 30 to 32 grains of prussian blue ; and he 
 estimates the iron which this contains at 18 or 
 20 grains. But in other places he proves, that 
 the iron contained in a substance forms at most 
 but the fifth part of the prussian blue which we 
 procure from its solution, and every-where else he 
 employs this valuation. We must therefore rer 
 duce to six grains, the iron he obtained from an 
 ounce of indigo. In the experiments which fol- 
 low the above, he proves, that the greater part of 
 this iron may be dissolved by muriatic acid, with- 
 out the colouring particles being affected; so that 
 the larger share of this metal does not enter into 
 their composition. From this it clearly follows, 
 that the colouring particles of this substance 
 must contain a quantity of iron so small, that it 
 can have but little influence on its colour. 
 
 * Analyse Chimique de l'lndigo. Mem. des Savans Etr. 
 torn. ix. 
 
52 OF DYEING 
 
 The means of chemical analysis which we pos- 
 sess, are so far from enabling us to determine the 
 composition of the colouring particles with suf- 
 ficient precision, for shewing to what principles 
 they owe their properties, that we often observe 
 a very different composition giving rise to a co- 
 lour of the same kind. The particles of indigo 
 differ much from those which colour several 
 flowers blue. A great number of yellow sub- 
 stances afford colours almost similar in appear- 
 ance, which notwithstanding differ much in their 
 properties. 
 
 There are simple colours, and there are others 
 arising from the mixture of these colours, which 
 are consequently compound. Newton has given 
 a general rule for forming any colour whatever, 
 by means of other prismatic colours. Le Blond 
 has proved, that we may procure all the colours 
 which the art of the painter can desire, by the 
 mixture of red, blue, and yellow.* Dufay has 
 shewn, that the same effect may be obtained in 
 dyeing ; and he has thence concluded, that there 
 was in nature only three primitive colours, which 
 gave origin to all the rest. This opinion has 
 been embraced by several philosophers ; but it 
 does not appear to be sufficiently established. 
 
 Between simple colours, and colours formed by 
 the union of different rays, there is this difference ; 
 — the former, viewed through the prism, retain 
 
 * L'Harmonie du Coloris dans la Peinture, reduite en 
 pratique. 
 
IN GENERAL. 53 
 
 their simplicity, while the latter are decomposed. 
 The green produced by the rays of this colour, 
 suffers no decomposition by the prism. It has, 
 therefore, the character of a simple and primitive 
 colour. But the compound green is separated 
 into yellow and blue. 
 
 Although the green formed in dyeing results 
 from a mixture of blue and yellow, we must not 
 consider all the greens as combinations of the 
 two species of colouring particles. Thus, the 
 green oxide (hydrated oxide) of copper cannot 
 be owing to molecules of a different nature ; and 
 the green of plants is undoubtedly produced by 
 a homogeneous substance, in the same way as the 
 greater number of hues which exist in nature. 
 This colour owes then its origin sometimes to 
 simple rays, and sometimes to an union of differ- 
 ent rays ; and some other colours are in the same 
 predicament. Were the green of plants due to 
 two substances, one of which is yellow and the 
 other blue, it would be extraordinary if we could 
 not separate them, or at least change their pro- 
 portions, by some solvent. There are, however, 
 some substances which contain colouring parts of 
 different species ; madder, for example, as we 
 shall see in the second volume. (Note A.) 
 
 The green, which we assume as an example of 
 a truly compound dyeing colour, shews that the 
 colouring molecules cover only one part of the 
 surface of the stuff, although this may appear of 
 a full and uniform colour ; for, after the stuff has 
 been dyed blue, the yellow parts fix themselves 
 
54) OF DYEING 
 
 on it, and produce the green ; and although the 
 dyeing has been begun with yellow, if a yellow of 
 little permanence be employed, it maybe destroyed 
 by air, and especially by chemical agents, while 
 the blue remains unaffected ; which proves that 
 it is on the stuff, and not on the indigo, that the 
 yellow particles have been principally fixed. 
 
 Hence we see, that in order to procure the 
 sensation of a simple colour, the rays of the dif- 
 ferent colours require merely to be approximated* 
 In fact, we may produce an uniform colour by 
 the exact mixture of wools of different hues ; and 
 in painting we obtain simple colours by the mix- 
 ture of different ingredients, which do not che- 
 mically combine. 
 
 The colouring particles form different combi- 
 nations, and they are applied either alone, or pre- 
 viously combined with other substances, to wool, 
 silk, linen, or cotton. The art of dyeing consists 
 in employing the affinities of the colouring par- 
 ticles so as to extract, dissolve, and thereafter 
 apply and fix them to the substances to be dyed, 
 which will be distinguished in this treatise by the 
 name of skiffs, whatsoever may be their nature 
 and their form. 
 
 It has been proposed to arrange colouring par- 
 ticles into extractive and resinous ; but this divi- 
 sion conveys only incomplete and false ideas of 
 their properties ; for there are colouring particles 
 which, being insoluble in water, might be regard- 
 ed as resinous, and yet they do not dissolve in 
 alcohol. Such are, the red portion of carthamus 
 
IN GENERAL. 55 
 
 (safflower), which dissolves merely by means of 
 an alkali ; and indigo, which, insoluble both in 
 water and alcohol, becomes soluble in alkalies 
 only under certain circumstances ; but it dis- 
 solves readily in sulphuric acid. 
 
 The colouring particles which are soluble in 
 water cannot be compared to the mucilaginous 
 and extractive parts of vegetables, since the pro- 
 perty of dissolving in water, like these substances, 
 gives no idea of the properties which it is essen- 
 tial to discover in them ; such as their relations to 
 the chemical agents employed in dyeing, to air, 
 to light, and to animal and vegetable substances. 
 
 It is, moreover, an abuse injurious to the pro- 
 gress of sound theorizing, to seek an explanation 
 of the properties of colouring substances in the 
 mucilaginous, resinous, earthy, saline, and oily 
 parts which may be supposed to enter into their 
 composition, as Poerner particularly has done. 
 
 We have just seen, that in trying to account 
 for the causes of colours, and the nature of the 
 colouring particles, two inconveniencies have 
 arisen : the one, from the attempt to explain the 
 action which the molecules of colouring sub- 
 stances exercise on the rays of light by their 
 density and thickness, without having any means 
 of determining these circumstances, and without 
 taking into view the affinity arising from their 
 chemical composition ; the other, to compare, 
 from some slight relations, the colouring particles 
 with the mucilages and the resins, and to seek to 
 explain their properties by the parts supposed to 
 
 
56 OF DYEING 
 
 enter into their composition ; whereas their co- 
 louring properties ought to be determined by 
 direct experiments, and not be explained by an 
 imaginary composition. We depart from true 
 theory, which is solely the result of observation, 
 when we ascribe to laws purely mechanical the 
 adherence of the colouring particles to the sub- 
 stances which they dye, as well as the action of 
 mordants, and the difference between permanent 
 and fugitive colours. Hellot, to whom otherwise 
 we are indebted for the best practical treatise 
 extant on dyeing wool, has fallen into a com- 
 plete illusion on this subject, and his theoretical 
 ideas have often influenced his observations and 
 the principles which he has laid down, as we may 
 ascertain by the perusal of his work. We may 
 judge of his theory by the following passage : — 
 " I believe it may be laid down as a general prin- 
 ciple of the art now treated of, that the whole in- 
 visible mechanism of dyeing consists in dilating 
 the pores of the bodies to be dyed, in depositing 
 within them particles of a foreign matter, and in 
 keeping them there by a species of coat (enduit), 
 which neither water, rain, nor the rays of the sun, 
 can affect ; in selecting colouring molecules of 
 such a tenuity that they may be retained suffi- 
 ciently incased in the pores of the subject, laid 
 open by the heat of boiling water, then contract- 
 ed by cold, and farther coated with a species of 
 cement (mastic), which is left in the very pores 
 by the salts chosen to prepare them. Hence it 
 follows, that the pores of the fibres of wool, from 
 
IN GENERAL. 57 
 
 which we have fabricated or are going to fabri- 
 cate stuffs, ought to be cleansed, enlarged, coated 
 over, then contracted, in order that the colouring 
 atom may be preserved in them nearly as a dia- 
 mond in the collet of a ring." * 
 
 We have reason to be surprised that Macquer 
 should have adopted the ideas of Hellot. " Here 
 would be the place," says he, " to explain the 
 manner in which mordants act in dyeing, and to 
 develop the cause of fast and fugitive dyes ; but 
 these objects have been treated with so much 
 sagacity by M. Hellot, that I think it my duty to 
 refer my reader to him."t 
 
 Dufay, however, had already perceived, that 
 the colouring particles were naturally disposed to 
 contract a stronger or weaker adhesion with the 
 fibres which received them;t and he remarks 
 very properly, that without this disposition the 
 stuffs would not take a colour similar to that of 
 the dye-vat, or divide equally with it the colour- 
 ing particles ; whereas the liquor of the bath 
 becomes sometimes as limpid as water, giving up 
 all its colouring matter to the stuff; " which 
 seems," says he, "to indicate that the ingredients 
 have less attraction for the water than for the 
 particles of the wool." He adds, that several 
 other phenomena may be accounted for in the 
 same way ; but that such an explanation leaves 
 
 * L'Art de la Teinture des Laines, p. 42. 
 f L'Art de la Teinture en Soie, avant propos, p. 8. 
 % Observations Physiques sur le Melange de quelques Co- 
 leurs dans la Teinture. Mem. de l'Academ. 1737. 
 
 
 
 
j 
 
 58 OF DYEING 
 
 still much to be desired, and that he would aban- 
 don it without difficulty were a more probable 
 one proposed. 
 
 Bergmann is the first who referred the pheno- 
 mena of dyeing entirely to chemical principles.* 
 Having dyed wool and silk in a solution of indigo, 
 in sulphuric acid much diluted with water, he 
 explains the effects which he observed in this 
 operation, by ascribing them to the precipitation 
 occasioned by the greater affinity of the wool and 
 the silk for the blue molecules, than of these 
 molecules and the acidulous water. He remarks, 
 that this affinity of the wool is powerful enough 
 to deprive the liquid entirely of its colouring par- 
 ticles ; but that the feebler affinity of the silk can 
 only diminish the proportion of these particles in 
 the bath ; and he shews, that on these different 
 affinities depend both the permanence and inten- 
 sity of the colour. 
 
 This is, in fact, the legitimate manner of view- 
 ing the phenomena of dyeing, which are true 
 chemical phenomena. 
 
 A short while thereafter Macquer adopted this 
 theory, and made just applications of it to the 
 action of mordants, and particularly of alumina.t 
 
 Whatever may be the physical cause of colours, 
 the colouring particles, which it is the object of 
 the art of dyeing to apply to stuffs, possess che- 
 
 * Analyse de 1' Indigo. Mem. des Savans Etrang. torn. ix. ; 
 Mem. envoye pour le prix propose en 1776, et dans les notes 
 sur le traite de Scheffer. 
 
 f Diction, de Chim. 2d edition, au mot Teinture, 1778. 
 
IN GENERAL. 59 
 
 mical properties distinguishing them from other 
 substances dependent on the affinities which their 
 particles collectively exercise, as well as on the 
 reciprocal action of these particles, and on their 
 constitution, which disposes them more or less to 
 assume the solid or the liquid state. 
 
 By virtue of these properties, they dissolve in 
 different liquids, they combine with acids, alkalies, 
 oxides, with some earths, and especially alumina ; 
 they frequently precipitate the oxides and alu- 
 mina from the acids which held them in solution ; 
 in other circumstances, they even form super- 
 compounds with the salts ; sometimes they unite 
 immediately to the stuffs ; more frequently they 
 form with these substances a combination much 
 more intimate through an intermedium, or even 
 they do not combine with it except through the 
 intermedium ; the intermedium modifying their 
 colour, their other properties, and even their 
 composition. • 
 
 The difference in the affinity of the colouring 
 particles for wool, silk, and cotton, is sometimes 
 so great, that they refuse to combine with one of 
 these substances, whilst they combine very well 
 with another ; thus, cotton takes no colour in the 
 bath that dyes wool scarlet. Dufay got a piece 
 of stuff made, the warp of which was wool, and 
 the weft cotton ; he passed this stuff through the 
 fulling-mill, to ensure the same preparation to 
 the wool and cotton j but the wool took the scar- 
 let dye, and the cotton remained white. It is 
 this difference of affinity which makes it neces- 
 
J 
 
 ) 
 
 60 OF DYEING 
 
 sary to vary the preparations and the processes, 
 according to the nature of the substance which 
 we wish to dye of a particular colour. 
 
 If the effects of the intermedia employed in dye- 
 ing, and if the fixation of the colouring particles 
 on a stuff by itself, or by means of an interme- 
 dium, be owing to the combinations which are 
 formed, we must still refer to chemical combina- 
 tion the changes produced, by acids and alkalies, 
 in several vegetable colours, which chemists em- 
 ploy for verifying the nature of different sub- 
 stances. We may compare the resulting com- 
 pounds to neutral salts, which possess qualities 
 distinct from those of their components, but in 
 which one of the components may be in excess, 
 so as to cause its properties to predominate. 
 This state of combination is observed between 
 the colouring particles of cochineal and the aci- 
 dulous tartrate of potash, or cream of tartar. On 
 evaporating slowly a solution of this salt in a 
 decoction of cochineal, crystals are formed, which 
 retain a fine ruby colour, much more intense and 
 more lively than that of the liquid in which they 
 were formed. 
 
 The reciprocal action of acids and alkalies be- 
 ing much greater than that which they exercise 
 in particular on the colouring particles, they can 
 mutually saturate each other, and then the re- 
 Suiting compound has little effect on the colour- 
 ing particles ; so that the changes which had been 
 produced by one of the substances disappear when 
 it is neutralized by an antagonist substance. 
 
IN GENERAL. 61 
 
 Blue colours are not the only ones which can 
 pass to red by the agency of acids, and to green 
 by that of alkalies ; the most part of the red 
 colours, that of the rose, for example, are exalt- 
 ed by acids, and pass to green by alkalies ; and 
 some green colours, such as that of the decoction 
 of burdock, according to the testimony of Nose,* 
 and the green juice of the buckthorn berries, 
 (rhamnus catharticus) according to Becker, red- 
 den also with acids. 
 
 This property, common to the most ordinary 
 colours of vegetables, appears to prove that there 
 is a close analogy between the greater part of 
 their colouring matters ; nor is it without founda- 
 tion that Linnaeus t thought the red colour ow- 
 ing to an acid, of which he maintained the exist- 
 ence ; but there are also several vegetables which 
 contain a free acid, without possessing a red co- 
 lour.t 
 
 In the combination which the colouring mole- 
 cules form with the stuff, they preserve only a 
 
 * Versuch eineger Beytrage zur Cheraie. 
 
 f Amaenitatum Acad. torn. iv. 
 
 J There are flowers whose colour appears to be naturally 
 modified by a very feeble acid, without being decidedly red : 
 such is the flower of violet, whose violet juice becomes blue 
 when we leave it for some time in a tin vessel, probably be- 
 cause the acid which it contained combines with a portion 
 of oxide on the surface of the tin ; such also is the flower of 
 the mallow, which becomes blue by simple drying. The 
 primitive colour is restored by the addition of a very small 
 quantity of acid. Observ. Physico-Chim. sur les Couleurs, par 
 Opoix. Journal de Physique, torn. viii. 
 
 
62 OF DYEING 
 
 part' of their original properties ; on being as- 
 sociated with alumina, with the oxides, and some 
 other substances, they are somewhat modified ; 
 but the properties of the latter combinations are 
 further modified when they unite with the stuff". 
 
 These modifications are analogous to what is 
 observed in other chemical combinations ; but 
 they are subject to a peculiar degradation from 
 the action of air and light j sometimes, on the 
 contrary, they receive from these agents a new 
 lustre or a different shade : there are also agents 
 which, after combining with the colouring par- 
 ticles, alter the colour which they first produced, 
 making it pass to yellow, and then destroy it ; 
 such in particular is oxygenated muriatic acid j 
 it acts by means of the oxygen which it yields, 
 and consequently differs in nothing except inten- 
 sity from that of the atmospheric air.* 
 
 It follows, from what has been stated, I. That 
 the colouring molecules have affinities which pro- 
 duce their solution and their combination, the 
 effects of which, combining with those of their 
 own constitution, form the differences that dis- 
 tinguish them from each other. 
 
 * This theory is no longer tenable, since it is known that 
 dry chlorine does not blanch dry litmus paper. When mois- 
 ture intervenes, muriatic acid is formed, and oxygen evolved ; 
 to the action of which body on the colour the bleaching 
 effect is to be ascribed. Water is the source of the dis- 
 coloration, both in the ancient and the modern process of 
 bleaching. — T. 
 
IN GENERAL. 63 
 
 2. That they unite directly with the stuff, or 
 by the aid of an intermedium ; but the stuff has 
 relations with them according to its nature. 
 
 3. That, in combining with a substance, they 
 experience a change which modifies their colour, 
 besides the modification resulting from the shade 
 peculiar to the substance to which they com- 
 bine. 
 
 4. That the colouring molecules differ not 
 only from one another by these different dispo- 
 sitions, but likewise by the ulterior changes 
 which they may suffer from the action of other 
 substances, and particularly from that of the air 
 and light. 
 
 In order to establish, on these grounds, the 
 principles of the art of dyeing, so as to explain 
 the peculiar phenomena which it presents, to guide 
 ourselves in its practice, and to obtain the surest, 
 easiest, and most economical processes, either 
 for executing known operations, or for fulfilling 
 the demands of the consumers, and improving 
 the art, we shall in this section examine more 
 particularly the effects arising from the action of 
 substances which serve as intermedia, and those 
 produced by the agents which may affect the 
 nature of the colours. 
 
 But stuffs possess different relations with the 
 colouring particles, and they must receive pre- 
 parations preliminary to the operations of dyeing : 
 under this point of view, we shall examine them 
 in the second section. 
 
6i< OF DYEING IN GENERAL. 
 
 The third section will be devoted to the art of 
 bleaching linen and cotton by the oxygenated 
 muriatic acid, (chlorine). 
 
 We shall be occupied, in the fourth, with the 
 manipulations of dyeing in general, and the means 
 by which we can ascertain the goodness of co- 
 lours. 
 
 We shall present, in the fifth, a summary ac- 
 count of the principal ingredients employed in 
 dyeing, in reference to dissolving, modifying, and 
 fixing the colouring particles. 
 
 After having thus exhibited, in the first part of 
 this work, the general facts which are to be applied 
 to particular operations, we shall detail, in the 
 second part, the processes of dyeing, arranging 
 them into genera and species of colour. Here 
 we shall examine every colouring substance ; we 
 shall apply to the different dyes the principles 
 established in the first part ; we shall unfold the 
 processes of the art, and, independently of the 
 explanations, we shall endeavour to improve it by 
 direct experiments. We shall then try to har- 
 monize the results of experiment with the princi- 
 ples' of chemistry ; but we shall stop whenever 
 these principles cannot conduct us to satisfactory 
 explanations, or we shall confine ourselves to con- 
 jectures, to be verified by the future advancement 
 of the science. 
 
 
OF MORDANTS. G5 
 
 CHAPTER II. 
 
 Of Mordants. 
 
 The term mordant is given to those substances 
 which serve as intermedia between the colouring 
 parts and the stuffs which they dye, either for 
 facilitating or modifying their combination. This 
 word is rendered appropriate by the use which 
 even the ancients made of it.* We may distin- 
 guish, under the title of alteratives, the ingredients 
 which are employed merely with the view of 
 changing the shade. 
 
 Mordants merit the greatest attention. It is 
 by them chiefly that we diversify the colours, 
 give them more brilliancy, fix them on the stuffs, 
 and render them more durable. 
 
 A mordant is not always a simple agent, but 
 in the mixture composing it different combina- 
 tions are sometimes formed, so that the substances 
 which have been employed do not act imme- 
 diately, but by the resulting combinations. 
 
 Sometimes the mordant is mingled with the 
 colouring particles ; sometimes the stuff is impreg- 
 nated with it before being exposed to the dyeing 
 bath. On other occasions these two methods are 
 combined. We may dye in succession with li- 
 quors which contain different substances, the last 
 of which acts only on the parts with which the 
 
 * Ameilhon. Mem. de 1'Irtstitut. Litter, torn. iii. 
 VOL. I. E 
 
66 OF MORDANTS. 
 
 stuff has been imbued by the preceding operation. 
 One solution, which is to yield its basis to the 
 stuffy has need of heat; another requires the ope- 
 ration to be made in the cold. The mordant is 
 frequently an oxide ; in which case its properties 
 may vary, not only according to its actual con- 
 dition, but also according to the action of the 
 substances with which it is associated, and even 
 according to the circumstances of the operation. 
 It is by the determination of all these conditions 
 that chemistry can particularly direct the art of 
 dyeing, can establish its processes in a constant 
 manner, removing from it whatever is useless or 
 prejudicial, and transferring to one kind of dye- 
 ing what, is found efficacious in another. 
 
 We shall describe, in the fifth section, the 
 essential properties of the chemical agents of 
 which the greatest use is made in the quality of 
 mordants : we shall determine, in the second 
 part, the particular effects which they produce on 
 every species of colouring substance, detailing 
 every fact which experience has taught concerning 
 those operations of dyeing in which they are em- 
 ployed. At present we shall confine ourselves 
 to the development of the general observations 
 which have been made on their action. 
 
 There are colouring substances on which acids 
 and alkalies appear to have but a feeble action, 
 which are soluble in water, and combine imme- 
 diately with stuffs ; such are several dun colours, 
 extracted from woods and roots, and the husks of 
 the walnut. These substances serve, therefore, 
 
OF MORDANTS. 67 
 
 the purpose of dyeing without the aid of any 
 mordants. There are some, again, which dissolve 
 only by alkalies, as, in particular, the safflower. 
 Its colouring part quits the alkalies, and fixes on 
 the stuffs, when those are saturated with an acid. 
 The anotto, which dissolves easily by means of 
 an alkali, abandons it to combine with the stuff, 
 without the necessity of employing an acid. 
 When indigo is deprived of oxygen; it becomes 
 yellow, and is then soluble in alkalies. Stuffs may 
 abstract it also from the alkalies, and then it 
 resumes its blue colour, through the agency of 
 oxygen. Dyes made with these colouring sub- 
 stances have no need of auxiliaries. But the 
 greater number combine only in small quantity 
 with the stuffs, when a base does not serve as an 
 intermedium to their union. They adhere feebly 
 to it, and resist much less the causes of destruc- 
 tion. 
 
 The substances employed as mordants should 
 therefore furnish a base which attaches itself to 
 the stuffs and to the colouring particles, and which 
 resists their redissolution and destruction. As to 
 those substances, however, which occasion merely 
 some modifications in the colours, it is sufficient 
 for them to be retained in small quantity in the 
 combination formed between the stuffs, the mor- 
 dant, and the colouring matter. Hencq, although 
 alteratives act equally by combining, they should 
 be distinguished, however, from mordants, which 
 serve to fix the combination. 
 
68 
 
 OF MORDANTS. 
 
 Acids can in general dissolve the colouring sub- 
 stances, but as they do not themselves possess the 
 property of combining with the stuff, they cannot 
 serve as bonds of union ; on the contrary, they 
 usually carry off the colouring particles which had 
 been retained by the stuff, and they contribute to 
 the colour which is fixed, only in the quality of 
 alteratives, by uniting in small quantity to the 
 coloured combination. 
 
 The alkalies, among which we must comprise 
 the earths that produce saturation with acids, can 
 combine with the most part of colouring sub- 
 stances ; but, in order to ascertain the effects 
 which they ought to produce according to their 
 differences, and to compare them with those due 
 to the acids, we must direct our attention to the 
 properties of the combinations which depend on 
 those of their elements. 
 
 While reciprocal affinity produces an union, 
 the dispositions of the substances to solidity or 
 liquidity are preserved in the combinations, with 
 the differences proceeding from the condensation 
 which they experience.* 
 
 It thence results that the alkalies, which possess 
 much solubility, ought to form soluble combina- 
 tions with the colouring substances which have an 
 affinity for them ; but those which have little 
 solubility ought, on the contrary, to produce in- 
 soluble combinations. 
 
 * Essai de Statique Chimique. 
 
OF MORDANTS. ' 69 
 
 These considerations, which are supported by 
 the results of the reciprocal action of acids and 
 alkalies, and by the properties of the combinations 
 in genera], lead us to distinguish the effects of 
 the different bases. Potash, soda, and ammonia, 
 cannot serve as intermedia to fix the colouring 
 substances on stuffs ; but they may, as well as 
 acids, effect the solution of colouring substances 
 on which they have an action. Their affinity 
 with the stuffs should also tend to operate their 
 solution. It is only as alteratives that these al- 
 kalies can enter into coloured combinations. If 
 they produce some precipitation in the watery 
 solutions of colouring substances, it must be 
 merely by separating a body much more soluble 
 from another in itself slightly soluble, or by oc- 
 casioning some change in a substance of some- 
 what unstable composition. 
 
 The other alkalies, namely, lime, barytes, stron- 
 tites, and magnesia, which possess little solubility, 
 or a much greater tendency to solidity, appear 
 fitter to serve as mordants. In fact, these alka- 
 line earths have sufficient affinity to form, with 
 colouring substances, combinations which are 
 precipitated from their solution ; but they consi- 
 derably affect their colours by their alkaline pro- 
 perties. They possess too weak an affinity to 
 enter into an insoluble combination with the 
 stuffs ; so that, far from promoting the union of 
 the colouring particles, on the contrary they 
 obstruct it, forming insulated precipitations. 
 
70 OF MORDANTS. 
 
 Magnesia, which is insoluble, afforded the 
 prospect of being usefully employed as a mor- 
 dant,. In order to try it, acetate of magnesia 
 was mixed with an infusion of brazil wood. A 
 precipitate took place of a dull violet colour. 
 After ascertaining the faculty it possesses of fall- 
 ing down with colouring substances, cotton was 
 impregnated with the above salt, as is done with 
 acetate of alumina ; but this cotton took no more 
 colour than if it had received no mordant. Wool 
 treated with acetate of magnesia, did not derive 
 from it the property of fixing the colour of mad- 
 der ; no more did silk. It appears, then, that 
 the alkalies in general can serve only as solvents 
 or alteratives ; but in this latter quality, those 
 which have the least solubility should be the 
 most efficacious. The same thing is true of the 
 acids ; whence the utility of the supertartrate of 
 potash in several processes. 
 
 The body which possesses in an eminent de- 
 gree the properties suitable for a mordant, is alu- 
 mina. Insoluble when it does not experience 
 the action of acids or alkalies, it has a strong dis- 
 position to combine with the colouring particles ; 
 it does not act on their colours as the alkalies do, 
 but it preserves very nearly their natural hue. It 
 separates also much more easily from the acids 
 which hold it in solution, than the alkaline bases 
 do. 
 
 To be convinced of this property which alu- 
 mina possesses, of combining with the colouring 
 particles, we have only to agitate alumina, preci- 
 
OF MORDANTS. 71 
 
 pitated from the sulphate of alumina by an alkali, 
 with an infusion of brazil wood, when all the 
 colouring particles separate from the water, and 
 remain fixed in the earth. It is this combination 
 which forms some lakes, and particularly the 
 stils de grains.* 
 
 This is not the method, however, in which it is 
 directly employed for the composition of the 
 most part of lakes. 
 
 A decoction of the colouring substance from 
 which we wish to obtain a lake, is mixed with a 
 solution of the sulphate of alumina. There is 
 usually formed a precipitate, which carries down 
 a portion of the colouring substance. With some 
 colouring matters, however, no precipitate ensues. 
 To cause, or to complete it, the acid of the salt 
 is saturated with an alkali, when the alumina 
 falls down, retaining in combination with it the 
 colouring substance. It is this precipitate, whose 
 colour varies with the substance employed, which 
 forms the lakes, after sufficient washing to carry 
 off the saline particles. For the stils de grains, 
 the decoction, mingled with the sulphate of 
 alumina, is passed through a calcareous carbo- 
 nate, which serves, at least in part, to decompose 
 the sulphate of alumina ; or through a clay, whose 
 action on the sulphuric acid contributes also to 
 the decomposition of the alum, and to the preci- 
 pitation of the lake. What occurs here by the 
 
 * Traite Theorique et Pratique sur l'Art de fairc et ri'appli- 
 qucr les Vernis, &c. par Tingry, torn. ii. 
 
7^ OF MORDANTS. 
 
 action of the alkali or the clay, which tend to 
 seize the acid, is effected in dyeing by an oppo- 
 site action, by the affinity between the stuff and 
 the coloured alumina. 
 
 The affinity of alumina for the different stuffs 
 may be easily proved. If an animal substance 
 be dissolved by an alkali, and if with this solu- 
 tion alum be mixed, the animal substance precis 
 pitates in. combination with the alumina. The 
 same combination is formed when, after mixing 
 gelatin with a solution of sulphate of alumina, 
 an alkali is poured into it. 
 
 The combination of alumina and the animal 
 substance may be sur-compounded (sur-compo- 
 see) with a colouring substance. For example, 
 when, in the preceding experiment, the decoction 
 of a colouring substance, such as brazil wood, is 
 mixed with the solution of sulphate Of alumina 
 and gelatin, the coloured precipitate thus ob- 
 tained represents the combination which is form- 
 ed with the stuffs in those dyes where a mordant 
 is employed. 
 
 Although it cannot be proved in the same 
 manner, that alumina enters into combination 
 with linen and cotton, yet the effects which alu- 
 minous mordants produce upon these substances, 
 leave no doubt that a combination with alumina 
 is formed. Hence, by means of aluming, colour- 
 ing substances which could not be fixed, or would 
 be speedily destroyed, quit their solvent, form 
 with the alumina more saturated and durable co- 
 lours, and even when the colour has disappeared, 
 
OF MORDANTS. 73 
 
 the stuff still retains the alumina, which can fix 
 new colouring substances, and impart to it the 
 requisite properties. Bancroft relates, that hav- 
 ing impregnated with acetate of alumina one 
 part of a cotton web, while the rest of it had no 
 mordant, and having dyed this cloth with saffron, 
 he exposed it on the grass : The colour soon 
 disappeared on the part which had received no 
 mordant, and some time afterwards on the por- 
 tion which had been imbued with the mordant. 
 He then dyed the cloth anew with saffron, when 
 the exposure on the grass produced the same ef- 
 fect. Finally, after a third dyeing, the mordant 
 still gave the same faculty to the portion of the 
 cloth to which it had been applied. Hence alu- 
 mina remained fixed, notwithstanding the three 
 dyeing operations. 
 
 It is manifest, therefore, when a stuff acquires, 
 by means of an aluminous salt, the properties 
 dependent on alumina, that it can decompose 
 this salt and combine with its alumina, whilst the 
 acid which held it in solution is disengaged and 
 remains in the bath ; but we must not thence 
 conclude, that no portion of the acid remains in 
 combination with the stuff, so as to have some 
 influence on the colour. (Note B.) 
 
 Metallic oxides possess with several colouring 
 particles such an affinity, that they abandon the 
 acids which kept them in solution, to precipitate 
 in combination with the colour. 
 
 On the other hand, all the oxides possess the 
 property, of combining with animal substances ; 
 
74 OF MORDANTS. 
 
 which several combinations may be formed, by 
 mixing with the metallic solutions an alkali satu- 
 rated with the animal substance.* 
 
 It is not therefore surprising, that the metallic 
 i oxides can serve as bonds of union between the 
 
 colouring particles and animal substances ; but 
 they differ greatly in this respect. Let us exa- 
 mine on what peculiarities these differences de^ 
 pend. 
 
 Although all the oxides have a disposition to 
 combine with the animal substances, they differ 
 much in this particular ; so that, especially when 
 the animal substances form a solid texture, there 
 are oxides to which they can hardly unite. Sup- 
 J posing the same degree of affinity, those oxides 
 
 which form a stronger combination with the acids 
 ought to abandon them with more difficulty ; 
 and again, the same oxide ought to be more 
 easily precipitated from feeble acids than from 
 such as act with more energy. Hence it is not 
 astonishing that there are only some metallic 
 solutions which can be employed as mordants, 
 and that in conformity with the purpose intend- 
 ed. 
 
 Some metallic substances carry into their com- 
 binations only a white and colourless base ; others 
 modify, by the association of their own colour, 
 that of the colouring matter ; but in several oxides 
 the colour varies according to the proportion of 
 oxygen fixed in them, or according to other un- 
 
 * Mem. de l'Academie, 1781. 
 
OF MORDANTS. 75 
 
 determined circumstances. The latter oxides 
 could not serve as a base to durable colours, 
 whose lustre would be easily affected by these 
 ready alteratives, unless it were russet huesj 
 whose slight changes would be imperceptible. 
 
 The oxide of tin surpasses all the others in its 
 property of becoming fixed on woollen and silk- 
 en stuffs, but especially on the former. It readily 
 abandons the acid which holds it in solution to 
 combine with them, so that it is sufficient to im- 
 pregnate wool and silk with solution of tin, al- 
 though they should be then thoroughly washed ; 
 a process which does not answer with other me- 
 tallic solutions. 
 
 Tin slightly oxidized has, in reality, only an 
 ashy colour. But since it has a great affinity for 
 oxygen, it takes enough of it in the ordinary 
 solutions to pass to the white colour ; or it may 
 complete its oxidizement even during the opera- 
 tions of dyeing. It retains its oxygen with force, 
 and hence, when highly oxidized, its oxygen ex- 
 erts but little action on a colouring matter. The 
 oxide of zinc appears to possess analogous pro- 
 perties, but it has much less affinity with stuffs 
 and with colouring particles ; while, on the other 
 hand, it retains the acids more powerfully, and is 
 thereby much less fit for a mordant. 
 
 The affinity of the oxides for substances of a 
 vegetable nature appears to be much weaker than 
 for animal substances ; whence it happens, that 
 metallic solutions are not well adapted to serve 
 as mordants for colours in cotton and linen. An 
 
76 
 
 OF MORDANTS. 
 
 J 
 
 
 . 
 
 
 
 
 ' 
 
 
 ■ 
 
 
 \ 
 
 i 
 i 
 
 i 
 
 ^ 
 
 exception must, however, be made in favour of 
 the oxide of iron, which may be applied in a very 
 solid manner to these substances, even when it is 
 precipitated from its solutions. To this purpose 
 Chaptal makes an interesting observation.* He 
 states, that a solution of iron disturbed by preci- 
 pitation may be cleared up by moving cotton 
 and linen through it. We must, however, ob- 
 serve, that the oxide of iron differs in colour 
 according to its state of oxidation ; and that the 
 action which it exercises on the colouring sub- 
 stance varies, as we shall see, according to that 
 state. The oxide of copper has also some affini- 
 ty for linen and cotton, so that its solutions may 
 be employed in some processes. Oxide of man- 
 ganese announces a similar disposition. 
 
 It follows from what we have now stated, 1. 
 That the acids and the alkalies are not fit for mor- 
 dants, that is to say, for intermedia or bonds of 
 union between the stuffs and the colouring sub- 
 stances, although those of sparing solubility can 
 produce species of lakes with colouring matters : 
 2. That of all the earthy substances, alumina is 
 the one eminently endowed with the properties 
 of a mordant, from its affinity with colouring sub- 
 stances and with stuffs, and from its feeble attrac- 
 tion to acids : 3. That among metallic substances 
 we must distinguish those which afford a white 
 base to the colouring substances, and those which 
 affect the colouring matters by their own colours. 
 
 * Mem. dc l'Instit. torn. iii. 
 
OF MORDANTS. 
 
 77 
 
 Among the former, which are fit for light and 
 splendid colours, the solutions of tin hold the first 
 rank, from the affinity of the oxide for the stuffs 
 of an animal nature, and for the colouring sub- 
 stances, as also from its weak attachment to 
 acids. The force with which it retains oxygen 
 contributes to its qualities. Among metallic sub- 
 stances, whose colour produces modifications, iron 
 is of the most extensive employment ; but its 
 effects vary according to its state of oxidation. 
 
 When the colouring particles have precipitated 
 an oxide from its solvent, the latter has usually 
 the power of dissolving a portion of the combina- 
 tion of the colouring substance with the oxide, 
 and the liquid remains coloured, although the 
 precipitation be facilitated, and rendered more 
 complete, by the presence of the stuff. The ef- 
 fects depend therefore in part, not only on the 
 proportion, but also on the species, of acid which 
 acts as a solvent to the oxide. This observation 
 is applicable to acids which hold alumina in solu- 
 tion ; but the acids, alkalies, metallic solutions, 
 and even the neutral salts, may serve as alter- 
 ants. 
 
 We observe, that by varying the mordants we 
 may greatly multiply the shades obtainable from 
 any one substance, especially with the co-opera- 
 tion of the alterants. It is sufficient merely to 
 vary the method of applying them. Thus we 
 shall obtain different effects, by impregnating a 
 stuff with a mordant, or by mixing the mordant 
 in the dyeing bath ; by. making the operation with 
 
 
//' 
 r/ 
 
 78 OF MORDANTS. 
 
 heat or cold, with the continued contact of air, 
 or without its intervention ; by means of a solu- 
 tion in a strong acid, or of one in a feebler or 
 more volatile acid. 
 
 Drying favours the combination of the bases 
 which have an affinity for the stuff, because the 
 water which produced the solution resists, by its 
 own affinity, the action of the stuff that tends to 
 bring it to the solid state. 
 
 But the circumstances by which we ought to- 
 be regulated vary according to the qualities of 
 the stuff, which, by a disposition whose cause 
 cannot always be assigned, requires sometimes 
 the aid of heat, whilst a stuff of a different na- 
 j ture combines better in the cold. 
 
 Finally, the processes which a stuff should re- 
 ceive in succession, to attain the proposed end, 
 sometimes decide the choice of the solution of 
 the mordant, and the manner of applying it* 
 This is particularly observable in reference to 
 cloths for printing, which should be able to pass 
 through several operations, without suffering in- 
 / jury from any one of them. 
 
 This beautiful art (calico printing), which was 
 introduced into Europe only in the middle of 
 the last century, has made the most rapid pro- 
 gress, having arrived at a perfection not only 
 very superior to the condition in which it has 
 remained for so many centuries in Hindostan, 
 but it has become one whose processes possess 
 the greatest precision, and are susceptible of the 
 most complete explanation. 
 
OF MORDANTS. 79 
 
 The perfection to which it has been carried 
 among us, principally by the active and enlight- 
 ened industry of the celebrated Oberkampf, re- 
 cently seconded by that of Widmer, is owing in 
 part to the necessity of insulating the processes, 
 in order to succeed, not only in varying the co- 
 lours and the shades, but likewise in securing to 
 them a permanence which may resist the opera- 
 tions requisite to give due whiteness to the inter- 
 vals which separate the printed spots. Hence it 
 has been possible to observe and ascertain the ef- 
 fects of every operation ; and hence every colour 
 has been subjected to the severest trials ; where- 
 as the other processes of dyeing often confound 
 together different effects, involving them in a 
 fleeting lustre. 
 
 Since the processes of this art are well fitted to 
 give an exact idea of the effects of mordants, and 
 of the different circumstances which modify them, 
 we shall here trace an outline of it. 
 
 The mordants possessed of great solubility, 
 whose acid, capable of being volatilized, is united 
 to its base by a feeble affinity, are preferred for 
 calico printing, because, as they can be put upon 
 the cloth in a greater state of concentration, and 
 can be more completely decomposed upon it, 
 more intense and substantial colours may be ob- 
 tained. Their solubility gives them the further 
 advantage of not rendering the mordant clotty, 
 by a species of crystallization when it is inspis- 
 sated, or unequable during its desiccation on the 
 cloth. 
 
/ 
 
 '/ 
 
 80 OF MORDANTS. 
 
 The acetate of alumina and the acetate of iron 
 possess these properties, and are sufficient to 
 produce, with different, colouring substances, the 
 greater number of the diversified hues observable 
 in printed goods. 
 
 To prepare the acetate of alumina, three parts 
 by weight of alum, and one of acetate of lead, 
 are dissolved in eight parts of hot water. An 
 eighth part of potash, and as much chalk, are 
 afterwards added. The oxideof lead contained 
 in the acetate, forms, with the sulphuric acid of 
 the alum, an insoluble salt, which precipitates ; 
 while the base of the alum, or the alumina, re- 
 mains in solution, combined with the acetic acid. 
 j Since in this, the generally adopted process, the 
 
 proportion of acetate of lead is not sufficiently 
 great to effect the entire decomposition of the 
 alum, the chalk and potash are added, which 
 serve to decompose a portion of this salt, whose 
 crystallization in the inspissated mordant might 
 have rendered its employment prejudicial. We 
 may produce, without the addition of the chalk 
 / or potash, an acetate of alumina, which has not 
 
 this inconvenience, by putting along with the 
 given proportions of alum and water three and a 
 half parts of acetate of lead.* (Note C.) 
 
 The acetate of iron is made by the direct solu- 
 tion of pieces of rusty iron in acetic acid, the 
 
 * There is an error in these proportions of M. Berthollet : 
 60 parts of alum are equivalent to about 100 of acetate of 
 lead— T. 
 
 i 
 
OF MORDANTS. 
 
 81 
 
 vinegar of commerce. (The crude vinegar, called 
 pyrolignous acid, is now usually employed for 
 this purpose in Great Britain. — T.) 
 
 The mordants are thickened with different 
 kinds of gum, starch, or flour. They should be 
 sufficiently so to preserve, in the impressions on 
 the cloth, the outlines of the objects engraven on 
 the plate, but not so much as to hinder their 
 leaving the plate equably in their application to 
 the cloth. This receives as many different im- 
 pressions as there are different mordants ; but no 
 more are applied at a time than are to be colour- 
 ed in the same dyeing bath. 
 
 When the cloth is in this condition, it is left 
 for several days, stretched in the workshop, ex- 
 posed to a moderate heat in a chamber, called in 
 the calico manufactories the hot-room (or stove). 
 This heat, by favouring the volatilization of the 
 acetic acid, accelerates and completes the decom- 
 position of the mordants, as well as the combina- 
 tion of their bases with the cloth. On coming 
 out of this chamber, it is passed into a boiler, 
 which contains cow-dung diffused through hot 
 water. The effect of this operation is to dissolve 
 the substance made use of for thickening the 
 mordant, as also the portion of this mordant 
 which, not having combined with the stuff, and 
 being diffused in the dye-bath, would soil it, both 
 by the combination which it would form with the 
 colouring matter, and by the action of the acid 
 which it might deposit upon it. Thus a twofold 
 injury would accrue to the cloth, by the impo- 
 
 VOL. i. f 
 
82 OF MORDANTS. 
 
 verishment of the dye-bath, and by the covering 
 of the portions which should remain white, with 
 the combination, difficultly detachable, of the su- 
 perfluous mordant with the colouring matter. 
 Widmer conceives, that there is formed, besides, 
 in the dunging, a triple combination of the ani- 
 mal matter with the alumina and the cloth, which 
 improves the beauty of the colours. This opinion 
 is the more probable, since water alone does not 
 produce the effect of the dunging ; in which 
 process an examination, not however very elabo- 
 rate, has not enabled us to perceive any other 
 substance capable of acting, except a matter ana- 
 logous to bile. (Note D.) 
 
 Before being dyed, the cloths ought still to be 
 carefully washed and beetled, to secure the re- 
 moval of all the combined mordant. Water and 
 mechanical beating are here employed. (The 
 wash-wheels of our print-fields answer this pur- 
 pose admirably. — T.) They are then introduced 
 into the dye-bath, where the whole surface be- 
 comes coloured ; but the colours are much deep- 
 er on the parts impressed with the mordant. The 
 colouring matter thus enters into a triple combi- 
 nation with the mordant and the stuff, thereby 
 acquiring the faculty of resisting external agents 
 much more than when it is insulated or combined 
 with the stuff without any intermedia. (NoteE.) 
 
 On this peculiarity are founded the processes 
 employed for restoring, to the parts of the cloth 
 which have received no mordant, the white co- 
 lour which they possessed before this dyeing. To 
 
OP MORDANTS. 83 
 
 produce it, the goods are boiled in water along with 
 bran, they are then exposed on the field, observing 
 to lay on the grass the surface of the cloth that 
 bears the colours. By the alternate repetition of 
 these operations, the colouring matters uncom- 
 bined with the mordants are changed in their 
 composition, dissolved and detached; whereas 
 those which are actually combined, far from suf- 
 fering change, acquire more lustre, and thus the 
 figures alone remain coloured. (Note F.) 
 
 This destruction of the colouring particles by 
 exposure in the field, and ebullition with bran, is 
 effected in the same manner as that of the colour- 
 ing particles of flax, and is explained in the same 
 way. The difference of the process consists 
 solely in the substitution of bran for alkalies ; be- 
 cause these would dissolve a portion of the colour- 
 ing substance fixed by the mordant, and would 
 alter its colour ; whereas the bran having a much 
 weaker action on this substance, affects merely 
 the colouring particles, rendered soluble by the 
 action of the air. The identity of the effects of 
 this process with those of common bleaching, 
 has led Widmer to substitute for this method the 
 employment of chlorine, modified by an alkaline 
 solution. Haussman has used this plan with suc- 
 cess ; and it is known to be practised in many 
 English manufactories.* (Note G.) 
 
 From madder, with acetate of alumina more 
 or less diluted with water, are obtained the deep 
 
 * See Section III. 
 
84 OF MORDANTS. 
 
 reds, and their different shades, down to a deli- 
 cate rose colour ; with acetate of iron, from black 
 to lilac, passing through all the intermediate violet 
 hues ; and finally, with the mixture of these two 
 mordants, in different proportions, the amaranths, 
 the mordores (brown-reds), the browns, and the 
 puce-coloured. By substituting woad for mad- 
 der, we procure, with the first of the above mor- 
 dants, the yellows ; with the second, only dull 
 olives ; but with their different mixtures, we have 
 agreeable olive and bronze colours. Combining 
 the action of these two tinctorial substances in 
 their turn on each of these mordants, very diver- 
 sified mingled hues are obtained. When we 
 treat of the particular processes of dyeing, we 
 shall enter into more details concerning those 
 which relate to the dyeing of printed goods. 
 
 The following are, in general, the steps of the 
 operations of this art. To apply to cloth the 
 most soluble and most easily decomposed mor- 
 dants ; to promote their drying and decomposi- 
 tion ; to remove, by animalizing the cloth at the 
 same time, whatever has not entered into combi- 
 nation with it ; to dye, and to restore to the por- 
 tions not printed the purest white. To these 
 operations the whole process is reducible. It 
 evidently proves, that linen and cotton are sus- 
 ceptible of combination with the bases of the 
 mordants ; that this combination possesses a great 
 affinity for colouring matters ; and that it com- 
 municates to them the property of being much 
 more unalterable by the ordinary agents of their 
 destruction. 
 
OF MORDANTS. 
 
 85 
 
 Some colours, however, may be directly print- 
 ed upon cloth, with all the solidity and lustre of 
 which they are susceptible : Such, for example, 
 is that of indigo, known under the name of 
 pencil blue, because it is usually applied with this 
 instrument ; that called rust-yellow », because it is 
 obtained by printing-on slightly oxidized oxide 
 of iron, resulting from the decomposition of two 
 parts of sulphate of iron with one of acetate of 
 lead, diffused in eight parts of water. These are 
 styled colours of application. They possess the 
 great advantage of requiring no operations except 
 those of printing and washing. The colours now 
 mentioned, which have been long used, are very 
 durable, and so much the simpler as they have 
 no need of a mordant ; but the number of those 
 possessed of this property are very limited. In 
 others, we must attach to the stuff, at the same 
 time, a mordant and a colouring matter, capable 
 of combining together, and of thus uniting with 
 the cloth. This method, analogous to that used 
 for wool and silk, of dyeing in a bath composed 
 of the mordant and the colouring substance, has 
 been hitherto successfully applied in only a very 
 few cases, in consequence of the weak affinity 
 which cotton and linen have for colouring sub- 
 stances united to mordants. 
 
 There is another method, still little known, of 
 producing upon cloth, at little expense, a diversity 
 of colours. It consists in applying to the cloth, 
 previously impregnated with the mordants and 
 the dyes, substances which, serving themselves as 
 
86 OF ASTRINGENTS. 
 
 mordants, modify the shade which the colouring 
 matter has given, with that already existing on 
 the cloth ; or to apply some others, which, carry- 
 ing with them an acid capable of dissolving this 
 mordant, and already combined with a colouring 
 matter, thus substitute a new mordant for that 
 which is on the rest of the cloth, and add also a 
 colouring matter to that which was there before. 
 By a similar process, a- white may be induced on 
 dyed goods. Oberkampf formerly employed, and 
 then abandoned' this process. Widmer has since 
 improved it much, and applied it to colours which 
 presented the greatest difficulties. The English 
 manufacturers make great use of it ; they employ 
 for this purpose an acid, sulphate of potash, and 
 lemon juice. This composition may answer for 
 cloth which has received little mordant, but it is 
 doubtful if it can serve for others.* (Note H.) 
 
 CHAPTER III. 
 
 Of Astringents hi general, and particularly of the 
 Gallic Acid and Tannin. 
 
 Astringents deserve peculiar attention, not 
 only because they are of great use in dyeing, but 
 
 * The principle of Mr Thomson's patent is excellent for 
 this purpose. Dyed cloth topically impressed with a thick- 
 ened solution of any vegetable acid, tartaric for example, is 
 passed through a solution of chloride of lime. — T. 
 
OF ASTRINGENTS. 87 
 
 because by this title is distinguished a property 
 common to a great many vegetables. 
 
 Perhaps there is no property in vegetables con- 
 cerning which such vague ideas have been cur- 
 rently received. A slight relation in taste has 
 frequently been deemed enough to rank them in 
 the class of astringents ; and every substance has 
 been commonly regarded as astringent or acerb, 
 which turned a solution of iron black. This 
 effect has been presumed to arise from one iden- 
 tical principle residing in all the bodies that pro- 
 duce it. Experience has subsequently shewn, 
 that two species of astringents ought to be admit- 
 ted, viz. tannin and gallic acid. Before describing 
 the distinctive properties of these two substances, 
 it is proper to consider the gall-nut, which contains 
 them both, the properties of which have been 
 particularly examined, as it is of great use in 
 dyeing. 
 
 The gall-nut is an excrescence found on the 
 young branches of the oak, and chiefly of that 
 species called rouvre, which grows in the Levant, 
 Istria, and the southern departments of France. 
 This excrescence is produced by the puncture of 
 an insect, which deposits eggs in the small inci- 
 sion which it makes in spring. The juice which 
 exudes from this wound becomes thick, accumu- 
 lates, and serves as a shelter to the young insect, 
 till such time as it can make its escape. When 
 there is found no outlet for it, it is found dead in 
 the gall-nut. Sometimes, after it has quitted its 
 cell, other insects come to occupy it. 
 
88 OF ASTRINGENTS. 
 
 Different kinds of nut-galls are distinguished ; 
 some of them are white, others yellow, green, 
 brown, red. Some are of an ash-colour, and even 
 blackish. They vary much in size, and are round 
 or irregular, light or heavy, smooth or covered 
 with tubercles. Such as are small, blackish, 
 granular, and dense, are the best. These are 
 known under the name of Aleppo galls, imported 
 from that town, from Tripoli and Smyrna. In 
 dyeing, galls are usually distinguished into white 
 and black. 
 
 Nut-galls dissolve almost entirely by long ebul- 
 lition in water. Sixteen drams vielded Neumann 
 fourteen drams of extract. Alcohol extracted 
 only four grains from the residuum, which weigh- 
 ed two drams. The same quantity treated at 
 first with alcohol, and then with water, afforded 
 12 drams and 2 scruples of spirituous extract ; the 
 residuum weighed half a scruple more than in 
 the preceding experiment. The spirituous ex- 
 tract has a stronger and more disagreeable taste 
 than the other.* 
 
 Lewis, Macquer, Monnet, and the Academi- 
 cians of Dijon, made different experiments to 
 determine the properties of the astringent which 
 is contained in nut-galls. They observed, that 
 the black colour afforded with solutions of iron 
 
 * The Chemical Works of Caspar Neumann, &c. by Wil- 
 liam Lewis. — From 500 gr. of Aleppo galls Sir H. Davy ob- 
 tained by aqueous infusion 185 gr. of solid matter, of which 
 130 was tannin, mucilage 12, gallic acid about 31, calcareous 
 earth and saline matter 12. — T. 
 
OF ASTRINGENTS. 89 
 
 depends on a combination formed between the 
 astringent and the iron. To the suspension of 
 these black molecules, the black colour of ink is 
 owing. If the solution be diluted with much 
 water, these molecules fall down under the form 
 of a deep blue powder. It is these which are 
 fixed on cloth dyed black. 
 
 We shall, for the present, confine ourselves to 
 these results, because the properties which the 
 astringent presents on different occasions, and in 
 different circumstances, will be better known by 
 an acquaintance with the two substances here in- 
 cluded under the same name. 
 
 To Scheele the discovery of the gallic acid is 
 due. We shall here introduce the description 
 which this great chemist gave of the method by 
 which he extracted this acid, and of its proper- 
 ties. 
 
 " I passed through a coarse sieve one pound 
 of nut-galls, and infused this powder in a kanne 
 (two pints three quarters French) of pure water, 
 in a glass globe, leaving it to act for four days, 
 during which it was frequently stirred with a 
 glass rod. I filtered this liquid,* which was lim- 
 pid, and which had the colour of French wine. 
 I left it freely exposed to the air, m the same 
 glass globe, covered merely with grey paper. 
 This was done in June. A month afterwards I 
 
 * " If hot water be employed, or if the mixture be digested 
 with heat, the infusion is not limpid : this determined me to 
 employ cold water, and digestion in the cold." Journ. de 
 Phys. 1787. 
 
90 OF ASTRINGENTS. 
 
 looked into this infusion, and found it covered 
 with a thick pellicle of mouldiness. In other 
 respects it had formed no precipitate, but it had 
 no longer its former astringent taste, and was 
 more acid. I returned this infusion into the 
 same balloon, covered in the same way with 
 paper. Five weeks thereafter I examined it 
 anew, when it was fully half evaporated : I 
 found a precipitate in it two ringers thick, and 
 at top a mucous pellicle ; it had lost all its styptic 
 taste, and it still coloured vitriol of mars black. 
 I filtered the infusion, and left it exposed to the 
 air. By the following autumn the greater part 
 was evaporated away ; what remained was mixed 
 with much precipitate. I united these precipi- 
 tates, and poured cold water upon them. After 
 they had fallen down, I decanted off the water, 
 and then poured on as much hot water as was 
 necessary for their solution. I filtered the whole. 
 The liquid, which was of a yellow-brown, was 
 evaporated at a gentle heat. During the evapor- 
 ation, one part of it precipitated like a fine sand, 
 and another formed at the bottom in radiated 
 crystals. This salt was grey ; and, notwithstand- 
 ing repeated solutions and crystallizations, it was 
 impossible for me to obtain it whiter. 
 
 " This salt of gall-nuts comports itself in the 
 following manner : — 
 
 " 1. It has an acid taste, causes effervescence 
 with chalk, and colours infusion of litmus red. 
 
 " 2. An ounce and a half of boiling water is 
 required for dissolving completely half an ounce 
 
OF ASTRINGENTS. 
 
 91 
 
 of this salt ; but whenever the solution cools, the 
 whole forms a concrete mass, composed of small 
 crystals. Half an ounce requires twelve ounces 
 of cold water for its solution. 
 
 " 3. It dissolves very easily in spirit of wine ; 
 for half an ounce of this salt, only one-half of 
 boiling spirit is necessary ; but if cold spirit of 
 wine be employed, then for half an ounce two 
 ounces of spirit are required. 
 
 " 4. It readily inflames in a crucible placed in 
 an open fire, melts with the diffusion of an agree- 
 able odour, leaving a charcoal which is difficultly 
 reduced to ashes. 
 
 " 5. Distilled in a retort, it becomes at first 
 fluid, and affords an acid phlegm. No oil passes 
 over, but at the end a white sublimate rises, which 
 attaches itself to the neck of the retort, and re- 
 mains fluid as long as it is hot, but afterwards 
 crystallizes. Much charcoal is found in the re- 
 tort. This sublimate has nearly the smell and 
 the taste of benzoic acid, or salt of benzoin ; it 
 dissolves equally in water and in spirit of wine ; 
 it reddens infusion of litmus ; and what is re- 
 markable, it precipitates metallic solutions with 
 their different colours, and the vitriol of mars 
 black. 
 
 " 6. The solution of the salt of gall-nut poured 
 into the solution of gold, renders it of a dull 
 green, and eventually throws down a powder 
 which is the gold revived. 
 
 " 7« The solution of silver becomes brown, and 
 deposits, with heat, a grey powder, which is re- 
 vived silver. 
 
 -Ju 
 
92 OF ASTRINGENTS. 
 
 " 8. The solution of mercury is precipitated 
 of an orange-yellow. 
 
 " 9. The solution of copper affords a brown 
 precipitate. 
 
 " 10. The vitriolic solution of iron becomes 
 black ; the more the water is charged with it, 
 the deeper is the colour. 
 
 "11. Lead dissolved in vinegar is precipitated 
 white. 
 
 " 12. Bismuth gives a precipitate of a lemon- 
 yellow. 
 
 " 13. Molybdic acid becomes of an obscure 
 yellow, without any precipitate taking place. 
 
 " 14. Platinum, zinc, arsenical acid, tin, co- 
 balt, and manganese, experience no change. 
 
 " 15. The (saline?) solutions of lime, magnesia, 
 alumina, and barytes, are not decomposed ; but 
 lime water causes an abundant grey precipitate. 
 
 " 16. The salt of nut-galls is changed into 
 oxalic acid when nitric acid is distilled from it 
 in the usual way. 
 
 " The white precipitate obtained when acetate 
 of lead is thrown down by nut-galls, may be 
 again decomposed by vitriolic acid, and the salt 
 of nut-galls is thus obtained in its greatest purity. 
 Since the infusion of nut-galls precipitates the 
 acetate of lead, I thought that I might be able 
 to procure this salt in a manner still more ex- 
 peditious ; but this did not succeed with me, for 
 when I had decomposed this precipitate by means 
 of vitriolic acid, I recovered my infusion of galls 
 with its ordinary astringent taste. 
 
OF ASTRINGENTS. 
 
 93 
 
 " If gall-nuts be distilled with a violent heat, 
 an acidulous phlegm is obtained, the smell of 
 which is not disagreeable ; no oil passes, but to- 
 wards the end a volatile salt rises, like that ob- 
 tained from the salt of gall-nuts distilled, and 
 which has the same properties. (No. 5.) It 
 hence appears, that this salt exists ready formed 
 in the infusion of gall-nuts, although we cannot 
 obtain it in the w T ay of ordinary crystallization, 
 for it is so intimately united with some mucila- 
 ginous principle or other matter, that it cannot 
 be separated from it without some interior move- 
 ment or fermentation." 
 
 Before prosecuting the examination of the pro- 
 perties of gallic acid, to which, since the experi- 
 ments of Scheele, chemists ascribed exclusively 
 the effects of astringents, we ought to describe 
 another substance, tannin, which has some pro- 
 perties in common with it, but differs in other 
 respects. 
 
 The art of tanning had been conducted by a 
 blind routine, till Seguin shewed that astringents 
 contained a peculiar substance, which, in com- 
 bining with skin, gave it the properties of tanned 
 leather, and that the tanning effect arose from 
 the combination thus formed. To regulate this 
 art, he had only to determine the circumstances 
 necessary for forming that combination, and for 
 giving it the requisite qualities.* He proved that 
 
 * Journ. de Manuf. et Arts, torn. iii. ; Annal. de Chim. 
 torn. xx. 
 
 — ... — — «_. 
 
 >, 
 
/ 
 
 I / 
 
 94> OF ASTRINGENTS. 
 
 animal glue had the property of forming a similar 
 combination with tannin ; for on mingling a solu- 
 tion of strong glue with an astringent infusion, a 
 substance fell down analogous to tanned leather. 
 By this test he could ascertain the quantity and 
 quality of tannin in an astringent substance, so 
 as to trace and measure its effects in the opera- 
 tions of tanning. 
 
 Since then, chemists have investigated the means 
 of separating the tannin from the gallic acid. For 
 effecting this object, Proust suggested the muriate 
 of tin, which, whatever be its state of oxidation, 
 is decomposed by tannin, but not by gallic acid. 
 The tannate of tin which falls down, is thereafter 
 decomposed by sulphuretted hydrogen, when the 
 tannin is pure.t But this skilful chemist has him- 
 self admitted, that his process was imperfect ; for 
 one portion of the tannin remained in solution, 
 while some of the extractive matter accompanied 
 the portion which precipitated.t 
 
 Fiedler pretended to separate the gallic acid 
 from the tannin by means of alumina precipitated 
 from its sulphate ;§ but on carefully repeating 
 this process, we have observed, that the gallic 
 acid combined also with the alumina, and we 
 have not been able to separate it by this method. 
 When gelatin precipitates tannin, the gallic acid, 
 which remains liquid, retains a portion of it ; for 
 
 j Ann. de Chira. torn. xxv. 
 
 £ Ibid. torn. xli. 
 
 § Journ. de Van. Mons. torn. i. 
 
OF ASTRINGENTS. 95 
 
 these two substances exercise a mutual action 
 which opposes their separation, and we have in 
 vain tried different processes for removing this 
 obstacle. 
 
 Gallic acid and tannin alike precipitate the 
 solutions of iron. Proust presumes that they 
 cannot combine with the iron, unless it be in the 
 last stage of its oxidation. This opinion has 
 been discussed elsewhere.* We shall content 
 ourselves with remarking here, that tannin, and 
 especially gallic acid, form with iron a solution 
 of a black-blue colour, as Delaval and Priestley 
 observed with infusion of nut-galls. There is a 
 decomposition of water ; but the iron can thus 
 be brought only to the lowest degree of oxidize- 
 ment. The solution of protoxide of iron in ace- 
 tic acid, is likewise rendered black by tannin or 
 gallic acid. These facts are sufficient to prove, 
 that if the slightly oxidized sulphate and muriate 
 of iron do not produce a black colour with tan- 
 nin or gallic acid, this effect depends only on the 
 stronger action which the acids in this case exer- 
 cise on the protoxide of iron, and Proust himself 
 points out this cause ; but whatever happens, it 
 is not the less, true, as he thinks, that these me- 
 tallic salts are of use in dyeing, only in so far as 
 they are highly oxidized ; or, that the oxide of 
 iron absorbs oxygen while it is in the dyeing 
 bath, or during the airing which the stuffs re- 
 ceive on coming out of the bath. 
 
 * Essais de Statique Chim. torn. ii. 
 
 6 
 
) 
 
 / 
 
 96 OF ASTRINGENTS. 
 
 ) The same chemist has very justly remarked the 
 
 difference between the precipitates produced by 
 tannin and by gallic acid. " The red sulphate 
 j is precipitated by tannin of a somewhat dirty 
 
 i blue ; the deposite is copious, coarse, and black 
 
 when it is dry. On comparing the precipitate 
 which the sulphate affords with gallic acid, we 
 find that it is very different. The latter is ex- 
 tremely fine, and floats for a long time in the 
 I water. It is perfectly black. While the gallate 
 
 of iron is soluble in acids, the tannate of iron is 
 decomposed by them, parting with its iron while 
 the tanning matter falls.*' 
 
 Lastly, he has observed, that tannin was not 
 a uniform substance ; but he regards that ob- 
 tained from catechu, dragon's-blood, sumach, and 
 yellow-wood, as possessing properties sufficiently 
 well marked to form distinct species. 
 
 Vauquelin has equally found a difference be- 
 tween the tannin of gum-kino, and that of ordi- 
 nary tan.* He remarks, that it precipitates iron 
 of a green hue, like that of cinchona and rhu- 
 barb. 
 
 This difference among the tannins is very per- 
 ceptible on making comparative experiments with 
 catechu and gall-nuts, or oak-bark. It may be 
 remarked, even on comparing the precipitates 
 obtained from gelatin, and those astringents 
 whose properties are most similar, such as gall- 
 nuts and sumach. The tannate produced with 
 
 * Annal. de Chim. torn. xlvi. 
 
OF ASTRINGENTS. 97 
 
 sumach falls down less readily ; it is less friable, 
 and less coloured than that afforded by the gall- 
 nut. 
 
 There is such a difference among astringents 
 as to prevent their properties from being con- 
 sidered as identical ; there is a like difference 
 among the tannates produced from the different 
 animal substances and the same kind of tannin ; 
 for this property of forming a combination with 
 tannin does not belong exclusively to gelatin. 
 Albumen also possesses it ; but the tannates 
 which it forms are much more friable and less 
 coloured than those due to gelatin. 
 
 From the preceding statement it appears, that 
 astringents may owe the property of colouring 
 black to the two distinct substances, gallic acid 
 and tannin ; and that the latter, far from being 
 identical, has properties which differ more or less , 
 in all the vegetables which contain it. One 
 mode of distinguishing substances containing tan- 
 nin alone, is by examining if the precipitate ob- 
 tained be readily formed, so as to leave the super- fj 
 natant liquid colourless. This happens when the 
 tannin of catechu, for example, is precipitated. 
 But if we add a little gallic acid to the solution, 
 the supernatant liquid retains a black colour for 
 a long time. Different astringents examined in 
 this manner, and among the rest oak-bark, ap- 
 peared to us not to contain gallic acid. Besides 
 gall-nuts, sumach alone exhibited evidence of the 
 acid of galls. That bark must, however, contain 
 but little ; for when it is subjected to the process 
 
 VOL. i. g 
 
98 OF ASTRINGENTS. 
 
 of Scheele, none of it is obtained. But all the 
 astringents afforded with blue test paper marks 
 of acidity, which are even somewhat considerable 
 in catechu, although the presence of gallic acid 
 in it cannot be suspected. Hence, the acidity is 
 not a proof of the existence of the gallic acid, 
 but may be owing to tannin, or a foreign acid. 
 
 White gall-nuts, subjected to the process of 
 Scheele, afford pretty soon an abundant deposite, 
 less coloured than that yielded by black gall-nuts. 
 Nor has it the crystalline appearance, though it 
 is the gallic acid which forms this deposite j nor 
 is it in a state of combination. We think it pro- 
 bable that the latter kind of gall-nuts contain a 
 greater quantity of it ; though our experiments 
 do not enable us to affirm that this is certainly 
 the case. We have compared the relative quan- 
 tities of tannin afforded by these two species of 
 gall-nuts, when they are precipitated by gelatin ; 
 we have obtained apparently the same quantity of 
 precipitate from both, so that we cannot yet point 
 out wherein that difference consists which dis- 
 tinguishes these gall-nuts, as is observed in the 
 operations of dyeing. 
 
 A portion of the gallic acid exists certainly in 
 the gall-nut ; but may not some of it be formed 
 in the long space of time which Scheele's process 
 requires ? We are hitherto unable to answer this 
 question j but we are led to suppose, that the 
 tannin is in a great measure destroyed, or that it 
 suffers an alteration which permits the gallic acid. 
 
 ■ 
 
OF ASTRINGENTS. 
 
 99 
 
 which was in a state of combination with it, to 
 crystallize ; for Scheele remarks, that the infusion 
 of gall-nuts loses all its astringent taste. A por- 
 tion of the tannin is, however, preserved from this 
 change by the action of the gallic acid itself, 
 which retains it in its precipitation and crystal- 
 lization. 
 
 It is this portion of tannin retained by the 
 gallic acid, as obtained by the process of Scheele, 
 which affects its colour, and prevents its proper- 
 ties from being properly insulated. Repeated 
 crystallizations only make it brown, by the de- 
 composition occasioned by the heat. We have 
 tried different methods of purifying this acid ; 
 that which succeeded best, consists in treating it 
 with oxide of tin, newly precipitated from its so- 
 lution by an acid. The gallic. acid then loses its 
 colour, the tannin which altered it being retained 
 by the oxide, and it crystallizes in very white 
 needles. In this state, it is perfectly similar in 
 its properties to that obtained by sublimation. 
 We have seen that Scheele observed this subli- 
 mate, but Deyeux has described it more in detail. 
 He prescribed the precautions which the distilla- 
 tion of the gall-nut requires to obtain this acid 
 sublimate, and he remarked that one part passed 
 over in the liquor, whilst another was decom- 
 posed by the fire. Hence, notwithstanding every 
 care, but a small quantity can thus be obtained. 
 Deyeux supposes, that when this acid is exposed 
 to distillation, as well as its combinations with the 
 oxides, pure oxygen gas is disengaged, and much 
 
 
100 OF ASTRINGENTS. 
 
 charcoal is left behind. But we obtained only 
 carbonic acid during this distillation, which we 
 conducted with the greatest care, with the view 
 of ascertaining the extraordinary result which had 
 been announced. 
 
 The oxide of tin, by means of which gallic acid 
 is purified, appears to retain a portion of it, and 
 to lessen its quantity a little ; but we have not 
 observed that decomposition of which Proust 
 speaks,* probably because it takes place only in 
 the portion combined with the oxide of tin, of 
 which we neglected the examination ; and as he 
 treated the infusion of nut-galls directly with the 
 oxide of tin, the quantity of tannin was capable 
 of causing the combination of all the gallic acid 
 associated with it, which does not happen when 
 we thus treat gallic acid retaining but a small 
 portion of tannin. 
 
 Gallic acid may also be purified by means of 
 albumen, which, on coagulating with heat, sepa- 
 rates the tannin with it ; but it retains at the same 
 time gallic acid, and a portion of the albumen re- 
 maining liquid along with the gallic acid, causes 
 this to be difficultly separable by crystallization. 
 Hence the first method is preferable. 
 
 Gallic acid, in its state of purity, excites an 
 effervescence with the alkaline carbonates, and 
 assumes, on combining with potash and soda, a 
 greenish-blue colour, which becomes so deep by 
 heat, that the liquid appears black at a certain 
 
 * Annal. de Chimie, torn. xlii. 
 
OF ASTRINGENTS. 
 
 101 
 
 degree of condensation. But it is green if we 
 dilute the liquid, or if we put it into a tube of 
 small diameter. It takes a blue colour with lime, 
 barytes, and strontites ; but on adding a greater 
 quantity of acid, the colour becomes red, after 
 passing through several shades. Though it forms 
 precipitates with these alkaline earths, the liquid 
 continues coloured. This acid can scarcely be 
 exposed to ebullition, without assuming a brown 
 shade, and suffering a degree of decomposition. 
 
 The observations now presented, concerning 
 the properties of gallic acid, differ from those of 
 Scheele, since, according to him, this acid forms 
 soluble salts with all the alkaline earths, except- 
 ing lime water. The reason of which is, that his 
 trials were made with solutions in the acids, so 
 that the acid present did not suffer these naturally 
 insoluble salts to precipitate. We conceive, that 
 this acid forms with all the oxides insoluble salts, 
 whenever this insolubility is not overcome by the 
 action of an acid or an alkali. 
 
 The affinities of tannin appear to differ very 
 little from those of gallic acid, at least in the 
 combinations connected with the art of dyeing. 
 The differences of their effects appear naturally 
 explicable from those of their solubility. 
 
 All the species of tannin seem to surpass gallic 
 acid in their tendency to solidity ; for, in the 
 first place, they form an insoluble substance with 
 gelatin, while gallic acid remains in a liquid com- 
 bination with it ; but albumen, which has more 
 disposition to coagulate than gelatin, can afford a 
 
102 
 
 OF ASTRINGENTS. 
 
 solid combination with gallic acid. 2. The combi- 
 nation of tannin with the solutions of iron, forms a 
 precipitate whic his speedily separated and depo- 
 sited, whereas gallic acid produces merely a trans- 
 parent liquid, whose colouring molecules settle 
 slowly, and only in particular circumstances. 3. 
 Proust has observed, that the alkaline carbonates, 
 and the most part of the very soluble neutral 
 salts, possess the property of precipitating tannin 
 from its solutions, in consequence of the great 
 affinity which they have for water, provided that 
 the proportion of water be not too great.* Sul- 
 phuric acid acts in the same way. 4. The same 
 chemist has observed, and the observation was 
 given in the first edition of these Elements, that 
 when several successive decoctions of gall-nuts 
 are made, the last are destitute of gallic acid. 
 
 It is only, indeed, by this superior tendency to 
 form solid combinations, that the properties of 
 tannin appear to differ, in reference to dyeing, 
 from those of several colouring substances, in 
 which it exists in merely a lower degree. Thus 
 the solution of logwood and brazil wood does not 
 form a precipitate with gelatin j but it produces 
 one with albumen when aided by heat. The so- 
 lution of yellow-wood (fustic) yields a precipitate 
 with gelatin ; wherefore it contains a substance 
 analogous to tannin, according to the observations 
 of Chaptal and Proust, t The portion which is 
 not precipitated affords a lighter and livelier yel- 
 
 * Ann. de Chim. torn, xxxiv. f Mem. de 1'Instit. torn. ii. 
 
OF ASTRINGENTS. 103 
 
 low ; but this portion is itself separated in a con- 
 crete form with albumen. On the one hand, se- 
 veral substances employed as astringents have 
 the property of dyeing different shades of fawn 
 and yellow ; on the other, the colouring sub- 
 stances which have a deep colour, produce also 
 a black colour with solutions of iron ; and the 
 blacks on printed goods are commonly obtained 
 from madder. 
 
 The astringents are employed not only to make 
 the baths of the black dye, but also to prepare 
 stuffs by the operation called galling, which con- 
 sists in impregnating the stuffs with the astrin- 
 gent principle of nut-galls, as will be afterwards 
 stated. 
 
 It became necessary to determine what part 
 the gallic acid and tannin might each have in 
 this operation. To throw light on this subject, 
 we impregnated with gallic acid specimens of 
 silk, wool, and cotton, and then passed them 
 through a solution of iron. None of these speci- 
 mens was coloured black, and the cotton even 
 took no dye ; but similar specimens, impregnated 
 in the same manner with infusion of nut-galls, 
 took a black colour with solution of iron. On 
 performing the contrary operation, that is to say, 
 impregnating the stuffs first with solution of iron, 
 we had a similar result. We next ascertained, 
 that by means of tannin, gallic acid also entered 
 into combinations with stuffs. Hence, in the 
 galling, the stuff unites to both the substances 
 
 
 1 
 
104 OF ASTRINGENTS. 
 
 which afford black with the solutions of iron. 
 When the stuff is impregnated with tannin alone, 
 it takes also a black colour. Both the substances 
 associated in gall-nuts contribute therefore to the 
 black dye ; while tannin, but not gallic acid, pro- 
 duces an analogous effect when it alone is pre- 
 sent. It thence follows, that as both the sub- 
 stances can yield a black precipitate with the 
 sulphate of iron, we may thus judge, at least 
 approximatively, of the effect of the different as- 
 tringent substances in dyeing black. 
 
 A discussion has arisen concerning the proper- 
 ties of oak-bark, which, it was asserted, might be 
 substituted with advantage for the gall-nut, even 
 weight for weight, in all black dyeing. In proof 
 of this it was stated, that oak-bark was substituted 
 in the ordinary proportion for the gall-nuts which 
 the hatters of Paris put into their dyeing baths. 
 But this effect proceeds from the circumstance, 
 that the dyeing of hats is produced particularly 
 by logwood, as we may ascertain by applying to 
 a hat any acid, the muriatic, for example, which 
 reddens it immediately, as happens to all the co- 
 lours derived from logwood. For this dye, there- 
 fore, nothing is required but a very little astrin- 
 gent matter, which seems useful merely to deepen 
 by another shade the colour given by the log- 
 wood. In fact, a very small quantity of galls 
 enters into the process commonly employed for 
 hats. We have seen an expert hatter employ 
 only one part of gall-nuts to thirty of logwood. 
 
OF ASTRINGENTS. 105 
 
 . The present discussion was brought before the 
 Academy of Sciences. The report of its com- 
 missioners contains details which may be^useful, 
 because they state the proportion of the astrin- 
 gent principle obtained from different substances, 
 and the comparative effect which they produce 
 in dyeing black. For this reason we shall give 
 an extract of it. 
 
 The commissioners, Lavoisier, Vandermonde, 
 Fourcroy, and the author of these Elements, com- 
 pared in their experiments, nut-galls, oak-bark, the 
 raspings of the oak taken from the interior of the 
 wood, the raspings of the alburnum (white bark) 
 of the oak, logwood, and sumach, in order to 
 determine the proportion of the dyeing principle 
 contained in these substances. They took in 
 succession two ounces of each, which they boil- 
 ed for half an hour in three pounds of water. 
 This first water was followed up by a second, 
 which underwent the same ebullition, and thus 
 they continued till these substances seemed to be 
 exhausted. They mixed together the decoctions 
 which they had obtained. They employed a very f 
 
 clear solution of sulphate of iron, the proportion 
 of sulphate and water in which was exactly de- 
 termined. They judged first of all of the quan- 
 tity of the astringent principle, by the quantity . 
 of sulphate which each liquor could decompose, 
 and next by the weight of the black precipitate, 
 which was more or less speedily deposited, adding 
 to it a sufficient quantity of water. In order to 
 stop precisely at the point where the addition of 
 
 
y 
 
 106 OF ASTRINGENTS. 
 
 / the sulphate became superfluous, it was necessary 
 
 / to proceed very slowly with the precipitation to- 
 
 / wards the end, pouring in the solution of the 
 
 I sulphate only drop by drop, and halting at the 
 
 moment when a new addition of this substance 
 no longer augmented the intensity of the black 
 colour. When the liquid is too opaque, and 
 / when the change of colour can no more be dis- 
 
 ( tinguished, a small portion of it was diluted with 
 
 J a good deal of water. To this was added from 
 
 ( the end of a glass tube a little of the solution of 
 
 j sulphate of iron, and it was thereby observed if 
 
 the point of saturation had been attained. After- 
 wards, when it was wished to make the precipi- 
 tate fall down in order to be collected, the liquor 
 was diluted with a great deal of water. 
 
 This operation deserves attention ; because it 
 is an easy means of determining in dye-houses 
 the just proportions of astringents and solutions 
 of iron ; but we must bear in mind, that the so- 
 lutions of iron ought to be highly oxidized, in 
 , order to produce the greatest effect. Although 
 
 , this consideration was not attended to in the 
 
 experiments of which we are about to state the 
 results, these merit no less confidence, because 
 j the same sulphate of iron was used in all the 
 
 trials. 
 
 To saturate the decoction of two ounces of 
 nut-galls, three drams and sixty-one grains of 
 sulphate of iron were required. The dry pre- 
 cipitate weighed seven drams and twenty-four 
 grains. 
 
OF ASTRINGENTS. 
 
 107 
 
 The decoction of oak-bark was of a deep yellow 
 colour. A small quantity of sulphate of iron gave 
 it a dirty reddish hue j a more considerable addi- 
 tion made it pass to a brown-black. Eighteen 
 grains of sulphate of iron were necessary to satu- 
 rate the decoction of two ounces of this bark. 
 The precipitate collected and dried was in coarser 
 particles, and more difficult to divide. It weigh- 
 ed twenty-two grains. The liber of the oak pre- 
 sented very nearly the same results. 
 
 The decoction of the raspings of the heart of 
 oak required one dram and twenty-four grains 
 of solution, and afforded one dram and twenty- 
 four grains of precipitate. The decoction of the 
 alburnum of oak produced very little precipitate. 
 
 The decoction of sumach assumed a violet red 
 colour, when there was added to it a little of the 
 solution of sulphate of iron, of which it required 
 two drams and eighteen grains. The precipitate 
 perfectly resembled that from the nut-galls ; but 
 an accident hindered its weight from being ascer- 
 tained. 
 
 The decoction of logwood was coloured sap- 
 phire-blue by the addition of the sulphate of iron. 
 On exceeding the point of saturation, the blue 
 became greenish and dirty. The quantity neces- 
 sary to reach the point of saturation, was two 
 drams and twelve grains. The circumstances of 
 colour which we have now mentioned, may differ 
 according to the state of oxidizement. 
 
 Trials of dyeing were thereafter made on pat- 
 terns of woollen cloth. These shewed, that the 
 
 > 
 
 
 f 
 
'<? 
 
 108 OF ASTRINGENTS. 
 
 quantities of astringents fitted to give, with an 
 equal weight of the same cloth, a black colour of 
 like intensity, were proportional to the quantities 
 of astringent principle, which had been deter- 
 mined by the experiments on each species ; but 
 the black obtained with the different parts of 
 the oak, did not resist boiling so well as that 
 produced with nut-galls. 
 
 If the astringents submitted to trial in the 
 preceding experiments, whose results agree with 
 those of Lewis and Beunie, prove that they can- 
 not be compared weight for weight with gall- 
 nuts, and if sumach alone approaches their ef- 
 fects, we must not thence conclude, that they 
 cannot be employed in dyeing black. But we 
 conceive that it would be much more advan- 
 tageous to make use of them in galling, than in 
 the dyeing bath, because the black molecules 
 which tannin forms with the oxide of iron, are 
 too quickly insulated and precipitated. We have 
 made a pretty deep black, by treating wool, and 
 even silk, in this manner, with oak-bark. 
 
 It is said in the Memoirs of Stockholm for 
 1763, that we may substitute for nut-galls uva 
 ursi, gathered in autumn and dried with care, so 
 that its leaves continue green. 
 
 If gallic acid, the different species of tannin, 
 and several other colouring substances, such as 
 logwood, brazil wood, and madder, afford with the 
 solutions of iron blacks more or less deep, there 
 must be something in common in the mode of 
 acting of these substances, whatever may be in 
 
OF ASTRINGENTS. 
 
 109 
 
 other respects the difference of their properties. 
 It is our present object to determine this. 
 
 Monnet, and the academicians of Dijon, for- 
 merly remarked, that the solution of gall-nut 
 revived the metal of the solutions of gold and 
 silver. Scheele observed, that gallic acid pro- 
 duced this effect ; and Proust has verified this 
 property, not only in tannin, but also in several 
 other colouring substances. We are warranted 
 to conclude from these facts, that the astringents, 
 and even the colouring substances in general, 
 possess the property of carrying off oxygen from 
 those substances which can yield it easily. 
 
 An observation of Proust informs us, that the 
 astringent produces a similar effect on the solu- 
 tions of iron. This celebrated chemist evaporated 
 a solution of iron highly oxidized, after precipi- 
 tating it with nut-galls, and he observed that the 
 liquid, after the evaporation, yielded crystals of 
 the green or slightly oxidized sulphate. It thence 
 results, that the black molecules which fall down 
 contain iron in only the lowest degree of oxida- 
 tion, since they leave in this state even that which 
 they could not abstract from the acid. 
 
 The black molecules then contain the iron in a 
 black state (protoxide). On the other hand, the 
 astringent, in thus absorbing oxygen, must expe- 
 rience the same changes that it suffers when it is 
 combined with oxygen ; but the infusion of an 
 astringent deepens in colour, and becomes brown 
 by simple exposure to air j and we shall see in 
 the following chapter, that it undergoes the same 
 
 / 
 
110 OF ASTRINGENTS. 
 
 changes which a slight combustion produces, 
 taking this word as signifying a diminution of its 
 oxygen and its hydrogen, so that the carbon be- 
 comes predominant. 
 
 The astringent ought to experience this effect 
 in a high degree, because it contains a great deal 
 of carbon ; for gall-nut leaves, after distillation, 
 more than three-eighths of its weight of charcoal. 
 But when we employ a highly oxidized sulphate, 
 it appears from the experiments of Proust, that a 
 portion of the tannin is altered in its nature by a 
 too energetic action of the oxygen. 
 
 We see now, how the black molecules may 
 result from a combination formed of black oxide 
 of iron and a substance which must assume by 
 degrees the same colour ; why astringents, al- 
 though differing in their other properties, ought 
 to produce an analogous effect ; and finally, why 
 colouring substances of very different kinds afford, 
 with solutions of iron, colours approaching more 
 or less to the black hue. 
 
 We may observe, that the gallic acid exhibits 
 in its action on solutions of iron a small difference, 
 which seems to announce, that it possesses in a 
 less degree the property of abstracting oxygen 
 from iron. Tannin produces a black colour in a 
 sulphate, so little oxidized that the gallic acid 
 does not change its hue, unless it remains ex- 
 posed to the air. 
 
 On comparing all the observations advanced on 
 astringents, we may draw the following conclu- 
 sions : — 
 
OF ASTRINGENTS. Ill 
 
 1. Gallic acid cannot serve by itself for the 
 black dye, but it may contribute to the effect 
 caused by the tannin, either by combining with 
 the stuff, or by becoming fixed in the dyeing bath 
 on the galled stuff. 
 
 °Z. Tannin may serve, without the aid of gallic 
 acid, for the black dye. The different species of 
 tannin possess in this respect different properties 
 as to the quality of the black, which can be de- 
 termined only by direct experiments. Astrin- 
 gents, besides the quality of the black which they 
 afford, differ also in the quantity. Thus oak- 
 bark, and the other parts of this wood, contain 
 far less astringent matter than gall-nuts. 
 
 3. It is especially for the galling that those 
 astringents which do not contain gallic acid may 
 replace the gall-nuts, because the black molecules 
 which these form fall down too slowly ; and be- 
 sides, the quantity which must be employed to 
 replace the gall-nuts would be too considerable, 
 and would embarrass the dye bath. Sumach is, 
 among the astringents at present known, the one 
 which approaches the most to gall-nuts, and 
 which is the fittest to replace them. 
 
 4. With regard to ink, in which the colouring 
 particles must not precipitate, no known astrin- 
 gent can be substituted for gall-nuts, not even 
 sumach, as Lewis has proved in his excellent 
 observations on this preparation, which deserve 
 to be somewhat dwelt upon.* 
 
 * Lewis' Exper. Essay on the Commerce of the Arts. 
 
112 OF ASTRINGENTS. 
 
 If too large a proportion of sulphate of iron be 
 added to the galls, the ink becomes speedily 
 brown, and then passes to yellow, because the 
 astringent is destroyed by the action of the oxy- 
 gen which the sulphate of iron affords, or pro- 
 gressively attracts from the atmosphere ; for we 
 shall see, that oxygen eventually destroys those 
 colouring substances with which it is combined in 
 too great quantity. When this accident happens 
 from age, Lewis found, that an infusion of gall- 
 nuts passed over the altered characters restored 
 them; and Blagden has indicated a means still 
 more efficacious, which is the prussiate of an 
 alkali.* Lewis ascertained, that the best propor- 
 tion for ink was three parts of gall-nuts to one of 
 sulphate of iron ; that cherry gum and plum-tree 
 gum were as good as gum arabic for giving the 
 necessary consistence, and for keeping suspended 
 the black molecules which tend to fall ; and that 
 decoction of logwood, employed instead of water 
 for the infusion of the gall-nuts, improved the 
 beauty of the ink. 
 
 We have remarked, that both gallic acid and 
 tannin gave to iron the property of decomposing 
 water, and of forming by this means a solution of 
 iron, which passes from blue or violet to black. 
 Delaval says, that he produced with the solution of 
 this metal and an infusion of nut-galls, the deepest 
 
 * A solution of ferroprussiate of potash, faintly acidulated, 
 or sulphuretted hydrogen water, are the best restoratives of 
 the characters of faded ink. — T. 
 
OF ASTRINGENTS. 113 
 
 black, and the most indelible ink.* He adds, 
 that on plunging into this tincture silks and 
 woollen stuffs, without adding any acid to it, he 
 obtained them of the deepest and most inde- 
 structible black colour. Proust also says, that he 
 would prefer, both as to durability and beauty, 
 the ink made by dissolving iron in an infusion of 
 gall-nuts, to that which is prepared with the sul- 
 phate of iron.t He remarks in the same place, 
 that the combination of gallic acid and tannin 
 with iron, is not changed into prussiate of iron by 
 the prussiate of potash ; an observation which had 
 already been made by the academicians of Dijon. 
 
 We have mentioned, that Lewis had observed 
 that a decoction of logwood increased the beauty 
 of ink. It is observed, especially in the black 
 dyes, that an addition of logwood gives more 
 lustre to black ; and we shall see, that it is advan- 
 tageous to fix a blue colour on stuff which is to 
 be dyed black. Now, logwood forms with the 
 oxide of copper, added to black dyes, a blue 
 colour, which contributes to the beauty of the 
 black by the mixture of that hue. 
 
 We must here remark, that the black of the 
 dyes is produced only by the condensation of 
 molecules, which when more diffused enjoy a par- 
 ticular colour, such as blue, dun, or violet. But 
 the mixture of two substances, whose diluted 
 colour is different, yields a more intense black. 
 This effect is readily observable in the mixture of 
 
 ' Experimental Inquiries. f Ann. de Chim. torn. xxxv. 
 
 VOL. I. II 
 
114 OF ASTRINGENTS. 
 
 two liquids of a deep colour, even when no pre- 
 cipitation occurs by their mutual action. On this 
 occasion we shall adduce an observation of Hooke, 
 quoted by Newton : " If we take two coloured 
 liquids, the one red the other blue, in sufficient 
 quantity for them to appear very dark, although 
 each apart be pretty diaphanous, they will cease 
 to be so on their mixture ; for the one transmit- 
 ting only red rays, and the other transmitting 
 only blue rays, none will any longer pass through 
 the two liquids mixed together."* 
 
 The result is not, however, exactly such as 
 Newton states it, provided the two liquids are 
 not of a nature to produce a precipitate. The 
 colour transmitted is always different from the 
 two insulated colours, and always deeper ; but 
 if the mixture appears opaque in a vessel of a 
 certain size, it will appear still transparent in a 
 vessel of a smaller diameter. 
 
 We perceive therefore that it must be advan- 
 tageous, for obtaining an intense black, to mingle 
 different astringents, the black of which is de- 
 rived from different colours. Perhaps gallic acid 
 may thereby augment the black occasioned by 
 the tannin ; and perhaps it would be beneficial to 
 employ a mixture of different kinds of tannin in 
 galling. 
 
 We have hitherto considered tannin only in re- 
 ference to black dyes ; but its use is not confined 
 to this kind of dyeing : it exerts on several other 
 
 * Optics, torn. i. 
 
OF AIR AND LIGHT. 
 
 115 
 
 colouring particles an affinity analogous to what 
 we have observed between it and gallic acid; 
 whence it serves to fix them on stuffs, and to 
 communicate stability to them. In this point of 
 view, it may be compared to mordants ; but as it 
 possesses in itself a colour which has a tinge of 
 yellow or dun, and as the effect of one colour 
 must be to modify and darken that peculiar to 
 another colouring substance, the use of astrin- 
 gents as a mordant does not suit bright colours, 
 particularly those of little intensity. 
 
 CHAPTER IV. 
 
 Of the action of different Substances, particularly 
 of Air and Light, on Colours. 
 
 Hitherto we have considered the colouring 
 molecules only as substances forming different 
 combinations, by which their properties are modi- 
 fied ; but they may yield more or less easily to 
 the action of other substances, which destroy the 
 combination thus formed, or which by a sur-com- 
 position deteriorate their properties. They may 
 suffer the alterations produced by external agents, 
 either from the mutual action of their principles, 
 or of the substances which form a combination 
 with them. 
 
 The power of resisting vegetable acids, alkalies, 
 soap, and, above all, the action of air and light, 
 constitutes the durability of a colour; but this 
 
116 OF THE ACTION 
 
 property has a very unequal standard, according to 
 the nature of the colour and the species of stuff; 
 for in certain silk dyes the same permanence is not 
 required as in those of wool. 
 
 There is no obscurity in the action of water, 
 alkalies, acids, and soap : a solution is effected by 
 means of these agents, or a small portion of acid 
 or alkali unites fo the combination which forms 
 the colour ; for this is not destroyed, but merely 
 changed, and can be restored by removing the 
 acid or the alkali. 
 
 This is not the case with the action of air and 
 light. Till lately, it was not known in what this 
 action consisted ; but we are at the present day 
 much farther advanced in this theory, which we 
 proceed to detail. 
 
 Scheele had observed, that oxygenated muria- 
 tic acid (chlorine) rendered the vegetable colours 
 yellow, and he ascribed this effect to the property 
 which it possesses, of seizing the phlogiston which 
 enters into their composition. 
 
 The author of the Elements proved,* that the 
 properties of oxygenated muriatic acid arose from 
 the oxygen, which it readily yielded to the sub- 
 stances exposed to its action ; that it commonly 
 brought the colouring particles to a yellow hue ; 
 but that, by a continuance of its action, it des- 
 troyed their colour, though he did not determine 
 wherein this action consisted. t 
 
 * Mem. de l'Acad. 1785. 
 
 f For the theory of blanching by chlorine, see Note to 
 page 62.— -T. 
 
OF AIR AND LIGHT. 
 
 117 
 
 With regard to the action exercised by oxygen 
 on the colouring particles, Fourcroy afterwards 
 made several observations, which throw much 
 light on the changes which they experience, espe- 
 cially when their aqueous solution remains ex- 
 posed to the air, or when it undergoes ebullition. 
 He remarked, that, by the action of the air, vege- 
 table decoctions formed pellicles, which lost their 
 solubility, and progressively changed their colour. 
 He traced the gradations of colour thus obtained, 
 and concluded from his observations, that oxygen 
 entered into the composition of these colouring 
 particles ; that when it combined with them their 
 hue changed ; that the more of it they absorbed, 
 the more fixed their colour became ; and, that 
 the mode of procuring unchangeable colours for 
 painting was, to select those which had been ex- 
 posed to the action of oxygenated muriatic acid.* 
 
 The author of these Elements sought to deter- 
 mine more peculiarly wherein the action of the 
 air consisted, when it combines with the colouring 
 particles, especially by examining the operation 
 of oxygenated muriatic acid upon them.t 
 
 We shall copy literally what had been stated in 
 the first edition of these Elements, because Ban- 
 croft, whose authority has great weight with us, 
 has attempted to refute the theory there esta- 
 blished, and because we are desirous of enabling 
 
 * Annal. de Chimie, torn. v. 
 
 f Annal. de Chimie, torn. vi. Mem. sur Taction que l'acide 
 rauriatique oxigene exerce sur les parties colorantes. 
 
 
118 OF THE ACTION 
 
 our readers to weigh his reasons, and the grounds 
 of our opinion. 
 
 " We must distinguish, in reference to the ef- 
 fects of the air, between the colours of metallic 
 oxides and those of the colouring particles. I 
 have proved, that the modifications of the former 
 are owing entirely to the different proportions of 
 oxygen ; but I have been led by my observations 
 to a different opinion concerning the modifications 
 of the other colouring particles. 
 
 " I have observed, that the oxygenated muria- 
 tic acid exhibited different phenomena with the 
 colouring particles ; that sometimes it discharged 
 their colour, rendering them white ; that more fre- 
 quently it caused them to become yellow, dun, 
 brown, and black, according to the intensity of 
 its action ; and that, when their colour seemed to 
 be discharged or blanched, heat, or the lapse of 
 time, was sufficient to render them yellow. 
 
 " I have compared the effect produced by oxy- 
 genated muriatic acid, when the colouring parti- 
 cles are rendered yellow, fawn, or brown, with 
 the effects of a slight combustion ; and I have 
 shown that they were identical, that they were 
 owing to the destruction of the hydrogen, which, 
 combining with oxygen more easily, and at a 
 lower temperature than charcoal, leaves this pre- 
 dominant, whence the natural colour of charcoal 
 is blended more or less with that which pre-ex- 
 isted. 
 
 " This effect is very perceptible, when sugar, 
 indigo, or the infusion of nut-galls or of sumach, 
 
OF AIR AND LIGHT. 119 
 
 is submitted to the action of oxygenated muriatic 
 acid. The sugar and indigo assume a deep 
 colour, and afford unequivocal traces of a slight 
 combustion. The infusion of gall-nuts and of 
 sumach forms a black deposite, which is charcoal 
 nearly pure." 
 
 These phenomena are analogous to those 
 observed in the distillation of an organic sub- 
 stance. In proportion as its hydrogen is disen- 
 gaged under the form of oil, or in the state of gas, 
 the substance turns yellow, and eventually only a 
 black charcoal remains. If we expel the hydro- 
 gen of an oil by heat, it becomes brown. 
 
 Other experiments which I have made on 
 alcohol and ether have satisfied me, that oxygen 
 united to muriatic acid possessed the property of 
 combining with the hydrogen, which abounds in 
 these substances, so as to form water. 
 
 When, therefore, oxygenated muriatic acid 
 renders a colour yellow, dun, or brown, this effect 
 is caused by the colouring substance suffering a 
 slight combustion, in which a greater or less part 
 of its hydrogen has formed water ; whence the 
 carbon becoming predominant, communicates its 
 peculiar colour. 
 
 I have shewn, that the art of bleaching goods 
 depended on this alteration of the colouring par- 
 ticles by the oxygen of the atmosphere, the dew, 
 and oxygenated muriatic acid. The colouring 
 particles of flax become soluble in the alkali of 
 the leys, which must be alternated with the 
 action of the oxygen.. We may afterwards pre- 
 
120 OF THE ACTION 
 
 cipitate from the alkali these colouring particles, 
 which when dried and collected are black. They 
 therefore prove the truth of this theory, both by 
 the colour they have assumed, and by the quan- 
 tity of carbon they afford in their analysis. 
 
 " The alkaline solution of the colouring parti- 
 cles of the cloth, which is blackish-brown, loses 
 nearly its whole colour on pouring into it a 
 quantity of oxygenated. muriatic acid; and the 
 same effect may be observed with several other 
 substances, which have derived a colour from a 
 commencement of combustion. 
 
 " A cloth may appear white, and yet become 
 yellow in process of time, especially if it be 
 exposed to certain degrees of heat, when the 
 oxygenized particles have not been removed by a 
 sufficiently efficacious ley. In like manner, the 
 green particles of vegetables are blanched by the 
 oxygenated muriatic acid, but become yellow on 
 ebullition. 
 
 " These facts prove, that oxygen may whiten 
 or render pale the colouring particles with which 
 it combines, whether it has begun to produce on 
 them the effects of combustion, or whether it may 
 produce these effects but slowly, and especially 
 when this combustion is subjected to a certain 
 degree of heat. 
 
 " It is very probable that, in every case, one 
 portion of the oxygen unites with the colouring 
 particles without combining particularly with the 
 hydrogen, and that thereby the colouring parti- 
 cles of the flax have become, from the action of 
 
OF AIR AND LIGHT. 121 
 
 the oxygen, more soluble in the alkalies than they 
 previously were. 
 
 " The action of oxygen has an undoubted 
 influence, in several other circumstances, on the 
 changes effected in the colouring particles of 
 vegetables. These particles are formed chiefly 
 in the leaves, the flowers, and the inner bark of 
 trees. By degrees they experience a slight com- 
 bustion, either by the action of the atmospheric 
 air which surrounds them, or by that of the air 
 carried into the interior of the vegetables by 
 particular vessels ; whence it happens, that the 
 most part of trees contain colouring particles of a 
 dun hue, verging more or less on yellow, red, or 
 brown, which, by means of this combustion, 
 thicken, and are eventually thrown out of the 
 vascular fibres of the bark, of which I have found 
 them to form the greater proportion. 
 
 " These observations teach us in what manner 
 the air acts on colouring substances of an animal 
 or vegetable nature : it first combines with them, 
 making them weaker and paler, and gradually esta- 
 blishes a slight combustion, by which the hydrogen 
 in their composition is destroyed ; they pass to 
 yellow, russet, dun ; their affinity with the stuff 
 seems to diminish, they are detached from it, 
 they are carried off by the water ; and all these 
 effects vary, and are finished more or less quickly, 
 and more or less completely, according to the 
 nature of the colouring particles, or rather ac- 
 cording to the properties which they possess in 
 their actual state of combination. 
 
122 OF THE ACTION 
 
 \ 
 
 " The changes which occur in colours, arising 
 from the combination of the colouring particles 
 with the metallic oxides, are a compound effect 
 of the change produced in the colouring particles 
 and the metallic oxide. 
 
 " The light of the sun accelerates greatly the 
 destruction of colours ; it ought then (if the 
 theory which I have laid down be just) to favour 
 the combination of the oxygen, and the combus- 
 tion thereby produced. 
 
 " Sennebier has given a great number of inte- 
 resting observations, concerning the effects which 
 light occasions in the different substances, and 
 particularly in colours ; he ascribes these effects 
 to a direct combination of the light with these 
 substances/' * 
 
 The influence of light on the colour of woods 
 has been long ago remarked. In obscurity, they 
 retain their natural state ; but when exposed to 
 light, become yellow, brown, and pass into other 
 shades. Sennebier observed the differences ex- 
 hibited by several species of wood in this respect. 
 He found that the changes were proportional to 
 the vivacity 'of the light ; that they took place 
 even under water; that moistened woods, how- 
 
 * Mem. Physico-Chimique sur l'influence de la lumiere 
 solaire, &c. tomes ii. et iii. This philosopher, to whom physics 
 is under so many obligations, has adopted, in a great measure, 
 (Physiol. Veget. torn, v.) the ideas exposed here; and among 
 which we must distinguish between the positive consequences 
 of observation, and the applications that are yet merely con- 
 jectural. 
 
OF AIR AND LIGHT. 123 
 
 ever, suffered changes less rapidly than those 
 which were dry ; that it required several folds of 
 ribbon to preserve a wood entirely ; that black 
 paper was sufficient, but with paper of other 
 colours the alteration was not prevented. A 
 simple envelope of white paper was insufficient, 
 but two intercepted the action of the light. 
 
 " This skilful philosopher extended his experi- 
 ments to a great number of vegetable substances. 
 They may serve to clear up several phenomena 
 of vegetation, with which I have at present no 
 concern. But to prove wherein the action of the 
 sun on colours consists, it would be sufficient to 
 examine the phenomena exhibited by the solution 
 of the green particles of vegetables in alcohol. 
 
 " If this solution, which is of a fine green colour, 
 be exposed to the light of the sun, it speedily 
 takes an olive tint, and then is discharged in some 
 minutes. If the light has little vivacity, the 
 effect is much slower; but in perfect darkness, 
 the colour is preserved without alteration, or at 
 least the alteration is very tardy. Sennebier says 
 that an alkali restores the green colour ; but if 
 the liquid has experienced all the discoloration 
 which it can undergo, the alkali produces no 
 change on it. He remarked, that in azote or 
 phlogisticated air the colour was not affected, and 
 that it suffered no change if the flask was full. 
 
 " I inverted over mercury a flask half filled 
 with the green solution, and exposed it to the 
 light of the sun. When the colour was discharg- 
 ed, the mercury was found to have risen in the 
 
124 OF THE ACTION 
 
 flask, and consequently the vital air had been 
 absorbed, the oxygen having combined with the 
 colouring particles. I have not observed the de- 
 posite of which Sennebier speaks ; the liquid re- 
 mained transparent, and of a clear yellow colour. 
 
 " I evaporated this liquor ; its colour soon 
 deepened, becoming brown ; and the residuum 
 was black, and in a carbonaceous state. 
 
 " The light acted therefore by favouring the 
 absorption of oxygen and the combustion of the 
 colouring matter. At first, the marks of the 
 combustion are not perceptible, the liquid pre- 
 serving merely a feeble yellow colour ; but the 
 combustion is soon consummated by the action 
 of the heat, when the liquid turns brown, and 
 leaves a black residuum. If the vessel in which 
 the liquid is put contains no oxygen gas, the 
 light has no action on the colouring particles. 
 The azotic gas suffers no diminution. 
 
 " The circumstance of ribbons and a simple 
 white paper not protecting from the action of 
 light merits attention. It can penetrate through 
 envelopes which appear to us opaque, so as to 
 exert its energy at greater or less depths. 
 
 " Beccaria, and after him Sennebier, have 
 compared the effects which light produces on 
 ribbons of different colours ; but the differences 
 which they observed ought to be ascribed to the 
 nature of the colouring substances with which 
 the ribbons were dyed, rather than to the colours 
 themselves ; for a ribbon dyed with brazil wood 
 will lose its colour much more speedily than one 
 
OF AIR AND LIGHT. 125 
 
 dyed with cochineal, though the shade be the 
 same. 
 
 " Although light greatly accelerates the com- 
 bustion of the colouring particles, and though its 
 presence even appears necessary for the destruc- 
 tion of some of them, yet this effect takes place 
 in other circumstances without the aid of light. 
 Having placed several plants in darkness, in con- 
 tact with oxygen gas, I observed that some of 
 them absorbed it. 1 also observed, that the rose 
 changed and took a darker tint without the con- 
 tact of the air, undoubtedly because it contains 
 a little oxygen, whose state of combination be- 
 comes afterwards more intimate ; but several spe- 
 cies of flowers preserved their colour perfectly 
 well in azote. 
 
 " I placed tincture of litmus in contact with 
 oxygen over mercury, in darkness, and in the 
 sun-light : the first was preserved very long with- 
 out alteration, while the gas experienced no di- 
 minution ; the second lost much of its colour, it 
 became red, the oxygen gas was in a great mea- 
 sure absorbed, and a little carbonic acid was 
 formed, which undoubtedly produced the change 
 of the blue colour into red. 
 
 " This observation may give some idea of the 
 changes of colours occasioned by a peculiar dis- 
 position of the principles existing in a vegetable 
 substance, when it experiences, by combination 
 with oxygen, the effects of a slight combustion, 
 which may generate some acid, as in the leaves 
 which redden in autumn previous to their turn- 
 
126 OF THE ACTION 
 
 ing yellow, and in the streaks observable in 
 flowers of languid vegetation. 
 
 " It is therefore proved, that light promotes 
 the absorption of oxygen by the colouring par- 
 ticles, and that a combustion thus takes place, 
 the ordinary effect of which is a predominance of 
 carbonaceous particles. 
 
 " To the same cause must be ascribed the de- 
 cay remarked in stuffs themselves by the action 
 of light. " Among several examples which I 
 might adduce," says Dufay, " I shall mention 
 only a curtain of fugitive crimson taffeta, which 
 had remained long stretched behind a window : 
 all the parts which were opposite the panes of 
 the glass were entirely deprived of colour, whilst 
 those which corresponded to the wood of the 
 casement were much less faded ; and further, 
 the silk itself was almost destroyed in the dis- 
 coloured parts, where the curtain could be torn 
 with the slightest effort, whilst it retained else- 
 where nearly its usual strength."* 
 
 " The colouring substances resist, therefore, 
 the action of the air in a greater or less degree, 
 according as they are more or less disposed to 
 combine with oxygen, and to suffer from its ac- 
 tion a combustion more or less speedy, more or 
 less considerable. Light favours this effect in 
 several circumstances ; its concurrence is essen- 
 tial ; but the insulated colouring particles are 
 much more subject to this combustion than when 
 
 * Mem. cle l'Academie, 1737. 
 
OF AIR AND LIGHT. 127 
 
 they are combined with a substance such as alu- 
 mina, whether this defends them by its incom- 
 bustibility, or whether the force of affinity binds 
 them up, so to speak, and enfeebles their action 
 on other substances ; and in this principally con- 
 sists the utility of mordants. Finally, the latter . 
 combination acquires still greater unchangeable- 
 ness when it is intimately united with the stuff. 
 
 " Thus the colouring matter of cochineal is 
 easily dissolved in water, and its colour is quickly 
 affected in the air. When combined with the 
 oxide of tin, it is much more lively, and scarcely 
 soluble in water ; but it is still readily altered by 
 the air and by chlorine. When it exists in triple 
 combination with woollen stuff, it resists these 
 agents better. 
 
 " From these observations we are not to con- 
 clude, that all the yellow colours proceed from 
 the carbonaceous portion of the colouring sub- 
 stances j different compositions may afford the 
 same colour. Thus indigo is entirely different 
 from the blue of our flowers, from the blue of 
 oxide of copper, and from prussian blue. 
 
 " Nor do I assert that oxygen may not unite 
 in a small proportion with some colouring par- 
 ticles, without weakening their colour, or chang- 
 ing it to yellow. We shall find in the chapter 
 on indigo, that this substance possesses a green 
 colour when combined with an alkali, lime, or a 
 metallic oxide ; but that it resumes its colour, 
 and separates from these solvents, on recovering 
 a small portion of the oxygen which it had lost. 
 
128 OF THE ACTION 
 
 The liquor of the buccinum, which served for 
 dyeing purple, is naturally yellowish ; on being 
 exposed to the air, and particularly to the sun, 
 it passes speedily through different shades, and 
 finally assumes that colour which was deemed so 
 precious by the ancients.* 
 
 " It may be regarded even as a general fact, 
 that colours assume more brilliancy by combin- 
 ing with a small portion of oxygen. It thence 
 happens that the stuffs, as they come out of the 
 bath, ought to be agitated in the air, and some- 
 times withdrawn from the bath at intervals, in 
 order to expose them to the atmosphere. But 
 the quantity of oxygen which fixes itself, thus 
 contributing to the lustre of the colour, is very 
 inconsiderable in some cases, and the degrada- 
 tion of shade soon begins. 
 
 " The action of the air affects not only the 
 colouring particles and the stuff, but also the 
 metallic oxides which serve as an intermedium to 
 them ; because the oxides, which are at first de- 
 prived of a portion of their oxygen by the colour- 
 ing particles, may recover some of it. Hence 
 the oxides, whose colour varies with the propor- 
 tion of their oxygen, exert an influence on the 
 changes experienced by the stuff. The alteration 
 of the colouring particles must also contribute to 
 this effect. 
 
 * Decouverte d'uneNouvelle Teinture de Pourpre, &c. par 
 Reaumur; Mem. de l'Academie 1711. According to the tes- 
 timony of Eudocia, the purple took its lustre, and arrived at 
 its perfection, only by exposure to the sunbeams. 
 
Of AIR AND LIGHT. 129 
 
 u I have stated, that the colouring particles, in a 
 state of combination, were less liable to be affect- 
 ed by the action of the air than when they are 
 insulated. This is a circumstance very commonly 
 observed. There are, however, particular excep- 
 tions. Alkali produces a contrary effect. I half 
 filled a phial with an infusion of cochineal, and 
 exposed it to light over mercury ; another phial, 
 similarly situated, contained an infusion of cochi- 
 neal made with a little tartar ; and in a third, some 
 alkali was added to the infusion. The second 
 phial suffered least alteration in the same space 
 of time, accompanied with the least absorption of 
 air. 
 
 " In the third, the liquid became at first brown, 
 then the colour disappeared, and the absorption 
 of the air, although inconsiderable, was greater 
 than in the two others. By evaporation it as- 
 sumed a brown colour, and the residuum was 
 yellow-brown. 
 
 " I have made similar experiments on several 
 colouring substances : the alkali deepened their 
 colour, which grew more and more brown ; and 
 it likewise favoured the absorption of the air. 
 Madder alone seemed to form an exception ; its 
 colour, which at first became deeper, was more 
 durable than that of the infusion without alkali. 
 
 "The usual effect of alkalies on colouring 
 particles is conformable to what they produce on 
 several other substances, such as sulphur. They 
 promote the absorption of the air, because they 
 
 vol. i. i 
 
ISO OF THE ACTION 
 
 have a strong affinity for the substance which 
 results from this absorption. 
 
 " From this operation of alkalies, I explain a 
 fact observed by M. Becker.* When alkalies have 
 rendered a vegetable infusion green, we see it 
 pass by degrees to yellow, if it be left exposed to 
 the air ; and when the yellow is once established, 
 acids can no more bring back the primitive co- 
 lour. But this effect does not occur when we 
 abandon in the same way, for some time, a vege- 
 table colour which has been turned red by an 
 acid. We must, however, except those acids 
 which act by giving up their oxygen ; for the 
 colour is equally destroyed in that case." 
 
 Bancroft advances, in opposition to what we 
 have thus stated : 1. That the colouring substan- 
 ces experience, from the action of acids and other 
 bodies, an alteration which cannot be compared 
 to combustion. In the preceding explanations, 
 however, the question is merely about the kind 
 of alteration which depends on the action of oxy- 
 gen. 
 
 2. That oxygen, far from destroying colours, 
 is sometimes necessary to them ; for example, to 
 indigo. Is not this what we have said ? But we 
 distinguish between the cases where it becomes 
 an element of the colour, and those where its 
 action is destructive. 
 
 3. That the changes of colours produced by 
 the air cannot be ascribed to the charcoal, which 
 
 * Specimen, &c. 
 
OF AIR AND LIGHT. 131 
 
 becomes predominant, because several substances 
 contain much charcoal without having a Colour 
 similar to what is ascribed to its excess, and be- 
 cause the colour of charcoal itself is due to oxy- 
 genation. 
 
 We have attempted to demonstrate, that the 
 changes produced by the air when its action is 
 favoured by light, are especially owing to a com- 
 bination of the hydrogen of the colouring sub- 
 stance with oxygen, whether this be absorbed 
 from the atmosphere, or be present in less inti- 
 mate combination, either in the colouring sub- 
 stance itself, or in the oxide united with it ; and 
 that the effect was similar to a slow combustion, 
 in which a combination of hydrogen with oxygen 
 was formed, so as to leave a residuum containing 
 a redundancy of charcoal. This opinion seems 
 to be an immediate consequence of the pheno- 
 mena that have been detailed, which indicate the 
 gradual decomposition of all bodies containing 
 hydrogen on being subjected to this action of 
 oxygen. 
 
 Bancroft regards charcoal as an oxide, which 
 he compares to the oxide of manganese. We do 
 not think it necessary to take up time in refuting 
 his opinion * concerning the nature of charcoal. 
 The only object is to know, if, in the circumstan- 
 ces under discussion, the change of colour may not 
 have some analogy with what is observed when 
 a vegetable substance is distilled. He pretends 
 
 * Essai de Statique Chimique, torn. ii. 
 
132 OF THE ACTION 
 
 that this substance becomes in that case brown, 
 merely by the accession of oxygen from the at- 
 mosphere. Let a distillation be made out of 
 contact of the atmospheric air, and he will ob- 
 serve that the same alteration of colour takes 
 place, either from the formation of water, or from 
 the disengagement of a greater proportion of hy- 
 drogen, so that the properties of the charcoal be- 
 come predominant. 
 
 Bancroft maintains, that the theory which he 
 combats is founded only on the phenomena of 
 the colouring particles of the cloth. The text 
 which we have adduced proves the contrary, and 
 we might easily multiply examples. 
 
 It was incorrect, according to him, to confound 
 the effects of the combination of oxygen gas with 
 those of the oxygenated muriatic acid ; but we 
 do not find in his work the experiments which he 
 announced as calculated to prove, that the oxy- 
 genated muriatic acid often produces effects con- 
 trary to those arising from the combination of 
 oxygen. 
 
 We ought, undoubtedly, in comparing the ef- 
 fects of oxygenated muriatic acid with those of 
 the absorption of oxygen gas, to take into consi- 
 deration the greater condensation of oxygen in 
 the former, and the natural effects of muriatic 
 acid.* We should also distinguish between the 
 
 * Translating M. Berthollet's idea into the modern lan- 
 guage of chemistry, we would say, " Take into consideration 
 the intense affinity of chlorine for hydrogen, the liberation of 
 oxygen from the decomposed water, and the peculiar action 
 of muriatic acid." — T. 
 
OF AIR AND LIGHT. 133 
 
 effects which the oxygenated muriatic acid can 
 produce, when it has made the whole colour dis- 
 appear, as we have seen, and the effects due to 
 the combination of its oxygen with the hydrogen 
 of the colouring particles, as well as those arising 
 from the difference of the colours, of which we 
 shall speak in the sequel. 
 
 The more lively oxygenation, by means of 
 oxygenated muriatic acid, prevents us from ob- 
 taining readily those gradations of colour which 
 are produced by the action of the air, and which 
 become more difficult the further they advance. 
 Thus, conformably to the observation of Four- 
 croy, when a colouring substance has experienced 
 some change by this action, it becomes, in simi- 
 lar circumstances, more fixed ; but in this first 
 effect, a part of its hydrogen must have entered 
 into combination. 
 
 While we conceive that we have been able to 
 refute the objections of Bancroft concerning at 
 least the most usual cause of the degradation of 
 colours by air and light, we admit, that the con- 
 sequences of the opinion which we endeavour to 
 maintain, should not have been extended to the 
 phenomena that we are now going to examine, 
 although this has been done with much diffidence, 
 and without overstepping the limits of a simply 
 conjecture. 
 
 Nitric acid, oxygenated muriatic acid, and sul- 
 phurous acid, exercise on animal substances a pe- 
 culiar action, which merits examination, because 
 it may furnish some processes to dyeing. 
 
134 QF THE ACTION 
 
 Brunwiser * having observed that woods as- 
 sumed different colours on exposure to air, sought 
 to determine the origin of these colours, and to 
 produce them artificially, He remarked, that on 
 moistening with nitric acid the surface of wood, 
 principally young wood not very dry, it took a yel- 
 low colour. On performing the same operation 
 with muriatic acid, and sulphuric acid, the wood 
 assumed a violet colour ; and he looked upon 
 this violet as composed of a blue and a red co- 
 lour. From these observations he concluded, 
 that as all the colours are produced by the mix- 
 ture of yellow, blue, and red, those which we 
 observe in the leaves, fruits, and flowers, arise 
 from the colouring particles which exist in the 
 wood, but which are disguised by an alkali j that 
 the mineral acids, on seizing this alkali, set the 
 colouring particles at liberty ; and that the fixed 
 air, in penetrating into the leaves, the fruits, and 
 the flowers, naturally produced the same effect, by 
 combining with the alkali w T hich masked them. 
 
 The author attempted to apply to the arts his 
 pretended discovery as follows.! After watering 
 chips of wood with nitric acid, he poured water 
 upon them, filtered the liquid, and made use of 
 it to dye wool, silk, and goat's hair, of a durable 
 
 * Versuche mit mineralischen sauern geistern, aus den 
 holzern farben zu ziehen, 1770. In abhandlungen der Baie- 
 rischen akademie. 
 
 f Entdeckung verscliiedener vegetabilischen farbemateria- 
 lem seiden und wollen zeuge schcm und dauerhaft gelb zu 
 farben, 1771. 
 
OF AIR AND LIGHT. 135 
 
 yellow ; a colour due, by his account, to the yel- 
 low particles which were contained in the wood, 
 and which had been extracted or set at liberty by 
 the nitric acid. 
 
 De la Folie relates,* that having plunged a 
 skein of white silk into nitric acid, or aquafortis, 
 of the usual commercial strength, the silk assum- 
 ed in three or four minutes a fine jonquil-yellow 
 hue. He washed it repeatedly with water, that 
 no adhering acid might remain to alter it. This 
 colour resisted several tests to which he exposed 
 it, and the silk retained its primitive lustre. When 
 dipped into an alkaline solution, it takes a beau- 
 tiful orange colour. 
 
 Several experiments on this process are to be 
 found in a dissertation published by Gmelin.t 
 He says, that he has given a fine sulphur colour 
 to silk by keeping it for a day in cold nitric acid, 
 or for a few hours when the acid was hot. Ebul- 
 lition with soap and water impaired the lustre of 
 this colour. It became of a fine lemon colour by 
 keeping the silk for twelve hours in an alkaline 
 solution ; and it assumed a fine gold hue when 
 this solution was hot. 
 
 All solutions of metals in nitric acid gave to 
 silk a yellow colour more or less deep, as well as 
 the solution of alumina in the same acid. But 
 
 * Journ. de Phys. torn. iv. p. 349. 
 
 f J. Frieder. Gmelin, Prof. Gotting. de tingendo per nitri 
 acidum, sive nudum, sive terra aut metalli saturatum serico. 
 Erfurti, 1785. 
 
1.36 OF THE ACTION 
 
 the solution of calcareous earth and of magnesia 
 produced no effect. 
 
 The solution of tin mixed with solution of gold 
 yielded, according to La Folie,* a purple colour, 
 which fixes upon silk ; but Gmelin obtained by 
 this process only a common yellow. He proves 
 also, that the different yellows which Struve said 
 he had obtained from different metallic solutions, 
 depend merely on the acid of these solutions.t 
 The only exception, perhaps, is the solution of 
 mercury, which gave silk a copper colour. 
 
 Baume describes a process capable of protect- 
 ing silk from any alteration.^ " A mixture of 
 two drams of nitrous acid and one pound of alco^ 
 hoi is made, into which a few ounces of silk are 
 put, mounted (montee), and yellow, or previously 
 whitened, for that is absolutely indifferent. The 
 vessel containing them is placed for about 24< 
 hours in a water-bath heated to 30 or 40 degrees 
 R. (100° or 120° Fahr.) The silk becomes of a 
 dull yellowish-brown. It is now repeatedly wash- 
 ed in water, to remove the acid with which it 
 was impregnated. It is then scoured with soap 
 in the usual way ; afterwards washed to free it 
 from the soap water, and finally dried. 
 
 " If we view this silk in the sun, it shines like 
 threads of gold. By the same process we may 
 
 * Journ. de Physique, torn. viii. 
 
 f Bernerisches Magazin der Naturkunst und Wissenchaf- 
 t.en, vol. i. 
 
 j: Ann. dc Chimie, torn. xvii. 
 
\ / 
 
 OF AIR AND LIGHT. 1,37 
 
 give silk different shades of the above colour, and \ 
 
 form what is called in dyeing degradation of co- 
 lour from white to the full tint. For this purpose 
 it is sufficient to let the silk infuse for a shorter 
 time ; the first shade is procured by one hour's 
 infusion, and the others in proportion to their 
 duration." 
 
 Bergman was aware of this process, when he 
 published his notes on the Treatise of SchefFer.* 
 He says, that ordinary aquafortis gives, in three 
 or four minutes, to wool and silk, a bright, fine;, 
 and durable yellow ; that they must be imme- ' 
 
 diately washed ; and the more dephlogisticated 
 the acid (the more colourless), the greater effect 
 it produces. 
 
 To recapitulate : nitric acid, diluted with a cer- 
 tain quantity of water, gives silk a yellow colour, 
 ofmoreorless depth, according to the concen- 
 tration of the acid, the temperature, and the time 
 of immersion : the silk must be carefully washed 
 on coming out of the acid. This colour has a 
 good deal of lustre. We may deepen the shade j 
 
 without perceptibly affecting the silk. This pro- 
 cess may be usefully applied, not only to silk, 
 but to other animal substances ; and the colour 
 may be modified by alkalies. 
 
 The solution (nitric) of calcareous earth, and 
 that of magnesia, produce no effect on silk, be- 
 cause they do not retain an excess of acid. So- 
 lutions of alumina, and of all the metallic sub- 
 
 * Essai sur l'Ait de la Teinturc. 
 
138 OF THE ACTION 
 
 stances, produces, on the contrary, a yellow of 
 greater or less depth, because they all retain a 
 greater or less excess of acid ; and it is the acid 
 in excess which acts on the silk as free acid. It 
 was the acid alone which coloured the animal 
 substances yellow in the experiments of Brun- 
 wiser, and not the extracts of the wood. 
 
 The yellow colour is not owing to iron, as De 
 la Folie pretended ; for the purest nitric acid, 
 which consequently contains no iron, produces it 
 as well as that in which the presence of a little 
 of this metal may be suspected. 
 
 If silk be put into concentrated nitric acid, it 
 speedily takes a deep yellow colour, loses its force 
 of cohesion, and is dissolved. During this solu- 
 tion, the azote which enters into the composition 
 of animal substances is disengaged, occasioning a 
 long effervescence.* If heat be applied, much 
 nitrous gas is formed, and the liquid at first as- 
 sumes a dark colour, becoming brown. At this 
 period, the oxygen of the nitric acid combines 
 particularly with the hydrogen which abounds in 
 animal substances, serving to form the oil ex- 
 tracted by distillation, which renders them so 
 combustible. One part of the oxygen enters into 
 a new combination, forming oxalic acid ; but, at 
 the same time, another substance of a detonating 
 quality is produced, which is yellow, and bitter, 
 whence it has been called amer by Welter.t 
 
 * Mem. de l'Academie, 1785. 
 f Ann. de Chimic, torn. xxix. 
 
OF AIR AND LIGHT. 139 
 
 Welter extracted this substance not only from 
 silk, but from other animal substances ; and he 
 observed, that it communicated to white silk a 
 beautiful yellow, which washing with water did 
 not impair. 
 
 It is to be desired that this expert chemist had 
 prosecuted his trials, in order to determine more j 
 
 exactly both the nature of this substance and the 
 circumstances of its production j we might per- 
 haps be able to deduce from it the cause of the 
 yellow colour which nitric acid communicates to 
 animal substances, when the action of this acid 
 is less lively than that just described. Perhaps, 
 when it is confined to the surface of the silk, the 
 formation of this substance on it is determined 
 by the tendency of the silk to combination. 
 
 Oxygenated muriatic acid gives likewise a yel- 
 low colour to animal substances ; but this does 
 not seem to be a general effect. We have seen 
 skins bleached by oxygenated muriatic acid, and 
 this colour is always much more intense than that 
 owing to nitric acid : thus, it appears to differ i 
 
 from it, and to arise merely from a feeble com- 
 bination of the oxygen with the animal substance, 
 which, when it is white, takes a nearly similar 
 hue on long exposure to the atmosphere. It is 
 also to be remarked, that the action of oxygenat- 
 ed muriatic acid weakens animal substances more 
 easily than nitric acid, although the latter be 
 more condensed. 
 
 Sulphurous acid exercises also a peculiar action, 
 which deserves more consideration, as it enters 
 into the practice of dyeing. 
 
y 
 
 140 OF THE ACTION 
 
 According to the observation of De la Folie, 
 roses blanched by the vapour of burning sulphur, 
 become green in an alkaline ley, and red in the 
 acids. Sulphurous acid reddens tincture of lit- 
 mus, which possesses a very fugitive colour ; but 
 it acts just like the other acids on infusions 
 of yellow wood, brazil wood, and logwood ; its 
 vapour however is much more active, in which 
 respect it resembles oxygenated muriatic acid.* 
 Hence it is not judicious to substitute the use of 
 this for the fumes of sulphur. 
 
 When silk has undergone the action of the 
 sulphur which is to complete its whitening, sul- 
 phuric acid disengages from it an odour of sul- 
 phurous acid, although this odour was not per- 
 ceptible beforehand. 
 
 From this circumstance we may conclude, that 
 sulphurous acid has the property of combining, 
 in small quantity, with animal substances, with- 
 out experiencing decomposition ; in which state it 
 can disguise some colours, particularly that aris- 
 ing from a combination of oxygen. But it would 
 seem, that in the lapse of time a more intimate 
 union is effected between the sulphurous gas and 
 the oxygen. 
 
 This latter effect immediately takes place when 
 sulphurous acid is made to counteract the oxy- 
 genated muriatic acid. The yellowed silk is 
 whitened by the sulphurous acid ; and the two 
 operations may be alternated. We shall have 
 
 * Journ. de Phys. 1774. 
 
•y^Mw^^ — ■ — ■■■ 
 
 OF AIR AND LIGHT. 141 
 
 occasion to speak of the use which Giobert has 
 made of this property. 
 
 We are obliged to confine ourselves to these 
 conjectural views concerning the action which 
 nitric acid, oxygenated muriatic acid, and sul- 
 phurous acid, exercise on animal substances, till 
 experience shall have conducted us to positive 
 results. 
 
 CHAPTER V. 
 
 Recapitulation of the Theory laid down in this 
 
 Section. 
 
 Substances which have constant colours should 
 not be confounded with those which owe their 
 variable and fugitive hues to the dimensions and 
 density of the plates of which they are formed ; 
 or, at least, the theory of the one cannot serve 
 for the explanation of the properties which the 
 others possess, in reference to the colours which 
 appear to depend on their peculiar affinity for 
 the rays of light. 
 
 Meanwhile, till chemistry can be reconciled 
 with physics, in explaining the phenomena ex- 
 hibited by colours, we must content ourselves, 
 in reference to the art of dyeing, with determin- 
 ing the affinities which characterize the colouring- 
 substances, and the physical dispositions which 
 modify their action in every variety of circum- 
 stance. 
 
\/ 
 
 14$ RECAPITULATION 
 
 Metallic colours must be distinguished from 
 those which belong to vegetable and animal sub- 
 stances. 
 
 The colours of metals are modified and chang- 
 ed by oxidation, and in proportion to the quantity 
 of oxygen combined with them. 
 
 The vegetable and animal substances, which 
 occasionally owe to plates on their surface some 
 plays of fugitive colours, may themselves have a 
 peculiar colour, or may indeed owe their colours 
 to coloured molecules which exist combined, or 
 simply mixed, with them. It is molecules of this 
 kind* extracted from several substances, which 
 receive different preparations in order tp serve 
 for the purposes of dyeing. 
 
 The affinities of the colouring particles for 
 acids, alkalies, earths, metallic oxides, and wool, 
 silk, cotton, and flax, constitute their chief dis- 
 tinctive properties ; but these are modified by 
 their physical qualities, and especially by their 
 tendency to assume the solid, or to continue in 
 the liquid states 
 
 In consequence of the affinity between the co- 
 louring particles, and wool, silk, cotton and flax, 
 they combine more or less easily, more or less 
 intimately, with each of these substances ; from 
 which arises a primary difference in the processes 
 employed, according to the nature of the stuff 
 and of the colouring substance. 
 
 Sometimes they unite immediately with the 
 stuffs, but more frequently they need an inter 
 medium, in order to be separated from the sol- 
 
OF THE THEORY. 143 
 
 vent, and to be fixed on the stuff, or at least to 
 acquire a greater permanence. 
 
 From the affinity of the colouring particles for 
 alumina and metallic oxides, they form com- 
 pounds with these substances, in which their co- 
 lour is more or less preserved, while it becomes 
 more stable, and more insensible to external 
 agents. This combination being formed of prin- 
 ciples which possess the faculty of uniting to 
 vegetable, and particularly to animal substances, 
 has also itself this property ; it enters into triple 
 combinations with the stuffy and the colour re- 
 sulting from this triple union thus acquires 
 greater fixity, or the faculty of better resisting 
 external agents. 
 
 The colouring particles have frequently such 
 an affinity for alumina and the metallic oxides, 
 that they separate them from the acids which 
 held them in solution, and fall down with these 
 bases ; but sometimes the affinity of the stuff 
 must determine this combination. We have to 
 distinguish between the chemical action of the 
 substances which dissolve the colouring particles, 
 and those which fix them, or effect their destruc- 
 tion. 
 
 Colours experience great changes from the ac- 
 tion of oxygen, which eventually destroys them ; 
 the other substances promote or obstruct this 
 action. 
 
 Of the two principles which compose the at- 
 mospheric air, it is only the oxygen gas which 
 acts on the colouring particles. It combines with 
 
144 RECAPITULATION 
 
 them, and thus impairs their colour or makes them 
 pale. But its action is soon chiefly exerted on 
 the hydrogen, which enters into their composi- 
 tion, and it thereby forms water. This effect 
 may be compared to that of a feeble combustion. 
 Hence, the carbon which enters into the compo- 
 sition of the colouring particles becomes pre- 
 dominant, and the colour usually passes to yel- 
 low, dun, or brown ; or this degradation, blended 
 with what remains of the first colour, or with the 
 effect at the same time suffered by a metallic 
 oxide, produces other appearances. 
 
 Light promotes this decomposition of the co- 
 louring particles, which frequently takes place 
 only with its concurrence ; and thus it contri- 
 butes to the destruction of colours. Heat favours 
 it also, but less efficaciously than light, unless it 
 have a certain intensity.* 
 
 The oxygen present in the colouring particles 
 may itself undergo a combination productive of a 
 slow alteration in the colouring particles, espe- 
 cially by the action of light and heat. 
 
 The oxygen which is absorbed does not, how- 
 ever, always and immediately produce that kind 
 of combustion which alters and destroys the co- 
 louring particles ; on the contrary, a certain ab- 
 sorption is usually necessary to give the colours 
 lustre, or even to bring them out, while a larger 
 proportion causes the colour to disappear ; and 
 it is but secondarily that the combination of 
 
 * Statique Chimique, torn. i. p. 197. 
 
OF THE THEORY. 145 
 
 hydrogen is formed, which produces the appear- 
 ances of a slight combustion. 
 
 The colours are more or less durable, more or 
 less fixed in the air, according to the greater or 
 less tendency which the colouring particles have 
 to experience that change, and to suffer it in a 
 greater or less degree ; for the resistance to this 
 decomposition increases as it advances. 
 
 The other substances exercise their action on 
 the colouring particles, either before they have 
 been applied to the stuffs, or after they have been 
 fixed on them ; they thus have a different use, or 
 they may produce destructive effects, 
 
 The substances capable of dissolving the 
 colouring particles, serve to separate them from 
 the particles with which they are confounded ; 
 and they prepare them, by the liquidity they 
 communicate, for the action of the stuffs that 
 are to fix them, or for the combinations they are 
 to form. 
 
 The colouring particles are sometimes modified 
 as to their colours by the action of these sub- 
 stances, and as they usually retain a portion of 
 them in the combinations which they afterwards 
 form ; or as, when the compound is formed, this 
 may take a portion of them by sur-composition, 
 we call these substances alterants, in order to 
 contrast their effect with that of mordants. 
 
 We give the name of mordants to substances 
 which, combining with the colouring matters, 
 serve to precipitate, to fix, and to render them 
 more durable. 
 
 VOL. I. K 
 
\/ 
 
 
 146 RECAPITULATION 
 
 / These two genera of substances, therefore, 
 
 which exercise the same chemical action, are 
 distinguishable by this ; — the alterants, in conse- 
 quence of their physical qualities, attenuate and 
 dissolve the colouring matters, so that only a 
 small portion can remain in combination when 
 the colouring substances assume the solid state ; 
 such are the acids and alkalies properly called, 
 which, when they act with a certain energy, even 
 deprive the stuffs of those colouring particles 
 j which were fixed on them. The power of resist- 
 
 ing the action of them and of the air, constitutes 
 ' J the durability (la solidite) of colours. 
 
 The substances, on the contrary, which natu- 
 rally tend to the solid state, communicate this pro- 
 perty to the colouring substances with which they 
 have an affinity, serving as intermedia between 
 them and the stuffs, with which also they must 
 have a tendency to combine. 
 
 The mordants produce this effect only some- 
 times, and change but slightly the natural colour 
 of a substance ; alumina, in particular, has this 
 property. Sometimes the colour of the combina- 
 tion results from that of the tinctorial substance, 
 joined to that of the mordant; such are the 
 metallic oxides, which, moreover, alter or amelio- 
 rate the natural colour by the action of their 
 oxygen. Thence arise their different effects. 
 
 1. The metallic oxides, to which the oxygen ad- 
 heres loosely, are not fit to serve as intermedia to 
 the colouring particles, because they produce in 
 them too considerable a combustion. The oxides 
 
OF THE THEORY. 147 
 
 of silver, gold, and mercury, are in this predica* 
 ment. 
 
 %. The oxides which, on giving up more or 
 less of their oxygen, experience considerable 
 changes in their colour, are also bad intermedia, 
 especially fbr light shades, because they produce 
 variable colours. Such are the oxides of copper, 
 lead, and bismuth. 
 
 3. The oxides which retain their oxygen with 
 force, and which change their colour very little 
 when they have lost a portion of it, are the most 
 proper for accomplishing this object. The oxide 
 of tin must be here particularly distinguished. It 
 easily abandons its solvent ; it has a strong affi- 
 nity for the colouring particles, and affords them 
 a very white base, one capable of giving brilliancy 
 to their hues, without altering them by the mix- 
 ture of another colour. The oxide of zinc pos- 
 sesses these properties in part. 
 
 In order to account for the colours that result 
 from the combination of the colouring particles 
 with the basis which a mordant gives them, we 
 must also pay attention to the proportion in which 
 the colouring particles are united with this basis. 
 Thus, the solution of tin, which forms a very 
 abundant precipitate with a solution of the co- 
 louring particles, proving thereby that the oxide 
 of tin enters in large proportion into the preci- 
 pitate, influences the colour of the precipitate, 
 by the colour of the base, much more than the 
 solution of (sulphate of) zinc and of alum does, 
 which bodies usually form a much less consi- 
 
148 RECAPITULATION 
 
 derable precipitate. The precipitates produced 
 by the two latter substances, retain very nearly 
 the natural colour of the colouring particles. 
 
 In the action of mordants, therefore, we must 
 distinguish the combinations formed, by their 
 means, between the colouring particles and the 
 intermedium which they furnish to the stuff; the 
 proportions of the colouring substance and the 
 intermedium ; the modifications of colour result- 
 ing from the association of the colour of the 
 colouring particles with the base to which they 
 are united ; and finally, the changes which the 
 colouring particles may suffer by the action 
 exerted on them by that base. 
 
 Astringents do not differ essentially from co- 
 louring particles ; but the latter take this name, 
 especially when employed to produce black with 
 oxide of iron, by restoring this metal to the state 
 of a black oxide, and by their assuming a dark 
 colour from the action of oxygen. 
 
 The notion of an astringent supposes, more- 
 over, the property of combining in a certain 
 quantity with animal substances, giving them 
 thus solidity and incorruptibility ; because these 
 two properties are most commonly united. These 
 again are derived from their large share of carbon, 
 a circumstance in their composition which gives 
 them increased tendency to solidity, and greater 
 stability. 
 
 The natural properties of vegetable and animal 
 substances must depend on those of their ele- 
 ments, and consequently on the proportions of 
 
6E*5PHE THEORY. 149 
 
 these. These elements are principally oxygen, 
 hydrogen, azote, and carbon. The first three, 
 naturally -Tfery elastic, enter into solid combina- 
 tions only by means of a force that subdues their 
 elasticity. This again produces more or less 
 effect, according to the temperature or the cir- 
 cumstances which may cause the repressing (con- 
 densing) force to vary. The carbon, on the 
 other hand, must have a great disposition to as- 
 sume the solid state, and to maintain its consti- 
 tution. 
 
„ „„Z„ 
 
 Itt: 
 
 SECTION II. 
 
 OF THE DIFFERENCES WHICH DISTINGUISH WOOL, 
 SILK, COTTON, AND LINEN (FLAX), AND OF THE 
 OPERATIONS BY WHICH THESE SUBSTANCES ARE 
 DISPOSED TO RECEIVE DYES. 
 
 CHAPTER I. 
 
 Considerations on the differences between Animal 
 and Vegetable Substances. 
 
 We must not flatter ourselves that we can account 
 for the different results of organization. The 
 knowledge which we have acquired, however, of 
 the composition of animal and vegetable sub- 
 stances, may, agreeably to the preceding conside- 
 rations, give us some idea of the cause of the dif- 
 ferent tendencies which wool, silk, cotton, and 
 flax have to unite with the colouring particles, 
 and with the bases which constitute their mor- 
 dants. 
 
 Wool and silk belong to animal substances ; 
 cotton, flax, and hemp, to vegetable. 
 
 The principal distinction between the compo- 
 sition of animal and vegetable substances is, that 
 animal substances contain the peculiar principle, 
 
BETWEEN WOOL, SILK, &C. 151 
 
 azote, in abundance, which, in the elastic state, 
 forms what was formerly called phlogisticated air, 
 or phlogisticated gas, and which exists in only a 
 very small quantity in vegetable substances. 2. 
 Animal substances contain much more hydrogen, 
 or the basis of inflammable air.* 
 
 From these two causes the differences observed 
 in the distillation of animal and vegetable sub- 
 stances arise. The former produce much ammo- 
 nia, which is a compound of azote and hydrogen ; 
 the latter yield very little, and they afford usually 
 even a good deal of acid, the characteristic pro- 
 perties of which flow from oxygen. From the 
 former much oil is obtained, whose predominant 
 principle being hydrogen, it has a great tendency 
 to volatilize, and to separate at a slightly elevated 
 temperature. The latter often afford no percep- 
 tible quantity of it. The former can produce 
 
 * Modern researches do not justify this position of M. Ber- 
 thollet. Sugar and starch, by the analyses of MM. Gay Lus • 
 sac and Berzelius, contain about as much hydrogen as fibrin 
 does, and very little less than gelatin and albumen ; while, by 
 my analyses, wool and silk contain less hydrogen than cotton 
 and flax. — See Phil. Trans, for 1822. 
 
 I subjoin the results of my analytical experiments on the 
 four principal subjects of dyeing. 
 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Azote. 
 
 Wool, 
 
 53.70 
 
 2.80 
 
 31.20 
 
 12.30 
 
 Silk, 
 
 50.69 
 
 3.94 
 
 34.04 
 
 11.33 
 
 Cotton, 
 
 42.11 
 
 5.06 
 
 52.83 
 
 
 Flax, 
 
 42.81 
 
 5.50 
 
 ' 51.70 
 
 
 The first two, independently of the azote, possess a marked 
 difference of composition, from their excess of carbon and 
 deficiency of oxygen. — T. 
 
 
152 OF THE DIFFERENCES 
 
 prussic acid, which is a combination of azote, 
 hydrogen, and carbon ; and vegetables possess 
 this property only in so far as they contain azote. 
 In consequence of this composition, animal sub- 
 stances yield, on being burned, a lively flame, 
 which bursts forth at the commencement ; but 
 this flame is, so to speak, speedily quenched by 
 the charcoal that is evolved, which has peculiar 
 characters. Their combustion is accompanied 
 with a penetrating odour, arising from the ammo- 
 nia and oil formed, which escape inflammation. 
 They are subject to putrefaction, during which 
 ammonia is produced, as it is in distillation, by 
 the more intimate union of the azote and the 
 hydrogen ; whereas vegetable substances undergo 
 a spirituous or acid fermentation. We merely 
 indicate in this place ideas which have been de-, 
 veloped in particular memoirs. 
 
 As animal substances contain a great deal of 
 those principles which tend to assume the elastic 
 state, they have less cohesion in their molecules 
 than vegetables, and less stability in their compo- 
 sition. We may observe, that when they acquire 
 solidity, they owe it most frequently to the mix- 
 ture, or rather combination, of a foreign sub- 
 stance, such as the phosphate or carbonate of 
 lime in the bones. 
 
 Hence, they are more subject to be destroyed 
 by different agents, and more disposed to enter 
 into combination with the colouring particles. 
 
 Thus, fixed alkalies, when pure or caustic, de- 
 stroy animal substances, because they combine 
 
BETWEEN WOOL, SILK, &C. 153 
 
 with them to saturation, and thereby lose their 
 causticity.* 
 
 From this action of alkalies on animal substances 
 it follows, that these substances cannot resist leys, 
 and that alkalies must be had recourse to with 
 much caution in the processes wherein such 
 bodies are dyed ; whereas the moderate use of 
 alkalies is not to be dreaded with regard to vege- 
 table substances. 
 
 Nitric and sulphuric acids have also conside- 
 rable action on animal substances. The former 
 decomposes them, with the disengagement of 
 azote, the separation of fat or adipocere, and the 
 formation of carbonic and oxalic acids from a 
 portion of the hydrogen and the charcoal. The 
 latter acid disengages from them inflammable gas, 
 and probably azotic gas, while it reduces the other 
 principles into the carbonaceous state. 
 
 Silk appears to approach a little towards vege- 
 table substances, from its inferior disposition to 
 combine with the colouring particles, and from 
 its greater resistance to the action of alkalies and 
 acids. This may arise either from the same prin- 
 ciples being here more intimately combined than 
 they are in wool, or more probably from the pre- 
 sence in it of less azote and less hydrogen. t But 
 
 although the alkalies and the acids exert a less 
 
 » 
 
 * Mem. de l'Academie, 1783. 
 
 f The organic structure, and state of condensation in ani- 
 mal and vegetable fibres, should be studied along with their 
 chemical composition, in order to learn their dyeing relations. 
 — T. 
 
 

 ) 
 
 154< OF WOOL. 
 
 lively action on silk than on wool, we must never- 
 theless use them with much precaution, because 
 the brilliancy of colour sought for in silk appears 
 to depend on the polish of its surface, which we 
 must beware of injuring. 
 
 Cotton resists the action of acids better than 
 flax and hemp ; and it is with difficulty destroyed 
 even by the nitric acid. 
 
 CHAPTER II. 
 
 Of Wool. 
 
 In the cloth manufactures wool is destined to 
 different purposes, according to the length and 
 fineness of its filaments j but there is a wide dis- 
 tance between the production of fine woolled sheep 
 and ordinary wool. Hence no little gratitude is 
 due to d'Aubenton for fixing public attention on 
 this important object of agricultural economy, 
 and to those individuals who have since prose- 
 cuted, with so much steadiness and success, the 
 project of renovating our degenerate breeds by 
 means of Merinos. 
 
 Wool is naturally coated with a species of fat, 
 called grease. This coating preserves it from 
 the moths'.* Hence it is not scoured till it is 
 going to be spun or dyed. 
 
 * Reaumur remarked, that it was sufficient to rub a stuff 
 with greasy wool to preserve it from moths. Mem. de V Aca- 
 demie, 1728. 
 
OF WOOL. 155 
 
 In order to scour wool, it is put for about a 
 quarter of an hour into a boiler which contains a 
 sufficient quantity of water, mingled with one- 
 fourth of putrefied urine. The whole is then heated 
 as high as the hand can endure it, and it is stirred 
 about from time to time with rods. It is now 
 washed, and set to drain. The wool is removed 
 thence into a large basket, placed in running 
 water, where it is stirred, till the grease having 
 entirely left it, the water ceases to be milky. It 
 is then taken to be drained. In this operation 
 it loses sometimes more than a fourth of its 
 weight. It is of great consequence that the 
 scouring be carefully performed, because the 
 wool is thus alone prepared for receiving the 
 dye. 
 
 The residuum of the first operation is preserved 
 in a tub, to which, from time to time, some putre- 
 fied urine is added, so that the grease present in 
 it may serve to render more soluble any thing 
 adhering to the new wool. The ammonia of the 
 putrefied urine contributes probably to this effect. 
 When wool resists this operation, a little soap is 
 added to the liquor ; but it is only with much 
 precaution that the use of soap is permitted on 
 fine wools, because it is apt to injure them. 
 
 Vauquelin * made experiments on the nature of 
 the grease, from which it appears to be formed, 
 1. of a soap, with basis of potash, which forms its 
 chief part ; 2. of a small quantity of carbonate of 
 
 * Ann. de Chimie, torn, xlvii. 
 
/ 
 
 / 
 / 
 
 156 OF WOOL. 
 
 potash ; 3. of a notable quantity of acetate of 
 potash ; 4. of lime, whose state of combination he 
 could not determine j 5. of a small quantity of 
 muriate of potash ; lastly, of an animal matter, to 
 which he ascribes the peculiar odour of the 
 grease. 
 
 He regards the ammonia contained in the 
 putrefied urine as not being conducive to its ac- 
 tion, and he even advises the use of ordinary soap 
 as better fitted to procure the desired whiteness 
 to wools ; but experience leads to results incom- 
 patible with the opinion of this skilful chemist. 
 
 Wool is dyed in the fleece, or without being 
 spun, principally when it is to be employed for 
 forming cloths of mixed colours ; or otherwise it 
 is dyed after being spun. It is then intended 
 chiefly for carpets, but it is most commonly dyed 
 in the form of cloth. 
 
 When wool is dyed in the fleece, its uncon- 
 nected filaments absorb a greater quantity of the 
 colouring particles than when it is spun ; for a 
 like reason, woollen yarn consumes more colour 
 than woollen cloth. Cloths, however, exhibit 
 much variety among them, according to their 
 degree of fineness, and the closeness of their tex- 
 ture : besides, the difference of their dimensions, 
 the variable qualities of the dyeing ingredients 
 made use of, and the different circumstances of 
 the operations, teach us not to confide in the 
 precise doses enjoined in the processes usually 
 described. This observation may be extended 
 to all dyes. 
 
OF WOOL. 157 
 
 For the generality of dyes, wool requires to be 
 prepared with a bath, in which it is boiled along 
 with saline substances, principally alum and tar- 
 tar. This is called the bouillon, which we shall 
 take care to describe under the different pro- 
 cesses. But there are dyes for which wool needs 
 none of these preparations. It must, however, 
 be well softened in tepid water, and thereafter 
 squeezed, or set to drain. This is a precaution 
 which must in general be taken with all substan- 
 ces which we wish to dye, that the colour may 
 more easily be introduced into them, and more 
 equally distributed. Wool, in particular, requires 
 heat to enable it to absorb the colouring particles ; 
 a circumstance which appears to depend on the 
 disposition of its filaments to form a dense tex- 
 ture. 
 
 Monge has explained the mechanism of felting, 
 and the effects of fulling, by the external confor- 
 mation of wool and the hairs of animals. He has 
 made interesting observations on this subject, of 
 which I shall relate the principal.* 
 
 Nothing peculiar can be discovered on the 
 outside of the fibres of wool and the hairs of ani- 
 mals by means of the microscope ; yet " the 
 surfaces of tnese objects are not smooth ; they 
 must be formed either of plates, which cover each 
 other from the root to the point, nearly as the 
 scales offish overlap each other from the head of 
 
 * Observations sur le Mecanisme du Feutrage. Ann. de 
 Chimie, torn. vi. 
 
} 
 
 158 OF WOOL. 
 
 the animal towards its tail ; or rather perhaps of 
 superposed zones, as is observed in horns. 
 
 " If we seize a hair by the root with one hand, 
 and draw it through the two fingers of the other, 
 from the root towards the point, we experience 
 scarcely any friction, or any resistance, nor do 
 we perceive any noise ; but if, on pinching it by 
 the point, we make it slide equally between the 
 fingers of the other hand, from the point towards 
 the root, we experience a resistance which does 
 not exist in the first case, and a tremulousness 
 perceptible to the touch is produced, which is 
 also manifested by an audible sound. 
 
 " We thus perceive that the contexture of the 
 surface of the hair is not the same from the root 
 J towards the point, as from the point towards the 
 
 root, and that a hair, when pressed, ought to ex- 
 perience more resistance in sliding and taking a 
 / progressive movement towards the point, than in 
 
 / sliding towards the root ; but as this very contex- 
 
 ture forms the principal object of this memoir, it 
 is necessary still farther to confirm it by some 
 other observations. 
 
 " If, after seizing a hair between the thumb 
 and the forefinger, we make the two fingers slide 
 alternately one over the other in the direction 
 of the length of the hair, the hair takes a pro- 
 gressive movement in the direction of its length, 
 and this movement is always towards the root. 
 This effect does not depend either on the nature 
 of the skin of the fingers or on its contexture, 
 for if we turn back the hair, so that its point is 
 
OF WOOL. 
 
 placed where its root was, the movement ta" 
 place reciprocally in the contrary direction j t 
 is to say, it is turned always towards the root. 
 
 " These observations, to which Monge adds 
 some others, are all referred to the hair of his 
 head taken as an example ; but they equally hold 
 true of horse hair, fibres of wool, and in general of 
 the hairs of all animals. The surface of all these 
 objects, therefore, is formed of rigid plates, super- 
 posed or tiled from the root to the point, permitting 
 the progressive movement towards the root, and 
 resisting a similar movement towards the point. 
 
 " This conformation is the main cause of the 
 tendency to felting, which the hairs of all ani- 
 mals in general possess. 
 
 " The hatter, in fact, on striking with the cord 
 of his bow the flocks of wool, detaches and dis- 
 perses in the air each of the particular fibres ; 
 these fibres fall down over one another in all 
 directions on the table, where they form a layer 
 of a certain thickness. The workman then covers 
 them up with a cloth, which he presses with his 
 outstretched hands, working them about in dif- 
 ferent directions. The pressure approximates 
 towards each other the woollen fibres, and multi- 
 plies their points of contact j the agitation gives 
 each of them a progressive movement towards the 
 root. By means of this movement the hairs in- 
 terlace, and the lamellce of each hair, by hooking 
 into those of other hairs which lie in an op- 
 posite direction, maintain the whole in the com- 
 pact texture which the pressure first gave. In 
 
'"••■"■'•. 
 
 OF WOOL. 
 
 Portion as the tissue is compacted, the pressure 
 ; hands ought to increase, both for the fur- 
 fer condensation, and for promoting the progres- 
 sive movement of the hairs, as well as their inter- 
 lacement, which now meets with greater difficul- 
 ty. But in all this operation the fibres of wool 
 grapple only with one another, and not with the 
 cloth, whose fibres, as we have already said, are 
 smooth, and do not present the same facility in 
 this respect. 
 
 " The conformation at the surface, of the fibres 
 of wool and the hairs of animals, does not constitute 
 their sole disposition to felting. It is not enough 
 that every fibre shall take a progressive movement 
 towards the root ; it is not enough that the inclin- 
 ed lamella?, on grappling with one another, shall 
 maintain the texture in the state into which the 
 compression has put it; — it is further requisite, 
 that the fibres shall not be straight like needles ; 
 in consequence of the agitation, each of them 
 would continue its progressive movement without 
 changing its direction, and the effect of the oper- 
 ation would be, to remove them all from the 
 centre without producing any tissue. It is neces- 
 sary, therefore, that each fibre should be twisted, 
 that the extremity which is on the side next the 
 root be disposed continually to change its direc- 
 tion, to interlace itself around new fibres, and to 
 turn back on the fibre itself, if so determined by 
 some change in the position of the rest of its 
 length. Wool being naturally constructed in this 
 manner, is peculiarly well adapted for felting, and 
 
OF WOOL. 161 
 
 may be so employed without being subjected to 
 any previous operation. 
 
 " But the furs of the rabbit, the hare, and the 
 castor, are naturally straight ; they cannot be em- 
 ployed alone for felting, without having under- 
 gone a preliminary operation, which is called se- 
 cretage ; and which consists in rubbing them, be- 
 fore they are stripped off, with a brush moistened 
 with a solution of mercury in nitric acid. This 
 solution, by acting on only one side of the sub- 
 stance of the hairs, alters their right-lined direc- 
 tion, and communicates the disposition for felting 
 which wool naturally possesses. 
 
 " The operation of fulling woollen stuffs, has 
 so close a relation with felting, that we cannot 
 dispense with entering into some details on this 
 subject. 
 
 " The roughness with which the fibres of wool 
 are bristled at their surface, and the disposition 
 which the fibres have to take a progressive move- 
 ment in the direction of the root, is an obstacle 
 to the spinning of wool and to the fabrication of 
 stuffs. In order to spin the wool, and afterwards 
 weave it, we are obliged to coat all the fibres with 
 a film of oil, which, by filling up the cavities, 
 renders the asperities less perceptible; just as a 
 film of oil is put upon a smooth file, when we 
 wish to render it still smoother. When the piece 
 of stuff is manufactured, it must be deprived of 
 this oil, which gives it a disagreeable colour, and 
 constitutes a kind of filthiness, which would be 
 an obstacle to dyeing. For this purpose, it is 
 
 vol. i. l 
 
162 OF WOOL. 
 
 carried to the fulling-mill, where it is beat with 
 mallets in a trough filled with water, through 
 which clay (fuller's earth) has been diffused. 
 The clay combines with the oil, which it renders 
 soluble in water ; both are carried off by the fresh 
 water which the machine itself brings upon it ; 
 and at the end of a certain time the stuff is 
 scoured. 
 
 " But scouring is not the only object of the 
 fulling. The alternate compressions which the 
 beetles exert on the piece of stuff, especially when 
 the scouring is well advanced, produce an effect 
 analogous to that of the hand-pressure of the hat- 
 ter. The fibres of wool which compose one of 
 the threads of the woof or of the warp, take a 
 progressive movement, get introduced into one of 
 the neighbouring threads, then into those which 
 follow, and soon all the threads both of the woof 
 and warp are felted together. The stuff, after 
 having suffered a narrowing in its two dimensions, 
 partakes of the nature both of web and felt ; it 
 may be cut without being liable to open out its 
 threads, and there is no necessity for hemming 
 the different pieces which enter into the compo- 
 sition of a garment. If it be ordinary knit wool, 
 the stitch is no longer apt to run when it hap- 
 pens to escape. Lastly, the threads of the woof 
 and the warp being no longer so well defined, or 
 so distinct from each other, the stuff, which in 
 other respects is thickened, forms a warmer cloth- 
 ing." 
 
OF SILK. 163 
 
 CHAPTER III. 
 
 Of Silk. , I 
 
 'i 
 
 Silk is naturally coated with a substance, which 
 has been regarded as a gum, to which it owes its 
 stiffness and elasticity. The silk most common 
 in our climates, contains besides a yellow colour- 
 ing matter. 
 
 The greater part of the uses to which silk is 
 destined, require it to be not only deprived of its 
 colouring matter, but also of the gum. This two- 
 fold object is accomplished by means of soap. 
 The name of decreusage (scouring), is given to 
 the operation by which silk acquires its pliancy 
 and whiteness. 
 
 The decreusage must not be so complete for 
 the silks which are to be dyed as for those in- 
 tended to remain white ; and it should even differ 
 according to the colours proposed to be given. 
 This difference chiefly consists in the proportion 
 of soap that is employed. Thus, for ordinary 
 colours, we content ourselves with boiling the 
 silk for three or four hours in a solution contain- 
 ing 20 parts of soap for every 100 parts of silk, i 
 taking care to fill up the boiler from time to time 
 with water, in order to have always a sufficiently 
 large bath. The quantity of soap is increased for 
 silks which are to be dyed blue, and more espe- 
 cially for those which are to be dyed ponceau 
 (flesh-red), cherry colour, &c. j because these 
 
164 OF SILK. 
 
 colours require a whiter ground than the less de- 
 licate ones. In treating of each colour, the pro- 
 portions of soap suitable for the silk are indicated. 
 
 When silk is to be used white, it is made to 
 undergo three operations. The first is called 
 degommage (ungumming). It consists in keeping 
 its hanks in a solution of 30 parts of soap for 
 100 of silk. This solution must be very hot, but 
 not in ebullition. When the dipped portion of 
 the hanks is entirely ungummed, which is known 
 by the silk assuming whiteness and flexibility, the 
 hanks are turned about (shaken over) on the 
 rods, in order to subject the portion which had 
 not been plunged to the same operation ; and 
 they are then withdrawn from the bath, and 
 fastened on pegs, in proportion as the ungumming 
 is finished. 
 
 The second operation is the boil. The silks 
 are enclosed in bags of coarse cloth, 12 or 15 
 kilogrammes of silk being put in each bag, called 
 a pocket (poche). A soap-bath similar to the 
 former is prepared, with a smaller proportion of 
 soap j and they are boiled for an hour and a half, 
 taking care to stir about the bags, so that those 
 which touch the bottom may not experience too 
 great a heat. 
 
 The third operation is called whitening (blanchi- 
 ment). This operation is intended principally to 
 give the silk a slight shade, which may render the 
 white more agreeable. Different names are given 
 to the white, according to the shade. Thus 
 we have china-white, silver- white, azure-white, 
 
OF SILK. 16,5 
 
 thread-white. A solution of soap is made, such 
 that, on beating it, a froth is obtained from which 
 we may judge if it be of a proper strength. For 
 the china-white, which should have a somewhat 
 red cast, a little anotto is added. The silk is 
 then left in it till it takes the desired shade. To 
 the other whites more or less of a blue cast is 
 given by means of azure, which is added to the 
 solution of the soap, though some of it has already 
 been put into the boil. 
 
 To prepare the azure, some fine indigo is 
 washed two or three times in water moderately 
 hot, when it is well ground in a mortar, and 
 boiling water is thrown over it. It is allowed to 
 settle, and the liquid is used, which retains only 
 the most subtile parts. This is called azure ; for 
 which may be substituted a little of the liquor 
 of a fresh vat of indigo. 
 
 At Lyons, where a more perfect white is given 
 than at Paris, no soap is employed for the third 
 operation ; but after the second, the silks are 
 washed, sulphured, and passed through azure 
 diffused in river water. In this method, it is of 
 importance to employ a very limpid water. — 
 When the silks have become very uniform, and 
 have taken the wished-for shade, they are wrung 
 out and dried. 
 
 The white obtained by the method now pointed 
 out, is not brilliant enough for silks intended for 
 white stuffs. They must still be exposed to the 
 fumes of sulphur. This operation will be des- 
 cribed in the article on sulphur. 
 
 I 
 
166 OF SILK. 
 
 Since soap appears to injure the lustre of silk, 
 the Academy of Lyons proposed, in I76I, as the 
 subject of a prize, to find a method of scouring 
 (decreuser) silks without soap ; and this prize 
 was adjudged to Rigaut de St Quentin, who pro- 
 posed to substitute for soap a solution of salt 
 of soda, or carbonate of soda, dissolved in a 
 quantity of water large enough not to affect the 
 silk. But inconveniencies must have been found 
 in the employment of this method, which was 
 probably too active, since no use is made of it, 
 although it is known, and may be easily practised. 
 
 Collomb* published some observations on the 
 bleaching of silk by the action of water alone, 
 which merit much attention. Having perceived 
 that a hank of yellow silk, which he had boiled 
 about three hours in common water, had lost 
 nearly an eighth of its weight, he repeated the 
 ebullition twice, and carried by this means the 
 diminution of weight to a fourth. 
 
 The silk which suffered this loss of weight, 
 preserves, however, a yellow, or rather a chamois 
 colour, which renders it unfit for making stuffs 
 intended to remain white, or to receive some 
 colours whose beauty depends on the whiteness 
 of the ground to which they are applied ; but it 
 answers very well for colours which that tinge 
 cannot injure. Thus the black dye which it 
 took appeared preferable to that of silk bleach- 
 ed with soap. 
 
 * Observations sur la Dissolution du Vernis de la Soie. 
 Journ. de Phys. Aout 1785. 
 
OF SILK. 167 
 
 After this operation, the silk remains very 
 strong and sinewy (yierveuse) ; and threads of it 
 supported weights which broke threads bleached 
 with soap. 
 
 Eight hours of brisk ebullition are required 
 for dissolving away the whole varnish of silk, in 
 which it loses a little more than one-fourth of its 
 weight; but the ebullition ought to last longer 
 when the barometer is low, because the greater 
 the weight of the atmosphere, the higher is the 
 degree of heat which boiling water takes. 
 
 This consideration led Collomb to try the 
 boiling of silk in a Papin's digester ; and in fact 
 it required only an hour and a quarter to effect 
 the complete solution of the varnish, although the 
 degree of heat was inferior to what produced 
 some of the phenomena observed by philosophers 
 in this concentrated ebullition. 
 
 The substance which the water dissolved, when 
 evaporated, is black, brittle, and brilliant in its 
 fracture. On distillation, it afforded the usual 
 products of animal matter. It dissolved readily 
 in hot water, leaving very little on the filter. 
 The solution, which was clear, and of a greenish- 
 yellow colour, was not sensibly affected by acids 
 or alkalies. 
 
 The solution of alum produced in it a precipi- 
 tate of a dirty-white colour ; that of sulphate of 
 copper, a black-brown precipitate ; that of sul- 
 phate of iron, a brown precipitate ; the nitro- 
 muriatic solution of tin, a white precipitate ; the 
 acetate of lead, a brown precipitate. 
 
168 Of SILK. 
 
 All these precipitates are scanty, and more or 
 less viscid. Infusion of nut-galls, and of sumach, 
 occasioned a white precipitate. 
 
 Alcohol does not dissolve this substance even 
 by ebullition, but only a yellow colouring portion. 
 This solution left, on evaporation, a scaly resi- 
 duum of an amber-yellow. On boiling a gramme 
 of this substance in 100 grammes of alcohol, 
 containing some drops of muriatic acid, its solu- 
 tion was effected ; but, on cooling, this substance 
 took the form of jelly. 
 
 The substance taken from silk in the scouring 
 (decreusagej, is therefore of an animal nature ; 
 whence the soap water which has served for the 
 scouring speedily putrefies. When this substance 
 is no longer retained by its affinity for silk, it 
 becomes soluble in water, but not in alcohol. 
 Although it is not of a vegetable nature, the 
 term gum seems sufficiently proper. The yellow 
 colouring matter dissolves in alcohol. When this 
 part is separated, the gum becomes brown. It 
 would seem that this colour is caused by the heat 
 of ebullition, since, when the yellow colouring 
 portion only is removed, by the process of Baume, 
 of which we shall presently speak, the silk re- 
 mains white. 
 
 In the process of Collomb, the gum is removed, 
 carrying with it only a portion of the yellow co- 
 louring particles ; while, in scouring with soap, 
 the gum, and yellow colouring parts, are both 
 carried off from the silk. 
 
OF SILK. 169 
 
 When silk is intended for the manufacture of 
 blonds, laces, and gauzes, it should have its na- 
 tural stiffness and elasticity. The greater part 
 of the silk produced in our climates has a yellow 
 colour. The white silk of China is therefore 
 principally employed for these objects, and a few 
 others. It is not yet positively ascertained 
 whether the Chinese silk is naturally white, or 
 rendered so by some unknown process.^ Accord- 
 ing to Poivre, this silk is bleached by exposing it 
 to the sun. But some other circumstance is ne- 
 cessary ; for this method has been tried without 
 success. Baume has published a process which 
 he considers as analogous to the Chinese one.* 
 
 This process consists, 1. In infusing the yellow 
 silk, or that which has not naturally a sufficiently 
 pure white, in water heated to 25° Reaum., to 
 destroy the mutual adherence which the threads 
 had contracted in the winding ; 2. In making this 
 silk undergo two successive macerations, longer 
 or shorter according to the temperature, in a mix- 
 ture of alcohol containing l-64th of its weight of 
 muriatic acid ; 3. In washing the silk with much 
 care immediately after this operation, which, on 
 losing its colouring part, has given up but a por- 
 tion of its gum ; 4. In drying this silk in a state 
 of extension, to hinder it from crisping. The 
 muriatic acid employed ought to be thoroughly 
 free from the nitric acid, which gives, as we have 
 seen, a yellow colour to animal substances. For 
 
 * Ann. de Chimie, torn. xvii. 
 
170 OF SILK. 
 
 the same reason, such muriatic acid must be 
 avoided as has been rendered yellow by chlorine. 
 Hermstadt affirms, that he repeated this operation 
 with success. 
 
 A skilful chemist, Giobert, makes objections 
 to this process, for which he substitutes a new 
 one. We shall remark, meanwhile, that in his 
 experiments he employed l-48th of muriatic acid, 
 while Baume prescribed only l-64th. We shall 
 here present the extract which has been given of 
 his work.* 
 
 " The preparation of the acid pointed out by 
 Baume is very embarrassing. The green colour 
 which the liquid assumes, the species of jelly 
 which it forms around each filament, and still 
 more the diminution of weight' in the silk, are 
 sufficient to indicate, that it would not be correct 
 to view in the action of this liquid only the des- 
 truction of the colouring matter. Even in re- 
 taining a portion of its rawness fcrndj, the silk 
 is far from preserving so much of it as is desired 
 in the arts ; and this process, which involves con- 
 siderable expense, becomes more costly than is 
 imagined, from the diminution in the weight of 
 the silk. 
 
 " Crell and Brugnatelli proposed chlorine. But 
 it is known, that silk comports itself in the same 
 way with this acid as animal substances do, that 
 is to say, it becomes yellow. Yet we shall pre- 
 sently see that it may be employed. When this 
 
 * Bibliot. Ital. torn. i. 
 
TT^ 
 
 ) 
 
 OF SILK. 171 ) 
 
 substance is used in the form of gas, Giobert 
 found that the silk was soon destroyed by it. 
 
 " On employing it in the state of a pretty con- 
 centrated solution, the yellow colour becomes 
 weaker, and apparently approaches to white ; 
 but on taking it out of the aqueous chlorine, the 
 silk is of a yellowish colour, and this hue is more 
 durable than its natural one. 
 
 " From this result it appears that chlorine ex- 
 ercises on silk a twofold action ; that is to say, it 
 destroys its colouring matter on the one hand, 
 and on the other, it makes the same impression 
 as on animal substances in general — a change in- 
 dicated by a yellow tinge. 
 
 " This last impression is destroyed by the 
 action of sulphurous acid ; and it is in the com- 
 bined and alternating action of it and chlorine 
 that the author has attempted a new mode of 
 bleaching. 
 
 " In the preceding experiments, and in all 
 those where aqueous chlorine, however little con- 
 centrated, was employed, Giobert observed that 
 the silk was considerably weakened. Very fre- 
 quently, after being well washed, the filaments 
 broke in the wringing. 
 
 " The same liquor diluted to a great degree 
 no longer produced this effect, yet it exerted a 
 well marked action on the colouring matter of 
 the silk. On coming out of it, the silk retains 
 a portion of its natural colour, and being a little 
 oxygenated by the agency of the chlorine, it ex- 
 hibits its effects and appearances. 
 
 
 \ 
 
172 OF SILK. 
 
 ." On passing it then into liquid sulphurous 
 acid, also very dilute, the yellow tint is destroyed. 
 
 " Giobert has succeeded in whitening- the silk 
 completely, and preserving its raw feel, by pass- 
 ing it alternately through these two liquids for 
 ten or twelve times, finishing the operation with 
 the sulphurous acid. 
 
 " It is of the greatest importance to multiply 
 the immersions, and not to employ strong gaseous 
 impregnations, by which the silk would be either 
 destroyed or considerably weakened. 
 
 " Silk bleached by this method is scarcely 
 diminished in weight. It retains its raw feel, its 
 flexibility, and does not appear to get stiff, while 
 the bleaching is uniform in all its parts. 
 
 " When it was compared with the silk bleached 
 by the process of Baume, the latter was found to 
 present a more agreeable gloss, while the former 
 had merely a dead-white. This circumstance 
 does not appear to Giobert very important, be- 
 cause the chief use of bleached raw silk is in the 
 manufacture of gauzes ; and much gloss is not 
 required in this kind of stuffs. 
 
 " The dyers believe that silk which has re- 
 ceived the fumes of sulphur is not well adapted 
 to receive colours. Giobert attempted to rectify 
 this principle, with raw silk bleached by the pro- 
 cess just detailed. This silk took every colour, 
 and particularly the finest black." 
 
 Aluming ought to be considered as one of the 
 general operations of silk dyeing, because with- 
 
OF SILK. 173 
 
 out alum the most part of colours applied to silk 
 would possess neither beauty nor permanence. 
 
 To execute the aluming there is put into a tun 
 or tub about 40 or 50 buckets of water, and 20 
 or 9,5 kilogrammes of Roman alum, previously 
 dissolved in a kettle-full of sufficiently hot water, 
 stirring carefully during the mixture, to prevent 
 the crystallization of the alum. 
 
 After washing and beetling the silks, and even 
 wringing them on the jack and pin,* to extract 
 the soap which they may have retained, they are 
 plunged into the alum bath. Here they are left 
 for eight or nine hours, after which they are 
 twisted by hand over the tun (vat), and taken to 
 the river to be washed. 
 
 We may pass as much as J5 kilogrammes of 
 silk through a bath like the preceding, without 
 being under the necessity of adding fresh alum. 
 But when it is perceived that the bath begins to 
 become weak, which habit teaches by the taste, 
 10 or 12 kilogrammes of alum are dissolved, 
 which are put into the bath, as at first ; and thus 
 it is continually renewed, till it begins to emit a 
 disagreeable smell. It is then thoroughly ex- 
 hausted by passing the silks through it which are 
 intended for dull colours, such as browns, ches- 
 nuts ; after which it is emptied out, and a new 
 alum liquor formed. 
 
 * The usual frame for wringing hanks of yarn, with the aid 
 of a screwed rod. — T. 
 
174 OF COTTON. 
 
 Silks are always alumed in the cold, because, 
 when they are alumed in a hot bath, they are apt 
 to lose a portion of their lustre. 
 
 CHAPTER IV. 
 
 Of Cotton. 
 
 Cotton is the down or wool (bourre) contain- 
 ed in the pod of a plant which grows in hot 
 \ countries. This down is separated from the 
 
 seeds which it envelops by means of a kind of 
 j mill. 
 
 /, \ Climate has a great influence on the qualities 
 
 / J of cotton, and the species of the cotton plant 
 
 j I seem to correspond to the degree of heat." But 
 
 a great variety are found in the West India 
 I islands ; and it appears from what Bennet says,f 
 
 that the colonists have hitherto neglected to make 
 a selection of those which would be most advan- 
 tageous, whence they have lost a great part of 
 the benefits which they might have derived from 
 this valuable production. 
 ,/ Five species of the cotton shrub have been dis- 
 
 tinguished, which contain many varieties. Lin- 
 naeus has distinguished these five species by the 
 following names : gossypeum arboreum, or the 
 
 * Essais sur les Caracteres qui distinguent les Cotons des 
 1 diverses parties du monde, &c. par M. Quatremere Disjonval. 
 
 f Transactions of the Society instituted at London for the 
 Encouragement of Arts, Manufactures, and Commerce, vol. i. 
 
OF COTTON. 
 
 175 
 
 cotton tree of India ; gossypeum religiosum, a 
 great shrub which grows also in India ; gossy- 
 peum Barbadense, a biennial shrub cultivated in 
 Barbadoes; gossypeum hirsutum, a shrub which 
 is perennial in the hot climates of America, and 
 annual in the cold ; gossypeum herbaceum, which 
 seems to be originally from Persia, but which is 
 cultivated in the islands of the Archipelago, in 
 Egypt, Malta, and Sicily. The Russians culti- 
 vate it even in the government of Caucasus. 
 
 To these species may be added the cotton of 
 Siam, remarkable for the fineness and silkiness of 
 its filaments. 
 
 According to Guthrie, there has been cultivat- 
 ed for some time in Germany an asclepias, ascle- 
 pias syriaca, Linn, which yields a very silky spe- 
 cies of cotton.* Manufactures have been esta- 
 blished in Saxony of stuffs with this cotton, which 
 rival silk in lustre. 
 
 The principal differences of cotton consist in 
 the length of its filaments, their fineness, their 
 solidity, and their colour. In the last point of 
 view, several species are distinguished in com- 
 merce, which differ not only in their absolute 
 value, but also in the uses for which they are 
 intended. 
 
 The colour of cotton varies from deep yellow 
 to white. The highest coloured is that of Siam 
 and Bengal ; with which stuffs are often made 
 that preserve the native hue. 
 
 * Memoirs of Manchester, vol. v. part 1. 
 
 7 
 
( 
 
 176 OF COTTON. 
 
 Cotton has become, by the extent and variety 
 of its uses, one of the principal objects of manu- 
 factures and commerce. From its manufacture 
 being conducted with little expense of labour, 
 India has particularly derived much of the trea- 
 sure constantly poured into it. 
 
 A nation celebrated for its genius in the arts, 
 has succeeded in compensating the difference 
 in the rate of wages by the expedition of ma- 
 chinery, and has thus drawn into its bosom this 
 source of prosperity. It must preserve exclu- 
 sively the great advantages which it now derives, 
 were other nations not to endeavour to promote, 
 by particular measures of administration, a com- 
 petition of manufacture capable of supporting a 
 part of their population.* 
 
 * Some respectable philosophers, while claiming freedom 
 for commerce and industry, appear to have made too wide 
 an application of their principles of political economy, when 
 they inveigh against those restraints which the vigilance of 
 government puts on the introduction of particular products 
 of foreign manufacture. 
 
 When manufactures have acquired a marked superiority by 
 peculiar processes, when long practice has carried these pro- 
 cesses to perfection, and when the dexterity acquired by their 
 workmen bids defiance to competition, we must for ever re- 
 nounce them, or these advantages must be balanced by import 
 duties, or even by prohibitions. 
 
 It is said, that we thereby force capital into other directions 
 less natural and advantageous. This maxim is true with re- 
 gard to objects in which manufactures possess natural advan- 
 tages or disadvantages. 
 
 But when merely temporary disadvantages are to be coun- 
 tervailed, when an object of great consumption is concerned, 
 
OF COTTON. 177 
 
 To prepare cotton to receive the dye, it is sub- 
 jected to an operation, called in French decreu- 
 sage (scouring). Some persons boil it in sour 
 water ; but most frequently an alkaline ley is 
 employed. In this the cotton is boiled for two 
 hours, after which it is wrung out. It is then 
 rinsed in the river till the water runs off clear, 
 when it is dried. 
 
 Cotton cloth intended for printing is immersed 
 for some time in water charged with one-fiftieth 
 at most of sulphuric acid, after which it is wash- 
 ed with care in running water, and dried. The 
 acid used in this operation dissolves the calca- 
 reous earth, and the oxide of iron, which might 
 have injured the colours. 
 
 The al uming is given in the proportion of a 
 quarter of alum for one part of cotton. The 
 alum is dissolved with the precautions pointed 
 out in the preceding article, but a solution of 
 soda is added to it, which may be estimated at 
 about one part of soda for six of alum. Some 
 persons introduce a very small quantity of tartar 
 and arsenic. The yarn is well impregnated with 
 this solution, by working it in small portions ; 
 
 which may afford employment to a large portion of the popu- 
 lation, it is the interest of the consumers themselves to sub- 
 mit to a temporary impost, which may serve as a premium to 
 a new branch of industry, and may even create sufficient capi- 
 tals to those who undertake it, by affording extraordinary 
 profits up to a certain stage. They are in the predicament 
 of a landed proprietor, who renounces, for some time, a part 
 of his revenue, to establish a canal of irrigation on his estate. 
 VOL. I. M 
 
178 OF COTTON* 
 
 after which the remainder of the bath is poured 
 upon the whole yarn collected in a vessel. It is 
 left there for twenty-four hours. On coming out 
 of the aluming, it is set to purge itself in running 
 water for an hour and a half or two hours, and it 
 is then washed. Cotton absorbs about one-for- 
 tieth of its weight in this operation. 
 
 The galling is made with different proportions 
 of gall-nuts or other astringents, according to the 
 quality of the astringent, and the effect wished to 
 be obtained. 
 
 The gall-nuts, bruised, are to be boiled about 
 two hours in a quantity of water, which ought to 
 be proportioned to the quantity of yarn to be 
 galled. The bath is then allowed to cool, so that 
 the hand may bear dipping in it. It is divided 
 into portions, which are made as equal as possible, 
 in order to operate with small parcels, as is men- 
 tioned under aluming ; and the remaining liquor 
 is in like manner thrown over the whole. Here it 
 is left for 24 hours, especially when it is intended 
 for maddering and for black ; with regard to 
 other colours, from 12 to 15 hours may suffice ; 
 after which it is wrung out and dried. 
 
 When the galling is given to stuffs that have 
 already received a colour, it must be done in the 
 cold, in order not to alter this colour. 
 
 Alumed cotton takes a greater increase of 
 weight in the galling than what is not alumed ; 
 for although alumina fixes in only small quan- 
 tity on cotton, it communicates to it the property 
 
OF FLAX AND HEMP. 179 
 
 of combining much better with the astringent 
 principle, as also with the colouring particles. 
 
 CHAPTER V. 
 
 Of Flax and Hemp. 
 
 Since flax and hemp present the same proper- 
 ties, in reference to dyeing, they are usually con- 
 founded together in this work. 
 
 If cotton be an important object to our indus- 
 try, flax and hemp merit peculiar attention, both 
 as a territorial production, and as the most exten- 
 sive source of employment to the people. This 
 manufacture is spread over the whole country, 
 and is subdivided into branches, from the fabrica- 
 tion of cordage to that of lace, and it fills up the 
 chasms of rural labours. 
 
 One consideration which ought not to be over- 
 looked, is, that the land most proper for hemp is 
 that of marshes, from which the water has been 
 drained, and that it is a production particularly 
 adapted to small cultivators.* 
 
 Flax and hemp must undergo several prepara- 
 tions before they can receive a dye. The first is 
 steeping, by which the bark of the plant is ren- 
 dered separable, so as to become fit for spinning. 
 Steeping is an operation of such importance, from 
 the influence which it possesses on the quality 
 
 * Instruction familiere sur la Culture etleRouidu Chanvre, 
 a l'usage des gens de la campagne, par Pertuis. 
 
180 OF FLAX 
 
 and quantity of the product, and from the dele- 
 terious qualities which it may communicate to 
 the air, that it is proper to give some idea of the 
 principles on which it should be conducted. The 
 steeping of flax, in particular, has engaged the at- 
 tention of practical men. 
 
 In steeping, it appears that a glutinous juice, 
 which holds the green colouring part of the plant 
 in solution, and which unites its cortical with its 
 ligneous portion, suffers a more or less complete 
 putrefaction, according to the method employed ; 
 for, as Rozier remarked,* carbonic acid gas and 
 inflammable gas are disengaged. This substance 
 seems to resemble closely the glutinous portion 
 dissolved in the juice expressed from green plants, 
 which is separated along with the colouring par- 
 ticles when it is exposed to a heat bordering on 
 ebullition, and which putrefies, and yields ammo- 
 nia by distillation. 
 
 Although this substance be held in solution in 
 the expressed juice of plants, there is a probabili- 
 ty that water alone cannot separate it sufficiently 
 from the cortical part ; and hemp which has been 
 steeped in too rapid a stream, wants pliancy and 
 softness. 
 
 If the steeping be performed in stagnant waters, 
 the hemp contracts a brown colour ; but, above 
 all, it loses its durability, and exhales vapours 
 productive of dangerous maladies. What is steep- 
 ed by exposing it merely to the action of the 
 
 * Essai sur la Culture et le Rouissage du Clianvre, par 
 1'Abbe Rozier. 
 
AND HEMP. 181 
 
 elements on the ground, is also weakened, and 
 requires much time and manual labour. 
 
 It appears, therefore, that steeping is performed 
 in the most advantageous manner in tanks placed 
 on the banks of rivers, in which the water may 
 be renewed, so much as to prevent a putrefaction 
 hurtful to the hemp and detrimental to health, 
 without obstructing the putrefaction necessary to 
 render the glutinous substance soluble in water. 
 
 Rozier found, that the steeping process went 
 on when the hemp was covered with a layer of 
 earth, and he recommends this method ; but it 
 has been ascertained that the hemp was too easily 
 affected in this operation, 
 
 Proset* has proposed to mix a small quantity 
 of caustic alkali with the / water in which the 
 steeping takes place, in order to increase its sol- 
 vent power, and to prevent the putrefaction j but 
 it appears from the experiments of Home, that 
 alkalies retard the operation of the steeping, and 
 render the flax liable to break.t 
 
 During the maceration, as well as the previous 
 and subsequent drying, the green colouring par- 
 ticles suffer an alteration, like that observed in the 
 green substance of plants which have been ex- 
 posed to the action of air and the influence of 
 light. Their colour passes to yellow, dun, or 
 even brown, by an agency which we have com- 
 pared to that of a slight combustion. 
 
 * Mem. sur le Rouissage tlu Chanvre. 
 f Essay on Bleaching. 
 
182 OF FLAX 
 
 That substance is partly reduced into powder, 
 which is dispersed during the dressing, rendering 
 this operation dangerous to those who practise it. 
 Another portion remains attached to the fibres ; 
 but perhaps dissolved in the alkaline leys em- 
 ployed before the bleaching, whereby all this fo- 
 reign matter ought to be separated. 
 
 For avoiding the acrid dust which rises during 
 the hatcheling, Marcandier has recommended to 
 macerate the fibres in small portions in hot water, 
 to wash them with much care, and thereafter to 
 dry them. By this means we may diminish the 
 colouring matter, and render the flax or hemp 
 softer and better prepared for the action of the 
 hackle. He has even suggested the use of an 
 alkaline solution.* 
 
 On a more complete solution of the colouring 
 particles, is founded a process published by the 
 Prince de Saint-Sever, to obtain fine dressed 
 hemp.t He recommends to put the tress of hemp 
 in a ley made with a solution of two parts of soda 
 to one of lime, next to impregnate it with soap, 
 to digest it for some time, then to wash it well, 
 and lastly, to hackle it. Several processes analo- 
 gous to the preceding have since then been prac- 
 tised, under the veil of mystery. Their results 
 had an imposing aspect. But experience has suf- 
 ficiently shown, that besides the expense which 
 they incurred, these processes increased the pro- 
 portion of tow, and the yarn obtained had less 
 
 * Traite de Chanvre. 
 
 f Journ. de Physique, introd. torn. ii. 
 
AND HEMP. 183 
 
 durability, and little advantage in beauty over 
 the yarn yielded by the unprepared hemp. 
 
 Bralle, an old curate of the department of the 
 Somme, occupied himself regularly for several 
 years with the means of improving the prepa- 
 ration of hemp, as an object of great national in- 
 terest. His first attempts consisted in steeping 
 hemp, as soon as it was taken from the ground. 
 On coming out of the steeping, he separated the 
 bark from it, which easily came off. After cutting 
 the stem near the root, and dipping it in a weak 
 solution of black soap, he washed it with much 
 care before desiccation. The colouring portion 
 which would have become insoluble, except in 
 alkalies, may also be dissolved and carried off by 
 water assisted by a little soap. The fibre is then 
 much whiter. By combining the action of the 
 sun with this process, he succeeded in making it 
 still whiter. 
 
 These operations had the inconvenience of re- 
 quiring long and minute manipulations. Bralle, 
 however, hit upon a process, by which a large 
 quantity of hemp may be steeped in a few hours, 
 with the advantage of freeing the stems from 
 their bark without any waste, of preserving the 
 length of the fibres, and consequently of produc- 
 ing much less tow. 
 
 The process of Bralle, whose efficacy has been 
 verified at the Conservatoire des Arts on hemp 
 intended for cordage and sail-cloth, has just been 
 published by order of government. It consists 
 in keeping the hemp plunged for two hours in 
 
184 OF FLAX 
 
 water, containing a forty-eighth part of green soap 
 (soft soap) in solution, which is maintained at a 
 temperature of from 72° to 75° Reaum. (Note I.) 
 
 A mode has been discovered of giving to the 
 dressed hemp, and even to the tow, a division 
 and fineness which qualify it for the same spin- 
 ning processes as cotton ; so that with this prepa- 
 ration alone, or mixed with cotton, stuffs may be 
 made which have a much more considerable va- 
 lue, than those of hemp in its natural state. 
 
 Marcandier seems to be the first who engaged 
 in this process. He recommends to give to the 
 tow, first of all, the preparation which he pre- 
 scribed for the dressed hemp. In carding it like 
 wool, a fine medullary white substance is got, for 
 which heretofore no use was known. It can be em- 
 ployed by itself in this state, not only to make ouates 
 (fine cotton), which, in many respects, is better 
 than the ordinary ouates, but it may also be spun 
 into a very fine yarn. It may likewise be mixed 
 with cotton, silk, wool, and even hair ; and the 
 yarn resulting from these different mixtures, fur- 
 nishes, in its numberless variety, materials for new 
 trials interesting to the arts, and to several manu- 
 factures. 
 
 This object has engaged much attention in 
 Germany. Hennstadt quotes several works which 
 treat of it* He states, that, according to Meidin- 
 ger, the staple of hemp acquires the elasticity of 
 cotton, when, after being purified by a solution of 
 
 * Grundriss der Farberkunst. 
 
AND HEMP. 185 
 
 potash and muriate of soda, it is fixed on cylin- 
 ders of wood, and dried in a stove. It is also as- 
 serted, says Hermstadt, that hemp takes a fine 
 texture when its moist fibres are put into a wood- 
 en chest, with alternate layers of wood-ashes, 
 closing the chest with a cover, and putting it 
 into a stove, heated not just so high as to burn 
 the wood. 
 
 Hermstadt informs us, that the hempen webs 
 which have received these preparations, lose 
 the appearances of cotton by repeated wash- 
 ings. 
 
 In treating of bleaching with oxygenated 
 muriatic acid, another process will be pointed 
 out. 
 
 Flax and, hemp intended to be dyed, must be 
 subjected to the same operations as cotton, name- 
 ly scouring (decreusage), aluming, and galling. 
 
186 
 
 OF BLEACHING. 
 
 SECTION III. 
 
 OF BLEACHING BY THE OXYGENATED MURIATIC 
 
 ACID. 
 
 INTRODUCTION. 
 
 The art of bleaching by oxygenated muriatic 
 acid (chlorine), is a direct application of the che- 
 mical properties of this acid ; for the first know- 
 ledge of which we are indebted to Scheele, but 
 which were developed and submitted to a regular 
 theory in 1785. 
 
 At this period, the first attempts at applying 
 this acid (now the element chlorine) to bleaching 
 were promulgated. These were soon prosecuted 
 in England by the celebrated "Watt, and after- 
 wards by Bonjour, Descroizille, Welter, Widmer, 
 and Haussmann. A description of this art, still 
 in its infancy, was published in the Annales de 
 Chimie for 1789 ; meanwhile it continued to 
 make some advances, which were successively 
 published. A second description was given of it, 
 chiefly on the data of Welter,* who had perse- 
 
 * Journal des Arts et Manufactures. An. 3. 
 
«=-i- . 
 
 
 OF BLEACHING. 187 
 
 vered in its practice on the great scale ; and those 
 who are acquainted with this able chemist, know 
 what confidence may be reposed in his observa- 
 tions. • 
 
 Since then, different treatises on this process 
 have appeared. We shall here give an idea of 
 such of them as have come to our knowledge. 
 
 Pajot des Charmes published one, * which ap- 
 peared in the year 8. In this, he speaks only of 
 the first description which had been given in the 
 Annales, and neglects one which had been made 
 public five years before his own work, and of 
 which several separate editions had been given. 
 
 He represents the process which had been pro- 
 mulgated as very difficult to execute ; but the 
 corrections which he pretended to introduce, do 
 not appear to us to have any other effect than to 
 diminish its precision or advantages. Thus he 
 suppresses the intermediate vessel, which we con- 
 sidered to be useful. He recommends, as a very 
 beneficial change, to substitute leaden tubes for 
 those of glass. He mixes potash with the liquor 
 (aqueous chlorine) to suppress its odour, the ef- 
 fect of which mixture had been appreciated in 
 the original description : he regards the odour of 
 oxygenated muriatic acid, in the way it had been 
 prescribed, as an insurmountable obstacle ; and 
 he gives an account of the distress which he had 
 suffered in repeating this process. He would 
 
 * L'Art du Blanchiment des Toiles, Fils, et Coton de tout 
 genre. 
 
188 
 
 OF BLEACHING. 
 
 have become satisfied that the process might be 
 executed without inconvenience, had he carefully 
 followed the directions, or had he visited the 
 establishments conducted by Widmer, Welter, or 
 several others who used it at that period. He 
 exclaims against the length to which the prescrib- 
 ed number of leys and immersions must give rise. 
 The limits of this number had been said to be be- 
 tweenjbur and eight, and we find (page 106 of his 
 treatise) that he increases the leys to six, and the 
 immersions to seven. He gives, moreover, a pro- 
 cess for making sulphuric acid, by which sul- 
 phurous acid only can be obtained, &c. 
 
 Chaptal published a notice about a process 
 long used for bleaching cotton in the southern 
 parts of France,* which had been pointed out in 
 our second account of bleaching. The cotton is 
 impregnated with a solution of soda, and sub- 
 jected to the vapour of boiling water in a close 
 vessel, where this vapour suffers compression j 
 after which it is exposed for some days on the 
 grass. This process gave occasion to O'Reilly 
 to publish a work on bleaching.t We shall not 
 discuss the method which he there extols, because 
 his assertions have not hitherto been confirmed 
 by the experiments to which they led several 
 operators. We shall merely remark, that in the 
 same work he describes an apparatus as well 
 adapted to the preparation of oxygenated muri- 
 
 * Bulletin de la Soci6te Philomatique. 
 f Essai sur le Blanchiment. 
 
 Brumaire, An. 8. 
 
OF BLEACHING. J89 
 
 atic acid ; but this apparatus is such, that the 
 vapour of the oxygenated muriatic acid, by its 
 elastic action, would cause all the water of the 
 intermediate vessel to spout out by the tube of 
 safety, which in fact would soon be emptied by 
 the same cause. Several of his details shew that 
 he described from imagination. 
 
 We owe to Westrumb* a work on the new 
 mode of bleaching ; but this skilful chemist in- 
 timates, that he describes this art only from his 
 own trials, without taking into account what ex- 
 perience had taught to actual practitioners. Rupp 
 has given interesting experiments on this subject, 
 of some of which we shall avail ourselves, t 
 
 We do not hope always to make the best se- 
 lection in the operations which we are about to 
 describe ; but we shall be guided particularly by 
 the observations of Widmer and Welter, who 
 have conducted this process for several years 
 with increasing success. We shall not advance, 
 on views simply conjectural, even the modifica- 
 tions which might be contrived ; but experience 
 will undoubtedly teach us more and more to sim- 
 plify, improve, and extend the usefulness of the 
 process. Those who wish to employ it only on 
 inconsiderable objects, by neglecting trifling in- 
 terests, or by resting satisfied with partial effects, 
 may easily simplify both the apparatus and the 
 manipulations. 
 
 * Bemerkungen and Vorschlagc fur Bleichcr. 
 f Mem. of Manchester, vol. v. 
 
190 
 
 THEORY 
 
 In particular cases, bleaching may be greatly 
 abridged, and even reduced to a few hours ; but 
 we must study, in a manufacture, to establish a 
 series of operations, the success of which shall be 
 proof against accidents, and which shall steadily 
 procure employment to the same workmen, ra- 
 ther than accelerate any particular process. 
 
 CHAPTER I. 
 
 Theory of Bleaching. 
 
 Chemistry has made such progress in our times, 
 as to render an acquaintance with it indispensable 
 to the practice of several arts ; but the one which 
 has for its object the bleaching of yarn and cloth 
 by the oxygenated muriatic acid, requires, in par- 
 ticular, an operator to whom the science is not 
 unknown. 
 
 Oxygenated muriatic acid (chlorine), is the 
 agent substituted in this mode of bleaching for 
 atmospherical air, which requires tedious expo- 
 sure on the grass. For directing its preparation 
 and effects, we must therefore be well skilled in 
 its properties. 
 
 Muriatic acid (the marine acid of the old 
 chemists, and the hydrochloric of the modern 
 French school) combines with oxygen, and there- 
 by assumes the properties of oxygenated muriatic 
 acid ; but to make this combination effective, the 
 oxygen must have lost its elastic state. Thus 
 
OF BLEACHING. 191 
 
 it exists in the oxide of manganese (manganese 
 of commerce) in very considerable quantity. 
 When, therefore, one part of oxide of manganese 
 is mixed with four parts of the fuming, or six 
 parts of ordinary muriatic acid, one portion of 
 the acid combines with the oxide of manganese, 
 with the disengagement of the oxygen superfluous 
 to this combination, which combining immediately 
 with another portion of the muriatic acid, thus 
 forms the oxygenated muriatic. The operation 
 is promoted and completed by the action of heat. 
 The oxygenated muriatic acid assumes on its 
 separation the gaseous state, when it is soluble 
 in water. The resulting liquid is of a greenish- 
 yellow colour, and of a very penetrating odour. 
 If the temperature approaches that of freezing 
 water, the oxygenated muriatic acid gas becomes 
 concrete, and adheres to the tube which conducts 
 it into the water, whence it precipitates, so that 
 the liquid is less impregnated than at a somewhat 
 higher temperature. 
 
 It is easy to shew that the oxide of manganese 
 contains much oxygen ; for on urging it with a 
 strong fire, it evolves a great quantity ; after 
 which the oxide can produce but very little oxy- 
 genated muriatic acid. 
 
 We may be easily satisfied also of the existence 
 of oxygen in the oxygenated muriatic acid. We 
 have only to expose to the light of the sun a 
 phial filled with the above liquid, from which 
 phial a bent tube dips under a receiver filled with 
 water. Bubbles of air are soon disengaged, which 
 
192 THEORY 
 
 pass into the receiver, constituting an elastic fluid, 
 which possesses all the properties of pure air or 
 oxygen gas. When these bubbles cease to issue, 
 the liquid has lost its odour, colour, and all its 
 distinctive properties. It is now water impreg- 
 nated with ordinary muriatic acid. The compo- 
 sition and decomposition therefore equally prove, 
 that oxygenated muriatic acid is simply a combi- 
 nation of muriatic acid and oxygen. But this 
 speedy decomposition by light shews, that the 
 oxygen very readily abandons the muriatic acid, 
 either to assume the elastic state, or to enter into 
 other combinations j and it is on this that the 
 characteristic properties of oxygenated muriatic 
 acid depend. 
 
 If vegetable colours be plunged into oxy- 
 genated muriatic acid, they disappear more or 
 less quickly ; and when there is a mixture of dif- 
 ferent colouring particles, some disappear more 
 readily than others, the whole, however, being 
 more or less affected. When the oxygenated 
 muriatic acid has thus exhausted its action, it is 
 found to be reduced to the state of ordinary mu- 
 riatic acid j the colouring particles have therefore 
 abstracted its oxygen. If we evaporate the liquid 
 in order to examine the state of the colouring 
 particles, we find that it yields a blackish resi- 
 duum, as if its particles had suffered a slight 
 combustion. (Note K.) 
 
 It is in this way also that colours are more or 
 less speedily destroyed by the action of the air, 
 especially when it is promoted by the solar beams, 
 
OF BLEACHING. 193 
 
 as was shewn in the preceding section. Hence 
 the oxygenated muriatic acid easily and quickly 
 produces the effects which air and light operate 
 in a longer space of time, because the oxygen, 
 deprived in part of its elasticity, and adhering 
 loosely to the acid, enters readily into combina- 
 tion with the substances for which it has an 
 affinity. 
 
 The filaments of flax and hemp are enveloped 
 in colouring particles, retained in them by a true 
 combination, and which mask their whiteness. 
 When these colouring particles combine with 
 oxygen, they are decomposed, so as to become 
 soluble in alkalies. Hence the potash of the ley 
 dissolves, and separates them from the filaments. 
 On repeating several times the exposure on the 
 grass, or the immersion in the oxygenated mu- 
 riatic acid, and the action of the leys, we separate 
 all the colouring particles of the filaments which 
 remain white. By these operations the yarn 
 loses nearly one-third of its weight. 
 
 If an acid be poured on the solution of the 
 colouring particles in potash, and if we dry the 
 precipitate formed, which remains upon a filter, 
 it is blackish, and has the appearance of a body 
 which has suffered a slight combustion, or has 
 been carbonized. The ley, when saturated with 
 the colouring particles, loses all its activity. 
 What is here said of potash, is equally applicable 
 to soda. 
 
 Yarn bleached by the ordinary process, or by 
 that just described, has lost a portion of its 
 
 VOL. I. n 
 
194 OF THE PREPARATION 
 
 strength, whence it no longer can sustain the 
 same weight as before bleaching ; but if both 
 operations be made with equal care, the yarn 
 bleached by means of oxygenated muriatic acid 
 preserves more strength than that which has been 
 treated by long exposure on the grass, because 
 the leys have been less numerous, and the opera- 
 tions not nearly so long. 
 
 This mode of bleaching, then, is produced by 
 the successive action of leys and of oxygenated 
 muriatic acid. We must therefore describe the 
 apparatus and operations which the oxygenated 
 liquor and the leys require, as well as the means 
 of promoting their action, preventing their incon- 
 veniencies, improving the whiteness, or giving 
 to bleached objects the qualities that are desired. 
 Lastly, we shall examine some other applications 
 of the properties of oxygenated muriatic acid. 
 
 CHAPTER II. 
 
 Of the Preparation of the Oxygenated Liquor. 
 
 The purpose of the apparatus used in this pre- 
 paration is, to disengage the oxygenated muriatic 
 acid (chlorine), and to combine it with water. 
 It is therefore divided into two parts, — the one 
 which comprehends the extrication of the gas, 
 and the other its combination with water. 
 
 For the first object, a furnace is employed, 
 capable of containing an iron pot to serve as a 
 
T r 
 
 OF BLEACHTNG LIQUOR. 195 
 
 sand bath. It is usually constructed of brick. 
 The inspection of the plate will give an idea of 
 one of these furnaces. In the sand bath is placed 
 a matrass containing the mixture, to be subse- 
 quently described. 
 
 Matrasses from 0.38 metr. to 0.43 in diameter 
 are preferable to those of greater dimensions, 
 because they are less liable to break, are more 
 easily managed, and much cheaper. The ellipti- 
 cal form is more advantageous than the spherical, 
 because with an equal diameter the capacity is 
 greater. If one matrass be inadequate for pro- 
 curing the liquor which is wanted, two furnaces 
 can be placed alongside of each other, (See fig. 
 1. 3, 4.) which can be put in action successively, 
 or at the same time. 
 
 The second part of the apparatus, in which the 
 gas is received, is the receiver. It has an interior 
 diameter of 0.9 metr. ; but it may be 2 metres 
 and even more in diameter. Its sides and its 
 bottom ought to be formed of strong oaken staves, 
 hooped with iron, and covered with a cement. 
 
 To protect the inside of the receiver, as well 
 as the cisterns, from the action of the liquor, they 
 must be covered with a resinous coat, of a consis- 
 tence not soft enough to run, or hard enough 
 to break off in scales. 
 
 The interior of the receiver is furnished with 
 three inverted tubs, (fig. 2. L L L.) destined to 
 receive the gas extricated from the matrass. The 
 depth of each tub ought to be 0.08 of a metre. 
 Their connexion with one another does not admit 
 
196 OF THE PREPARATION 
 
 of iron, which would be attacked by the oxygen- 
 ated muriatic acid. They are secured by trans- 
 verse bars fixed tothecircumference of the receiver. 
 The space between the tubs and the sides of the 
 receiver is closed, with the exception of an open- 
 ing, which permits the liquor to communicate from 
 one tub to another, and which ought to be placed 
 alternately on the opposite sides, as may be seen, 
 (fig. 1,2.)^ 
 
 The inferior tub, as well as the middle one, 
 carries in its bottom a glass tube, destined to 
 transmit into the upper the oxygenated muriatic 
 acid gas, when the former are filled with it. This 
 tube is 0.013 metr. shorter than the interior edge 
 of the tub, (fig. 2. PP.) 
 
 Between the matrass and the receiver is a bottle, 
 into which a little water is put. It has three 
 tubulures. To one is adapted the tube of com- 
 munication between the matrass and itself; from 
 the second proceeds the conducting tube (K. fig. 
 2.) destined to convey the gas under the lowest 
 tub of the receiver; the third receives a tube, 
 open at both ends, which bears the name of tube 
 of safety, because it obviates absorption. To ac- 
 complish this object, it must have, reckoning from 
 the level of the water in the bottle, a greater 
 height than that of the portion of the conductor 
 tube, which plunges into the liquor of the receiver; 
 otherwise the water of the bottle, pressed upon 
 by the gas, would escape at its upper part. The 
 portion of this tube which dips into the water of 
 the bottle should also be shorter than that of the 
 
OF BLEACHING LIQUOR. 197 
 
 conductor tube, which is above the level of the 
 water of the receiver j so that when the vessels 
 become cool, and a partial vacuum is formed, the 
 external air may enter by the tube of safety be- 
 fore the water of the receiver can rush in through 
 the conductor tube. 
 
 All the tubulures are shut with accuracy, but 
 in different ways. The tube of safety and the 
 conductor tube are permanently fixed. With this 
 view, they are passed across a hollow cork, which 
 is coated inside and outside with a mixture of 
 wax and turpentine, and forcibly pressed into the 
 tubulure. 
 
 The tube of communication between the matrass 
 and the intermediate bottle should have a stopper 
 at each extremity ; but as the stoppers must be 
 removed at the end of each operation, they are 
 not strongly pressed in, but merely covered with 
 a bladderj coated with the same mixture, to pro- 
 tect them from the action of the gas ; and they 
 are fixed down by packthread, or rather by levers 
 loaded with a weight at one of their ends. 
 
 Between the furnace and the intermediate bottle 
 a deal partition is made, having an opening cut in 
 it for the passage of the tube of communication. 
 
 It is useful to attach to the upper tub a pipe, 
 with a bent extremity dipping into a vessel filled 
 with solution of potash. When, by any circum- 
 stance, the gas comes to fill the cavity of this tub, 
 the excess escapes by this pipe, and is absorbed 
 by the potash, thus protecting the manufactory 
 
198 OF THE PREPARATION 
 
 from the inconvenience which would result from 
 its diffusion. 
 
 We may employ muriatic acid and oxide of 
 manganese directly, or we may substitute for the 
 muriatic acid sulphuric acid and muriate of soda, 
 which salt, when decomposed by this acid, gives 
 out the muriatic. The choice depends on the 
 price of those substances at the establishment. 
 The process which we are going to describe is the 
 second one. It is the best, on the whole. 
 
 Oxide of manganese (manganese of commerce), 
 when of good quality, is in black masses of greater 
 or less size, composed of small needles of a me- 
 tallic lustre. It should contain very little foreign 
 mineral. It is reduced into powder, and well 
 mixed with the salt, in the proportions to be pre- 
 sently stated, 
 
 If a manufacture of sulphuric acid be at hand, 
 we may dispense with purchasing it concentrated, 
 as it may be employed in the state in which it 
 comes out of the leaden chamber, provided it 
 have a proper degree of concentration. 
 
 Concentrated sulphuric acid, such as is found 
 in commerce under the name of oil of vitriol, 
 marks nearly 66° by the areometer of Baume, 
 (1.848 specific gravity). It is here presumed to 
 be in that state. 
 
 The proportions of the ingredients which ap- 
 pear to us most suitable, are, 10 parts of oxide of 
 manganese, 20 parts of sulphuric acid concen- 
 trated to the above degree, and TJ parts of mu- 
 riate of soda. We do not, however, affirm, that 
 
OF BLEACHING LIQUOR. 199 
 
 these are the most exact proportions which can 
 be determined. (Note L.) 
 
 If the manganese is of inferior quality, which 
 is discovered by the residuum of the operation not 
 retaining its black colour, the proportion of it 
 must be increased in the following operations till 
 a residuum be left which preserves a tinge of 
 black. 
 
 The sulphuric acid should be diluted with an 
 equal weight of water. Rupp and Westrumb re- 
 commend a larger proportion. This mixture is 
 best made in a leaden vessel. 
 
 Our process is presumed to be made with 5 
 kilogrammes of manganese, 10 of acid, and 13.5 
 of salt. 
 
 After mixing the salt and manganese, they are 
 introduced into the matrass, which is then placed 
 in the sand bath, when the sulphuric acid, pre- 
 viously diluted and cooled, is poured into it. 
 The tube of communication is now fitted to the 
 orifice of the matrass. The ascent of the water 
 of the intermediate bottle into the tube of safety 
 denotes that the openings are air-tight. This 
 may be further ascertained, by presenting to 
 them the moistened stopper of an ammonia bot- 
 tle ; for however small the portion of oxygenated 
 muriatic acid may be which escapes, it becomes 
 manifest by a white vapour. 
 
 We may kindle the fire in the furnace before 
 placing the matrass in the sand bath, taking care 
 that the heat is not so great as to expose the 
 matrass to be cracked when set in it j or we may 
 
200 OF THE PREPARATION 
 
 wait till the whole apparatus is arranged, before 
 lighting the fire. The heat is then to be very cau- 
 tiously raised, till the intermediate bottle ceases 
 to be filled with yellow vapours, and till the con- 
 ductor tube begins to grow warm. The fire must 
 now be extinguished. An operation for the above 
 quantities lasts from six to eight hours. We must 
 not delay withdrawing the matrass from the sand 
 bath till the movement of ebullition be entirely 
 calm. The tube of communication is to be un- 
 luted, and whenever the smell is somewhat dissi- 
 pated, the matrass is taken out, and placed in a 
 basket containing dry straw. It is emptied when- 
 ever there is no danger of cracking the neck with 
 the heat. 
 
 During the operation, the part of the matrass 
 exterior to the sand bath must be covered with 
 woollen cloth, pasteboard, or any similar sub- 
 stance capable of confining the heat. 
 
 The accidents to be feared in this operation are 
 the boiling over, and concretion of the residuum. 
 The former occurs during the heats of summer. 
 It is also occasioned by the bad quality of the 
 manganese. It may be avoided in both cases, by 
 diminishing the doses. To guard against the 
 obstruction of the tubes, which might arise from 
 the boiling over, they must be made of sufficient 
 magnitude. If, however, through inadvertency, 
 the intermediate phial should be filled, so as to 
 make it doubtful if the mixture can pass into the 
 receiver, the matrass ought to be immediately re- 
 moved. For if the mixture contained in it passes 
 
"■ 
 
 OF BLEACHING LIQUOR. 201 
 
 into the receiver, yarn turned through the liquor 
 would take a yellow colour, which must be re- 
 moved by means of sulphurous acid diluted with 
 water. 
 
 The concretion of the residuum, which exposes 
 the matrass to be cracked during the emptying, 
 may be occasioned by three causes : The first is, 
 too small a proportion of manganese ; the second 
 is, a lower temperature of the atmosphere than 7 
 or 8 degrees, (about 46° F.) ; and the third is, 
 keeping the matrass in the sand bath some time 
 after the operation, which happens when the heat 
 has been pushed too far. The causes being 
 pointed out, it is easy to avoid them. 
 
 As the temperature approaches that of freezing 
 water, the gas occasionally takes a concrete form 
 in the conductor tube, so as to obstruct it. To 
 prevent this misfortune, very wide tubes must be 
 employed. 
 
 Let us now turn our attention to the receiver. 
 On adjusting each tube, care must be taken to 
 cover it with water, and to extract all the air. 
 This is done by means of a syphon introduced 
 into the side opening, from which the water is 
 expelled by blowing forcibly into its upper ex- 
 tremity. 
 
 The receiver being furnished with its tubs, and 
 these being covered with water, with the excep- 
 tion of the upper one, we adapt the conductor 
 tubes, passing them through the free space be- 
 tween the upper and lower tubs and the side of 
 the receiver, and through an opening made in the 
 
202 OF THE BLEACHING LIQUOR. 
 
 board, which closes in the middle tub on the same 
 side. This opening must be exactly shut as soon 
 as the tubes are arranged. Lastly, the receiver 
 is rilled with water, which is not to be emptied 
 again unless when repairs are to be made : care 
 must however be taken every morning to evacuate 
 the air which may exist under the upper tub, 
 when the pipe just mentioned has not been placed 
 in it. 
 
 From the arrangement of the tubs and the con- 
 ductor pipe, it is obvious that the gas always 
 arrives beneath the lowest tub, and the liquor 
 must consequently be strongest at the bottom of 
 the receiver. From this place also it must be 
 drawn off, for which purpose we adapt to the re- 
 ceiver a pipe (fig. 2. Q.) of wood, sand-stone, 
 earthen-ware, or porcelain, which penetrates to 
 the bottom, and whose upper end is on a level 
 with the edges of the receiver. The liquor is run 
 off by plunging a syphon into this extremity, the 
 longer branch of which terminates in the water 
 of the tub of immersion, (fig. %. R.) In proportion 
 as the liquor flows out of the receiver, care is 
 taken to replace it by the addition of water or 
 spent liquor. (Note M.) 
 
OF LEYS. 
 
 203 
 
 CHAPTER III. 
 
 Of Leys. 
 
 The defective manner in which leys are usu- 
 ally drawn, is the most frequent, most powerful, 
 and yet the least suspected cause of the weaken- 
 ing of the substances subjected to bleaching. 
 This part of the art, practised at all times, impor- 
 tant both by its bad effects when ill-conducted, 
 and by the economy which it introduces into 
 bleaching when suitably performed, has received 
 in modern times very little amelioration ; yet it 
 has acquired considerable improvements from 
 more recent researches, especially those of Welter 
 and Widmer. 
 
 It is necessary to know the exact quantity of 
 alkali employed in each ley, so as to be able to 
 graduate its respective force, and to proportion it 
 to the quantity and nature of the materials to be 
 bleached. Since the wood ashes, sodas, and the 
 different species of potash made use of, are com- 
 posed of a mixture of earths, salts, and alkalies, 
 their weights indicate nothing ; nor is the areo- 
 meter a more faithful criterion, since the salts 
 mixed with the alkali also act upon it. Hence 
 its indications are more delusive as the propor- 
 tions of the mixtures vary, not only in the dif- 
 ferent species, but as they are not constant even 
 in any one. 
 
204 OF LEYS. 
 
 Home,* aware of the necessity of estimating 
 exactly the strength of leys, attempted to deter- 
 mine the quantity of alkali contained in the dif- 
 ferent substances employed by the bleachers, by 
 saturation with an acid. He thus assigned the 
 order which they ought to hold relative to their 
 quality, and he has explained the nature of the 
 substances found mixed with the alkali, very in- 
 geniously making allowance in his experiments 
 for the imperfection of the means of analysis then 
 known. But his results have not the precision of 
 those since published. Long afterwards, Kirwanf 
 employed, for appreciating the real alkali of pot- 
 ashes, the comparative precipitation of a certain 
 weight of alum, by pure potash, and by the pot- 
 ash under trial. Notwithstanding the precautions 
 which he suggested for removing the causes of 
 uncertainty attached to this mode of testing, he 
 was not able to give it either sufficient accuracy 
 or simplicity.^ Lastly, Vauquelin took the task 
 in hand, exhibiting the proportions of the sub- 
 stances found in several species of commercial 
 potashes. He estimated the proportion of alkali, 
 by saturating with a nitric acid, of a very deter- 
 minate degree of concentration, the potashes sub- 
 mitted to examination, and by comparing the 
 quantity of acid necessary to its saturation with 
 the pure potash which it had required. 
 
 * Essay on Bleaching. 
 
 f Ann. de Chimie, torn. vii. ; and Treatise on Bleaching. 
 
 J Ann. de Chimie, torn. xl. ] 
 
"WW-T", .«.!' J I 
 
 TT-^ 
 
 OF LEYS. 205 
 
 It is obvious, that since, in the art of bleaching, 
 the alkaline parts alone are of use, the value of pot- 
 ashes are to each other as the quantities of acid 
 necessary to their saturation ; and consequently we 
 become acquainted with that whose employment 
 is most advantageous, by comparing the price of 
 each species with the quantity of alkali which it 
 contains. On these considerations, Vauquelin 
 constructed the following table : — 
 
 At the time of making his experiments, the pot- 
 ashes of 
 
 America, containing 0.743, was worth 70 Hvres. 
 Pearl-ashes, 0.656, 60 
 
 Dantzic, 0.524, 57 1.10s. 
 
 Treves, 0.625, 55 
 
 Russia, O.67O, 55 
 
 Vosges, 0.385, 35 
 
 Hence he concluded,, that if the consumer wished 
 to fix the prices which he should give for each 
 potash, according to the alkali which it contains, 
 taking for a standard the one which the above 
 table presents as most advantageous, he would 
 have, — 
 
 1. For the potash of Russia, 55 livres. 
 
 2. America, 6l 
 
 3. Pearl-ashes, 54 liv. 3 sous. 
 
 4. Treves, 51 6 
 
 5. Dantzic, 43 
 
 6. Vosges, 31 12 
 
 He justly observes, that the data of these tables 
 are subject to variations, which fraud may in- 
 
206 
 
 OF LEYS. 
 
 crease ; but they may serve in all circumstances 
 as terms of comparison. 
 
 The testing of potashes is useful, therefore, 
 both for determining their commercial value, and 
 as a guide in their subsequent employment. As 
 the trials must be frequently repeated, it is im- 
 portant to have a simple manner of doing it ; and 
 under this point of view, we know none prefera- 
 ble to that of Welter. The process pointed out 
 by the general administrators of gunpowders and 
 saltpetres,* though better adapted to the end 
 which they proposed, is not so easy of execution. 
 
 We here give the process of Welter exactly as 
 he practises it. 
 
 The principle of the testing is saturation with 
 an acid. But to render the different trials com- 
 parative, the acid must be of a degree of concen- 
 tration which is uniform, and easily ascertained. 
 Sulphuric acid, diluted with water till it is brought 
 to a determinate point of concentration, answers 
 well. By saturating a certain weight of this di- 
 lute acid with a fixed weight of fine pure chalk, 
 dried by the heat of boiling water, the standard 
 may be fixed. This acid is the one most readily 
 to be had, and whose constitution is most uni- 
 form. The chalk selected for determining its 
 concentration is a substance equally common ; it 
 does not present the difficulties which occur in 
 procuring pure potash, and the temperature of 
 boiling water, employed for drying it, can be very 
 
 * Ann. de Chimie, torn. xli. 
 
 
OF LEYS. 207 
 
 easily observed with precision. To avoid the em- 
 barrassment attending the preparation of standard 
 acid, a quantity of it sufficient for the trials of 
 many years may be made at once. 
 
 Were these analyses made on pieces of potashes, 
 taken at random from the barrels, only ambigu- 
 ous results would be got, because in the same 
 barrel there are often different qualities. The 
 experiment should therefore be made only on so- 
 lutions prepared on the great scale as leys, and 
 always with the same weights of alkali to the same 
 number of measures of water. The most expe- 
 ditious manner of making these solutions in the 
 cold, is to suspend the potash at the surface of the 
 water in a vessel of iron, pierced with a great 
 number of holes, or formed of coarse iron wire. 
 They should not be drawn of! till we are certain 
 that the whole potash is dissolved, and till by agi- 
 tation the liquid is rendered uniform. 
 
 Besides these circumstances, the assay of pot- 
 ashes requires slips of paper stained with litmus, 
 or any other colour equally sensible to acids, as 
 that of mallows, radishes, &c. We should also 
 procure a glass rod, a small glass measure, and 
 lastly, a tube having as many times the capacity 
 of the small measure, as measures of water have 
 been employed to one quintal of potash. — (See 
 Plate II.) 
 
 We fill the tube with the solution of potash, 
 and transfer it into the goblet. We next fill the 
 same tube with the test acid, which is also pour- 
 ed into the goblet ; we agitate with the glass rod, 
 and then draw a trace on one of the slips of 
 
208 OF LEYS* 
 
 stained paper with the extremity of this rod 
 moistened with the mixture. If the trace do 
 not become red, we add to the goblet a small 
 measure of the test acid, stir, and then make 
 another trace on the paper, alongside of the for- 
 mer. If the colour of the paper be not now 
 changed, we add one measure of acid more, and 
 continue thus till the last drawn trace is red. 
 
 If we wish to compare the qualities of several 
 potashes, it is obvious, that we must regard as 
 the best that which has required the greatest 
 number of measures of acid to produce a red 
 streak, since it is the one which saturates most 
 acid. It is also obvious, that we might express 
 numerically" the qualities of the different species 
 of potash, representing them by the number of 
 measures of acid which each of them has saturat- 
 ed ; which amounts to counting the traces form- 
 ed on the paper in each trial, taking the first for 
 as many as the tube contains of little measures, 
 and adding unity for each of the following marks 
 till the last, which we should not reckon, because 
 its colour indicates that we have passed the term 
 of its saturation. 
 
 To obtain a suitable variation of the leys, it is 
 convenient to have solutions of potash of an uni- 
 form strength, one for example with which an equal 
 number of measures of test acid and solution of 
 potash are required to produce saturation. But 
 whatever be the value of a potash, its solution 
 may be brought to this point by adding to it, 
 for every quintal of alkali, as many measures of 
 
OF LEYS. 209 
 
 water as there were measures of acid required, 
 to effect saturation on the quantity primarily em- 
 ployed.' Hence the number of measures of wa- 
 ter forming the solution, ought always to be equal 
 to that which expresses the standard (Jitre) of the 
 potash. 
 
 If in an assay it should happen that the first 
 trace was red, it would be necessary to add mea- 
 sures of the solution instead of measures of acid ; 
 and hence potash should be added to the solu- 
 tion to bring it to the fixed degree of concentra- 
 tion. 
 
 To make this more clear, suppose that we have 
 employed 50 measures of water to dissolve one 
 quintal of potash, (consequently the tube con- 
 tains 50 times the small measure), and that we 
 have 8 traces on the stained paper. The first 
 counting 50, each of the following 1, and the 
 last being red, we would say that the potash is of 
 the standard 56 ; which would denote, that to 
 bring the solution to the fixed degree, (in this 
 case 50), we must add as many times 6 measures 
 of water as we have employed in quintals of pot- 
 ash ; and employing potash taken from the same 
 cask, we should use 56 measures of water for the 
 solution. An assay made on opening the cask, 
 is sufficient for the whole period of employing 
 that potash, remembering to put, every time a 
 new solution is made, as many measures of water 
 as the standard indicates. 
 
 The degree of concentration of these solutions 
 does not allow them to be employed directly in 
 
 vol. i. o 
 
210 OF LEYS. 
 
 the leying. Only such a number of measures is 
 taken as is necessary to give them sufficient 
 strength, when diluted with the water which fills 
 the boiler and the bucking tub, and for them to 
 have the quantity of alkali suited to the weight 
 of the substances to be bleached. But before 
 pouring the alkali into the boiler, it is advanta- 
 geous to render it caustic ; for it has been prov- 
 ed, (Ann. de Chim. torn, vi.), that in this state 
 alkalies dissolve a fourth more of colouring mat- 
 ter than when they are carbonated. The almost 
 general practice, however, is to ley in a mild 
 state. It has even been pretended, in some 
 houses, that the lime employed to render the al- 
 kali caustic, injured the stuffs. The observations 
 which we have collected satisfy us, that this 
 effect must be ascribed solely to the increased 
 energy acquired by the alkali, the consequences 
 of which may be prevented by a diminution of 
 its quantity. 
 
 To perform this operation, the lime newly 
 slaked is put into a large tub, the solution of 
 potash is poured over it, they are stirred together, 
 and, after settling, the clear liquid is to be de- 
 canted off by means of a syphon. The residuum 
 is then to be washed two or three times, and the 
 washings added to the ley. 
 
 One part of lime is sufficient to render two 
 parts of potashes caustic. These proportions 
 ought, however, to vary with the qualities of the 
 potashes j and it is proper to ascertain that the 
 proportion of lime is not too great, because the 
 
OF LEYS. 211 
 
 property which this substance possesses, of pre- 
 cipitating the colouring matter held in solution 
 by the alkalies, (Ann. de Chim. torn, vi.), may 
 render an excess of it injurious. On this ac- 
 count, some solution of potash is to be mixed 
 with the liquor floating over the lime, in the tub 
 in which the potashes are made caustic. If it 
 become turbid, it contains lime in solution, and 
 solution of potash must therefore be added, till it 
 no longer yields a precipitate. 
 
 We might probably apply this property of lime 
 with advantage, to carry off from spent leys the 
 colouring matter with which they are charged, 
 and render them once more fit for bleaching, by 
 adding the proportion of alkali necessary to re- 
 place that with which the stuffs remain imbued, 
 so as to raise the leys to the suitable standard. 
 On the small scale, yarns have been completely 
 bleached, by employing in this way the very 
 same alkali in all the leys. It may be likewise 
 beneficial, especially in places where fuel is cheap, 
 to evaporate the spent leys, and to calcine the 
 residua so as to destroy the colouring matter. 
 But these operations need only be performed on 
 the first leys, which are more concentrated than 
 the last. 
 
 According to the experiments of Kirwan,* the 
 use of alkaline sulphurets might be tried. They 
 have indeed the inconveniencies of producing 
 spots in places which come into contact with 
 
 * Ann. de Chimie, torn. vi. 
 
212 OF LEYS. 
 
 metals ; but these will disappear by employing 
 in the last leys an alkali free from the sulphu- 
 rets, or by passing them at the end of this bleach- 
 ing through an acidulated water. The follow- 
 ing is the order in which this celebrated chemist 
 has classed, according to their energy, the sub- 
 stances possessing the faculty of dissolving the 
 colouring matter of flax: 1. The alkaline sulphu- 
 rets ; 2. Caustic potash ; 3. Caustic soda ; 4>. 
 Carbonate of potash ; and 5. Carbonate of soda. 
 Lime water appeared to him to dissolve but a 
 very little of it, which he ascribes to the small 
 solubility of the lime ; but independently of this 
 cause, it is not probable that lime, which forms 
 an insoluble combination with colouring matter 
 held in solution by potash, could of itself dissolve 
 it. Kirwan observes, that sulphur did not aug- 
 ment the solvent faculty of lime. Higgins, how- 
 ever, has stated, that there is a remarkable eco- 
 nomy in employing sulphuret of lime in bleach- 
 ing. Trials on the small scale have not had the 
 success that O'Reilly announced. — Journal des 
 Arts. (Note N.) 
 
 The sulphurets present two inconveniencies, 
 which must greatly diminish the benefit which 
 their solvent faculty promises. One is, to dete- 
 riorate rapidly boilers and metallic instruments 
 containing them ; another is, to waste a consider- 
 able quantity of the oxygenated muriatic acid, if 
 the washings have not taken it completely out of 
 the matters that are bleaching. 
 
OF LEYS. SIS 
 
 . The colouring matter acquires the property of 
 being dissolved by the alkalies only in the suc- 
 cessive operations, between every one of which 
 whatever has become soluble ought to be remov- 
 ed. Experience has proved that these steps are 
 necessary to obtain a fine white, not subject to 
 vary ; a white which cannot be attained at a 
 single operation.* The alkali deemed necessary 
 to dissolve the whole colouring matter of the 
 substance we are bleaching, must therefore be 
 divided into a certain number of leys ; and as it 
 should be proportioned according to the quantity 
 of this colouring matter presumed to be present, 
 less of it may be employed in the last leys than 
 in the first. 
 
 The most general manner of leying is the fol- 
 lowing : — 
 
 The large tub is so placed, that its bottom may 
 be near to, and on a level with the edges of a 
 boiler, which is somewhat sunk into excavated 
 ground, to avoid too great an elevation of the 
 tub. A little above its bottom this is perforated 
 with a hole, into which is fitted a small tube, that 
 conducts the ley into the boiler. The stuffs to 
 be bleached are arranged in the tub in horizon- 
 tal layers. The boiler is then filled with water, 
 which is poured into the tub after closing the 
 pipe that leads into the boiler ; and this opera- 
 tion is continued till the water stands in the tub 
 a little above the goods, taking care to mingle 
 
 * Annates de Chimie, torn. xi. 
 
 
£14 OP LEYS. 
 
 with each boiler-full of water a number of mea- 
 sures of solution of potash, equably divided, so 
 that with the last boiler-full the whole alkali in- 
 tended for the ley shall have been expended. 
 The boiler being equably filled, the fire is kin- 
 dled, the pipe of communication is opened, and 
 the water is kept at a uniform height in the tub, 
 by lifting it with a copper pail or bucket from 
 the boiler, and pouring it into the tub. When 
 the ley (thus continually lifted into the tub in 
 proportion as it flows into the boiler) has begun 
 to boil in the caldron, the operation (of bucking) 
 is prolonged more or less, according to the kind 
 of matters that we bleach, and the period of 
 bleaching at which they have arrived. The ley- 
 ing being finished, it is allowed to flow off by 
 a stopcock fitted to the bottom of the boiler ; 
 water is then poured into the tub to cool it, and 
 expel the remainder of the ley, after which the 
 tub is emptied. 
 
 Since the tub contains several times the capa- 
 city of the boiler, and since, independently of 
 the time which a considerable volume of water 
 takes to acquire a high temperature by the mix- 
 ture (in rotation) of a small quantity of heated 
 water, the ley is continually cooled by the trans- 
 fer from the boiler into the bucking-tub, the 
 ebullition in the boiler must be but very slowly 
 brought on. However long continued the 1 eying 
 may be, the temperature cannot be carried higher 
 than 72° or 73° (about 195° Fahr.) in the tub. 
 From this arrangement it follows, therefore, 1. 
 
OF LEYS. 215 
 
 That a great body of water must be heated, in 
 order that the substances bleaching may be equa- 
 bly impregnated with the ley ; and, 2. That we 
 can give the leys only a heat inferior by several 
 degrees to that of boiling water. Hence the 
 length of the operation, as also the waste of com- 
 bustibles, and the great labour : nor can the term 
 of 80° (212° Fahr.) be obtained. Several pheno- 
 mena, however, and especially the superiority 
 found in patterns bleached in boiling leys, show 
 how advantageous the temperature of ebullition 
 would be. 
 
 From these considerations Widmer contrived 
 to place directly above his boiler a tub, whose 
 bottom was merely a strong lattice work of wood. 
 In the middle of the boiler there is a pump which 
 raises the ley to the top of the tub, where it is dif- 
 fused by four pipes equal to the radius of the tub, 
 and which are turned circularly by a movement 
 adjusted to the arm (lever) of the pump. The 
 ley is thus equably dispersed on the surface of the 
 goods ; it filters through them, and falls into the 
 boiler. Far from being liable to cool, it preserves 
 its temperature in this passage, because the goods 
 are heated by the steam rising from the boiler, 
 which cannot escape except by passing through 
 their interstices. Two thermometers placed in 
 an apparatus, where the boiler was two metres in 
 diameter, one at the base and another at the top 
 of a tub two metres high, constantly marked 
 the same degree of heat. In three hours of an 
 
21 8 OF LEYS. 
 
 uninterrupted flowing, they both indicated 80°, 
 (212° Fahr.) In the first trials, Widmer made 
 use of a tub whose height was two metres, and 
 whose diameter, equal to that of the boiler on 
 which it stood, was only 0.8 of a metre. The 
 ley was drawn off by a stopcock adjusted to the 
 bottom of the boiler, and it was poured in with 
 a bucket quicker than it could run completely 
 away. That remaining on the top of the goods 
 boiled strongly some minutes after the boiler was 
 in ebullition, notwithstanding the small surface 
 which this apparatus presented to the vapour, 
 the cooling which the ley must have experienced 
 in getting back into the boiler from the top of the 
 tub, and the distance between this point and the 
 boiler. By this method we may communicate to 
 goods a heat superior to that of boiling water. 
 The thermometers of the large apparatus rose to 
 84° (221° Fahr.) ; but as soon as they passed the 
 boiling point of water, the pump could no longer 
 raise the liquid ; and we do not know how far it 
 may be right to ley at higher temperatures. To 
 prevent the pressure of the steam from stopping 
 the working of the pump, Widmer next establish- 
 ed four pipes, which opening a communication 
 between the upper part of the boiler and that of 
 the tub, gave a free outlet to the vapour. 
 
 This apparatus unites the advantages of leying 
 in much less time, at a boiling heat, and with less 
 consumption of fuel ; for instead of having to 
 heat a ley incessantly cooled by the transfer, and 
 
OF LEYS. 217 
 
 which occupies the capacity of both the tub and 
 the boiler, the latter alone is filled, while the 
 heat is preserved during the running by the agen- 
 cy of the vapour. 
 
 Nearly 400 pieces, of from 21 to 22 metres 
 each, may be leyed at a time in an apparatus of 
 the above dimensions. The longest leying lasts 
 six hours : it consumes five measures of coals. 
 Its efficacy is sufficiently proved by the uses to 
 which the goods of Widmer so bleached are ap- 
 plied, since there can be no more delicate test 
 for white, than the clearing the madder grounds 
 of printed calicoes ; and it has also diminished the 
 number of operations to which he subjects the 
 goods. We have had occasion ourselves to as- 
 certain these good effects on cotton cloth ; and 
 we believe that they will be experienced on 
 applying this method to the bleaching of linen 
 webs. (Note O.) 
 
 Bosc has asserted in a paper,* on which we 
 have some reflections to offer, that it was preju- 
 dicial to the action of the alkali to water the 
 goods continually ; an idea which he founded on 
 his philosophical notions of bleaching. Accord- 
 ing to him, the solution of the colouring particles 
 in the alkali is a true combustion, effected only on 
 the colouring matter, because it is combustible at a 
 lower temperature than the fibres. Our only bu- 
 siness, therefore, is to raise sufficiently the tem- 
 
 * Bulletin <le la Societe" d'Encouragement pour l'lndustric 
 Nationale. Germinal, An. xi. 
 
218 
 
 OP LEYS. 
 
 perature of the steam, so as to operate by its de- 
 composition the combustion of the colouring par- 
 ticles, which thus become soluble in the alkali. 
 
 When water is decomposed by means of char- 
 coal at a much higher temperature, there are 
 produced carbonic acid, and an inflammable gas, 
 holding charcoal in solution ; but the charcoal 
 which has not entered into a gaseous combination 
 has not become more soluble in alkalies. This 
 observation would be sufficient to prove that the 
 explanation of Bosc is not founded on the received 
 theories. 
 
 He makes Lavoisier say, that at 85 degrees of 
 Heaumur, (about 223° Fahr.J, water forms a per- 
 manently elastic gas. This illustrious chemist 
 styled permanently aeriform fluids, those which 
 preserve this state notwithstanding changes of 
 temperature and pressure. The vapour of water 
 formed at 80° (212° F.) under the ordinary pres- 
 sure of the atmosphere, differs from that formed 
 at 85° only in being more dilated, and resisting a 
 higher (less) pressure. 
 
 He certifies, that in the apparatus which he 
 describes, the heat is carried beyond the 100th 
 degree of Reaumur ; but at nearly 17 degrees 
 above the term of ebullition, (250° F.), steam ac- 
 quires a double elastic force. His vast apparatus 
 should therefore be able to resist an effort superior 
 to two atmospheres. He should have bethought 
 himself of determining the thickness necessary to 
 the great boiler which is to furnish this vapour, 
 and have shewed us by what means he could fix 
 
OF LEYS. 219 
 
 down the different parts of the apparatus to the 
 masonry. 
 
 In making a comparative calculation of differ- 
 ent modes of bleaching, he regards as a matter 
 of indifference the employment of oxygenated 
 muriatic acid without mixture, or combined with 
 potash and lime. We shall afterwards see how 
 far this position is right. 
 
 When the results of different methods are com- 
 pared, especially on cotton, where some days' ex- 
 posure on the grass forms a part of these methods, 
 and when it is not the object to attain the most 
 perfect white, it is easy to be led into error, be- 
 cause all these methods readily yield a white, 
 with which people may often be satisfied. 
 
 CHAPTER IV. 
 
 Of the Immersions in the Oxygenated Muriatic 
 
 Acid. 
 
 If linen or cotton yarn is to be bleached, for 
 its immersion in the oxygenated muriatic acid, 
 we may place near the receiver a tub of the same 
 size, but a foot lower, (fig. 1, 2. A.) It is to be 
 two-thirds filled with water ; the liquor of the re- 
 ceiver is then run into it by means of a syphon, 
 as we have explained, agitating meanwhile, but 
 without raising air bubbles. The hanks are ar- 
 ranged in a basket of the same height as the tub 
 of immersion, so as to form two layers in it, leav- 
 
220 OF TUB IMMERSIONS 
 
 ing 0.2 metr. empty. The basket should contain 
 from 100 to 150 kilogrammes of yarns. This 
 basket is then raised by means of a crane or other 
 equivalent machine, and plunged into the immer- 
 sion tub ; from which it is withdrawn, and re- 
 plunged into it continually, so as to renew inces- 
 santly the liquid which moistens the yarn. As 
 soon as the liquor is observed to be weakened, the 
 basket is raised above the tub, and fresh liquor is 
 run in from the receiver. This process is con- 
 tinued until the liquor retains its strength, not- 
 withstanding the repeated immersions of the yarn. 
 This first operation usually lasts two or three 
 hours. 
 
 Instead of heaping the yarn in baskets, it may 
 be plunged much more freely in the liquor, by 
 hanging it at two rods, which pass through the 
 middle of the hanks, and are supported by a 
 frame of the same size with the immersion tub. 
 There is then no danger of the yarn being bleached 
 unequally. Less of it, indeed, enters at a time 
 into the tubs. The mode of working is in other 
 respects the same. 
 
 The oxygenated muriatic acid weakens and 
 even destroys yarns, as leys do, if it be employed 
 without precaution. Hence, when yarn is put 
 into a very strong liquid it soon loses its tenacity. 
 But it is very easy to avoid this occurrence, by 
 not dipping the yarn till the liquid which comes 
 out of the receiver be well mixed with water, or 
 be a dilute liquor with a supportable odour. In 
 this state of concentration, the oxygenated muri- 
 
IN THE BLEACHING LIQUOR. 221 
 
 atic acid does not attack yarn, though plunged in 
 it even for several days. We must not rest satis- 
 fied with so vague a manner of judging, especially 
 if we wish to compare together several effects. 
 
 From the outset of his operations Descroizilles 
 made use of a solution of indigo in sulphuric 
 acid, to estimate the comparative strength of his 
 liquors ; and he has since published a description 
 of the instrument which he contrived for this 
 purpose.* The solution of indigo ought to be 
 prepared with seven parts of concentrated sul- 
 phuric acid, and one part of indigo, (jiore). 
 These two substances are mixed in a small ma- 
 trass, which is plunged for a few hours in water 
 slightly tepid j and the solution is then mixed 
 with 992 parts of water. 
 
 The strength of a liquor is judged of by the 
 quantity of it requisite in order that the colour 
 of a stated measure of this solution, in which the 
 indigo forms l-1000th, be destroyed or turned 
 to a yellow hue. This trial is conveniently made 
 with a measure glass and a goblet, similar to those 
 pointed out for the trial of potashes. 
 
 For a first immersion, the liquor may be of such 
 a strength that one measure of it shall deprive of 
 colour from one-half to two measures of solution 
 of indigo. If the odour gives annoyance, it may 
 be diminished by diffusing some chalk and water 
 in it. We have ascertained, that this easy me- 
 thod of obviating the inconvenience of the smell, 
 
 * Journal d'Agriculturc ct dcs Arts, torn. i. 
 
222 OF THE IMMERSIONS 
 
 does not perceptibly impair the energy of the 
 liquor. The strength and duration of the im- 
 mersions which follow the first, are progressively 
 less. Their number varies also according to the 
 fineness and quality of the yarns. In general, 
 they are limited to between five and nine. 
 
 Too weak a liquor should not be made use 
 of, from fear of weakening the yarn ; for its de- 
 ficiency of action cannot be compensated by a 
 greater number of immersions. It is easy, more- 
 over, to avoid any accident from the liquor, by 
 never omitting to try its strength. Attention 
 must also be paid, not to let the yarn that is im- 
 pregnated with it dry in the air ; it is thereby 
 injured, although no inconvenience happens while 
 it is wet. 
 
 The bleaching of piece goods requires the 
 same precautions. The finer the cloth the more 
 economical, because it consumes less liquor ; but 
 to execute it commodiously, there must be, in- 
 stead of a single tub of the size of the receiver, 
 four tubs sufficiently large to contain each from 
 ten to twelve pieces, twenty-four metres long. 
 These tubs, arranged one after the other, near 
 the receiver, are each surmounted by a reel or 
 winch. In front of the first tub a table is placed, 
 to which are attached at their corners the ten 
 pieces that are to be immersed together. After 
 bringing the liquor to the requisite degree, the 
 end of the last attached piece is thrown upon the 
 winch of the first tub. A workman immerses 
 the pieces with a rod, in proportion as they pass 
 
IN THE BLEACHING LIQUOR. 223 
 
 over the winch, which is turned by a child. The 
 end of the last piece is tied to a cord fixed to 
 the frame-work of the winch, in order that this 
 end, which enters last into the tub, and which 
 finds the liquid now weakened by the pieces to 
 whose train it is attached, may enter first in- 
 to the second tub, and that the end which has 
 been first in the preceding may, by passing last 
 into the next, be placed in the same circum- 
 stances as the other. By giving this rotation to 
 the goods in the tubs, with a view of changing 
 them, and by successively passing each end first, 
 they whiten very equally. When the pieces have 
 been passed from the first into the second tub, 
 new ones are introduced, which pass into the 
 second as soon as the former have entered the 
 third, and which pass in their turn into this, 
 when the preceding pieces are in the fourth. 
 At the same time, fresh pieces should be put into 
 the first two tubs ; so that as soon as the pieces 
 shall have travelled from one tub to another, 
 others may enter immediately into the former. 
 When they have arrived at the fourth, and have 
 remained the requisite time in the liquor, they 
 are piled up on the winch to let them drain, 
 then turned over on a wheelbarrow, to be carried 
 to wash. Whenever the pieces are taken out of 
 a tub, the liquor of it is tested, that it may be 
 restored to the proper degree before introducing 
 fresh pieces into it. Care should be taken to 
 plunge the pieces thoroughly, and not to let any 
 
 7 
 
224 
 
 OF THE WASHINGS. 
 
 of their parts float above. The number, the 
 strength, and duration of the immersions, vary 
 with cloths, as with yarns. 
 
 CHAPTER V. 
 
 Of the Washings. 
 
 Whoever projects an establishment, should 
 examine if the place where he proposes to erect 
 it, unites the advantages of fabrication, com- 
 merce, and carriage j but, above all, he must 
 have pure water at command ; for, without this 
 condition, he will not succeed in obtaining a fine 
 white. Muddy water, which leaves a blackish 
 deposite, may however be employed with success; 
 but that whose deposite is yellow, gives always an 
 unfavourable shade. These observations are par- 
 ticularly applicable to the bleaching of cotton, the 
 white of which should have the greatest lustre. 
 
 Immediately after each operation, we must, by 
 a careful washing, discharge from yarns and 
 stuffs the liquor with which they are impreg- 
 nated ; because, if it were carried into that of 
 the next operation, it would neutralize a portion 
 of it, and thus impair its action. This precau- 
 tion, moreover, adds much to the perfection of 
 the white. 
 
 To wash linen or cotton yarns, a workman 
 takes a hank in each hand, plunges them in the 
 
OF THE WASHINGS. 225 
 
 water, agitates, withdraws, and replunges them 
 for three or four times, seizing the hank each 
 time by a different point. He then puts the two 
 hanks together, wrings them, and throws them 
 down. 
 
 The washing of piece goods requires more ap- 
 paratus, in order to be well executed. They are 
 pretty generally washed by hand, and beat with 
 a rod or a mallet ; but this method is imperfect, 
 especially because of the inequality of the wash- 
 ing. In some establishments machines are em- 
 ployed, which accomplish this object better. We 
 are acquainted with none preferable to that of 
 the celebrated manufacture of Oberkampf, of 
 which he has had the kindness to impart the 
 knowledge to several bleachers. It consists of a 
 strong beetle or mallet, which strikes the pieces 
 arranged on a circular table, moveable round a 
 pivot. A description, detailed enough to guide 
 to its construction, would require too much room 
 for us to give it a place here. 
 
 We may, however, obtain a pretty complete 
 washing, sufficient for the most part of goods, by 
 making use of two wooden rollers, placed one 
 above another on frames, set in the direction of 
 the breadth of a river. Their length is 0.4 of a 
 metre, the under one is 0.48 in diameter, while 
 the upper is only 0.40 of a metre. The latter is 
 fluted parallel to its axis, the depth of each fur- 
 row being nearly equal to one-half of the ridge. 
 At each extremity it has a pivot, fitted to a 
 groove cut in the frame (support). These pivots 
 
 vol. i. p 
 
226 
 
 OF THE WASHINGS. 
 
 are not fixed, hence this cylinder can rise freely 
 above the other. The surface of the under roller 
 is smooth ; and it carries a handle at one of its 
 pivots. When we wish to wash goods by its 
 means, we throw the piece into the water, laying 
 hold on one of its ends, and putting it between 
 the two cylinders. On turning the winch, the 
 cloth passes between them, pressed by the upper 
 one, which, at every groove, receives a small 
 stroke, and communicates it to the cloth in its 
 tumbling round. Pieces passed in this way five 
 or six times successively, are very well washed. 
 
 To moisten goods, or to wash them slightly, 
 we may also employ a species of reel (winch), 
 with four leaves, placed on a river, like the 
 rollers. The piece whose end is laid on the 
 reel is thrown into the water, and, turning on 
 the reel, the piece passes over it, and falls on 
 the other side into the water. If it be rapidly 
 enough turned, and if the pieces be thus passed 
 several times, they will be tolerably well washed 
 by this simple means. 
 
 What has now been stated shews the advan- 
 tages of arranging the workshops as near as pos- 
 sible to the water placed at our disposal. (Note 
 
OF THE OTHER OPERATIONS; 227 
 
 CHAPTER VI. 
 
 Of the other Operations of Bleaching. 
 
 The bleaching of goods commences by leaving 
 them for some time in tubs full of water. In a 
 few days a fermentation commences, which pro- 
 motes the separation of the colouring matter, and 
 particularly of the paste with which weavers im- 
 bue the webs. This operation, which is called 
 ungumming, may, without injury, last for eight 
 or nine days, at mean temperatures* It may be 
 longer when the air is cold, and ought to be 
 shorter in summer, because it is to be feared that 
 fermentation, pushed too far, would affect the 
 texture of the goods. Old leys are also used for 
 this purpose ; but the experiments of Home 
 prove, that it is more advantageous to employ 
 only pure water. 
 
 As to yarns, it is sufficient for them to be 
 steeped for two or three days. 
 
 If the moist grey yarn, on coming out of the 
 ley, be piled up, it gradually heats, and eventual- 
 ly takes fire ; but if it reaches only the animal 
 temperature, it is not perceptibly weakened ; the 
 slight combustion which it thereby experiences 
 even contributing to the effect of the leys. If it 
 be shut up in the dark, however, when ill-dried, 
 it is speedily destroyed. 
 
 When no more greyness remains in linen yarn, 
 or linen cloth, which commonly occurs after the 
 
228 OTHER OPERATIONS 
 
 fourth immersion, it is passed into water acidu- 
 lated with sulphuric acid. For this purpose, into 
 a small tub containing water sulphuric acid is 
 poured, till the mixture has assumed a degree of 
 sourness, approaching to that of lemon juice. In- 
 to this the yarn is dipped, handful after handful, 
 so as thoroughly to imbue it. It is then thrown 
 into another tub large enough to hold 1200 pounds 
 of it, in which it is left for about 15 or 20. hours 
 before being removed. A longer continuance, of 
 two or three days, for example, can do no harm, 
 provided care be taken that no portion of the yarn 
 rises out of the acid. As to piece goods, they are 
 attached end to end, and passed by means of a 
 reel through large tubs full of acidulous water. 
 Linen yarns and cloth are passed three or four 
 times through the acidulous water, making it 
 progressively weaker. It is sufficient for cotton 
 goods and yarn to be passed once. The quantity 
 of acid employed in the first liquor is 85 kilo- 
 grammes, for 600 kilogrammes by weight; and 
 this proportion is diminished at each subsequent 
 operation. 
 
 Great pains must be taken to wash perfectly 
 before and after the acidulous water, otherwise a 
 fine white can never be obtained. It is no less 
 important to prevent the yarns or cloth impreg- 
 nated with acidulous water from remaining long 
 exposed to the air ; for as the water evaporates, 
 the acid becomes concentrated, acts on the fibre, 
 and destroys it. 
 
OF BLEACHING. 229 
 
 The acid dissolves the iron which in the course 
 of the operations had been deposited on the 
 stuffs, communicating to them a faint yellowish 
 tint. In proof of this, the prussiate of potash 
 occasions, after some time in the sour, a blue pre- 
 cipitate. But is the action of the acid confined 
 to the above use ? If it be, why repeat this 
 operation four times, and apply a ley between 
 each of them, while for cotton, equally exposed 
 to be stained by the ferruginous deposite, a single 
 sour is sufficient ? 
 
 In Flanders, Holland, and Ireland, the bleach- 
 ing of cloth by the ancient methods is accelerated, 
 by letting them stand for several days in the aci- 
 dulous liquors. Sour milk is commonly employ- 
 ed for this purpose ; sometimes, also, bran or rye- 
 meal is mixed with the cloths, and the liquor 
 of the tubs becomes sour from fermentation. It 
 was long believed that the fermentation itself pro- 
 moted the bleaching ; but it is now well proved, 
 that it is the acid alone which acts. Home has 
 satisfied himself, that the vegetable and mineral 
 acids may be substituted for milk and rye-meal ; 
 that sulphuric acid, however, combines most ad- 
 vantages ; that muriatic and nitric acid produce 
 the next greatest effect, which effect is aided by 
 a gentle heat. He assures us, that sulphuric acid 
 does, in five hours and less, what could be obtained 
 only in five days with bran or milk. To these 
 substances he also makes the serious objection, 
 that they frequently run into putrefaction, and 
 thus affect the fabric. We may hesitate the less 
 
230 OTHER OPERATIONS 
 
 to substitute water acidulated with sulphuric acid 
 for milk or rye-meal, as this change has been long 
 adopted in England, and in several French bleach- 
 works. 
 
 Notwithstanding all these operations, the thread 
 has not yet got all the whiteness of which it is 
 susceptible. There remains a matter insoluble in 
 acids and alkalies, which is removed by powerful 
 washings in water frequently repeated, and by 
 some days' exposure on the grass. There is a 
 certain yellowish tint, which is more effectually 
 destroyed by the action of air and light, than by 
 that of the oxygenated muriatic acid. In general, 
 yarns of a yellow colour bleach with more dif- 
 ficulty than those of a grey hue bordering on 
 brown. For those, it is right to lengthen some- 
 what the exposure on the ground. 
 
 For giving softness to yarns, some pounds of 
 soap are added to the last leys. Immediately 
 afterwards they are laid out on the green, on 
 being lifted from which they are washed with 
 great care ; for if they retain any soap, their 
 white might change. In linen webs, the selvages 
 being of a denser texture than the rest, preserve 
 for a longer time a tint, which can be completely 
 removed only by reiterated washings and soft 
 soap. It is the same with all the places on the 
 body of the cloth where there are broken threads 
 repaired during the manufacture. These con- 
 stantly preserve a black hue, which yields only 
 to rubbing with a hot solution of soap, of greater 
 or less strength. Some persons are in the prac- 
 
OF BLEACHING. 231 
 
 tice of treading the cloths in tubs, along with 
 this solution, one or two times, towards the end 
 of the bleaching. This operation is performed 
 with the feet, tramping more or less, according 
 to the hardness of the web. To cleanse the cloth 
 completely, it is soaped by hand in tubs, whose 
 edges, instead of being perpendicular to the bot- 
 tom, are turned considerably outwards, forming 
 an inclined plane, on which the workmen rest 
 their webs, so as to rub them more conveniently. 
 If the goods are almost quite cleared by the two 
 treadings, a single rubbing is sufficient to bring 
 the selvages to the same tone of white as the rest 
 of the piece ; most frequently two are given, 
 especially to webs of a dense texture, or of a 
 coarser yarn. Occasionally they are obliged to 
 rub, even separately, the spots where the black 
 threads are observed. All these manipulations, 
 by cleansing thoroughly the goods, give them, 
 moreover, a certain pliancy, and that marrowy 
 feel which is in request. The whole of the soap 
 that may possibly remain is removed, by expos- 
 ing them on the field, and washing them several 
 times in limpid water. The soaping does not 
 begin till the webs have passed once through the 
 acid, care being had to lay them down on the 
 grass on their quitting each operation, and to 
 water them on it. They are next washed and 
 lixiviated. The acid and soap are alternated, till 
 a perfect white be formed. 
 
 Cotton stuffs do not present the same diffi- 
 culties. The black threads are easily cleared 
 
232 
 
 OTHER OPERATIONS. 
 
 towards the end of the bleaching, by soaping the 
 places where they are .observed ; but the sel- 
 vages whiten as rapidly as the body of the web ; 
 and exposure on the green may be dispensed 
 with. 
 
 When a perfect white is attained, the blueing 
 is given in the following way : — 
 
 The most beautiful azure-blue (smalt) is select- 
 ed, the colour of which proceeds from oxide of 
 cobalt reduced to very subtile powder. It is dif- 
 fused through a little clear water. Some of the 
 water thus charged is drawn off, and passed 
 through a silk searce, into a small tub filled with 
 the most limpid water ; and when the workman 
 judges, by a trial made on a handful of thread, 
 that the water is sufficiently charged, he passes 
 through it all the thread in succession, squeezing 
 it, and taking care to add blue from time to 
 time, to keep the shade uniform. The yarn is 
 now carried to the wringing frame, and then 
 dried in the open air. 
 
 The preparation is the same for piece goods. 
 They are wrung at the peg, and dried. As to 
 gauzes, linons, and some other cotton stuffs, a 
 little starch is added to the water containing the 
 azure-blue. Cambrics are usually passed twice 
 through the blue, letting them dry between eacli 
 operation. 
 
NUMBER, &c. OF THJE OPERATIONS. 233 
 
 CHAPTER VII. 
 
 Number and Order of the Operations. 
 
 Suppose there is a solution of potash made in 
 the proportion of 40 measures of water, each 
 weighing 16 pounds, for a quintal of potash, and 
 1250 pounds of thread. 
 
 The linen or hempen yarns having been steep- 
 ed in water for three days, are to be well-wash- 
 ed, and arranged in the ley-tub. 
 
 First ley ; 20 measures of solution of potash, 
 three hours of boiling. The ley, on cooling, be- 
 comes thick like a jelly. 
 
 Second ley, for completing the removal of as 
 many of the colouring particles as possible. This 
 ley contains 10 measures of solution ; and the 
 boiling lasts for two hours. 
 
 Washing, to carry off the ley and the colour- 
 ing particles which it has dissolved. 
 
 First immersion. Liquor at 2° ; that is, of such 
 strength that one measure of liquor discolours 
 two measures of solution of indigo. The immer- 
 sion is continued till the yarn no longer weakens 
 the liquid, after it is restored to its standard 
 strength. 
 
 Washing. 
 
 Third ley. 12 measures of solution ; three 
 hours of ebullition. 
 
 Second immersion. Liquor of the same strength 
 as the first. 
 
 
234 NUMBER AND ORDER 
 
 Fourth ley. 8 measures of solution ; two hours 
 of ebullition. 
 
 Third immersion. 
 Washing. 
 
 Fifth ley. 5\ measures of solution j two hours 
 of boiling. 
 
 Fourth immersion. Departing from this point, 
 the liquor is brought down to 1°. 
 
 Washing. At this period the white is usually 
 manifest. 
 
 Acidulated water. 
 
 Washing. 
 
 Sixth ley. 5h measures ; two hours of ebulli- 
 tion. 
 
 Exposure on the green for six days. 
 
 Washing. 
 
 Fifth immersion. 
 
 Washing. 
 
 Acidulous water. 
 
 Washing. 
 
 Seventh ley. 4>h or 5 measures ; one hour of 
 ebullition at least. 
 
 Sixth immersion. 
 
 Washing. 
 
 Acidulous water. 
 
 Washing. 
 
 Ley and soap. 3 measures of solution. To 
 this, 8 pounds of black soap are added j and the 
 solution is heated till the hand cannot be tolerated 
 in it. When the soap has penetrated thoroughly, 
 the process is stopped. 
 
 Exposure on the grass, three days. 
 

 OF THE OPERATIONS. 23.5 
 
 Washin 
 
 & 
 
 Blueing. 
 
 After this operation the bleaching is finished, 
 the thread is wrung out, and is set to dry. 
 
 The operations are the same for linen cloth, 
 only they must be preceded by the ungumming. 
 There may also be run upon them, before the 
 first ley, hot water, to which no alkali is added ; 
 an affair which lasts three hours. If the goods 
 be not sufficiently whitened, the bleaching must 
 be continued in the order indicated, setting out 
 from the last ley. 
 
 The cotton cloths are ungummed (freed from 
 the dressing), then receive the hot water, and 
 the operations prescribed for yarns down to the 
 last immersion. At this time they are white. 
 They are passed into blued acidulous water, and 
 next dried. In the first immersion, the liquor 
 should be of only 1°, and somewhat weaker for 
 the subsequent ones. A few measures less should 
 likewise be put in each lixivium. The black 
 threads are soaped after the third immersion,, 
 For cotton in hanks, the same mode of operating 
 is proper. 
 
 CHAPTER VIII. 
 
 Of the Different Preparations of the Oxygenated 
 
 Liquor. 
 
 In the first experiments which were attempted 
 on bleaching, though it was proposed merely to 
 
 
236 OF THE. DIFFERENT 
 
 employ the property which the oxygenated mu- 
 riatic acid possesses of destroying colours, yet 
 potash was mixed with it, which seemed to acce- 
 lerate its effect. It was soon perceived, that in 
 order to obtain a uniform white, without weaken- 
 ing the cloth, the operations of ordinary bleaching 
 must be imitated ; the oxygenation of the colour- 
 ing particles by a liquor weak enough to do no 
 injury to the fabric, being followed up by the 
 action of leys which serve to dissolve them. 
 
 Soon after the practice of the new bleaching 
 had begun to be established, a liquor mysterious- 
 ly talked of was prepared at Javelle, which is 
 still employed under the name of the lixivium of 
 Javelle. * It is a combination of oxygenated 
 muriatic acid with a certain proportion of fixed 
 alkali. This liquor can be imitated, by employ- 
 ing the following proportions for the distillation 
 and the alkaline solution : — Muriate of soda 77 
 grammes ; sulphuric acid 61 gr. ; oxide of man- 
 ganese 30 gr. The gas disengaged from these 
 materials is received in a litre of water, in which 
 120 gr. of common potash or soda have been dis- 
 solved. This liquor is to be diluted for use with 
 10 or 12 parts of water. 
 
 To diminish the offensive odour of the oxyge- 
 nated muriatic acid, Descroizilles mixed with it 
 carbonate of lime or chalk. 
 
 A short time since, Tennant made a prepara- 
 tion for which he obtained a patent in England : 
 
 * Annales dc Chimie, torn. ii. 
 
BLEACHING LIQUORS. 237 
 
 it is a combination of oxygenated muriatic acid 
 and lime, or oxygenated muriate of lime. This 
 substance has the property of absorbing readily 
 a great quantity of oxygenated muriatic acid. 
 To obtain this combination, it is requisite merely 
 to pass the gas, as it is disengaged, through slaked 
 lime till it be saturated. This lime is afterwards 
 dissolved in a certain proportion of water ; which 
 solution is employed in bleaching. Its effect 
 may be augmented by the addition of a little sul- 
 phuric acid. 
 
 To judge of the effect obtained from these 
 different preparations, and of their relative utility, 
 we must call to mind, first of all, the results of 
 observations collected from the theory. 
 
 Oxygenated muriatic acid is composed of two 
 elements, which are feebly united, and which 
 are disposed to enter into other combinations j 
 whence the easy oxygenation of substances ex- 
 posed to its action. But this action is exerted 
 with greater facility and energy when not impair- 
 ed by any combination which the oxygenated 
 muriatic acid may have previously made. Thus, 
 in the gaseous state, it acts with more energy than 
 when it has been combined with water before- 
 hand ; and in that case its activity may be too 
 great for the object proposed in bleaching. The 
 action of the water, however, being very feeble, 
 the liquid retains a lively odour, and there may 
 be obtained from it its whole sensible effect, only 
 retarded and modified at will, according to the 
 concentration which is given it. 
 
238 OF THE DIFFERENT 
 
 The alkalies exercise a much more powerful 
 action on the oxygenated muriatic acid than 
 water does, and thereby can give it a much 
 greater condensation, repressing almost entirely 
 its smell, which requires freedom of expansion, 
 and solution in air. The above (alkaline) liquor 
 is dissolved in a sufficient quantity of water to 
 accomplish the intended object of obviating the 
 inconveniencies of too brisk an action. It pro- 
 duces its effect more quickly, probably because 
 the potash tends to form a more intimate and 
 more energetic combination with the muriatic 
 acid, while the colouring matter exerts its action 
 on the oxygen. 
 
 The advantages presented by the lixivium of 
 Javelle, — the oxygenated muriate of potash or 
 soda, are therefore, I. To require a less complex 
 apparatus, for it is sufficient to employ a receiver 
 containing the alkaline solution, in order to con- 
 dense the oxygenated muriatic gas* with the 
 single precaution of plunging the conductor-tube 
 to the bottom of the receiver, and receiving the 
 gas under a tub ; 2. To repress almost entirely 
 the suffocating odour of the oxygenated muriatic 
 acid ; 3. To furnish the agent of oxygenation, 
 much more condensed, under the same volume, 
 and consequently to render it of easier and less 
 expensive carriage ; 4. lastly, To produce its 
 effect somewhat more speedily. — Let us next 
 examine the disadvantages of this preparation. 
 
 When a fixed alkali acts on the oxygenated 
 muriatic acid, the effect is not simple ; a portion 
 
■» 
 
 BLEACHING LIQUORS. 239 
 
 of the oxygenated muriatic acid is merely con- 
 densed, retaining the proportion of its elements, 
 and the properties dependent on the tendency 
 which they preserve to enter into other combina- 
 tions. 
 
 Another portion is decomposed ; and the re- 
 sult of the two new combinations which are esta- 
 blished in its stead, gives from five to six parts of 
 muriate of potash for one of superoxygenated 
 muriate of potash, a salt which contains nearly 
 0.38 of its weight of oxygen, to which it owes 
 its characteristic properties. Now, the oxygen 
 present in this last combination, in which it is 
 accumulated, is so fixed down, that it can no 
 longer attack the colouring particles, nor resume 
 the elastic state by the action of light. The 
 whole of the oxygenated muriatic acid which 
 suffers this transmutation of combination, is there- 
 fore lost for bleaching. Its quantity varies accor- 
 ding to the condensation of the alkaline liquor 
 which receives the gas, and it appears to increase 
 when the liquor is kept ; probably temperature 
 causes the results to vary.* 
 
 We thus perceive, that liquors, analogous to 
 the lixivium of Javelle, ought not to produce in 
 their agency on the colouring particles so much 
 effect as a simple aqueous solution, which con- 
 tains, under the same liquid volume, a quantity 
 of oxygenated muriatic gas equal to what has 
 been condensed by the alkali. 
 
 * Essai de Statique Chimique, torn. ii. 
 
 4 
 
240 OF THE DIFFERENT 
 
 It has even been found, that by adding simply 
 an alkaline solution to the oxygenated muria- 
 tic acid, its discolouring effect was diminished. 
 Rupp has made decisive experiments on this sub- 
 ject. He employed a solution of indigo for com- 
 paring, by the quantities of which the colour was 
 destroyed, the oxygenated muriatic acid without 
 mixture, with the same after adding to it dif- 
 ferent proportions of potash ; but to avoid the 
 uncertainty which might have proceeded from 
 the action of the sulphuric acid on the potash 
 combination, he decomposed the solution of sul- 
 phate of indigo by acetate of lead, thus render- 
 ing what he used, a solution of indigo in acetic 
 acid. He made similar trials with an infusion 
 of cochineal, which is still less liable to objec- 
 tions. It results equally from both, that the 
 more potash he put into a like quantity of oxy- 
 genated muriatic acid, the less liquor he could 
 blanch. The difference between the simple oxy- 
 genated muriatic acid, and that with which he 
 had mixed most potash, was nearly one-fourth in 
 favour of the first. 
 
 It is therefore proved, by theoretical conside- 
 rations and direct experiments, that the addition 
 of an alkali, when even it is not employed to con- 
 dense the oxygenated muriatic gas, impairs the 
 effect which this ought to produce. But in the 
 lixivium of Javelle, it raises the price of the 
 liquor nearly three times higher. It is obvious, 
 that these disadvantages ought to make the use 
 
 1 .. 
 
BLEACHING LIQUORS. 241 
 
 of it be rejected in a manufacture, where economy 
 is an indispensable condition. 
 
 The oxygenated muriate of lime has one ad- 
 vantage over the lixivium of Javelle, from the 
 great difference of price between lime and pot- 
 ash or soda j and its state of condensation, and 
 desiccation, renders its carriage less expensive. 
 But it has also the inconvenience of transforming 
 a portion of the oxygenated muriatic acid, and 
 of containing superoxygenated muriate, which 
 cannot be indicated in this combination by no- 
 menclature, which is precise only with regard to 
 very uniform combinations : it appears even that 
 the proportion of superoxygenated muriate is 
 considerable ; for if, after expelling by a slight 
 degree of heat the oxygenated muriatic acid 
 which had retained its properties, the remain- 
 ing substance be examined, it is found no longer 
 to produce discoloration ; and if it be urged 
 with a stronger heat in this state, much oxy- 
 gen gas is disengaged. Welter tells us, that in 
 his comparative experiments he had observed, 
 that the gas condensed by lime produced only 
 one-tenth of the effect which may be obtained 
 when it is received in water. The use of the 
 oxygenated muriate of lime must therefore be 
 disadvantageous ; but it may be convenient for 
 certain purposes, from the facility of carriage 
 and preservation, where the economy of the pro- 
 cess is of secondary consequence. Under this 
 point of view, it merits the commendation which 
 it has received. (Note Q.) 
 
 vol. I. Q 
 
242 
 
 OTHER, APPLICATIONS 
 
 The addition of sulphuric acid to the solution 
 of the oxygenated muriate of lime, increases the 
 effect, by the decomposition of the superoxyge- 
 nated muriate ; but to produce this effect fully, a 
 quantity of acid is required, which might become 
 dangerous. 
 
 These objections do not apply to the addition 
 of chalk, which has been recommended by Des- 
 croizilles, of which he makes use in his elegant 
 manufactory. Its value is very trifling j and al- 
 though our experiments appear to prove, that it 
 somewhat lessened the total effect of the oxy- 
 genated muriatic acid, yet this diminution is so 
 small that it may be neglected. Hence, though 
 the process with the simple oxygenated muriatic 
 acid may be executed without inconvenience, 
 there is no harm in employing the addition of 
 chalk, so as to repress the greater part of the 
 odour. We even recommend not to omit its use, 
 whenever persons are not very well instructed in 
 conducting the operations with the customary 
 attentions which are required. 
 
 CHAPTER IX. 
 
 Of the other Uses of the Oxygenated Muriatic 
 
 Acid. 
 
 The property of discolouring and whitening 
 which the oxygenated muriatic acid possesses, has 
 met with several applications, which their analogy 
 
OF CHLORINE. 243 
 
 to bleaching, and their relation to the art of dye- 
 ing, induce us to enumerate. 
 
 When cloths have been printed with different 
 mordants, they are passed into the madder, where 
 the designs assume different hues, according to 
 the nature of the mordants ; but the (vacant) 
 ground of these cloths also receives the madder 
 colour. This colour is much less fast than that 
 which has been fixed by the mordants ; and it 
 must be destroyed by means of cow dung and 
 bran, and long exposure on the grass. Nearly 
 the same process is employed to destroy the yel- 
 low ground of printed goods, which have been 
 passed through weld to give the figures those 
 hues which belong to yellow. At Manchester, 
 the properties of oxygenated muriatic acid, modi- 
 fied by ^certain operations, which have not been 
 made public, were speedily applied to that pur- 
 pose. 
 
 Widmer and Haussman made some trials, each 
 in his own way, from which it was ascertained, 
 that a liquor, composed in the proportions which 
 we have pointed out for the lixivium of Javelle, 
 might be employed with success, but with the 
 precaution of diluting it for use with a larger 
 quantity of water. "We shall state the result 
 which Widmer has given of his experiments. 
 
 " When the cloth comes out of the madder, it 
 is exposed for four or five days on the grass ; it 
 is then passed through a bath of cow dung, after 
 which it is laid down four days longer on the 
 grass, as at first. It is now submitted to an im- 
 
244 OTHER APPLICATIONS 
 
 mersion of about half an hour in the bleaching' 
 liquor, previously diluted-with about 35 parts of 
 water. After this operation, the cloth must be 
 exposed for two days on the grass. It is then 
 subjected to a new immersion, and exposed for 
 other two days on the field. Betwixt each opera- 
 tion the cloth must be well washed and beetled. 
 The exposure on the field, here prescribed, is 
 understood to be during fine weather ; for in bad 
 weather it must be exposed some days longer. 
 In general, the ground of a cloth which has been 
 well maddered, in order to have fast thorough- 
 proof colours, should be perfectly white after this 
 manipulation. 
 
 " It appears from this detail, that we no longer 
 employ bran at all for the whitening of maddered 
 goods. It is also obvious, that we have infinitely 
 reduced the heating operations, since formerly, 
 a piece of goods, after the maddering, received 
 at least from three to six boils, whilst at the pre- 
 sent day it gets one or two at most, and it is an 
 infinitely less time on the grass. 
 
 " 1 have often bleached maddered goods with- 
 out giving them any boil, submitting them merely 
 to immersions every twenty-four hours, and ex- 
 posing them alternately on the field. But this 
 has several inconveniencies. In the first place, 
 the goods are liable to have spots of a brick-red 
 colour, which the workmen call madder stains; 
 they proceed frequently from adulterated mad- 
 ders ; an inconvenience felt only with the madders 
 of Alsace. At other times, fat or oily matters, 
 
OF CHLORINE. 245 
 
 which are present in the goods, are the cause of 
 them. These stains oblige us pretty often to 
 subject the cloth to two boils, because the action 
 of the acid, and the exposure on the grass, are 
 insufficient. 
 
 " The goods, on coming out of the madder, 
 are laid on the field, because the large quantity 
 of colouring matter deposited on their ground, 
 destroys too great a quantity of the acid, and the 
 colours are thus much impaired, which has led 
 me to believe that they need the contact of air 
 to be rendered fast, if it be permitted me to make 
 use of this expression. 
 
 " The cloth, after the first exposure on the 
 grass, is subjected to a boil with cow dung. This 
 operation has the advantage of predisposing the 
 cloth to become white, to heighten by its heat 
 the colours fixed by the mordants, and to render 
 them more durable under the action of the air, 
 and of the oxygenated muriatic acid holding 
 potash in solution. I have diluted the liquor very 
 much, because I do not then fear injury to any 
 colour. I also pass through a colour that has a 
 black ground, or its derivative hues, with as much 
 confidence as those which have a mordant of 
 alumina. The cloth, on coming out of these im- 
 mersions, sometimes appears not to be sufficiently 
 bleached, but they are wonderfully disposed to 
 receive the action of the atmospheric oxygen. I 
 have found several times, that on a piece of cloth 
 being cut in two, when one-half of it had an im- 
 mersion, and the other none, the former bleached 
 
246 OTHER APPLICATIONS 
 
 more in two days on the field, than the latter in 
 fifteen. 
 
 " When we are obliged to make the cloth un- 
 dergo a second boil, it is given on its return from 
 the grass, immediately after the first immersion 
 in the liquor. By this second boil, we succeed 
 in reducing entirely into a species of soap, and 
 removing, those spots of grease which I have 
 mentioned above. This likewise dissolves the 
 colouring matters which have begun to oxyge- 
 nate. 
 
 " The cloths which come out of the weld, 
 whether with a yellow ground or a white, are first 
 exposed for four or five days on the grass, and 
 are then, in like manner, subjected to an immer- 
 sion in the same liquor. The ground of the goods 
 does not appear at all bleached ; but as I have 
 already stated, they are disposed to receive the 
 action of the oxygen, and at the end of two or 
 three days' exposure on the grass, they are of a 
 superb white. When these cloths return for the 
 last time from the field, the yellow has a deep 
 cast, which renders it somewhat dead. This pro- 
 bably depends on the action of the oxygen of the 
 liquor, and of the atmosphere, which seems to 
 have effected a commencement of combustion. 
 Its vivacity is easily restored, by passing the 
 cloths through a water very slightly acidulated 
 with muriatic acid ; but the water must be no 
 sourer than weak lemonade. This operation has 
 moreover the advantage of carrying off the last 
 portions of the yellow, which may have remained 
 

 OF CHLORINE. 247 
 
 on the ground, or on the red 5 and which, conse- 
 quently, would dull the lustre of both. This 
 little manipulation, which lasts at farthest five 
 minutes, has also the advantage of rendering the 
 olive colours more of a greenish cast, tints which 
 the dyer has usually much difficulty to obtain. 
 
 " I forgot to mention, that it is the strength of 
 the colours which directs me as to the strength 
 of the liquor. When the colours are powerful, I 
 contrive it so, that the oxygenated muriatic acid 
 may predominate in the liquor ; on the contrary, 
 if the colours be weak, it is the alkali which 
 ought to predominate. But if a saturated oxy- 
 genated muriate (chlorate) of potash were made, 
 it would no longer have the property of bleach- 
 ing. I suspected, that by passing cloths merely 
 into an alkaline water, it would dispose them 
 equally to whiten on the grass - t but experience 
 has not realized this expectation. 
 
 " I was a long while of obtaining complete suc- 
 cess with the oxygenated muriatic acid holding 
 potash in solution, because I employed it in too 
 strong a dose, and, of consequence, I injured the 
 colours. But at present M. Oberkampf becomes 
 every day more attached to this new method, 
 which is infinitely less costly than the old one, 
 and by which we obtain a more beautiful white, 
 and far livelier colours." 
 
 Widmer has however been obliged to abandon 
 this process, because it required to be conducted 
 by himself, and because the accidents, from in- 
 attention of workmen, rendered this method too 
 
248 
 
 OTHER APPLICATIONS 
 
 uncertain and too expensive. We know not 
 whether a like cause has made it be equally given 
 up in the other manufactories, or if they have 
 found out some modifications which render the 
 process less uncertain ; but it should be retained 
 for bleaching cloths in the texture of which there 
 is linen or cotton dyed with some colour, which 
 could not resist the too lively action of the oxy- 
 genated muriatic acid, or even exposure on the 
 grass. (See Note G.) 
 
 When we wish to deprive of colour a piece of 
 cloth which has some defect of dyeing or design, 
 or whose colours have been rendered dull by use, 
 a ley should first be given to it, and then one 
 immersion, which is commonly sufficient. It is 
 now submitted to a second ley, and passed through 
 water acidulated with sulphuric acid. Without 
 this last operation it would preserve a great part 
 of its mordant, and could not, for this reason, re- 
 ceive a new impression or another design. 
 
 Chaptal made, at an early period, a happy ap- 
 plication of the properties of the oxygenated mu- 
 riatic acid to the bleaching of paper, and the 
 restoration of engravings and books. We shall 
 insert here the description which he gave of his 
 processes. 
 
 " Blotting paper put into oxygenated muriatic 
 acid becomes white in it, without being altered 
 in its texture. The rags of coarse and bad cloth, 
 made use of in paper mills to form this paper, 
 are bleached in this acid, and then afford a paper 
 of superior quality. I have whitened by this pro- 
 
OF CHLORINE. 249 
 
 cess a quintal of paste intended to furnish blot- 
 ting paper, and the increase of value in the pro- 
 duct was estimated at 25 per cent, while the cost 
 of the operation, rigorously calculated, did not 
 raise the expense above 7 per cent. 
 
 " The property which this acid possesses, of 
 bleaching paper, without affecting the texture, 
 renders it valuable for repairing old books, and 
 smoked engravings. Engravings injured to such 
 a degree as to render the design difficult to be 
 distinguished, have been repaired and refreshed 
 in so astonishing a manner as to appear new. 
 Old books, soiled with that yellow tint which 
 time leaves on them, may be so restored as to make 
 us think they had just issued from the press. 
 
 " Simple immersion in the oxygenated muria- 
 tic acid, and a longer or shorter continuance in 
 it, according to the strength of the liquor, are 
 sufficient to bleach a print ; but when a book is 
 the object, other precautions are necessary. As 
 it is requisite that the acid should moisten all the 
 leaves, care must be taken to open the book well 
 up, and to make its boards rest on the edge of 
 the vessel, so that the paper alone dips into the 
 liquor. Such leaves as are sticking together, 
 must be adroitly separated, that they may be all 
 equally impregnated. The liquor assumes a yel- 
 lowish tint, the paper becomes white, and after 
 two or three hours the book is withdrawn, in or- 
 der to be plunged into pure water, which is to 
 be renewed from time to time to carry off any 
 
250 OTHER APPLICATIONS 
 
 remaining oxygenated muriatic acid, along with 
 its disagreeable smell. 
 
 " This process has succeeded with me pretty- 
 well. It was the first which I employed. But 
 too frequently the colour of the leaves was varie- 
 gated j sometimes several pages have not been at 
 all bleached ; and I was forced to adopt a surer 
 process. We begin by unstitching the books, 
 and reducing them to leaves. These leaves are 
 set in squares contrived in a shallow leaden tub, 
 with very thin plates, so that the leaves, laid flat, 
 are separated from one another by hardly per- 
 ceptible intervals. The acid is then poured gent- 
 ly in, making it fall on the sides of the tub ; and 
 to prevent the leaves from being deranged after 
 the operation is finished, the acid is drawn off by 
 a stop-cock placed in the bottom of the tub. 
 This liquid is replaced by fresh water, which 
 washes the paper, and deprives it of the odour of 
 the oxygenated acid. It is now hung up to dry, 
 smoothed and bound. I have restored by this 
 means several precious works, which were of no 
 value from their bad condition. The leaves may 
 be set also upright in the tub, a position which 
 offers some advantages, as they are less readily 
 torn. For this purpose I constructed a wooden 
 frame, which I fixed down at the height which I 
 thought suitable, conformably to the height of 
 the leaves that I wished to bleach. This frame 
 supported very thin slips of wood, leaving be- 
 tween them intervals of half a line. I placed two 
 
_ _ 
 
 OF CHLORINE, 251 
 
 leaves in each of these intervals, and fastened 
 them with two small wedges of wood, which I 
 pushed between the slips so as to press the leaves 
 against them. I give the more preference to this 
 process, because, when the operation is done, I 
 lift out the frame with the leaves, and plunge the 
 whole into fresh water. By this operation, not 
 only books are restored, but the paper receives a 
 degree of whiteness which it never had. This 
 acid has also the advantage of effacing spots of 
 ink which frequently depreciate books and prints. 
 This liquor does not attack the stains of grease or 
 oil ; but it has been long known, that a weak so- 
 lution of potash (caustic alkali) is a sure means 
 of removing these marks. 
 
 " When I have had to repair engravings in 
 such bad condition that they exhibited merely 
 fragments pasted down on paper, I was afraid of 
 spoiling these fragments in the liquor, from the 
 loosening of the paste. In this case, I took the 
 precaution of enclosing the print in a large cylin- 
 drical jar, which I inverted over a glass, into 
 which I put the proper mixture for disengaging 
 oxygenated muriatic gas. This aeriform sub- 
 stance filled the interior of the jar, and acted on 
 the print, consuming the filth, destroying the 
 spots of ink, while the fragments remained glued, 
 and thus preserved their relative position." 
 
 Loysel has prosecuted particularly the applica- 
 tion of oxygenated muriatic acid to the bleaching 
 of the paste of paper, because he was charged, as 
 member of the committee of assignats and coins, 
 
252 
 
 OTHER APPLICATIONS 
 
 to inspect this process, which was used for the 
 assignat paper. We shall present a summary of 
 the observations which he published.* 
 
 By the ordinary processes, only a small por- 
 tion of the rag can furnish fine white paper j all 
 the rest being appropriated to papers of inferior 
 quality. 
 
 The bleaching of the paste of paper, even when 
 derived from the most ordinary rags, can give it 
 the quality of that of the finest rags. 
 
 The sinew of the paper depends on that of the 
 fibres of which it is fabricated. The rags of new 
 cloth and cordage afford a more sinewy paper 
 than old rags. In the first rank are put rags of 
 fine new webs, either green, or bleached by the 
 oxygenated muriatic acid ; after these come cor- 
 dage and old rags. 
 
 The paper intended for bank-notes, or bills of 
 commerce and service, should be sinewy, to ren- 
 der it less apt to be torn than its thinness would 
 otherwise occasion. For this, it is right to em- 
 ploy in whole, or in a great measure, materials of 
 the first class. 
 
 The processes prescribed for the bleaching of 
 threads and cloths must be employed here, that 
 is to say, the substance must be subjected to lixi- 
 via and immersions in the oxygenated liquor, 
 when it is green (unbleached) ; but in operating 
 upon rags, it is sufficient to give them an immer- 
 
 * Annates cle Chimie, tom.xxxix. 
 
OF CHLORINE. 253 
 
 sion, and to pass them afterwards into acidulated 
 water. 
 
 An inconvenience has been experienced in 
 operating upon the paste of paper. It appeared 
 very white, and yet it furnished an unequal paper. 
 It was because this paste subsided, so that the leys 
 and the liquors could hardly penetrate it. This 
 inconvenience was remedied by taking the matter 
 in a medium state, between that of a paste and of 
 rags. This was secured by tearing it asunder 
 under a first cylinder, thus destroying the texture 
 of the rags, and separating the fibres that com- 
 posed the thread. 
 
 When a very tough paper is wanted, the green 
 rags must be submitted to the successive opera- 
 tions of bleaching. But when whiteness is the 
 principal object, the cost of the operation may be 
 considerably diminished, by leaving the rags for 
 some time in the fermenting tub, and washing 
 them with care. After this, one lixivium, two 
 oxygenated liquors, and acidulated water, will be 
 sufficient. 
 
 In this operation, the combination of oxygen- 
 ated muriatic acid with potash, dissolved in twenty 
 times its weight of water, has been employed. 
 Undoubtedly, with a suitable apparatus, there 
 might be used without inconvenience simple oxy- 
 genated muriatic acid, or this mingled with chalk. 
 
 Notwithstanding the increase of expense caused 
 by this addition of alkali, Loysel shews, that the 
 value added to the paper by the process affords 
 a considerable profit. 
 
254 OTHER APPLICATIONS 
 
 In treating of hemp and flax, we have described 
 the processes by which it has been attempted to 
 give them the appearance of cotton ; but the 
 oxygenated muriatic acid may be beneficially em- 
 ployed for this purpose. 
 
 Pajot des Charmes seems to have been the first 
 who made this application. We shall recite the 
 passage where he points it out.* 
 
 After having announced that the loose fibres 
 bleach very quickly, that is to say, at one or two 
 immersions less than average yarns, he adds : " It 
 is to be remarked, that the tow of flax or hemp 
 proceeding from the fibres thus bleached, or 
 bleached separately, cut, if it be too long, and then 
 carded, singularly resembles the cotton of Siam, 
 which is known to be the shortest and the most 
 common of the cottons of commerce. When it 
 is well carded, their difference cannot be discern- 
 ed j nor is it possible to distinguish between them 
 in spinning. I took occasion to make some of it 
 be woven at the end of a web : it would have 
 been taken for real cotton. I took occasion, in 
 like manner, to employ some of it for candle- 
 wicks, without any perceptible difference being 
 found by the quantity of light or the brightness. 
 It would be very interesting, without doubt, to 
 know all the benefits which could be derived 
 from this application of the oxygenated muriatic 
 acid to the arts of life." 
 
 * L'Art de Blanchiment, page 106. 
 
OF CHLORINE. 255 
 
 Some time thereafter, but without knowing 
 what has been now detailed, a description of 
 operations made in the laboratory of the Poly- 
 technic school, to accomplish the above object, 
 was published in its Journal. But Giobert has 
 given us more extended and more exact obser- 
 vations, capable of directing this new branch of 
 art, which may probably acquire some import- 
 ance.'* 
 
 " The process which I have followed," says he, 
 " is in general the same as what Berthollet has 
 just proposed, but with this difference, that in the 
 trials made at the Polytechnic school, long fibres 
 cut in fragments about six centimetres in length 
 were employed ; whereas, in all my attempts, and 
 in my operations on the large scale, I employed 
 merely hemp tow of the worst quality, at three 
 sous the pound. 
 
 " The process which Berthollet describes is 
 the same, and consists of the following operations. 
 
 " The fibres are covered with water, and left 
 in it for three or four days ; after which they are 
 boiled in simple water. 
 
 " 2. They are treated with a ley, and then 
 assed into the oxygenated muriatic acid ; oper- 
 tions which should be repeated alternately four 
 times. 
 
 " 3. The fibres are now transferred into a bath 
 of water, charged with one-hundredth of sulphu- 
 ric acid, and left in it for half an hour. 
 
 * Bibliot. Ital. vol. ii. 
 
 8 
 
256 OTHER APPLICATIONS 
 
 " 4. The fibres, when taken out of this bath, 
 are washed very carefully, and plunged in soap 
 water. They are then stretched out without 
 wringing, on hurdles, and left to dry. 
 
 " On this process Berthollet has remarked, 
 1. That it requires only from five to six hours 
 when small quantities are operated on j 2. That 
 the loose fibres thus prepared, were capable of be- 
 ing spun into very fine yarn of sufficient strength, 
 although the filaments had been cut very short in 
 his trials ; 3. That the leys should not be too 
 strong, but that they should be boiling hot j 4. 
 That whether the finest flax, or the coarsest hemp 
 tow be employed, we obtain filaments equal in 
 their fineness and whiteness ; finally, he adds, 
 that by preventing too strong desiccation, the last 
 immersion in soap water might be suppressed. 
 
 " The different observations which we are go- 
 ing to make on this process, are the result of 
 operations on a large scale, which have brought 
 into the market cottony cloth, and bales of this 
 hemp-cotton, which were not distinguishable from 
 ordinary cotton. From these results, various 
 ameliorations have suggested themselves. We 
 shall follow in our operations the same order as 
 ought to be pursued in the practice of the above 
 process. 
 
 "1. Preliminary maceration of the fibres, (fi- 
 lasse.J 
 
 " This operation is not absolutely necessary, 
 and it may be supplied by a good ley. But a 
 previous maceration is more economical. Instead 
 
OF CHLORINE. 257 
 
 iof pure water, old ley should be used in prefer- 
 ence ; but if there be none of this, plants, espe- 
 cially mucilaginous ones, boiled in water with the 
 addition of a little potash, afford a better solvent. 
 The steeping may also be continued longer, even 
 for five or six days without risk in the hottest 
 season, along with the employment of alkalies 
 that seem to favour the putrid fermentation. 
 In spring, autumn, and winter, it may be prolong- 
 ed with advantage from seven to nine days. By 
 this longer maceration, the fibres become finer, 
 that is to say, the filaments come asunder, and 
 the operations to which they are subjected in the 
 sequel have a greater effect. 
 
 " When the fibres are well steeped, it is abso- 
 lutely useless to wash them with hot water, which 
 only augments the cost. Cold water is sufficient ; 
 but it must be in a stream, treading the fibres with 
 the feet till the water issues very clear. 
 
 " 2. Of the leys and immersions in oxygenated 
 muriatic acid. 
 
 " The leys might be dispensed with, by aban- 
 doning the fibres to fermentation, in the manner 
 above stated, after having passed them through 
 the oxygenated muriatic acid ; but this practice 
 is too tedious. Nothing however occasions more 
 inconvenience here than the lixiviation. Every 
 filament of hemp or flax which has been lixivi- 
 ated thence derives stiffness, especially in its ex- 
 tremities, which are to be joined continuously in 
 the formation of yarn. Hence its spinning be- 
 comes difficult, disagreeable, and unequal. The 
 
 vol. I. R 
 
258 OTHER APPLICATIONS 
 
 spinster loses patience ; while the ends of the 
 fibres do not twist well together, their adhesion is 
 imperfect, and by sliding on each other, when 
 the thread is slightly pulled, render it feebly tena- 
 cious. This may be regarded as a general fact. 
 Yet leys can hardly be dispensed with in a great 
 manufacturing establishment of hemp-cotton. 
 For this reason, we must try to remedy these in- 
 conveniencies, which cannot be economically 
 avoided. We shall point out by and by two 
 methods which succeed pretty well. As to the 
 leys, they ought not to be strong, as Berthollet 
 rightly says ; but they should be very caustic, 
 carefully preventing an excess of lime or of lime 
 water in the liquor ; for, in this case, the fibres 
 are too much weakened on one hand, and grow 
 stiff on the other. A ley is not too caustic, when 
 on evaporating a portion of the liquor, it is not 
 disturbed, nor lets fall lime. The ley-boil ought 
 not to exceed three hours ; but after this the 
 greatest part of the liquor must be drawn off, and 
 the fibres must be allowed to cool in a heap in the 
 tub before washing them. It is useful to place 
 on the cloth which covers the fibres, large com- 
 pressing weights. This repose of the fibres, with 
 little liquor, has a more decided effect than the 
 lixiviation ; and the larger the quantity operated 
 upon, the better does it answer. 
 
 " It is useful to arrange the apparatus, so that 
 the fibres can be thereafter washed by a stream of 
 water in the very tub in which the lixiviation has 
 taken place - 7 and it is in this same tub that it is 
 
OF CHLORINE. 259 
 
 afterwards subjected to the oxygenated muriatic 
 acid, which ought to be very weak. 
 
 " 3. Bath of sulphuric acid. 
 
 " An acid bath is indispensable to give a 
 shining whiteness to the fibres. But these when 
 bleached contain lime, which, forming an insoluble 
 salt with sulphuric acid, causes this to be ill adapt- 
 ed for the purpose. The resulting sulphate of lime 
 adheres to the fibres, making them rigid j nor is 
 it possible to carry it entirely away by washing. 
 I have found, that by substituting muriatic acid 
 for the sulphuric, the fibres have more pliancy. 
 Muriatic acid has a somewhat higher price in 
 commerce; but by making it within the manufac- 
 tory, the expense incurred by this substitution is 
 not very considerable, and it ought to be pre- 
 ferred. 
 
 " 4. Soaping. 
 
 " The last operation is the soaping. This is 
 indispensable ; nor ought any person to imagine 
 he can do without it, for it is only by the soaping 
 that we succeed in thoroughly separating the fila- 
 ments. Besides, it is only by the soaping that 
 we begin to correct the rigidity which the ley 
 gave to the fibres, and to give them the pliancy 
 of ordinary cotton. But to attain this end, we 
 must proceed in a different manner from that 
 described by Berthollet. 
 
 " The fibres, on coming out of the preceding 
 bath of muriatic acid, instead of being washed 
 with much care, as is stated in Berthollet's pro- 
 cess, ought not to be washed at all. They should 
 
260 
 
 OTHER APPLICATIONS 
 
 be plunged, while still wet with the acid liquor, 
 into the hot soap water, without fearing in the 
 least the action of the acid. The soap is decom- 
 posed by the acid, the resulting muriate of soda is 
 carried off by successive washings, and the oil of 
 the soap being absorbed by the fibres, gives them 
 pliancy and softness. The filaments remain more 
 delicate, and the successive operations of carding 
 and spinning become consequently easier. This 
 is the first of the two methods which we an- 
 nounced for removing from the fibres the stiffness 
 which the alkalies of the lixivia gave them, 
 
 " 5. To give pliancy to hemp-cotton. 
 
 " Notwithstanding the preceding processes, 
 the cotton has not yet got all the pliancy which 
 is required. This will be completely given by 
 the following operation. The dried fibres are 
 formed into large bales, and kept well packed up 
 in a somewhat damp place for two or three 
 months. A species of fermentation is by this 
 means excited in the fibres, which gives them the 
 desired fineness. 
 
 " 6. To give the appearances of ordinary cotton 
 to hemp-cotton. 
 
 " The cotton procured from hemp by the preced- 
 ing operations, whatever care may have been be- 
 stowed, is always different from ordinary cotton, 
 and it is easy to distinguish it. The fibres pre- 
 serve a peculiar glitter, very different from the 
 dead white of cotton. This lustre is sufficiently 
 agreeable, and may possibly be sought after for 
 several objects of manufacture j but it is not a 
 
OP CHLORINE. 261 
 
 property of cotton, and must therefore be re- 
 garded as a defect in •our attempts to imitate 
 ordinary cotton. I have discovered only one 
 method of remedying it, which consists in mixing 
 by the cards from 10 to 15 per cent of ordinary 
 cotton with that of hemp. The cotton yarn made 
 by this means is no longer distinguishable from 
 ordinary cotton yarn." 
 
262 OF DYEING OPERATIONS 
 
 SECTION IV. 
 
 OF DYEING OPERATIONS IN GENERAL. 
 
 CHAPTER I. 
 
 Of Dyehouses and the Manipulations of the Art 
 
 of Dyeing. 
 
 If it may be regarded as a general principle, that 
 processes performed in a great manufactory are 
 more advantageous than those which are insulat- 
 ed fisolesj, since from the subdivision of labour 
 each workman, occupied with a single object, 
 acquires celerity and perfection in his employ- 
 ment, and since every thing being concatenated, 
 each portion of the work is carried forward with- 
 out loss of time ; this principle should be applied 
 to dyeing for a peculiar reason, because the 
 residuum of one process can frequently serve 
 for another. A bath which is found to be too 
 much exhausted for one colour, or even for what 
 is called the suites (gradations) of a colour, may 
 either give a ground (footing) to other dye stuffs, 
 or form a new bath, by mixing other ingredients 
 with it. Gall-nuts which have been employed for 
 galling silk, may still be useful for other opera- 
 
IN GENERAL. 263 
 
 tions on wool and cotton. A great number of 
 similar examples might be adduced. 
 
 By such considerations, it would be easy to 
 prove how adverse to the advances of the art 
 were that division into the great and little dye, 
 that classification of silk, wool, and linen dyers, 
 and those regulations which prohibited a dyer of 
 one class to keep by him the ingredients assigned 
 to another class. On the contrary, it seems pro- 
 per to encourage large undertakings in dyeing ; 
 and those who are to direct them ought to lay 
 down a plan of the operations, so that there may 
 be a relation between them all, and that there may 
 be no waste of ingredients, time, fuel, or manual 
 exertion. This arrangement should be made sub- 
 servient to the probable demands of commerce. 
 
 A dyehouse ought to be spacious, well lighted, 
 and as near as possible to a stream of water. It 
 should be floored with lime and cement ; it 
 should be provided with ready outlets for the 
 water and the spent dye-baths j and the whole so 
 ordered as to secure the utmost cleanliness. 
 
 The boilers, whose arrangement and size de- 
 pend on the operations for which they are in- 
 tended, should be made of copper or brass ; 
 except for dyeing scarlet, for which it is better to 
 employ boilers of tin, as well as for other delicate 
 colours, where a solution of tin is made use of. 
 Brass is less liable to be attacked by saline sub- 
 stances, and to stain the goods, than copper. We 
 shall see, however, that in many cases vessels of 
 wood may be substituted for metal boilers. It is 
 
264 OF DYEING OPERATIONS 
 
 of consequence to cleanse the boilers well after 
 every operation ; and such as are of great capa- 
 city ought to have in their bottom a copper pipe, 
 with a stopcock at its outer end, which is opened 
 when the baths are to be emptied. 
 
 Above each boiler, holes are pierced in the 
 chimney-piece or wall, for resting the ends of 
 poles, which serve to sustain the hanks of wool 
 or silk while draining, or stuffs of which only 
 small portions are to be dyed. Thus also the 
 bath-liquor falls back into the boiler. 
 
 For piece-goods, a winch or reel is employed, 
 the two ends of which rest in two forks of iron, 
 placed, at pleasure, in holes bored in the curb 
 that supports the edges of the coppers. 
 
 Several silk and cotton dyes, for which ebulli- 
 tion ought not to be employed, are performed in 
 long vessels of copper or wood, called troughs or 
 backs, (barques ou baquetsj. 
 
 As the most part of colours applied on silk 
 are very delicate, they require to be speedily 
 dried, to prevent their changing. For this pur- 
 pose a drying room is provided, which is heated 
 by means of a stove. The silk is stretched on 
 a moveable pole, called a shaker (brariloire), 
 which is hung up and agitated to accelerate 
 the desiccation. A drying room is also used for 
 cotton cloths which have been impregnated with 
 a mordant. 
 
 Long details must be entered into, were we to 
 describe every thing which constitutes a dye- 
 house. Inspection will instruct much more 
 
IN GENERAL. %C)5 
 
 speedily and exactly than a minute description 
 of these objects could do. The distribution of a 
 dyehouse ought also to be subservient to the 
 operations for which it is destined. It should be 
 so regulated, that these operations may follow 
 one another with most advantage. 
 
 But it is desirable for the advancement of the 
 art, as well as that of the science itself, that a 
 small place may be reserved, in which the appa- 
 ratus necessary for the common experiments of 
 chemistry and the trial of dyes may be collected. 
 
 The manipulations of dyeing are neither dif- 
 ficult nor complex. Their object is, to impreg- 
 nate the substance which we wish to dye with 
 the colouring particles held in solution in a bath ; 
 to make the agency of the air co-operate in the 
 fixation of the colouring particles, or in giving 
 them lustre j and to discharge with care such, as 
 have not been fixed in the dyed stuff. We shall 
 content ourselves with giving an account of the 
 most common manipulations, and of the deno- 
 minations. 
 
 When one or more pieces of goods are to be 
 dyed, the winch (reel) is employed, as above des- 
 cribed. One end of the cloth is wrapped round 
 this reel, which being turned quickly, carries 
 round the whole piece in succession. The winch 
 is next turned in the opposite direction, in order 
 that the part of the web which was first plunged 
 the former time, may be last at the second im- 
 mersion, whereby the dyeing is rendered as 
 equable as possible. If the piece of goods be 
 
%66 OF DYEING OPERATIONS 
 
 long enough, or if several are to be dyed of the 
 same colour, their two extremities are stitched 
 together, the winch is passed within, and then 
 set on its forks. 
 
 When a solution of iron is employed, especially 
 to give different shades to cotton goods, which 
 are, for example, to be afterwards passed through 
 madder, we must prevent with great care the 
 progressive and unequal oxidation of the metal, 
 according to the directions of Chaptal on this 
 subject,* which we shall take occasion to recite. 
 
 If wool in the fleece is to be dyed, there is set 
 over the boiler a very broad kind of ladder, 
 (called by English dyers, a scraw or serai/), the 
 bars of which are very close together. On this 
 the wool is laid to be drained and aired, as well 
 as during the changing of the bath. 
 
 When the wool is in skeins, a rod is passed 
 through each of them, and the manipulation is 
 the same as for silk and thread. This manipula- 
 tion consists in turning round in the bath the 
 hanks of silk, and the skeins of thread or woollen 
 yarn on the rods. This is called User (shaking 
 over), and to the rod the name lisoir (skein stick) 
 is given. 
 
 After silks and yarns have been dyed, it is 
 necessary to wring them, in order to squeeze out 
 the excess of the colouring particles. This ope- 
 ration is performed on a cylindrical piece of 
 wood, which is fixed at one end in a wall or to a 
 
 * Memoires de l'lnstit. torn. iii. 
 
IN GENERAL. 267 
 
 post. It is called espart. When this operation 
 is repeated several times in succession, in order 
 to dry and give lustre, it is called cheviller, (wring- 
 ing by the jack and pin). 
 
 When a certain quantity of ingredients is add- 
 ed to a bath, it is said that a brevet is given it ; 
 and it is pallied (on le pallie) by stirring it about 
 and mixing it with a rake. 
 
 Sometimes a first colour is given in order to 
 apply another one above it, thus forming a com- 
 pound, colour. This is what is called giving a 
 ground, (donner un pied J. 
 
 Disbroder (rinse J is to wash silk from its dye, 
 or its soap water, in a small quantity of water, to 
 which the name of disbrodure (rinsing J is given. 
 
 When a stuff must be passed several times 
 through the same bath, the name passe (dip J is 
 given to each particular operation. 
 
 A colour is rosed, when the yellow tone of a 
 red colour is changed into a shade which borders 
 more on the crimson, or on the colour of roses ; 
 and a colour of a red-yellow is veered (vireej, 
 when it is made to turn to a more decided red. 
 
 Although the manipulations of dyeing may not 
 be very various, and may appear very simple, 
 they require peculiar care, as well as a skilful 
 eye, to judge of the qualities of the bath, to raise 
 and support the heat at the degree suited to each 
 operation, to remove all the circumstances whicli 
 might produce inequality in the colour, to judge 
 with precision of the shades as they come out of 
 the bath, to match those which serve for patterns, 
 
268 OF FUEL. 
 
 and to establish the desired relation between a 
 succession of hues. 
 
 CHAPTER II. 
 
 Of Fuel 
 
 As fuel is one of the chief articles of expense 
 in dyeing, it is of great consequence to diminish 
 its consumption as much as possible, and to select 
 the kind which may afford the desired effect with 
 the least cost. It is proper, therefore, to be ac- 
 quainted with the philosophical principles of the 
 production of heat by combustion, the theory of 
 which we owe chiefly to Lavoisier, as well as 
 with the laws of its communication, in order to 
 be able to guide ourselves afterwards in their 
 application to the various circumstances that 
 may occur. 
 
 When a body is burned, none of its ponderable 
 principles are destroyed. They previously formed 
 a mere combination with each other, and they are 
 separated at the high temperature to which they 
 are exposed ; thus forming other combinations 
 with the oxygen with which they come into con- 
 tact. Such of these principles as cannot combine 
 with it, that is to say, earth, certain salts, and 
 metallic ingredients, constitute the ashes. 
 
 The combinations formed, when the reciprocal 
 action of the oxygen gas and of the inflammable 
 principles present in the combustible becomes 
 
, — - 
 
 OF FUEL. 269 
 
 complete, are carbonic acid and water. The 
 proportion of these new products varies, accord- 
 ing to that of the carbonaceous particles, and of 
 the hydrogen or base of inflammable air which 
 exists in the combustible. Let us take common 
 charcoal for an example : — 
 
 If 100 parts of charcoal be burned in a glass 
 bell, whose orifice is plunged under mercury, 
 there is found, after the combustion, a weight of 
 carbonic acid, equal to that of the charcoal burn- 
 ed, and of the oxygen, which has now lost its 
 properties. This acid so formed is composed, in 
 100 parts, of about 72 of oxygen and 28 of char- 
 coal. A little water is however generated, which 
 is taken up by the carbonic acid, or remains in 
 the liquid state. The unknown quantity of water 
 prevents us from regarding the determination 
 now given as rigidly exact. 
 
 If alcohol or spirit of wine be burned, the re- 
 sult is different. A weight of water is obtained 
 exceeding that of the alcohol, because the com- 
 bustible principle of alcohol is chiefly hydrogen, 
 which forms water by combining with oxygen. 
 Oil also affords much water, for the same reason. 
 Charcoal and alcohol, or rather ether, may be 
 regarded as the two extremes, of which one yields 
 most carbonic acid, and the other most water ; 
 and the other combustibles may be viewed as 
 mean terms, which approach more or less to one 
 of the two extremes, according to their composi- 
 tion. 
 
270 OF FUEL. 
 
 While the hydrogen and the carbon combine 
 with the oxygen, which forms a little less than 
 the fourth part of the atmospheric air, the caloric 
 or principle of heat, which was combined with 
 the oxygen gas, giving it the elastic state, is in 
 a great measure disengaged. A portion of it is 
 also probably disengaged from the charcoal, and 
 especially from the hydrogen j but as the heat 
 produced when oxygen passes from one combina- 
 tion into another, appears nearly proportional to 
 the quantity retained, we depart very little from 
 the truth, in ascribing to it the whole heat disen- 
 gaged in combustion. Hence the heat produced 
 in combustion, must be regarded as proportional 
 to the quantity of water and carbonic acid form- 
 ed. We must however remark, that the same 
 quantity of oxygen which enters into combina- 
 tion with hydrogen to form water, gives more 
 heat than when it produces carbonic acid with 
 charcoal. Hence combustibles which contain 
 much hydrogen, such as the oils, the resins, and 
 pit coal, produce in equal weight, and in circum- 
 stances equally favourable, more effect than those 
 which owe their inflammability to charcoal. 
 
 If the proportion of oxygen gas which com- 
 bines be insufficient (for saturation), water and 
 carbonic acid are not the sole products. A gas- 
 eous substance is formed, which may be regard- 
 ed as intermediate, being convertible into water 
 and carbonic acid, by means of a new proportion 
 
.OF FUEL. 271 
 
 of oxygen. It has been named oxycarburetted 
 hydrogen, in order to denote its composition.* 
 
 Oxycarburetted hydrogen gas produces the 
 blue flame over furnaces, when its temperature 
 is great enough to burn on passing into the at- 
 mosphere, where it finds the oxygen which was 
 deficient in the furnace. 
 
 The conditions necessary to obtain the greatest 
 effect of combustion may be established on the 
 foregoing considerations : 1. The quantity of oxy- 
 gen ought to be sufficiently great for the whole 
 charcoal and hydrogen to enter into complete 
 combination, without producing oxycarburetted 
 hydrogen gas, and without the combustibles es- 
 caping under the form of soot or smoke. 
 
 2. On the other hand, too great a proportion 
 of air must be avoided, for whatever is useless 
 to the combustion, by abstracting the heat disen- 
 gaged from the fuel entering into combination, 
 would obstruct the elevation of temperature which 
 is the object of the combination. 
 
 3. The current should be rapid, that the heat 
 may become intense, and the temperature be suf- 
 ficiently elevated for every thing combustible to 
 undergo the oxygenous combination. 
 
 In order to obtain the greatest effect of a com- 
 bustible, none of its particles capable of combin- 
 ing with oxygen should escape the operation ; 
 there should be neither soot nor smoke ; a result 
 obtained chiefly by the just proportion between 
 
 * Statique Chim. torn. ii. 
 
 7 
 
TJ% OF FUEL. 
 
 the lower opening of a furnace, its grate and 
 
 ] chimney. 
 
 / The current of air which maintains combustion 
 
 should be easy •, but if the chimney is too large, 
 the carbonic acid formed is carried off with diffi- 
 culty ; it remains too long in contact with the 
 combustible body, thereby opposing its combus- 
 tion, while an interior circulation is established, 
 which brings back the cold air towards the boiler, 
 and pushes down the smoke. If the chimney is 
 not high enough, a portion of the inflammable 
 gas escapes without burning, as well as the car- 
 bonaceous particles that form the soot ; whence 
 the effect of the combustible is diminished. A 
 higher column of air, rarefied, and rendered lighter 
 by heat, and next its condensation, as well as that 
 of the steam and carbonic acid, towards the top 
 of the chimney, would have contributed to esta- 
 blish a more rapid aerial current. These effects 
 are peculiarly observed in reverberatory furnaces, 
 in which it is easy to verify the benefit of a chim- 
 ney whose opening is in due proportion to the 
 size of the furnace, and whose activity is increas- 
 ed by adding to the upper orifice a certain extent 
 of pipe. But too lofty a chimney is another in- 
 convenience to be avoided ; because the combus- 
 tible parts which rise have time to cool below 
 the degree at which their combustion takes place, 
 forming merely a mass, which, with the carbonic 
 acid, opposes the circulation of air. 
 
 When a furnace is intended for a boiler or a 
 series of boilers, it must be so managed that the 
 
OF FUEL. 273 
 
 combustion is completely executed in front of 
 the space in which the heat should be concen- 
 trated. In order to obtain this effect, it is proper 
 that the grate (hearth) in which the combustion 
 takes place be in front of the boiler, as Curadau 
 recommends,* to whom we owe several interest- 
 ing observations on the regulation of furnaces. 
 Since the current of air is greatly more rapid 
 when the furnace has a high temperature, it is 
 proper to diminish its column by means of a 
 register (damper) placed in the chimney. This 
 register serves likewise to intercept the current 
 when the combustion is finished, and when we 
 wish to turn the remaining heat to account by 
 preventing it from being hurried off by the air. 
 
 The form of boilers is not unimportant towards 
 obtaining the greatest effect of fuel with the least 
 cost and loss of time. It should be subordinate, 
 however, to the kind of operation that is intend- 
 ed. We shall restrict ourselves to a few observa- 
 tions on this subject. 
 
 The boilers should present the utmost possible 
 surface to the fire, and the heat should be applied 
 to the greater part of their outer surface by mak- 
 ing the flame circulate round them. Consequent- 
 ly, when they are intended for evaporation, dis- 
 tillation, or the heating of liquids, as leys for 
 example, their width should be greater than their 
 height. Chaptal recommends, moreover,t to con- 
 
 * Ann. de Chimie, torn. xlvi. 
 f Elemcns de Chimie, torn, i, 
 VOL. I. S 
 
274} OF FUEL. 
 
 struct them so that the bottom shall be convex 
 within. By this construction, the insoluble parts 
 thrown off upon the sides obstruct less the com- 
 munication of the heat, while the copper at the 
 bottom is longer preserved. 
 
 It is not enough to pay attention to the com- 
 bustion, but the resulting heat must be distribut- 
 ed also, so as to produce most advantageously 
 the desired effects. 
 
 There are bodies which afford a ready passage 
 to heat ; such, in particular, are metallic substan- 
 ces. There are others, on the contrary, which 
 conduct it slowly and with difficulty ; such are 
 glass, pottery, bricks, woollen tissues, ashes, and 
 especially charcoal. The latter substances ought 
 therefore to be made use of, either directly or as 
 envelopes, when it is desired to maintain the tem- 
 perature ; but metallic substances, when the heat 
 is to be diffused. The colours of the surfaces 
 which disseminate or receive heat, may also pos- 
 sess an influence, according to the recent inge- 
 nious observations of Count Rumford ; but we 
 are not yet acquainted with their applications to 
 the arts. 
 
 When the object is to form a solution, attention 
 ought to be paid to the effect that specific gravi- 
 ty may produce on the solution, or on the com- 
 munication of the heat. 
 
 Every chemical combination, and that of calo- 
 ric, which follows its laws, are more speedily ef- 
 fected the more distant the point of saturation. 
 Hence, when a salt is dissolved at the bottom of 
 
^ 
 
 OF FUEL. S75 
 
 a liquid, which thus acquires a greater specific 
 gravity by its saturation, the successive layers of 
 liquid are kept in their respective position, and 
 the most saturated remain at the bottom. There 
 is but a slight difference in saturation between 
 each of the layers, and thus the equilibrium of 
 the whole is long of being acquired. But if the 
 salt is placed at the surface, the portion of the 
 liquid which becomes saturated falls to the bot- 
 tom in consequence of the specific gravity which 
 it has acquired. A current is established which 
 continually brings the least saturated liquid in 
 contact with the salt, whence the solution is more 
 quickly made, even without employing manual 
 agitation, which also acts by approximating the 
 less saturated portions to those which are com- 
 pletely so. 
 
 On these grounds we have recommended, after 
 Welter, to operate at the surface of the water the 
 solution of potash intended for leys. If a gaseous 
 substance is to be dissolved, the solution should, 
 on the contrary, be effected in the lower portion, 
 in order to keep at a distance, by a less specific; 
 gravity, the liquid which may be already satu- 
 rated. 
 
 When water is converted into vapour by ebul- 
 lition, it contains a great deal of caloric in a la- 
 tent state, which it gives up when restored to the 
 liquid condition. It results from the experiments 
 of the celebrated Watt, that this quantity would 
 be sufficient to raise the thermometer of Fahren- 
 heit 900°, or the centigrade thermometer 500° j 
 
276 OF FUEL. 
 
 whence it follows, that one part of steam at the 
 temperature of ebullition can raise, by losing it- 
 self the vaporous state, five parts of water from 
 the temperature of zero to the boiling point. 
 
 We thus perceive what advantages might be 
 derived from the steam that issues from boilers ; 
 but the requisite manipulations would seldom 
 permit us to take the full benefit of it. 
 
 The celebrated Rumford, to whom we owe a 
 great many ingenious observations on heat, its 
 distribution, and the economical use of fuel, has 
 pointed out modes of employing the vapour of 
 water for the communication of heat, which may 
 be peculiarly advantageous in the art of dyeing. 
 We shall give some account of them. 
 
 The purpose of the apparatus is to generate 
 steam, to be carried into a vessel filled with any 
 liquor which we may wish to heat by its agency. 
 A boiler must therefore be procured for keeping 
 up the ebullition of water. It ought to be spa- 
 cious enough to form a sufficient quantity of va- 
 pour ; and agreeably to what has been described, 
 it ought to have greater length than height, and 
 be so placed in the furnace as that most part of 
 the circumference shall be exposed to the cur- 
 rent of flame. 
 
 This boiler must give origin to a large pipe, 
 which serves as a reservoir of steam. From this 
 reservoir the conductor tubes branch out, which 
 are to transmit the vapour into the receivers to 
 be heated. These tubes should have a slight in- 
 clination, that whatever vapour has resumed the 
 
OF FUEL. 277 
 
 liquid state may flow back into the boiler. Into 
 the end of each a vertical tube enters, which car- 
 ries the steam into the lower part of the receiver, 
 and which may be placed even in the inside of 
 the receiver, or on its outside surface. Above 
 the level of the liquid the latter tube should have 
 an accurate stopcock, to prevent the liquid from 
 rushing back into the boiler when its steam is 
 condensed by cold, or has lost some of its elastic 
 force. To prevent the accidents, however, which 
 might be occasioned, either by negligence in 
 shutting the stopcock, or, on the other hand, 
 from so rapid a formation of steam as might burst 
 the apparatus, the boiler ought to be provided 
 with two valves, one intended to permit the in- 
 troduction of air when a vacuum is formed inte- 
 riorly, the other to give an outlet to the steam 
 when its force becomes too considerable. 
 
 To supply the steam-boiler with water, a re- 
 servoir is needed, which communicates with it by 
 means of a tube. This ought to have a stopcock 
 opening by means of a floater, when the water of 
 the boiler is diminished to a certain point. This 
 tube should be more or less elevated, according 
 to the degree of temperature which the steam is 
 to possess ; for without sufficient pressure, the 
 vapour of water could not raise the water which 
 condenses it to the degree of ebullition. This 
 circumstance obliges us to give the boiler suffi- 
 cient thickness to support the expansive action 
 of the steam at a temperature above the boiling 
 point. The water contained in the reservoir 
 
278 OF FUEL. 
 
 may be prepared to produce its effect, by pre- 
 vious heating .through the prolongation and dis- 
 tribution of the chimney of the furnace. 
 
 The whole outside of the apparatus must be 
 preserved from the loss of heat, by surrounding it 
 with non-conducting substances. The author re- 
 commends to apply, by means of paste, to the 
 surface of the tubes, two or three coats of paper ; 
 and still better, hemp wrapped round in the di- 
 rection of its filaments. He has made curious 
 experiments on the power which this envelope 
 gives. They are next surrounded with a wood- 
 en case filled with charcoal dust, or pounded 
 bricks. 
 
 In this way dye-baths may be heated, substi- 
 tuting wood for metals, and heating several by 
 means of a single furnace, which may be at the 
 same time portable. Different degrees of heat 
 are given, according to the dimensions of the 
 tubes which conduct the vapour into each bath ; 
 and an uniform temperature is obtained. Lastly, 
 the same method may be applied to the construc- 
 tion of drying rooms and stoves, the condensed 
 water being reconducted into the boiler. 
 
 This method, which may be varied and multi- 
 plied in its applications, deserves peculiar atten- 
 tion, since English industry has already turned it 
 to several purposes. (Note R.) 
 
 Having thus given an idea of the phenomena 
 of combustion, and pointed out the means of pro- 
 fiting by the heat, it remains to consider the dif- 
 
N . 
 
 OF FUEl. 279 
 
 ferent kinds of fuel, in reference to their peculiar 
 advantages. 
 
 To compare the effect of different combustibles, 
 the process described by Lavoisier may be em- 
 ployed.* It consists in burning each species of 
 combustible in the same furnace, over which a 
 boiler is placed. Into this boiler an equal quan- 
 tity of boiling water is poured, and what has 
 been evaporated is replaced by letting in an 
 equal weight of water at each operation. The 
 quantities of fuel required to evaporate the same 
 quantity of water are afterwards compared. It 
 is obvious, that the qualities of the combustibles 
 are proportional to the quantities necessary to 
 produce the same effect. We have to compare, 
 then, merely the quantities of each combustible 
 employed in the evaporation, with its respective 
 price, in order to determine what are the most 
 advantageous, and ought to be preferred. For 
 this calculation, the weight or volume of each 
 combustible may be made use of indifferently, 
 provided the price of the measure be known. 
 
 Instead of evaporating the same quantity of 
 water, the desired result may be equally attained, 
 by burning either the same weight or the same 
 measure of each kind of fuel, and comparing 
 thereafter the quantities of water evaporated. 
 
 As the bulks and weights of fuel should be 
 compared with the price, and as this price varies 
 considerably in each country, nothing of an abso- 
 
 * Mem. de l'Academie, 1781. 
 
280 OF FUEL. 
 
 lute nature can be established concerning the 
 combustibles whose employment is the most pro- 
 fitable. In one place it will be pit-coal ; in ano- 
 ther, it will be wood or turf; the ratio of the 
 prices may vary even in a short time, either by 
 opening a canal, by working a mine of pit-coal, 
 or by the destruction of a forest. Several opera- 
 tors retain a prejudice against the use of pit-coal ; 
 but it is enough to observe, that it is at present 
 employed in so great a number of dyehouses, 
 without any inconvenience being experienced, 
 that there can be no doubt of its answering as a 
 substitute for other fuel ; but as in equal weight 
 it yields much more heat, a little practice is re- 
 quired in its management. 
 
 Pit-coal requires in the furnaces a construction 
 somewhat different from that of the furnaces in 
 which wood is used. As it kindles with difficulty, 
 it must be burned on a grate, which affords pas- 
 sage to a current of air. Its qualities are more- 
 over very variable ; and the kind useful for one 
 purpose is not fit for another. Even should ex- 
 perience prove, that there is no advantage in 
 our country in preferring pit-coal to wood, the 
 use of it should be begun; because it is very pro- 
 bable, that the price of wood will progressively 
 increase, while, on the contrary, that of pit-coal 
 will fall, because its mining will be promoted by 
 being made with more intelligence than it has 
 hitherto been in France, and because it is to be 
 hoped that canals for facilitating its carriage will 
 be multiplied. 
 
OF FUEL. 281 
 
 Pit-coal is reduced into a true charcoal, by an 
 operation analogous to that by which wood is car- 
 bonized ; an operation to which the name of des- 
 soufrage (cokeing) is given. This charred coal 
 affords a real advantage in the great furnaces, 
 which serve to smelt ores of iron, because pit-coal 
 swells and agglutinates when it is highly heated, 
 thereby choking the furnaces ; inconveniencies 
 which it no longer possesses after being coked. 
 But for other uses, it is preferable in its natural 
 state; because all the bituminous oil, burned off 
 when it is reduced into charcoal, is wasted, with- 
 out producing any effect ; and this operation re- 
 quires labour, which must be paid for. 
 
 Turf (peat) is also reduced to charcoal ; but 
 this operation presents a difficulty not easily over- 
 come. When the recent charcoal of turf is ex- 
 posed to the air, it takes fire of itself, like a 
 pyrophorus ; an inconvenience which has, how- 
 ever, been eventually obviated. 
 
 What has been said of pit-coal is applicable to 
 turf. When it can be employed in its natural 
 state, it is more profitable to do so than to incur 
 the necessary expense of converting it into char- 
 coal, with the loss at the same time of the whole 
 portion which is consumed in this operation, and 
 which could have served to produce heat. 
 
282 OF DYE-TESTS. 
 
 CHAPTER III. 
 
 Of the Means of ascertaining the Goodness of a 
 Colour {Dye.) 
 
 As colours differ greatly from one another, in 
 their manner of resisting the action of air, light, 
 and other agents to which they may be exposed j 
 and as in this circumstance an important quality 
 consists, of which the eye is no competent judge, 
 methods have been sought after for verifying 
 their goodness by easy and ready tests. 
 
 The purpose of these tests was to condemn the 
 dyes which could not resist them. It is truly 
 important to protect commerce from the frauds 
 which may impair the confidence of which it 
 stands in need ; and its interests would be pro- 
 moted, were we able to assign the standard of 
 manufactured productions like that of gold and 
 silver. But is it possible to find means sufficient- 
 ly certain, and at the same time expeditious, capa- 
 ble of determining the solidity (durability) of a 
 colour, as well as its lustre, and the other quali- 
 ties which it is desired to possess ? Were these 
 means found out, could they be applied with 
 equal success to the processes which an active 
 industry discovers and introduces every day ? 
 
 Much importance has been assigned to those 
 tests formerly called debouillis, at a time when 
 the processes of the arts were subjected to regu- 
 lations which sometimes directly counteracted 
 
OF DYE-TESTS. 283 
 
 their advancement. By these, the workman in 
 the fugitive dye was punishable for employing cer- 
 tain ingredients, capable of giving fast colours. 
 
 These shackles were perhaps necessary to the 
 establishment and the early progress of industry ; 
 but at the present day, they are irreconcileable 
 with its interests. With regard to goods which 
 are to be exported, it is possibly wrong to depend 
 upon such indications of manufactures as are 
 exacted from the chefs des pieces, (inspectors of 
 dyes). It is well known how much our com- 
 merce has lost in the Levant by fraudulent fabri- 
 cations and dyes, under known appellations. 
 
 We shall not examine this question ; but we 
 shall recapitulate what experience has taught 
 concerning the methods which may be employed, 
 among which a dyer may select some profitable 
 even for his own use. We are peculiarly induced 
 to do this, because the tests at first prescribed 
 have been rectified by the experiments of Dufay, 
 a philosopher possessed of much sagacity. We 
 shall now, before transcribing the instruction 
 founded on his trials, present the history which 
 Hellot has given of them, with his judicious re- 
 flections. 
 
 " Since it cannot be exactly ascertained, either 
 by informations taken from different dyers, or by 
 the perusal of ancient regulations, what are the 
 precise characteristics of the colours of the good 
 dye (fast), or those of the small dye (fugitive), 
 it became necessary, in order to acquire this 
 knowledge, to take the longest, the most difficult, 
 
284 0£ DYE-TESTS. 
 
 but, at the same time, the most secure, or to 
 speak more properly, the only method on which 
 it was possible to depend with certainty. The late 
 M. Dufay, of the Royal Academy of Sciences, 
 whom the government appointed to labour to- 
 wards the perfection of this art, caused woollens 
 to be dyed, under his eye, of all colours, and 
 with all the ingredients which are used in dyeing 
 both in the great and little dye, (in fast and fugi- 
 tive colours). He even brought from different 
 provinces articles not employed at Paris. Lastly, 
 he collected most of the materials which he sus- 
 pected to be made use of in dyeing, and he tried 
 a very great number of them, without attending 
 to the prejudices of dyers relative to their good 
 or bad qualities. 
 
 " He began his trials on woollen yarns ; but 
 he found in the sequel, that pieces of white cloth 
 were more convenient for the experiments which 
 he had the intention of making. 
 
 " In order to ascertain among the different 
 colours, those which were solid, and those which 
 were not so, and consequently distinguish the fast 
 from the fugitive dyes, he exposed to the sun and 
 the air, during twelve days, patterns dyed by 
 himself of all these colours, with whose composi- 
 tion he was acquainted. This period seemed 
 sufficient to prove them ; for good colours are 
 either not at all damaged, or very little, while the 
 spurious are in a great measure effaced. Hence, 
 after twelve days' exposure to the sun in summer, 
 and to the moisture of the air during the night, 
 
 
OF DYE-TESTS. 285 
 
 no doubt could remain about the class to which 
 each colour ought to be assigned, when it was 
 tried in this manner. 
 
 " Nevertheless, one difficulty still remained ; 
 for, not having exposed all these colours to the 
 air precisely at the same time, or in the same 
 season, some of them must have had more sun 
 than others, and must, of consequence, have lost 
 more in the same space of twelve days than 
 those which had been exposed in gloomy weather, 
 or when the days were shorter. But he obviated 
 this inconvenience, so as to leave no more diffi- 
 culty or doubt of the correctness of the test; 
 for he selected one of the worst colours, that is 
 to say, one of those on which the sun had taken 
 the most sensible effect during the space of 
 twelve days. This colour served him as a com- 
 parison piece for the whole course of his experi- 
 ments, and every time that he exposed the pat- 
 terns to the air, he annexed to them a piece of 
 this same stuff. It was now no longer the num- 
 ber of days to which he had respect, but the 
 colour which his comparison specimen assumed, 
 and he kept this exposed till it had lost as much 
 as the piece which had been exposed during 
 twelve days of summer. As he always noted 
 the day on which he exposed his specimens, he 
 had occasion to observe, that in winter it was 
 sufficient to leave them in the open air four or 
 five days longer, for them to lose as much colour 
 as they had done in summer. By pursuing this 
 
/ 
 
 I 
 
 286* OF DYE-TESTS. 
 
 method, no scruples remained in his mind about 
 the accuracy of his experiments. 
 
 " In this proof, by exposure to air and the rays 
 of the sun, he had still another object ; it was to 
 find the debouillis suitable to each colour. The 
 ) term debouilli, or debout, denotes the test which 
 
 | is applied in order to learn if a stuff has a fast 
 
 I dye or otherwise. A pattern is boiled with 
 
 alum, tartar, soap, vinegar, lemon juice, &c. ; 
 and from the effect of these drugs on the colour, 
 its quality may be judged of. The debouillis 
 practised up to the year 1*733 were so insufficient, 
 that they could not serve to M. Dufay as indica- 
 tions for finding out surer ones. Indeed some 
 good colours were thus carried off, while the bad 
 ones were very little damaged. Hence he was 
 obliged to fix on several tests, each of which 
 serves for a great number of colours. The fol- 
 lowing is in a few words the path which he pur- 
 sued in order to find them. 
 
 " After having observed the effect of the air 
 on each colour, whether good or bad, he tried on 
 the same stuff different species of debouillis, and 
 he kept by that which had the same effect on 
 this colour as the air had produced. Noting 
 afterwards the weight of the drugs, the quantity 
 of water, the duration of the trial, he was sure to 
 produce on that colour an effect equal to what 
 the air ought to make on it, supposing that it 
 had been dyed in the same manner as his own 
 had been, viz. according to the method either of 
 
■ ■'■ " " 
 
 OF DYE-TESTS. 287 
 
 the fast or fancy dyers. Making thus a survey 
 of all the colours, and of all the ingredients used 
 in dyeing, he discovered a method which may be 
 regarded as accurate, of knowing the good or bad 
 quality of each colour, making by the debouilli a 
 kind of analysis of its composition. We cannot 
 without injustice fail to acknowledge, that the 
 means which led M. Dufay to the discovery of 
 these deboirillis, or tests of colours, are very in- 
 geniously imagined •, because the trial by the air 
 and sun cannot be put in practice in cases where 
 it must be decided on the spot, whether a stuff, 
 exposed to sale, in a fair or elsewhere, is of good 
 dye, should its price correspond to this quality. 
 
 " The debouillis of the new instruction, found- 
 ed on the memoirs of M. Dufay, cause the dye 
 to lose in a few instants, if it be spurious, all that 
 it would lose on being exposed during 12 or 15 
 days to the air. But as general rules for similar 
 trials must be subject to many exceptions, which 
 are either not foreseen, or, being foreseen, cannot 
 be detailed, without running the risk of causing 
 confusion, or numberless subjects of controversy, 
 it follows that these rules, advanced perhaps as 
 too general, are also too severe in several cases, 
 where light colours admit of salts, or doses of 
 salts, which will be less active than deeply 
 charged dyes, which may lose a considerable 
 quantity of their colouring ingredients in the 
 active liquor of a particular debouilli, without 
 exhibiting any very sensible change. It would 
 have been requisite, therefore, to have prescribed 
 
/ 
 
 i 
 
 288 OF DYE-TESTS. 
 
 ) a debouilli for almost every shade; which was 
 
 / impossible, considering their infinite varieties. 
 
 / Hence the air and the sun will be always the true 
 
 tests; and whatever colour shall not suffer altera- 
 tion during a certain time, or shall thus acquire 
 what the dyers call a body (fond J, must be re- 
 puted of good dye, even though it should change 
 j considerably in the debouillis prescribed by the 
 
 new instruction. Scarlet is an example of this. 
 As soap carries off this colour almost entirely, it 
 was subjected to the proof of alum ; and when it 
 is made with cochineal alone, without a mixture 
 of other ingredients, it should assume, in a boil- 
 ing-hot solution of alum, a purple colour. If 
 scarlet be exposed to the sun, however, it loses a 
 part of its vivacity, and becomes deeper ; but this 
 shade is not the one which alum gives it. Hence 
 the debouillis, in certain cases, cannot be substi- 
 tuted for the action of the air and sun, at least 
 with regard to parity of effect. 
 
 " I have made with brazil wood, which, like all 
 the other woods charged with colour, is a false 
 dye, a much more beautiful red than the madder 
 reds, and as lively as the reds made with the 
 grain of kermes. This red, from its peculiar 
 preparation, of which we shall speak in its place, 
 remained exposed to the air during the last two 
 months of 1740, which were very rainy, and 
 during the first two of 1741. Notwithstanding 
 the rain and the bad weather, it stood ; and far 
 from losing, it gained body (fond J. Yet this same 
 red, so solid in the air, does not resist the proof 
 
OF DYE-TESTS. 289 
 
 of tartar. Would it be right to proscribe it, 
 because this salt destroys it; or are the stuffs 
 which we employ for our clothing intended to be 
 boiled with tartar, alum, or soap ? I do not pre- 
 sume, however, to disapprove of the trials by the 
 debouillis. They are useful, because they are 
 speedy. But there are cases where they ought 
 not to serve as rules for pronouncing a sentence 
 of confiscation, especially when they do not de- 
 monstrate that a colour, which ought to have been 
 made with drugs of the good dye, has been made 
 with the ingredients of the spurious dye." 
 
 Instructions concerning the Debouilli {chemical 
 trials) of Wool and Woollen Cloths. 
 
 " Since it has been admitted, that the method 
 prescribed for the debouillis of dyes, by Arti- 
 , cle XXXVII. of the regulations for dyers in the 
 great and good tint, of cloths, serges, and other 
 woollen stuffs, of the month of August 1669, — by 
 the Articles CCXX. and following, of the general 
 instruction for dyeing of wool of all colours, and 
 for the culture of drugs and ingredients used in 
 it, of March I67I, — is not sufficient for judging 
 exactly of the goodness or spuriousness of several 
 colours ; and since this method may even some- 
 times lead into error, and give rise to disputes, 
 there have been made, by order of his Majesty, 
 different experiments on the wools destined for 
 the fabrication of tapestry, in order to learn the 
 
 vol. 1. T 
 
290 OF DYE-TESTS. 
 
 goodness of each colour, and its appropriate 
 debouillis. 
 
 " To attain this object, fine wools have been 
 dyed with all kinds of colours, both in the good 
 and little tint, and they have been exposed to the 
 air and the sun during a suitable period. The 
 good colours stood perfectly well, and the spuri- 
 ous were more or less discharged, according to 
 the badness of their quality. Since a colour 
 should not be reputed good, unless inasmuch as 
 it resists the action of the air and the sun, this is 
 a test which has served as a rule for deciding on 
 the goodness of the different colours. 
 
 " Different proofs by debouilli have afterwards 
 been made on the same woollens, of which patterns 
 had been exposed to the sun and air. It has 
 been observed at first, that the same ingredients 
 could not be employed indifferently in the de- 
 bouillis of all colours, because sometimes a colour 
 found good by exposure to air, was considerably 
 altered by the debouilli, while a spurious colour 
 resisted the same debouilli. 
 
 " These different experiments have shewn the 
 inutility of lemons, vinegar, soured waters, and 
 strong waters (aquafortis), from the impossibility 
 of ascertaining the degree of acidity of these 
 liquors. It has therefore appeared, that the 
 surest method is to make use of ingredients, 
 whose effect is always equal, along with common 
 water. 
 
 " In pursuing this object, it has been judged 
 necessary to separate into three classes all the 
 
OF DYE-TESTS. 291 
 
 colours of which woollens can be dyed, both in 
 the fast and fading tint, and to define the ingre- 
 dients that should be employed in the debouillis 
 of the colours comprised in each of the three 
 classes. 
 
 " The colours comprehended in the first class 
 should be tested with Roman alum ; those of the 
 second, with white soap ; and those of the third 
 with red tartar (argal.) 
 
 " It is not enough for ascertaining the goodness 
 of a colour by the trial of the debouitli, to employ 
 ingredients whose effect may always be equal ; it 
 is requisite, moreover, not only that the duration 
 of this operation be exactly determined, but even 
 that the quantity of the liquid be fixed ; because 
 more or less water diminishes or increases con- 
 siderably the activity of the ingredients which 
 enter into it : hence the manner of proceeding 
 with the different debouillis will be prescribed in 
 the following articles. 
 
 " Article I. 
 
 " The debouilli with Roman alum shall be 
 made in the following manner. 
 
 " Into an earthen or stoneware vessel, one 
 pound of water and half an ounce of alum shall 
 be put : the vessel is to be set on the fire, and 
 when the water boils with large bubbles, there 
 shall be put into it the wool whose trial is to be 
 made, and it shall be allowed to boil there for 
 five minutes, after which it is to be withdrawn 
 
29& OF I>YE-TEST&. 
 
 and washed in cold water. The weight of the 
 pattern ought to be about one gros, (nearly 60 
 grains troy)» 
 
 " Article II. 
 
 " When there are several samples of wool to 
 be tested together, it will be necessary to double 
 the quantity of water and alum, or even to treble 
 it, which will in no respect change the force and 
 effect of the debouilli, if the proportion of water 
 and alum be observed. 
 
 " Article III. 
 
 " In order to make the effect of the debouilli 
 more certain, care must be taken not to test to- 
 gether wools of different colours. 
 
 " Article IV. 
 
 " The debouilli with white soap shall be made 
 in the following manner. 
 
 " Into a pound of water there shall be put 
 only two gros of white soap, cut into small bits. 
 The vessel being then set upon the fire, care shall 
 be had to stir the water with a rod, so as to cause 
 the soap -to melt properly. When it is melted, 
 and the water is boiling briskly, the sample of 
 wool shall be introduced, and it shall in like man- 
 ner be made to boil for five minutes, counting 
 from the instant of its being put in, which shall 
 be only when the water boils with large bubbles. 
 
OF DYE-TESTS. 
 
 " Article V. 
 " When several samples of wool are to be 
 tested together, the method prescribed in Article 
 II. shall be observed ; that is to say, for every 
 pound of water, two gros of soap shall be taken. 
 
 " Article VI. 
 
 " The debouilli with red tartar shall be made 
 precisely in the same way, with the same doses, 
 and in the same proportions, as the debouilli with 
 alum, observing to pulverize the tartar well before 
 putting it in the water, that it be entirely dissolved 
 before the samples of wool shall be put into it. 
 
 " Article VII. 
 
 " The following colours shall be tested with 
 Roman alum ; namely, crimson of every shade, 
 scarlet of Venice, scarlet of a fire colour, scarlet 
 of a cherry colour, and its other shades ; violets 
 and gridelins of every shade, purples, langoustes 
 (pinks), jujubes, pomegranate flowers, blues, slate- 
 greys, lavender-greys, violet-greys, wine-greys, 
 and all other similar shades. 
 
 " Article VIII. 
 
 " If, contrary to the articles of regulation con- 
 cerning dyes, there has been employed, in the 
 dyeing of fine wools crimson, ingredients of the 
 spurious tint, the infringement will be easily 
 recognized by the debouilli with alum, because 
 it renders fine crimson only a little deeper, that 
 
294 OF DYE-TESTS. 
 
 is to say, makes it verge a little towards the gri- 
 delin hue ; but it destroys the lightest shades of 
 false crimson, rendering them of a very pale flesh 
 colour, and even blanching almost entirely the 
 deep shades of false crimson. Hence this de- 
 boullli is a certain means of distinguishing the 
 spurious crimson from the true. 
 
 " Article IX. 
 
 << 
 
 The scarlet of kermes or grain, commonly 
 called scarlet of Venice, is in no respect injured 
 by this debouilli. It causes scarlet of a flame 
 colour, or of cochineal, to pass to a purple hue, 
 and strengthens the low shades, so that they 
 get a gridelin tinge ; but it carries off almost the 
 whole false colour of brazil, and reduces it to an 
 onion-skin hue. It has a still more sensible effect 
 on the deep shades of this false colour. 
 
 " The same debouilli also carries off almost 
 entirely the scarlet dyed with bourre, and all its 
 shades. 
 
 " Article X. 
 
 " Although violet is not a simple colour, but 
 is formed of blue and red hues, it is, neverthe- 
 less, so important as to merit a particular exa- 
 mination. The same debouilli with Roman alum 
 has almost no effect on the fine violet, whereas it 
 greatly injures the spurious ; but it will be ob- 
 served, that its effect is not always to carry off 
 equally a large portion of the false violet hue, 
 
OF DYE-TESTS. 295 
 
 because this has sometimes a ground (pied) of 
 pastel or indigo. This ground being of good 
 tint, is not carried off by the debouilli ; but the 
 redness is effaced, the brown shades becoming 
 almost blue, and the pale ones of a disagreeable 
 wine-lees colour. 
 
 " Article XI. 
 
 " With regard to half-fine violets, prohibited 
 by the present regulation, they shall be put in 
 the class of spurious violets ; nor do they stand 
 the debouilli any better. 
 
 " Article XII. 
 
 " The fine gridelins will be distinguished in 
 the same manner from the spurious, but the dif- 
 ference is slight. Gridelin of good tint loses 
 only a little less than that of spurious tint. 
 
 " Article XIII, 
 
 ie Fine purples resist the debouilli with alum 
 perfectly ; whereas the spurious lose the greatest 
 part of their colour. 
 
 " Article XIV. 
 
 " The colours of langouste (pinks), jujubes, 
 pomegranate flower, will incline towards purple 
 after the debouilli, if they have been made with 
 cochineal ; whereas they will become consider- 
 ably paler if fustet has been employed, the use of 
 which is prohibited. 
 
. I 
 
 296 OF DYE-TESTS. 
 
 " Article XV. 
 " The blues of good tint will lose nothing in 
 the debouilli, whether the colour be pastel or in- 
 digo ; but those of spurious tint will lose the 
 greatest part of their colour. 
 
 " Article XVI. 
 
 " Slate-greys, lavender-greys, violet-greys (red- 
 dish greys ?), wine-greys, lose almost their whole 
 colour if they are of spurious tint, whereas they 
 will stand perfectly if they are of good tint. 
 
 " Article XVII. 
 
 " The following colours are to be tested with 
 white soap : namely, yellows, jonquilles, lemons, 
 oranges, and all the shades which are derived from 
 yellow; all the shades of green, from yellow-green, 
 or nascent-green (pomona-green), to cabbage or 
 parrot-green j madder-reds, cinnamon, snuff co- 
 lour, and other similar hues. 
 
 " Article XVIII. 
 
 " This debouilli shews perfectly if the yellows 
 and their derivative shades are of good or spu- 
 rious tint ; for it carries off the greatest part of 
 their colour, if they are made with Avignon ber- 
 ries, annotto, turmeric, fustet, or saffron, the use 
 of which is prohibited for the fine dyes ; but it 
 does not affect the yellow made with sarretie 
 
OF DYE-TESTS. 297 
 
 (saw-wort), genestrolle (dyer's broom), fustic 
 (yellow-wood), weld and fenugreek.* 
 
 " Article XIX. 
 
 " The same debouilli will also shew perfectly 
 well the goodness of greens, for those of spurious 
 tint lose almost all their colour, or become blue, 
 if they have a ground of pastel or indigo ; but 
 those of good tint lose scarcely any of their hue, 
 and continue green. 
 
 " Article XX. 
 
 " The reds of pure madder lose nothing in the 
 soap debouilli, becoming, in consequence, only 
 more beautiful ; but if brazil-wood is mixed with 
 it, they lose some of their colour in proportion to 
 the quantity of the latter which has been intro- 
 duced. 
 
 " Article XXI. 
 
 " Cinnamon, snuff, and other similar colours, 
 are scarcely affected in the debouilli if they are 
 of good tint ; but they lose a great deal if an- 
 notto, fustet, or fonte de bourre have been em- 
 ployed in it. 
 
 * The botanical names of the above vegetable substances 
 are as follows : Rhamnus infectorius, (French or Avignon 
 berries) ; lira orellana, from which annotto frocouj is made ; 
 curcuma longa, turmeric flcrra merita) ; thus cotinus, fustet; 
 crocus sativus, saffron ; serratula tinctoria, saw-wort ; (genet) 
 genista tinctoria, dyer's broom ; moms tinctoria, fustic ; reseda 
 lulcola, weld ; trigonclla fccnugrcecum, fenugreek. — T. 
 
298 OF DYE-TESTS. 
 
 " Article XXII. 
 " The debouilli made with alum would be of 
 no utility, and might lead even into error, with 
 regard to several colours of this second class ; for 
 it does not injure fustet or annotto, which do not 
 however withstand the action of the air ; and 
 it carries off a portion of saw-wort, and dyer's 
 broom, which give, however, very good yellows 
 and very good greens. 
 
 " Article XXIII. 
 
 n 
 
 All the fawns (duns) or root colours shall be 
 tested with red tartar. Thus, all those colours 
 are termed which are not derived from the five 
 primitive colours : such colours are made with 
 walnut peel, the root of the walnut tree, alder 
 tree bark, sumach or roudoul, sanders, and soot. 
 Each of these ingredients affords a great number 
 of different shades, which are all comprised under 
 the general name, dun, or root colour. 
 
 Article XXIV, 
 
 " The ingredients enumerated in the preceding 
 article are good, with the exception of sanders- 
 wood, and soot, which are a little less so, and 
 which make woollens harsh when too large a 
 quantity is taken. Hence, all that the debouilli 
 can teach concerning these kinds of colours is, 
 whether they have been surcharged with sanders- 
 wood or soot, in which case they lose considerably 
 by the debouilli of tartar ; and if they are made 
 
OF DYE-TESTS. 299 
 
 with other ingredients, or if there be but a mo- 
 derate quantity of sanders-wood or soot, they 
 stand much better. 
 
 " Article XXV. 
 
 " As black is the only colour which cannot be 
 comprehended in any of the three classes above 
 stated, and since it is necessary to make use of 
 a debouilli much more active, in order to learn 
 whether wool has had the deep blue ground con- 
 formably to regulation, the debouilli shall be made 
 in the following manner : — 
 
 " One pound or one pint of water shall be 
 taken : into this shall be put one ounce of Roman 
 alum, and as much pulverized »od tartar ; the 
 whole shall be made to boil, and a sample of wool 
 shall be introduced, which ought to be kept boil- 
 ing briskly during a quarter of an hour. It is to 
 be thereafter washed in fresh water, when it will 
 be readily seen whether it has had the proper 
 blue ground -, for in this case the wool will re- 
 main of a blue, nearly black ; if that be wanting, 
 it will become considerably grey. 
 
 " Article XXVI. 
 
 " As it is the practice to brown colours some- 
 times with nut-galls and copperas, and as this 
 operation, called browning (bruniture), which 
 should be permitted in the good tint, may have 
 a peculiar effect on the debouilli of these colours, 
 it will be observed, that although after the de- 
 bouilli the bath appears charged with the dye, 
 
SOO OF DYE-TESTS. 
 
 because the browning has been carried off, the 
 wool will be not the less reputed of good tint, if 
 it has preserved its body. If on the contrary it 
 loses this, it will be declared of spurious tint. 
 
 " Article XXVII. 
 
 " Although the browning given with copperas 
 and nut-galls be of good tint, as it usually renders 
 wool harsh, it will be proper, as far as possible, to 
 employ the indigo or pastel vat in preference. 
 
 " Article XXVIII. 
 
 «« 
 
 The ordinary greys made with gall-nuts and 
 copperas should not be subjected to any trial of 
 debouilli, becajise these colours are of good tint, 
 and are not made otherwise. But it must be ob- 
 served to gall them first, and to put the copperas 
 into a second bath, not nearly so hot as the first, 
 because in this way they are finer and more fixed." 
 
 From the remarks of Hellot, it appears, that 
 there has been heretofore only one certain manner 
 of ascertaining the permanence of colours, namely 
 exposing them to the air, the sun, and moisture, 
 for an adequate length of time. The debouillis, 
 whatever care be taken to make a good choice of 
 them, can be applied only to determinate pro- 
 cesses, such as those prescribed by the regulations 
 to which they were to be subjected. One of these 
 debouillis might, however, be excepted, that which 
 is applied to black, with the view of determining 
 whether a blue ground has been given, and 
 
OF DYE-TESTS. 301 
 
 whether it be strong enough to inspire confidence 
 in the goodness of the dye. 
 
 " The oxygenated muriatic acid affords a ready 
 and easy means of determining the degree of 
 solidity (durability) of a colour. Hence, when a 
 colour is wished to be examined, a pattern of the 
 stuff has only to be put into the oxygenated mu- 
 riatic acid, along with a pattern of a like colour 
 which had been dyed by a good process. The 
 degree of resistance which the colours of the two 
 patterns oppose, becomes the measure of their 
 goodness j but as this liquor has a very lively 
 action on the colouring particles, it must be em- 
 ployed in a very dilute state. This proof has the 
 further advantage of making known, pretty nearly, 
 the shades and degradations through which the 
 stuff is to pass, when it shall be altered by the 
 air , — were it required, however, to examine a 
 stuff juridically, the action of the oxygenated 
 muriatic acid could not be entirely trusted to j 
 nor would it be possible to pronounce with cer- 
 tainty, unless from the results afforded by ex- 
 posure to the air." 
 
 We extract this passage from the first edition 
 of the Elements of Dyeing, because Bancroft has 
 objected to the testing of colours by the oxy- 
 genated muriatic acid, as being entirely illusory 
 and deceitful. We persist in the opinion, that 
 this easy test may be useful, especially in experi- 
 ments on dyeing ; and that it rarely affords un- 
 faithful indications, when the precaution is taken 
 which has been prescribed, of comparing two 
 
302 OF DYE-TESTS. 
 
 patterns of the same colour, one of which has a 
 known durability ; but we might be led into error, 
 if we wished to make the comparison of different 
 colours with one another. We should run the 
 risk, for example, of ascribing to yellow and 
 fawns a greater comparative solidity than they 
 really possess in the air ; because the oxygenated 
 muriatic acid giving this hue to substances of an 
 animal nature, this effect might be easily con- 
 founded with the preservation of these colours. 
 
 For trying colours on silk, it is usually held 
 satisfactory to expose them to heat in acetic acid, 
 or in lemon juice. They are regarded as perma- 
 nent and fine if they resist this trial ; and in fact, 
 when woods or archil are simply made use of, 
 the colour passes to red by the action of the vege- 
 table acid ; but if the solution of tin has been used 
 in dyeing with these substances, the colour which 
 had been prepared in an acid liquid is not affect- 
 ed by the vegetable acids ; and in this case a 
 colour might be regarded as fine, which had cost 
 much less for its preparation, and which is easily 
 altered. Hence, with regard to silk, the oxy- 
 genated muriatic acid must be had recourse to, 
 or above all, exposure to the air. 
 
 As to cotton and linen goods which are in- 
 tended to be submitted to soap and leys, they 
 must be tried by the action of soap and alkalies. 
 
 There is another species of test which ought 
 not to be neglected ; the purpose of which is to 
 determine the goodness of colouring substances 
 of the same nature. The look, and some other 
 
 
OF DYE-TESTS. 303 
 
 criteria, are generally trusted to ; but they afford 
 only uncertain estimates, and can furnish no scale 
 of comparative value. The oxygenated muriatic 
 acid possesses this property in a degree which 
 leaves nothing to be desired j because, whenever 
 indigo is compared with indigo, the nature of the 
 colouring particles is the same, or nearly the same, 
 and no foreign affinity prevents the action of the 
 oxygenated muriatic acid from determining the 
 proportional quantity of colouring matter. 
 
 If an inconsiderable difference existed between 
 the nature of the colouring particles that were 
 assumed as the same, it is very probable that the 
 action of the oxygenated muriatic acid would be, 
 moreover, a measure of their respective goodness. 
 
 Whenever, therefore, it is wished to compare 
 two or several substances which have the same 
 colour, and to determine their quality or value in 
 reference to the purpose for which they are in- 
 tended, it is necessary merely to compare the 
 quantities of the same oxygenated muriatic acid 
 requisite to reduce an equal weight of each of 
 these substances to the same degree of destruc- 
 tion ; then the qualities of these substances, or 
 the quantity of colouring particles which they 
 contain, are in direct proportion to the measures 
 of liquid which have been necessary to produce 
 the same effect upon each. For making this valu- 
 ation, the colouring particles of each substance 
 ought to have been dissolved in a proper liquid, 
 and every circumstance of the comparative oper- 
 ation should be equal. 
 
304 OF DYE-TESTS. 
 
 If it is desired to compare several species of 
 indigo, for example, an equal weight of each is 
 taken, and pulverized with care ; they are then 
 put into separate matrasses, with eight times their 
 weight of concentrated sulphuric acid. The 
 matrasses are kept in a heat of from 30° to 40° 
 R,. for a few hours. Each solution is afterwards 
 diluted with the same quantity of water. The 
 liquids are filtered ; and the residua collected on 
 the filters being bruised in a glass mortar, with 
 the addition of a little sulphuric acid, they are 
 left again to digest. These last solutions are 
 diluted with an equal quantity of water, then 
 filtered, and added each to its correspondent 
 liquor. Lastly, into each solution there is poured 
 the quantity of liquid oxygenated muriatic acid 
 which is requisite to destroy its colour, or rather 
 to bring it to the same shade of yellow. The 
 qualities of the different species of indigo are 
 proportional to the measures of oxygenated mu- 
 riatic acid which was needed to destroy their 
 colour. 
 
 The tests for colouring particles soluble in 
 water are much more simple. After exhausting 
 them, equal volumes of the decoctions of the 
 same weight of these substances are taken ; and 
 then the quantities of oxygenated muriatic acid 
 necessary to bring them to the same tint, are 
 compared. 
 
OF THE CHEMICAL AGENTS. 305 
 
 SECTION V. 
 
 OF THE CHEMICAL AGENTS EMPLOYED IN DYEING. 
 
 In order to form an exact idea of the effects 
 produced by the substances employed in dyeing, 
 their chemical properties must be known, for 
 these effects are merely consequences in parti- 
 cular cases. 
 
 We shall here present a summary view of the 
 history and properties of the substances most 
 commonly used in dyeing, and in the arts imme- 
 diately related to it, stating, at the same time, 
 the general principles which may serve to explain 
 their action. We shall so order it, that those 
 persons who have but a limited acquaintance 
 with chemistry, may find in this summary the 
 most useful notions, and that those who are further 
 advanced in the speculations of the science, may 
 perceive the relations connecting the particular 
 phenomena to the general laws of combination. 
 
 CHAPTER I. 
 
 Of the Acids. 
 
 The acids are recognized by their taste, their 
 property of reddening the blue colour of several 
 VOL. i. u 
 
306 OF THE ACIDS. 
 
 vegetables, such as that of litmus, flowers of 
 mallow, and violets, and by the effervescence 
 which they produce when mixed with mild cal- 
 careous earth and alkalies. But these characters 
 being merely a consequence of their action, af- 
 ford no idea of the properties by which they act 
 in the production of these very effects. 
 
 All the chemical properties of a substance de- 
 pend on its affinities to other substances ; but the 
 effects of an affinity differ according to the phy- 
 sical dispositions of the substance which exercises 
 it, and of that on which it exerts its action. The 
 latter acts reciprocally on the former by its affi- 
 nity, and according to its physical dispositions. 
 
 The affinity by which two substances form a 
 combination, in which their properties have be- 
 come more or less latent, produces an effect de- 
 pendent not only on its energy, but also on the 
 quantity of the substance exercising it. 
 
 In proportion as an affinity is satisfied, or as it 
 experiences saturation, its energy diminishes ; 
 and when it is exactly counterbalanced by the 
 action of the substance that produces saturation, 
 the combination is neutral, or affords no farther 
 indication of the action peculiar to each of the 
 elements which compose it. 
 
 The substances which produce in the highest 
 degree the saturation of the characteristic pro- 
 perties of the acids, and which make them en- 
 tirely disappear, are the alkalies, whose properties 
 experience, on their part, a like saturation. The 
 reciprocal action of these substances is thereby 
 
OF THE ACIDS. 307 
 
 capable of even disclosing the laws of chemical 
 action, or of the tendency to combination. 
 
 The acidity, or the power of combination of 
 the different acids with the alkalies, should there- 
 fore be proportional to the quantity of the same 
 alkali which they can saturate, or to their capa- 
 city of saturation ; and reciprocally. 
 
 The physical qualities of the substances diver- 
 sify the effects of affinity. We understand here 
 by physical qualities, all such as do not depend 
 on the tendency of a substance to form with 
 another a combination whose weight results from 
 the two, although some of these qualities be still 
 derived from affinity ; for example, solidity, which 
 is a result of the reciprocal action of the mole- 
 cules of any one substance, whether simple or 
 compound. 
 
 Those physical qualities which change the re- 
 sults of affinity are principally solidity, liquidity, 
 expansibility, or the disposition to assume or re- 
 tain these different states. They do not disap- 
 pear by the action of affinity ; they thence expe- 
 rience no saturation ; but they receive modifica- 
 tions from it, while they themselves act as forces 
 which contribute to the immediate effect of affi- 
 nity, or which are opposed to it. 
 
 The disposition to solidity determines the com- 
 binations which precipitate when an acid is mixed 
 with an alkaline solution, and similarly when se- 
 veral acids and several alkalies exercise a recipro- 
 cal action ; whence proceed the precipitates or 
 the salts which separate by crystallization. This 
 
308 OF THE ACIDS. 
 
 disposition is increased by the approximation or 
 condensation which affinity produces ; and the 
 compound which separates in consequence, rea- 
 dily acquires an excess of the element in which 
 this quality predominates. Hence two substan- 
 ces, possessing liquidity, may form an insoluble 
 combination, or a salt less soluble j and the com- 
 pound which separates may preserve an excess of 
 acid or of alkali, according as one or other of 
 these has a greater disposition to solidity. Thus 
 may be explained the precipitations produced by 
 the acids or the alkalies, and the formation of 
 acidulous or alkalinulous salts. 
 
 Heat, whose function it is to dilate bodies, and 
 separate their particles, diminishes insolubility, 
 and increases the tendency to the liquid state. It 
 augments especially the disposition to elasticity ; 
 and as the latter exercises a force contrary to 
 the tendency to combination of a fixed substance, 
 with a substance possessing the elastic condition, 
 it is obvious, that by increasing it to a sufficient 
 degree, the whole effect of the tendency to com- 
 bination may be destroyed. If several acids and 
 several bases exert a reciprocal action, by the 
 same means, the most volatile elements will be 
 determined to form a compound, which will se- 
 parate by volatilization from that contracted by 
 the more fixed elements. 
 
 The acids act, therefore, by their affinity or 
 tendency to combination, in the ratio of their ca- 
 pacity of saturation ; and the physical qualities 
 of their compounds depend on those of the ele- 
 
OF THE ACIDS. 309 
 
 ments composing them, and of the modifications 
 produced on them by the condensation due to 
 the combination, or the expansion which- is the 
 effect of heat. 
 
 When an acid acts on a neutral combination, 
 the base divides its action in the ratio of the 
 quantity of the two acids, and of the energy of 
 their affinity ; but the result depends principally 
 on the dispositions to the solid, liquid, or elastic 
 state of the elements which are in action. The 
 capacity of saturation of two acids usually differs 
 too little to produce an effect capable of counter- 
 balancing one of the causes just designated. 
 
 Hence, when an acid which has a certain fix- 
 ity (sulphuric acid for instance) acts on a muri- 
 ate N whose acid is volatile, the latter ought to be 
 expelled, especially by increasing its elasticity 
 with heat, although it has a greater capacity of 
 saturation for soda. 
 
 From the physical qualities of two substances 
 which enter into combination, may therefore be 
 inferred those which subsequently exist in the 
 compound itself ; and as the same causes act 
 when there is a rival ship of different acids for one 
 base, or of different bases for one acid, or of seve- 
 ral acids for several alkalies, there will be found, 
 in considering the qualities of each of these 
 substances, the reason of the peculiar compounds 
 which separate by precipitation or volatilization, 
 or which remain liquid, and of the changes that 
 different temperatures may produce on these com- 
 binations. 
 
310 OF SULPHURIC ACID. 
 
 The acids and alkalies exercise a pretty power- 
 ful action on most of the colouring substances. 
 We have shewn that the results of this action are, 
 more soluble compounds with such of these sub- 
 stances as have in themselves greater disposition 
 to solubility. Thus the acids act in general. 
 But we have remarked, that the crystals of tartar 
 retain the colouring matter of cochineal. Pot- 
 ash, soda, and ammonia, act also as solvents ; 
 while the slightly soluble alkalies, lime, barytes, 
 and strontites, form insoluble compounds. Few 
 experiments have hitherto been made in this 
 point of view. 
 
 Some acids act on colouring substances by the 
 oxygen which enters into combination with them, 
 or with their elements. This subject has been 
 already sufficiently discussed. 
 
 Neutral salts possess but a feeble action on 
 colouring particles ; they change their solubility 
 little ; and they produce but a moderate effect on 
 their shades. Sometimes, however, this effect is 
 taken advantage of when they are employed as 
 alterants. 
 
 Article I. 
 
 Of Sulphuric Acid. 
 
 Pure sulphuric acid is without smell or colour, 
 transparent as water ; and when concentrated it 
 is of an unctuosity approaching to that of oil. 
 To denote this unctuosity, it was called oil of 
 
OF SULPHURIC ACID. 311 
 
 "vitriol, a designation which may lead to dangerous 
 mistakes concerning its nature. 
 
 This acid was at first extracted from the sul- 
 phate of iron or vitriol of iron, whence its- old 
 name of vitriolic acid. At the present day, near- 
 ly the whole that is employed in the arts is obtain- 
 ed from sulphur, by a much less expensive pro- 
 cess. It is the result of the combustion of sulphur, 
 which, by burning, combines with the oxygen 
 present in the atmospheric air, and in the nitre 
 which is added to a certain quantity of the sulphur 
 before setting it on fire. The latter, however, 
 seems to be especially useful for exciting the 
 high temperature necessary to the formation of 
 sulphuric acid ; for it has to enter into the com- 
 position of the sulphate of potash produced. 
 The mixture of sulphur and nitre is kindled, and 
 its vapours are received in a leaden chamber, 
 whose bottom is covered with a stratum of water. 
 The vapours which collect and unite to the water, 
 form the sulphuric acid, which should be consi- 
 dered as sulphur completely burned. (Note S). 
 
 The sulphuric acid, as it comes out of the 
 leaden chamber, is not in a concentrated state, 
 but is mixed with a certain quantity of redundant 
 water. It retains the odour of sulphurous acid, 
 which differs from sulphuric acid in its composi- 
 tion ; as the former is not sufficiently saturated 
 with oxygen, while this element is less condensed 
 in it. It retains also a little nitrous acid, pro- 
 ceeding from the nitre mixed with the sulphur. 
 If it be left for some time exposed to the air, the 
 
312 OF SULPHURIC ACID. 
 
 smell of sulphurous acid is dissipated. But ano- 
 ther method is employed to deprive it of odour, 
 and at the same time of a portion of its redun- 
 dant water. It is evaporated with heat. 
 
 Only a very small quantity of vegetable or 
 animal substance is required to give this acid a 
 brown colour ; and the acid of commerce has 
 rarely a very clear colour. But this limpidity 
 may be obtained by boiling it for some time in a 
 retort. By this operation it is deprived at once 
 of a portion of nitric acid usually present, and of 
 a portion of water which it had retained. It be- 
 comes white and transparent ; the concentration 
 being the greater the more water has been driven 
 over by the distillation. To procure it of thorough 
 purity, we must, after having separated the first 
 portion, which is impure and feebly acid, con- 
 tinue the distillation till no more liquid remains 
 in the retort. The residuum consists of a little 
 alkali derived from the nitre, which remains com- 
 bined with an excess of sulphuric acid ; a com- 
 bination named acidulous sulphate of potash ; 
 sometimes a little sulphate of lead is also left. 
 
 For this rectification, there must be selected a 
 retort not very lofty, which is to be well secured 
 in an open furnace, or placed in a sand bath, so 
 that the movements occasioned by the ebullition 
 of the acid may not break it. 
 
 Sulphuric acid powerfully attracts the humi- 
 dity of the air. To preserve it concentrated, it 
 must therefore be kept in glass vessels carefully 
 corked. 
 
warn 
 
 OF SULPHURIC ACID. 313 
 
 When it is mixed with water, a great heat is 
 produced. Hence this mixture should be gra- 
 dually made to prevent the fracture of the ves- 
 sel, an accident which is avoided by making the 
 mixture in a leaden vessel. In order to effect 
 a complete mixture, the liquid must be long 
 stirred with a glass rod ; for notwithstanding the 
 great affinity of this acid for water, the difference 
 of their specific gravities opposes their combina- 
 tion. 
 
 The difference of volatility, and the mutual 
 action of the sulphuric acid and water, explain 
 the effects which arise from this action in diffe- 
 rent circumstances. It attracts water, causing 
 the moisture which is held dissolved in the at- 
 mospheric air to lose its elasticity ; and it is only 
 by increasing the elastic disposition of the latter 
 by heat, that it can be again separated. But to 
 reduce the water into vapour, a greater heat is 
 required than if it were not retained by the affi- 
 nity of the acid ; a heat which must be augment- 
 ed according as the proportion of water dimi- 
 nishes. Lastly, the acid passes over itself in the 
 distillation along with a decreasing proportion of 
 water, which must in its turn promote this effect 
 by reason of its volatility. 
 
 The fixity of this acid, its concentration, the 
 property it has of freezing, shew that it must 
 carry into its combinations a great disposition to 
 insolubility, when the base has the same disposi- 
 tion. Hence it produces slightly soluble combi- 
 
/ 
 
 
 ) 
 
 i 
 
 814 OF SULPHURIC ACID. 
 
 nations with lime, barytes, strontites, and several 
 metallic oxides. 
 
 The condensation of sulphuric acid proves that 
 the combination of oxygen with sulphur is here 
 very intimate, and consequently it should not 
 easily part with its oxygen. For this reason, it 
 produces no decomposition of the colouring sub- 
 stances which it dissolves, unless this solution be 
 exposed to a strong heat. Then the hydrogen 
 and the carbon of these substances may combine, 
 particularly with a portion of the oxygen of the 
 acid, which is thereby brought to the state of 
 sulphurous acid, which, being volatile, escapes in 
 the progress of the decomposition. As the oxy- 
 gen is endowed with greater elasticity in the lat- 
 ter acid, it abandons the sulphur more easily, al- 
 though this substance be in larger proportion than 
 in sulphuric acid. 
 
 Sulphurous acid, therefore, acts on colouring 
 substances, by giving up oxygen to them less 
 easily and less efficaciously than the nitric or 
 oxygenated muriatic acids ; but in other circum- 
 stances, it may carry off even oxygen, as it does 
 from oxygenated muriatic acid on being mixed 
 with it. 
 
 Highly concentrated sulphuric acid has a spe- 
 cific gravity, nearly double of that of distilled 
 water. When it is weak, that is, diluted with a 
 great deal of water, the fallacious name of spirit 
 of vitriol has been given to it. 
 
 In order to obtain uniform effects, it is right to 
 employ for the same operations a sulphuric acid 
 
It I 
 
 OF SULPHURIC ACID. 31£ 
 
 which has always the same degree of concentration. 
 Its specific gravity must be therefore ascertained, 
 which is commonly done by means of the areo- 
 meter of Baume. For this purpose, the acid is 
 put into a glass cylinder, and the areometer for 
 salts is plunged into it. The denser the liquid, 
 the less the areometer sinks, and the degree on 
 that part of its scale which rests at the surface 
 of the liquid, indicates its concentration. Sul- 
 phuric acid is regarded as highly concentrated 
 when it is at 66° of this areometer. 
 
 Hitherto sulphuric acid has been used in dye- 
 ing, principally for making solutions of indigo ; 
 for which purpose it must be strongly concen- 
 trated, and very pure. But a great deal of it is 
 employed for preparing cotton goods intended to 
 be printed, as well as for the bleaching of cloths 
 and yarns, whether by oxygenated muriatic acid, 
 or by exposure on the grass. 
 
 These latter purposes do not require a concen- 
 trated sulphuric acid. If therefore a manufac- 
 ture of sulphuric acid exist in the neighbour- 
 hood, it is more advantageous to purchase it 
 before being concentrated, and thus avoid the 
 cost of this operation. But if such an establish- 
 ment be at a distance, the diminution of the ex- 
 pense of carriage may render it more profitable 
 to purchase it in a state of concentration, than if 
 it were diluted with a certain quantity of water, 
 
316 OF NITRIC ACID. 
 
 Article II. 
 Of Nitric or Nitrous Acid. 
 
 Chemists have given different names to this 
 acid, according to the processes by which it is 
 extracted from nitre. What is obtained from a 
 mixture of nitre and clay is called aquafortis ; 
 that procured from nitre distilled with sulphate 
 of iron, spirit of nitre ; and the fuming nitrous 
 acid is derived from a mixture of nitre and sul- 
 phuric acid. These distinctions are not made in 
 commerce, but the name aquafortis is usually 
 given to this acid, whatever process may have 
 been employed. In fact, it is always the same 
 acid, differing only in the degree of concentra- 
 tion, and in colour. It is sometimes white, some- 
 times red and fuming. The colour and property 
 of fuming, are owing to the nitrous gas which it 
 holds in solution, as we shall explain hereafter. 
 
 If the reddest acid be exposed to a sufficient 
 heat, the nitrous gas is disengaged, and the acid 
 remains white. In this state it is called nitric 
 acid, while the name nitrous is given to the red 
 acid. 
 
 As there is no great consumption of this acid 
 in dyehouses, and as these are often at a great 
 distance from the places where the acid is manu- 
 factured, it may often be useful and economical 
 to prepare it one's self. This motive induces us 
 
^" 
 
 OF NITRIC ACID. 317 
 
 to describe here the process by which it is ex- 
 tracted from nitre by means of sulphuric acid. 
 
 Pure nitre, called nitre of the third boiling, 
 being the result of a third crystallization, is pul- 
 verized, and put into a retort with half its weight 
 of concentrated sulphuric acid, or a little more, 
 in such a manner that one-half of the capacity of 
 the retort remains empty, in order that the mate- 
 rials in boiling up shall not pass over into the re- 
 ceiver. To the neck of the retort a bent tube is 
 adapted, whose orifice must be sufficiently large 
 to embrace and receive it. The other end of this 
 tube, which ought to have a much smaller dia- 
 meter, is introduced, through a cork, into a re- 
 ceiver with a double neck. To the other open- 
 ing of this receiver a tube is also adapted, which 
 terminates in a little water contained in a matrass. 
 The communication of the retort with the first 
 tube, and the openings of the first receiver, must 
 be carefully coated and covered with fat lute, 
 consisting of pulverized white clay, boiled lin- 
 seed oil, and a little litharge. This lute must be 
 beaten for a long time in a mortar, to render it 
 smooth and ductile. The lutings must be wrap- 
 ped round with strips of linen cloth soaked with 
 white of egg t and. bedusted with powdered quick- 
 lime. It is of advantage to have a tubulated re- 
 tort to prepare the whole apparatus, before intro- 
 ducing the sulphuric acid into it by the tubulure, 
 and even to dilute the sulphuric acid previously 
 with a certain quantity of water. 
 
 
 
318 OF NITRIC ACID. 
 
 The second matrass should maintain a free 
 communication with the air, that the vapours in- 
 condensable in water may escape. The quantity 
 of water put into the second vessel must bear a 
 proportion to the quantities of materials operated 
 upon. The fire must be nicely tempered at the 
 beginning, and be gradually augmented up to 
 the end of the operation. The acid which is 
 obtained in the first receiver is highly concen- 
 trated ; that which is in the second is weakened 
 by the water put into it for condensing the va- 
 pours. The colour of the latter acid is blue or 
 green ; colours owing to the nitrous gas ; their 
 diversity depending on the proportion of water. 
 Thus, if a little water be added to that which is 
 green, it becomes blue ; and when the gas is ex- 
 pelled by heat, the liquor remains limpid. The 
 acid of the second matrass is always pure, but 
 that of the first contains sometimes a little sul- 
 phuric acid, arising from the heat not being right- 
 ly regulated at the commencement of the opera- 
 tion. For, when tempered with discretion, a per- 
 fectly pure acid may be obtained, if the sulphuric 
 acid does not exceed the half of the weight of 
 the nitre. 
 
 It is of importance to test the nitric acid of 
 commerce, because a considerable quantity of 
 sulphuric acid is frequently present in it, whether 
 it may have come over in a distillation negligent- 
 Iv conducted, or have been added to the nitric 
 acid in order to augment its specific gravity. 
 For testing it, we dilute it with an equal weight 
 
 J 
 
OF NITRIC ACID. 319 
 
 of distilled water, and then drop in a little of the 
 solution of nitrate of barytes. If the acid which 
 we try contain sulphuric acid, a precipitate takes 
 place, because this acid forms an insoluble salt 
 with barytes. Nitric acid may likewise contain 
 some muriatic acid, proceeding from the sea-salt 
 which might exist in the nitre employed. This 
 mixture cannot be prejudicial to the operations 
 of dyeing. If, however, we desire to discover it, 
 the acid must in like manner be mixed with dis- 
 tilled water, and a nitric solution of silver is to 
 be then poured into it. A precipitate occurs if 
 muriatic acid be present. 
 
 To deprive the nitric acid of the sulphuric, it 
 must be redistilled from a little nitre, or solution 
 of lead may be added to it, which produces a pre- 
 cipitate that is to be separated. After this, the 
 acid is submitted to a new distillation. By this 
 operation the nitric acid is separated, not only 
 from the sulphuric acid, but also from the muri- 
 atic which it may contain. To accomplish the 
 latter object entirely, the first portion of liquid 
 that comes over must be removed, because it 
 may contain some oxygenated muriatic acid. 
 
 Nitric acid may serve for several metallic solu- 
 tions, whose use as mordants may be various, but 
 its principal employment is for aqua regia, or 
 nitro-muriatic acid, which shall be treated of in a 
 particular article. It appears that sulphuric acid 
 is injurious to it, when it is to serve for the solu- 
 tion of tin ; and the acid prepared in manufac- 
 tories, by means of the sulphuric, usually con- 
 
320 OF NITRIC ACID. 
 
 tains some ; whence dyers often prefer that ex- 
 tracted by the agency of clay. 
 
 For understanding a great number of pheno- 
 mena, it is essential to have an exact idea of the 
 nature of the nitric acid, and of the action which 
 it exercises on other substances. 
 
 Nitric acid is composed of two substances, 
 which, when they are insulated, assume the elas- 
 tic, aeriform, or gaseous state. These substances 
 are oxygen and azote, which also compose our 
 atmosphere. The different action (of these two 
 compounds) depends on the state in which they 
 exist. In the atmosphere they are endowed with 
 elasticity, which is an obstacle to their combina- 
 tion with other substances ; but this obstacle, 
 and the intensity of their action, vary, by reason 
 of their state of expansion and their condensation. 
 
 The elastic force of oxygen gas, and azotic 
 gas, like that of other gaseous substances, being 
 diminished by the affinity which produces their 
 combination, and which reduces their volume, 
 they can act in a greater mass on the other sub- 
 stances, and the energy which they thereby ac- 
 quire may exceed by much the diminution which 
 results from their reciprocal saturation. 
 
 But these two gases may contract an union, 
 which differs according to their proportions, ac- 
 cording to the condensation derived from it, and 
 according to the concurrence of other substances, 
 and particularly of water, which may augment 
 their condensation without acting on them by a 
 great saturation. 
 

 OP NITRIC ACID. 321 
 
 These circumstances determine the different 
 states of combination of these two elements, and 
 the properties of these compounds. 
 
 Nitrous gas must be regarded as the first state 
 of combination. It dissolves in only a small 
 quantity in water ; it does not combine with alka- 
 lies ; it is easily decomposed by substances which 
 tend to unite with oxygen ; but it unites by mere 
 contact with a greater proportion of oxygen. It 
 thereby passes to another state; and as its two 
 elements are little condensed, the action of heat 
 alone, or the dilatation which it produces, has but 
 little efficacy to separate them. The proportions 
 that constitute it are nearly 44 parts by weight 
 of azote to 56 of oxygen, (47 to 53.) 
 
 When an oxygenable substance deprives the 
 nitrous gas of a portion of its oxygen, such as a 
 sulphite, which thereby passes to the state of a 
 sulphate, another combination is established, in 
 which the elements, by reason of the proportions 
 in which they exist, exert more powerfully their 
 reciprocal action, so that their condensation is 
 greater. This is the gaseous oxide of azote, 
 whose specific gravity, according to Davy, is to 
 that of oxygen gas in the ratio of 147 to 100 ; 
 and which contains, by the determinations of the 
 same chemist, 63 parts by weight of azote to 37 
 of oxygen. 
 
 This greater condensation, which proves a 
 stronger reciprocal action, and the composition, 
 explain the properties which characterize this gas. 
 It dissolves more copiously in water than the 
 
 vol. i. x 
 
322 OF NITRIC ACID. 
 
 nitrous gas, and yet it has no acid taste, but on 
 the contrary a saccharine one. The oxygen 
 present in it, is too strongly saturated by the 
 azote, to produce the acidity which depends on 
 its combinations. It no longer acts on oxygen 
 gas, and is not decomposed at an ordinary tem- 
 perature, by the substances which operate the 
 decomposition of nitrous gas ; but if the temper- 
 ature be elevated, the expansive action of the 
 heat, which tends to separate its two condensed 
 elements, determines its decomposition, and the 
 oxygen produces a vivid combustion. 
 
 When nitrous gas acts on pure oxygen gas, or 
 on that present in the atmosphere, it becomes 
 ruddy, and the new substance designed by the 
 name nitrous vapour, which condenses very little, 
 and preserves a livelier ruddiness, as the temper- 
 ature is higher, forms another combination when 
 it is placed in contact with water. This decides 
 the formation of nitric acid, of which it is itself 
 an essential part ; for nitric acid resumes the 
 state of nitrous vapour when it is deprived of 
 water, unless it be retained in a state of conden- 
 sation by another base, as in the nitrates. 
 
 If nitrous vapour contain too great a propor- 
 tion of nitrous gas, this excess remains in the 
 gaseous state ; if the oxygen gas be in excess, a 
 portion of it remains gaseous. 
 
 A portion of the nitrous gas may, however, 
 be held in solution by the nitric acid j but this 
 quantity varies according to the proportion of 
 water, giving the acid an orange, green, or blue 
 
■■■■■■■■■■■■■■■■■MBIHVnMHHMMBHqniHaHaOTMWVHMHH 
 
 OF NITRIC ACID. 323 
 
 colour. This excess of nitrous gas attracts oxy- 
 gen by degrees from the atmospheric air, passing 
 itself to the state of nitric acid. 
 
 In nitric acid, the proportion of oxygen is 
 to that of azote nearly in the ratio of 3 to 1 
 by weight. It is not surprising, therefore, that 
 this compound, containing oxygen in so large a 
 proportion, should have the qualities of an ener- 
 getic acid, whilst the gaseous oxide of azote, 
 where the azote predominates, has perceptibly 
 none. But the nitric acid owes its liquid state 
 only to the action which water exerts upon it. 
 
 When it is combined with an alkaline base, and 
 when a more fixed acid, as the sulphuric, divides 
 its action on this base, heat augments its elastic dis- 
 position, so as to volatilize it with the water which 
 the sulphuric acid contained. This water is in- 
 adequate to make the whole of it preserve the 
 acid condition ; a portion is therefore disengaged 
 in the state of nitrous vapour, and by the con- 
 densation of this in the water presented to it, 
 some nitric acid is reproduced. But the acid 
 which has assumed the liquid state, retains nitrous 
 gas, and is^more or less ruddy. The correspond- 
 ing portion of the oxygen gas is disengaged in 
 the elastic state. 
 
 If nitre, or nitrate of potash, be decomposed by 
 means of clay, this seems to retain the water with 
 sufficient strength, so that a quantity of it, capable 
 of maintaining the nitric acid in the liquid condi- 
 tion, may come over even to the end of the opera- 
 
 
324 OF NITRIC ACID. 
 
 tion. Hence, in this case, the acid is not fuming, 
 or is very slightly so. 
 
 The substances which have a great action on 
 oxygen, may decompose nitric acid, according to 
 the energy of this action. Thus the very oxidable 
 metals especially, produce gaseous oxide of azote, 
 while the oxide thereby formed dissolves in a 
 portion of the undecomposed acid. But the less 
 oxidable metals give rise only to nitrous gas, 
 which retains a greater proportion of oxygen. 
 
 The facility with which nitric acid is decom- 
 posed, when it is not condensed by a base which 
 gives it stability, renders it little fit for being em- 
 ployed with the colouring particles, which sepa- 
 rate the oxygen from it more or less speedily, 
 and thereby suffer destruction. In destroying 
 these particles, it causes them to undergo the 
 changes due to an imperfect combustion, in which 
 the hydrogen enters into combination with the 
 oxygen, in larger proportion than the carbon, 
 making the latter principle predominate in the 
 residuum. 
 
 In purchasing this acid, we must not let our- 
 selves be imposed upon by its more or less ruddy 
 colour. It is easy to give it this appearance, 
 by a small quantity of iron, or other substance, 
 which generates nitrous gas. It must, indeed, 
 have a certain degree of concentration to be 
 fuming; but it may be highly concentrated with- 
 out possessing this appearance. 
 
 The specific gravity may likewise lead to fal- 
 lacies, because it can be increased by the addi- 
 
■mMPHHHHUHl HiiiilipuLiiiL... u. l 
 
 OF MURIATIC ACID. 32,5 
 
 tion of sulphuric acid. It is only after ascertain- 
 ing that this cause of error does not exist, that 
 we can repose confidence in that criterion. 
 
 Article III. 
 Of Muriatic Acid. 
 
 Muriatic acid is particularly distinguished by 
 being more volatile, or more disposed to preserve 
 the gaseous state, than the preceding acids, and 
 by having much less affinity for water. Hence, 
 when combined with it, its elastic action needs 
 only be increased by heat for it to quit it, and 
 to resume the state of gas, till little enough re- 
 mains to make the attraction of the water be equi- 
 valent to the elasticity of the acid. 
 
 Although muriatic acid has a greater capacity 
 of saturation for the alkaline bases than sulphuric 
 acid, it is however expelled from its combinations 
 by this acid, especially when its elasticity is aug- 
 mented by heat. Hence the effect of its elasticity 
 overcomes the excess of affinity, which tends to 
 maintain its combination with the base. 
 
 Muriatic acid gas, combined with water, forms 
 muriatic acid, which was known under the name 
 of marine acid, or spirit of salt. It has a pecu- 
 liar odour, analogous to that of saffron. When 
 concentrated it gives white vapours to the air, 
 which are produced by the combination of this 
 acid with the water present in the atmosphere. 
 It ceases to afford these vapours at the point in 
 
'326 
 
 OF MURIATIC ACID. 
 
 which it is saturated with the whole water which 
 it can take from the atmosphere. It has usually 
 a yellow colour, derived from a little iron or 
 oxy muriatic acid ; for, when very pure, it is as 
 limpid as water. 
 
 This acid is extracted on the great scale from 
 sea salt, or muriate of soda, distilled along with 
 clay. But by this process it is always weak. It 
 is disengaged from the same salt by means of 
 sulphuric acid. 
 
 This process has much resemblance to that des- 
 cribed under nitric acid ; but there are some dif- 
 ferences which depend on the greater volatility of 
 the acid. 
 
 •A tubulated retort is made use of, or which is 
 preferable, a large matrass, to whose orifice there 
 is adapted a tube bent in its middle, with an en- 
 largement in the lower part of its curvature. By 
 this tube the sulphuric acid is introduced, a por- 
 tion of which being retained in the curvature and 
 the swelling, serves to stop the issue of the gas, 
 whose pressure disturbs only the level at which 
 it stands in the two branches of the curvature. 
 The obstacle resulting from the elevation of the 
 column of sulphuric acid, determines the gas, 
 therefore, to pass off by a conductor tube, where 
 it finds less resistance. 
 
 The salt is first introduced into the matrass ; 
 after which there is poured in three-fourths (f) of 
 its weight of sulphuric acid, which should be pre- 
 viously diluted. The rest of the apparatus should 
 have been also arranged beforehand. It consists 
 
F-S-«-H^^P 
 
 OF MURIATIC ACID. 3Tj 
 
 of two bottles, into which is distributed a weight 
 of water equal to that of the salt employed. But 
 as the vapour which is disengaged unites speedily 
 with the water, a vacuum is readily formed, which 
 makes the liquid of the second bottle pass back 
 into the first, and from the first into the retort. 
 To prevent these reabsorptions, the first bottle 
 ought to be furnished with the tube of safety 
 contrived by Welter. This tube is introduced 
 into a particular tubulure, or still better through 
 one of the corks which give passage to a tube of 
 communication. If a vacuum be formed, the 
 atmospheric air returns into the bottle ; but 
 while the issuing vapour presses on the liquid, 
 this rises in the tube, till its column counter- 
 balances the pressure of the vapour. It is requi- 
 site to lute with much care, because the vapours 
 of muriatic acid are very penetrating ; and when 
 they have once forced a passage through the lute, 
 it is very difficult to repair it. Should this acci- 
 dent, however, happen, the best means of reme- 
 dying it is, to rub the outlet with some alkali, so as 
 to saturate the acid, and immediately after to stop 
 it with ihe lute. It is necessary to wait till the 
 effervescence produced by the affusion of the 
 sulphuric acid be assuaged, before putting fire 
 under the retort, which should be placed on a 
 sand bath, and the fire should be nicely tempered, 
 especially at the beginning of the operation. 
 
 The acid obtained in the first bottle is highly 
 concentrated and smoking, especially if it had 
 been plunged in cold water or pounded ice - f but 
 
328 OF MURIATIC ACID. 
 
 it may contain sulphuric acid, which is discovered 
 by diluting it with distilled water, and pouring 
 into it a little solution of barytes, which produces 
 a precipitate. It may be rectified by distilling 
 it from a little sea salt. 
 
 The acid of the second bottle is much less 
 concentrated. If too weak for the purposes for 
 which it is intended, it may be used instead of 
 water in a second operation. It has, however, 
 the advantage of being pure. 
 
 Muriatic acid is hardly ever employed directly 
 in the processes of dyeing ; but it serves to form 
 metallic solutions fit for making mordants, alone, 
 or in conjunction with nitric acid. Muriate of 
 tin is the combination which deserves most atten- 
 tion. We owe to Pelletier and Proust very inte- 
 resting observations on this muriate.* We shall 
 detail such of them as relate to our subject. 
 
 To prepare the solution of tin by muriatic acid, 
 Pelletier directs to put one part of tin, and four 
 parts of concentrated muriatic acid in a matrass, 
 placed in a sand bath, which is gradually heated 
 to ebullition. The heat of ebullition cannot be 
 favourable to the combination of the muriatic 
 acid, on account of the elastic force which it gives 
 it. It seems therefore that a more moderate 
 degree of heat is suitable ; but ebullition may be 
 afterwards produced, in order to expel the excess 
 
 * Mem. et Observat. de Chimie de Pelletier, torn. i. Proust, 
 Journal de Physique, torn. li. 
 
^i^z*m**FiB^m >> a ji mi **.m!»^uk-. 
 
 _W< Ml 
 
 OF MURIATIC ACID. 329 
 
 of acid, which may be condensed in a second 
 matrass. We then proceed to crystallize. 
 
 The muriate produced by this process contains 
 the tin in the lowest degree of oxidation requisite 
 for its combination with an acid. In this state 
 it carries off the oxygen, not only from the oxy* 
 genated muriatic acid and sulphurous acid, but 
 also from the atmospheric air, and from all bodies 
 which do not retain this element with force. 
 Hence, it may obviously be a very proper guide 
 in researches on the properties of colouring sub- 
 stances ; and since the oxide of tin combines easilv 
 with stuffs and colouring particles, this muriate 
 may be very useful in the processes of dyeing. 
 
 Its effects must vary according to its state or 
 actual oxidation. Pelletier concludes from some 
 
 - 
 
 trials, that in its most oxidized state it is most 
 advantageous in dyeing. This conclusion is per- 
 haps too general, and we believe that experiments 
 must decide what is proper in this respect for 
 each species of dyeing. 
 
 To obtain muriate of tin in the most oxygenated 
 state, Pelletier prescribes the transmission of oxy- 
 genated muriatic gas into a solution of tin in mu- 
 riatic acid, till this retains the odour of it j after 
 which the excess of acid must be volatilized by 
 heat. The muriate of tin may be oxygenated by 
 leaving its solution simply exposed to the atmos- 
 pheric air. But the operation is slow. 
 
 It is particularly for cotton and linen that the 
 muriate of tin may be advantageously employed 
 in dyeing, or at least it cannot be used in quantity 
 
/ 
 
 330 OF MURIATIC ACID. 
 
 for substances of an animal nature, because mu- 
 riatic acid exercises too keen an action on them. 
 This fact is applicable to the other metallic mu- 
 riates. 
 
 The alkaline muriates are used only as altera- 
 tives. In general they give a deeper shade to 
 colours. 
 
 We have discussed at sufficient length the pre- 
 paration and properties of oxygenated muriatic 
 acid, in treating of bleaching. We shall confine 
 ourselves here to some considerations on the pro- 
 perties which distinguish it from the preceding 
 acids, and on the differences thence resulting as 
 to their preparations. 
 
 Muriatic acid naturally possesses considerable 
 elasticity ; yet the action of water can condense 
 a very large quantity, and give it the liquid state, 
 although it is much less powerful than on nitric 
 and sulphuric acids. It combines with oxygen 
 to form oxygenated muriatic acid. But this com- 
 bination is feeble, so that it produces but a slight 
 change on the natural qualities of the oxygen and 
 muriatic gases. The oxygenated muriatic acid is, 
 therefore, much less soluble in water ; hence the 
 apparatus for the preparation of liquid oxygenated 
 muriatic acid ought to be so contrived, that the 
 gas may be disengaged in the lower part of the 
 receiver, so as to be retained in contact with the 
 water under a first tub, that that which arrives 
 next may flow out under a second, and lastly 
 under a third tub. Thus, by the length of the 
 contact, the solution requiring longer time as it 
 
^gjf/0Ummm*^*7*r^^rf^*****^*Tirw*^m" .1 w> 
 
 OF MURIATIC ACID. 331 
 
 I 
 
 is effected by a feeble affinity, may have leisure 
 to take place. (Note T.) 
 
 The apparatus which we have described, and 
 which may be modified in different manners, is 
 adapted to maintain the contact of the gas with 
 the water j but it would be too troublesome and 
 expensive, when oxygenated muriatic acid is 
 wanted only for some tests or experiments. In 
 this case, an apparatus similar to what we have 
 pointed out for the preparation of muriatic acid 
 may be substituted. It is necessary to employ 
 merely three successive receivers, or three bottles 
 furnished with their tubes of safety. The con- 
 ductor tubes, intended to transmit the gas from 
 one bottle into another, must issue from the upper 
 part of the one bottle, and dip into the lower part 
 of the next. If the gas be received into an al- 
 kaline solution, two receivers, or even one, may 
 suffice. 
 
 Instead of the mixture of muriate of soda and 
 sulphuric acid which we have prescribed, muria- 
 tic acid may be directly employed. One part of 
 manganese is then necessary for four parts of con- 
 centrated muriatic acid, or for an equivalent 
 quantity of weak muriatic acid ; and the latter is 
 preferable on account of the too tumultuous dis- 
 engagement of gas, produced by the concentrated 
 acid. The heat can hardly be too slowly con- 
 ducted. The operation should cease whenever 
 the first tube becomes hot. Oxygenated muriatic 
 acid acts differently, according to the affinity 
 which the other substances have for the two ele- 
 
332 OF MURIATIC ACID. 
 
 ments that compose it. If these bodies tend to 
 combine particularly with oxygen, they carry off 
 this element from the muriatic acid, which is re- 
 tained by the water. Thus light disengages the 
 oxygen, restoring it entirely to its elastic state, 
 while the water retains the plain muriatic acid. 
 Thus, also, the colouring substances take posses- 
 sion of the oxygen, which thereafter exerts its 
 action on such of their elements as have most 
 affinity for it. 
 
 The alkalies tend to combine with the two ele- 
 ments of the oxygenated muriatic acid, although, 
 in some circumstances, the action which they 
 exercise on the muriatic acid determines, by the 
 formation of a muriate, the separation of a por- 
 tion of the oxygen, which resumes the gaseous 
 state. But, excepting this effect, the action of 
 the alkalies condenses the oxygenated muriatic 
 acid, and, by a necessary consequence, lessens or 
 represses its odour. 
 
 When the condensation arrives at a certain de- 
 gree, the action of the alkalies, becoming propor- 
 tionally more energetic, decides the formation of 
 two new combinations, one of which is a simple 
 muriate, and the other a superoxygenated mu- 
 riate. The oxygen accumulated in the latter un- 
 dergoes on the part of the alkalies so strong an 
 action, that light and colouring substances can no 
 longer disengage it. The whole oxygenated mu- 
 riatic acid, which contributes to the formation of 
 a superoxygenated muriate when we receive the 
 
«aWB»^5P^5» 
 
 OF MURIATIC ACID. 333 
 
 oxygenated muriatic gas into an alkaline solution, 
 is therefore lost as to the power of discoloration. 
 
 The difference of action between nitric acid 
 and the oxygenated muriatic acid, on colouring 
 substances, and in general on vegetable and ani- 
 mal bodies, depends on the affinity of the oxygen 
 for azote, and for muriatic acid. The first is by 
 much the stronger. Hence, nitric acid gives up 
 its oxygen with far greater difficulty ; but when 
 the resistance of this affinity is overcome, the re- 
 sults of the action of both are similar. 
 
 The same difference is observed in the action 
 of the two acids on the metals. Nitric acid is 
 decomposed only in part by the action of the 
 metals ; and while one portion gives up its oxygen, 
 another usually combines with the metallic oxide 
 without changing its nature. But the oxygenated 
 muriatic acid is entirely destroyed by the action 
 of the metals. From the metals, merely super- 
 oxidized muriates are obtained ; and only alka- 
 line muriates in the precipitation by the alkalies. 
 Hence, the denomination of oxygenated muriate 
 of mercury, for example, might give a false idea 
 of this combination, which is merely a highly 
 oxidized muriate of mercury. Oxygenated mu- 
 riates of the metals may, however, be formed, by 
 combining the oxygenated muriatic acid with a 
 metal already saturated with oxygen, as Chenevix 
 has shewn. (Note U.) 
 
I 
 / 
 
 334 OF NITRO-MURIATIC ACID. 
 
 Article IV. 
 Of Aqua Regia, or Nitro-muriatic Acid. 
 
 To this compound acid, the name aqua regia 
 has been given, because it has the property of 
 dissolving gold, which was called the king of 
 metals. But it should be regarded as a mixture 
 of muriatic acid and nitric acid, which combine 
 their forces to effect solutions which they could 
 not separately do. 
 
 By the reciprocal action of these two acids, a 
 portion of the nitric acid is decomposed. Hence 
 results a production of oxygenated muriatic acid 
 which exhales, diffusing its odour j and nitrous 
 gas is proportionally formed, which remains dis- 
 solved in the compound acid, and which colours 
 it progressively, till an equilibrium of combination 
 be effected. But neither the oxygenated muriatic 
 acid, which is volatilized as it forms, nor the nit- 
 rous gas, which is also expelled whenever the acid 
 exerts its action on another substance, contribute 
 to its action on the metals. As its operation only 
 is considered, the name nitro-muriatic acid is re- 
 tained for it, whatever be its composition. 
 
 Nitro-muriatic acid may be prepared, either by 
 simple mixture of the nitric and muriatic acids, 
 or by dissolving muriate of ammonia or of soda 
 in nitric acid. Other salts might be made use of, 
 for example nitre (nitrate of potash), which might 
 be dissolved in muriatic acid. Several other pro- 
 
qnrmmmmmKm*m*—**mm*m*s**^—!~ ui* »u 
 
 OF NITRO-MURIATIC ACID. 335 
 
 cesses might be employed, which it is needless to 
 describe. 
 
 It is especially for the solution of tin that nitro- 
 muriatic acid is to be examined, because it is the 
 principal use which is made of it in dyeing. 
 
 Dyers do not prepare in an uniform manner the 
 solution of tin, to which they give the name of com- 
 position (spirit). Every one has his recipe. This 
 solution, however, produces different effects, ac- 
 cording to the process made use of. It is essen- 
 tial that the same artisan should prepare it always 
 in the same manner, in order to obtain uniform 
 effects, and to guide himself by the observations 
 which he may have made in the preceding oper- 
 ations. 
 
 Several dyers make use merely of the aqua- 
 fortis of commerce ; and it seems, that when they 
 began to employ the solution of tin, they used 
 no other solvent. This aquafortis is a species of 
 nitro-muriatic acid, because there has been em- 
 ployed for its preparation an impure nitre, which 
 is mixed with a greater or less quantity of marine 
 salt. But this quantity varies ; and the concen- 
 tration of the aquafortis is likewise subject to 
 many variations. Hence this acid must produce 
 uncertain effects. 
 
 Pure nitric acid dissolves tin only when it is 
 very much weakened, and when care is taken to 
 keep the vessel with the materials in cold water. 
 The metal is, in this case, at the lowest degree of 
 oxidation, according to Proust's observation. But 
 
336 OF NITRO-MURIATIC ACID. 
 
 it speedily falls down, even at an ordinary tem- 
 perature. 
 
 Vogler employed a similar solution in dyeing. 
 He prevented the precipitation of the oxide, by 
 adding muriate of soda or ammonia : but it is 
 better to employ immediately the nitro-muriatic 
 acid, which requires less attention. 
 
 When a more concentrated nitric acid is used, 
 or when heat is applied, the tin passes to the 
 maximum of oxidation, and is entirely precipi- 
 tated. This process is had recourse to for ascer- 
 taining the weight of tin which exists in an alloy ; 
 the tin having thus taken 40 parts of oxygen for 
 100 of metal. 
 
 Hellot took 32 parts of nitric acid, which he 
 mixed with an equal quantity of filtered water 
 (distilled water ?) ; he dissolved in it, by little at a 
 time, two parts of very white muriate of ammo- 
 nia, and one part of nitrate of potash ; and lastly, 
 two parts of granulated tin. Scheffer dissolved 
 one part of tin in four parts of nitro-muriatic 
 acid.* Macquer dissolved three parts of tin in 
 eight parts of nitric acid, with which he mixed 
 one part of muriate of ammonia, and six parts of 
 water. Pcerner employed other proportions, &c. 
 These solutions, so very various, possess un- 
 doubtedly different properties. In them all, one 
 essential object is wanting, which is a preparation 
 constantly uniform. For this purpose, it is indis- 
 pensable to make use of a pure nitric acid, and to 
 
 * Essai sur l'Art de la Teinture. 
 
mmmm^m^^mBBmBme— 11 . mmm^^^m^^mBmmm 
 
 OF NITRO-MURIATIC ACID. 337 
 
 determine its specific gravity by means of the 
 hydrometer. The process which was resolved 
 upon, after several trials, in the first edition of 
 these Elements, consists in taking nitric acid 
 at 30° B. (1.26. sp. grav.) ; to dissolve in it one- 
 eighth of its weight of muriate of ammonia, to add 
 by small portions at a time one-eighth of its weight 
 of tin, and afterwards to dilute this solution with 
 a fourth of its weight of water. 
 
 A pure tin, such as the Malacca tin, or good 
 English tin, must be selected ; because the com- 
 mon tin (of France) contains copper and lead, 
 metals which would be injurious to the beauty of 
 the colours. Even in the fine tin of England 
 some copper is found ; but common tin contains 
 occasionally nearly one-half its weight of lead, 
 and antimony and bismuth besides.* The tin 
 must be reduced into granulations, by melting it 
 and pouring it into water, which is agitated with 
 a bundle of small rods ; an operation which 
 ought to be cautiously made, to avoid explosions. 
 
 In the solution of tin, there is usually formed a 
 small blackish deposite, from which the liquid 
 should be decanted. 
 
 The solutions which contain a great proportion 
 of tin are brown, and afford deeper and duller 
 colours ; yet occasions may be found where they 
 can be useful. One may be obtained highly 
 charged with tin, which may be advantageous in 
 
 * Recherches sur l'Etain ; par MM. Bayen et Charlard. 
 By common tin, the Author must mean what we call Pewter. 
 — T. 
 
 VOL. I. Y 
 
338 OF NITRO-MURIATIC ACID. 
 
 certain cases, by decomposing in a retort, at a 
 very moderate heat, muriate of ammonia, mixed 
 with an equal weight of oxide of tin. The re- 
 siduum is dissolved, filtered, and evaporated so 
 as to crystallize. By this means crystals are pro- 
 cured of a triple salt, composed of muriatic acid, 
 ammonia, and oxide of tin. To make use of 
 this salt, a little muriatic acid must be added to 
 its solution, which prevents the precipitation of 
 the oxide of tin. 
 
 The solution of tin in nitric acid is accompa- 
 nied by a production of ammonia. We have 
 ascertained that the same production took place, 
 when the solution was effected with the simple 
 mixture of muriatic acid and nitric acid, although 
 it be made with great slowness and precaution, 
 and although the oxide of tin be only in the lowest 
 state of oxidation. It thence appears, that there 
 must be less difference than might be thought 
 between the action of simple nitro-muriatic acid, 
 and that of the preparation into which muriate of 
 ammonia is put. 
 
 It is probable that a new quantity of ammonia 
 is produced in the very process of scarlet dyeing, 
 which is performed at a degree of heat approach- 
 ing to ebullition. 
 
 It has been attempted to explain, by the action 
 of this ammonia, which saturates the muriatic 
 acid, and whose formation contributes at the same 
 time to the destruction of the nitric acid, why the 
 nitric acid does not attack (corrode) wool ill dye- 
 ing scarlet, which is done at so high a degree of 
 
mm^m 
 
 OF NITRO-MURIATIC ACID. 339 
 
 heat, although this acid be very destructive to it 
 when it is insulated. 
 
 In this saturating action, has been also seen the 
 explanation of an observation of Bancroft. In 
 dyeing scarlet, he wished to substitute muriate of 
 tin * for the nitro-muriate ; but a larger propor- 
 tion of it was required, and the wool was found 
 to be deteriorated. In this operation no ammo- 
 nia could be formed, and the muriatic acid* which 
 weakens the woollen fibre, exerts all its action on 
 it. 
 
 Muriate of tin may be more useful for cotton 
 and linen, on which substances muriatic acid has 
 much less action. 
 
 No consideration ought to be neglected for 
 varying the mordant best fitted to procure fine 
 colours in dyeing. 
 
 The solution of tin assumes more or less quickly 
 the consistence of a jelly. When this occurs, the 
 dyers say that the composition has turned. For 
 avoiding this, it is proper to make the preparation 
 only a short while before it is to be used. When 
 the jelly is merely beginning to form, the solu- 
 tion may be restored, by adding a certain quan- 
 tity of muriate of soda. This inconvenience 
 proceeds from the tin continuing to get more 
 oxidized by means of the oxygen which it attracts 
 from the atmosphere, or receives from the nitric 
 acid ; and from a greater quantity of ammonia 
 being formed, which, rendering the tin insoluble 
 
 * He prescribed also murio-sulphate. — T. 
 
340 OF NITRO-MURIATIC ACID. 
 
 in the acid, causes it to precipitate. Heat pro- 
 motes this effect ; hence the solution of tin does 
 not keep so long in summer as in winter. 
 
 Uniform observation has taught, that when the 
 solution of tin is briskly made with the copious 
 evolution of vapours, the colours obtained from 
 its employment are less lively and less agreeable, 
 than when the solution is made slowly and with- 
 out effervescence. Hence, at least for the dyeing 
 of wool, tin should be at the lowest stage of oxi- 
 dation. It does not remain in this state ; and it 
 seems to pass to a more advanced degree of oxi- 
 dation in the very operation of dyeing. It would 
 not otherwise afford a white basis to the colour. 
 But this circumstance is undoubtedly advanta- 
 geous. It is a reason for preferring solutions 
 which are recent, and made with slowness, to 
 those which are old, with whatever care they 
 may have been prepared. 
 
 Haussman has recommended, for some pur- 
 poses, the acetate of tin obtained by means of a 
 solution of tin (muriate) and acetate of lead. 
 
 Other (metallic) solutions are made with nitro- 
 muriatic acid, which may be useful in dyeing. 
 De la Folie has proposed that of bismuth ; and 
 although he begins to dissolve the metal in the 
 nitric acid, it is however a combination with the 
 nitro-mufiatic acid, which is formed in this pro- 
 cess by means of the muriate of soda which he 
 adds. The solution in nitric acid alone would 
 not answer, because, whenever it is mixed with 
 water, the metallic oxide falls down, forming an 
 
^^^^^^mm^^fmimmm^mKHmmmmm^ 
 
 ACIDULOUS TARTRATE OF POTASH. 341 
 
 insoluble salt, and thereby separates without be- 
 ing able to unite to the colouring particles. 
 
 According to the description of this process 
 given by Dambournay, of which he himself made 
 much use,* one part of bismuth is to be dissolved 
 in four parts of nitric acid. This solution is to 
 be poured into a bath which contains tartar, 
 along with a solution of muriate of soda. 
 
 It has been found, that whether the solution of 
 bismuth had been made directly with nitro- 
 muriatic acid, or whether the solution in nitric 
 acid was mixed with a solution of sea salt and 
 tartar, a considerable precipitate was always 
 formed on contact with water, although less 
 copiously than when the simple solution in nitric 
 acid was mixed with water. It has been remark- 
 ed, moreover, that the precipitates which this 
 solution occasioned with the decoctions of co- 
 louring substances, had an unequal colour, and 
 speedily became brown. 
 
 Article V. 
 
 Of the Acidulous Tartrate of Potash, and of some 
 
 other Acids. 
 
 The tartaric acid, which predominates in the 
 acidulous tartrate of potash, owes the properties 
 which distinguish it from other acids, the features 
 of which are traceable in its combinations, to its 
 
 * Recueil de procedes et d'exp6riences sur les Teintures 
 solidcs. 
 
342 OF THE ACIDULOUS 
 
 fixity and disposition to take the solid state, which 
 is so great, that notwithstanding its affinity for 
 water, it separates from it, and crystallizes at 
 ordinary temperatures. 
 
 The effects of this tendency are increased by 
 the condensation which affinity produces ; while, 
 at the same time, the action which it exerts on 
 water, as well as that of its base, is diminished 
 by their mutual saturation. 
 
 These considerations shew, that the tartaric 
 acid might produce, with alkaline bases in them- 
 selves very soluble, combinations of little solu- 
 bility, when circumstances permit them to retain 
 an excess of the least soluble element, which is 
 the acid. Thence arise the acidulous tartrates, 
 or salts with excess of tartaric acid, as also the 
 oxalates, the acidulous sulphates, which equally 
 proceed from acids having more disposition to 
 the solid state than their bases. 
 
 For the same reason, this acid produces with 
 the bases that have little solubility insoluble salts, 
 which have no need of an excess of acid to ac- 
 quire this quality. This same insoluble combina- 
 tion is formed every time that combinations of 
 acid and of bases are brought together, some of 
 which may be sparingly soluble, provided there 
 be no excess of acid to oppose this effect by its 
 solvent power. This disposition determines there- 
 fore the precipitates, and the exchanges of base 
 which take place, by means of the tartaric acid, 
 in the reciprocal action of the acids and alkalies, 
 or of their combinations. 
 
TARTRATE OF POTASH. 343 
 
 If in an acidulous and slightly soluble tartrate 
 the proportion of base, which has of itself much 
 solubility, be increased, proportions are attained 
 which yield a neutral salt. Such are the tar- 
 trates of potash, soda, or ammonia, which, by 
 this increase of base, have acquired a greater so- 
 lubility than in the acidulous state, although they 
 still possess the property of crystallizing. Should 
 an insoluble base abstract their acid, the alkali 
 does not part with it entirely. Thus Vauquelin 
 observed, that on decomposing the acidulous tar- 
 trate of potash by quicklime, which forms an 
 insoluble tartrate of lime, the remaining alkali 
 retained a portion of tartaric acid. 
 
 If instead of lime we make use of the carbonate 
 of lime, it is only the excess of acid which, by its 
 action on the lime, produces a disengagement of 
 carbonic acid, and forms a proportional quantity 
 of tartrate of lime. When the tartrate of potash 
 has thereby attained the neutral state, the tartaric 
 acid has no longer a strong enough action on the 
 lime to separate its carbonic acid. 
 
 Hitherto tartaric acid has not been employed 
 in the art of dyeing. It is the acidulous tartrate 
 of potash which is used. (See Note H.) i 
 
 This salt, usually called tartar, is deposited on 
 the sides of casks, from which it is afterwards 
 detached. In its natural state it is mingled with 
 impurities deposited at the same time. When it 
 is separated from red wine, it retains a great deal 
 of the colouring matter of the wine, whence it is 
 called red tartar. 
 
344 OF THE ACIDULOUS 
 
 Tartar is purified by different processes at 
 Montpellier and Venice. At Montpellier the 
 tartar is dissolved in hot water, and crystallized 
 by cooling. The crystals are boiled in another 
 copper, and there is added five or six kilogrammes 
 of the white clay of Murviel for every myrio- 
 grame of the salt, (five or six parts for ten). This 
 earth is boiled with it, and by evaporation we 
 obtain the purified tartar, cream of tartar, the 
 acidulous tartrate of potash. 
 
 The process practised at Venice consists, ac- 
 cording to the description given of it by Desma- 
 rets,* 1. In drying the tartar in iron boilers; 2. 
 In bruising and dissolving it in hot water, by the 
 cooling of which purer crystals are obtained ; 3. 
 In redissolving these crystals, and clarifying the 
 solution with whites of eggs and wood-ashes. 
 
 In the latter process the alkali of the ashes must 
 saturate a portion of the acidulous tartrate ; the 
 calcareous earth must also effect a decomposi- 
 tion ; and, towards the end of the evaporation, 
 tartrate of potash should be obtained. 
 
 The acidulous tartrate of potash, or cream of 
 tartar, retains always a little calcareous tartrate. 
 
 Water dissolves less than one-hundredth of 
 this salt at 10° Reaumur (about 55° Fahr.) ; but 
 boiling water dissolves much more of it. 
 
 Much use is made of acidulous tartrate of pot- 
 ash, or tartar, in dyeing. For delicate colours 
 it is indispensable to employ the purified salt, and 
 
 * Journ. de Physique, 1771 • 
 
mm^mmmmmvmmm^ 
 
 TARTRATE OF POTASH. 34)5 
 
 it is preferable in every case. In some processes 
 red tartar is recommended as proper to contri- 
 bute by its colour to the colour that is wanted. 
 But the red particles separate from the tartar 
 when the salt is dissolved, and they should be 
 regarded merely as hurtful impurities. 
 
 Of the effects produced by tartar in dyeing, a 
 clear explanation cannot yet be given. Experi- 
 ence teaches merely, that it moderates the action 
 of alum on woollens, the fibres of which are easi- 
 ly degraded. It is probable that the colouring 
 particles, in fixing themselves on the stuffs, either 
 alone or with a base, carry a small portion of it 
 into their combination, thereby modifying the 
 colour. 
 
 There is another salt, which has some analogy 
 with tarta?, and which may perhaps produce good 
 effects on several occasions. This is the acidu- 
 lous oxalate of potash, or salt of sorrel, extracted 
 from wood-sorrel in several parts of Switzerland 
 and Germany. Scheele has shewn, that the acid 
 of this salt is the same as that obtained from su- 
 gar, and from several animal and vegetable sub- 
 stances, on treating them with nitric acid, whose 
 oxygen enters into combination with a due pro- 
 portion of hydrogen and carbon. But it exists 
 native, combined in excess with potash, in wood- 
 sorrel and some other plants. Oxalate of lime, 
 which is insoluble, is found in several roots. 
 
 The properties which oxalic acid communi- 
 cates to the different bases, and the effects which 
 it produces on the other combinations, are to be 
 
34>6 OF THE ACIDULOUS 
 
 explained, like those of the preceding acid, from 
 its insolubility, which causes it in like manner 
 to crystallize. Hence it is made use of in che- 
 mistry to discover the existence and the quantity 
 of calcareous earth held in solution. But for the 
 complete production of this effect an excess of 
 acid must be avoided, and all its combinations 
 must be nearly in the neutral state. The acidu- 
 lous oxalate of potash, or salt of sorrel, produces 
 analogous effects. 
 
 This oxalate readily dissolves iron, forming a 
 soluble salt, which renders it useful for removing 
 spots caused by that metal. Oxalic acid produ- 
 ces also an oxalate of iron, which dissolves easily 
 in an excess of acid. This property makes it be 
 employed at present, in some manufactures, for 
 destroying the colours whose basis is oxide of 
 iron. 
 
 Acetous acid, or the acid of vinegar, was dis- 
 tinguished from acetic acid, or radical vinegar, 
 on a supposition that the latter contained a lar- 
 ger proportion of oxygen, and had thereby a 
 greater acidity. But Adet and Darracq have 
 shewn, that between these acids there is no dif- 
 ference which can authorize their being distin- 
 guished. Acetic acid is merely more concen- 
 trated, and the processes by which it is prepared 
 serve only to exclude its water. We shall there- 
 fore designate them by the common appellation 
 of acetic acid. 
 
 Acetic acid has qualities opposed, as it were, 
 to those of the preceding acids. It is volatile, 
 
TARTRATE OF POTASH. 347 
 
 but it has a great affinity for water. It ought 
 therefore to form combinations which have in 
 general much solubility. It seems to have a 
 small capacity of saturation ; hence its combina- 
 tion must produce but a feeble condensation. 
 From these causes it retains its bases but weakly, 
 and is easily expelled from them by the action of 
 other substances, as well as by heat. As it is 
 volatile, and can assume the gaseous state, ac- 
 cording to the experiments of Priestley, the action 
 of the air promotes its separation. 
 
 This acid is formed, not only by the fermenta- 
 tion which is termed acid (acetous), but also by 
 putrefaction, as Fourcroy and Vauquelin have 
 proved. It would appear that the substances 
 which contain no azote are not capable of yield- 
 ing this acid ; for they receive no azote from the 
 atmosphere during fermentation ; and the experi- 
 ments of Proust shew that this acid contains a 
 certain portion of it. (Note V.) 
 
 Acetic acid is also formed in the distillation 
 of several substances, and particularly of wood. 
 To acid thus formed the name pyrolignous was 
 given ; but Fourcroy and Vauquelin have proved 
 that it did not differ essentially from the acetic 
 acid, and that it is merely this very acid holding 
 in solution a bituminous oil, which is produced 
 in the same operation, a part of which separates 
 by keeping. It gives up the greater part of it 
 when rectified by a second distillation. It may, 
 however, be distinguished by the name of pyro- 
 lignous acid, not in order to indicate any differ- 
 
348 ' SULPHATE OF ALUMINA. 
 
 ence of acidity, but its bituminous condition and 
 uses. 
 
 Bosc has shewn * that this acid possessed pe- 
 culiar properties for black dyes on cotton, which 
 it derived from its carbonized oil. We shall, 
 elsewhere, point out the interesting process, which 
 we owe to him. 
 
 This acid merits much attention, not only for 
 this purpose, but for several others, because it 
 can be obtained at little expense, and its car- 
 bonized oil may be useful, or is at least not inju- 
 rious. Guyton,t by distilling in an iron retort 
 chips of very dry beech-wood, and rectifying the 
 first product by a second distillation, extracted a 
 quantity of acid, which exceeded in weight one- 
 third of the wood employed, and the charcoal 
 remained. 
 
 CHAPTER II. 
 
 Of Alum, or the Sulphate of Alumina. 
 
 Alum is designated in chemistry by the name 
 of sulphate of alumina; and although this denomi- 
 nation does not indicate rigorously the elements 
 of which it is composed, it is however useful, 
 and fulfils the usual purpose of nomenclature, 
 because it denotes the ingredients which should 
 
 * Annates des Arts et Manufactures, torn. v. 
 f Encyclop. Method, au mot Lignique. 
 
 L 
 
\ 
 
 SULPHATE OF ALUMINA. 349 
 
 fix attention in the greater number of the pheno- 
 mena that are investigated. 
 
 This combination is of very frequent use in the 
 art of dyeing ; it is also employed in several other 
 arts. Hence, for directing its application, we 
 must be well acquainted with its properties and 
 diversities; and its preparation becomes an ob- 
 ject of considerable importance. 
 
 Alum is found in some mineral springs. It 
 effloresces on the surface of schists in coal mines, 
 or on the lavas in the neighbourhood of volca- 
 noes, and on several rocks. But the greatest 
 part of the alum employed is extracted from pe- 
 culiar ores, or is fabricated by an artificial com- 
 bination of alumina and sulphuric acid. 
 
 Alum is mentioned in the works of the ancients, 
 and that from Melos in particular was esteemed 
 among the Greeks;* but Bergman t thinks that 
 the alum of the ancients was a substance which 
 is found native, and which differs greatly from 
 the salt to which this name is now given ; that 
 the species of alum of which Dioscorides speaks, 
 was rather a stalactite which might contain alum, 
 but only in small quantity, and blended with 
 other sulphates. In the time of Pliny, t the best 
 alum came from Cyprus ; and its species was 
 selected according to the colours for which it was 
 
 * Voyage de Jeune Anacharsis, torn. iv. 
 
 f Bergman, de Confect. Alum. Opusc. vol. i. This disser- 
 tation is of date 1767.. Beckman established the same opi- 
 nion in the Mem. de Gottingen, 1778. 
 
 ^ Amailhon, Mem. de l'lnstit. Beaux Arts, torn. iii. 
 
 \ 
 \ 
 
( / 
 
 3.50 SULPHATE .OF ALUMINA. 
 
 intended. But it appears that the kind appro- 
 priated to brown colours was very impure, and 
 contained much sulphate of iron, since Pliny dis- 
 tinguished it by the name nigrum, stating that it 
 afforded a black colour with gall-nuts, which cir- 
 cumstance cannot apply to any factitious alum. 
 
 It was in the East that factitious alum began 
 to be known. It is not ascertained at what place, 
 or at what period it was at first fabricated. One 
 of the most ancient manufactories was that of 
 Rhodes, a city of Syria, called at the present day 
 Edessa. Thence comes the name of i^oche alum, 
 which, by a confusion of words, is still given to 
 the crystallized masses of alum. This art was 
 carried in the 15th century into Italy, from which 
 it was spread into Germany and the rest of Eu- 
 rope. 
 
 At Solfatara, near Naples, an aluminous ore is 
 found, under the form of a w T hite earth. The 
 alum is formed in this ore by the action exercised 
 on the argillaceous lavas by the sulphurous acid 
 disengaged from the volcano by heat. 
 
 The purest alum ore is that of Tolfa, near 
 Cevita-Vecchia. It is composed, according to 
 Monnet, who first made its analysis, of 40 parts 
 of sulphur and 50 of clay, consisting of a mix- 
 ture of argillaceous and siliceous earths ; and 
 besides these, a small quantity of carbonate of 
 potash, and a very little iron. Bergman also ana- 
 lyzed it, and gave nearly the same proportions. 
 Vauquelin has still further confirmed this analysis, 
 bestowing on it very great precision. 
 
SULPHATE OF ALUMINA. fh* 351 
 
 The other ores from which alum is extracted, 
 are schists more or less pyritous and bituminous. 
 Those which are too pyritous ought to be reject^ 
 ed, because they yield an alum which contains 
 much sulphate or vitriol of iron, of which it 
 would be difficult to get rid. 
 
 The operations by which alum is extracted 
 from its ores, when it is not found ready formed 
 in them, as at Solfatara, have for their objects 
 the alumation, the extraction of the alum, and 
 its crystallization. 
 
 These ores, exposed to the air and the rain, 
 may be alumed, for the most part, without being 
 prepared ; but those which contain either too 
 much bitumen or too much sulphur, require to 
 be roasted before being exposed to the action of 
 the air and humidity ; and in all, the torrefaction 
 accelerates the formation of alum. 
 
 The alumation consists in the combination of 
 oxygen, which uniting to the sulphur changes it 
 into sulphuric acid, as Lavoisier has shewn. But 
 usually it is the sulphate of iron which is formed, 
 and the iron oxidizing to a maximum by exposure 
 to the air, is decomposed by the alumina. There 
 is only the mine of Tolfa, among those which are 
 known, where the acid appears to combine imme- 
 diately with the alumina. (Note X.) 
 
 When the alum is formed, the ore must be lixi- 
 viated, and the liquid be afterwards evaporated 
 till it be in a condition to yield crystals. The 
 first crystals are to be washed, redissolved in a 
 small quantity of boiling water, and the solution 
 
852 
 
 SULPHATE OF ALUMINA. 
 
 poured into peculiar casks, whose staves are then 
 unhooped and separated, in order to get at the 
 mass of alum which is formed. 
 
 The residuum of the crystallizations, mixed 
 with more or less of the lixivium of the mineral, 
 is evaporated till it be in a state to crystallize ; 
 and the process is carried on by adding the resi- 
 duums of the preceding crystallizations to the 
 new solutions. 
 
 This mixture is the principal cause of the im- 
 purity of alum, and of the differences which exist 
 among its species. 
 
 In the progress of the chemical arts, the fabri- 
 cation of alum by the direct combination of sul- 
 phuric acid and alumina has been discovered. 
 For this purpose, a clay should be selected as free 
 as may be from iron and calcareous earth ; it 
 must be roasted to prepare it for combining with 
 the sulphuric acid. This combination is either 
 made immediately with the acid, or by exposing 
 balls of baked clay to the vapour of the sulphuric 
 acid, in the leaden chamber in which this acid is 
 itself manufactured. Chaptal has published the 
 details of this process, which he established at 
 Montpellier.* 
 
 This mode of forming alum requires, as we 
 shall see, an addition of potash, or sulphate of 
 potash ; and the salt obtained by this process 
 appears to be peculiarly liable to have an excess 
 of acid. 
 
 * Mem. de 1' Academic, 1788. 
 
SULPHATE OF ALUMINA. 353 
 
 Before prosecuting the examination of the pre- 
 paration of alum, it is proper to determine the 
 nature of this combination. 
 
 It was at first imagined, that alum was a salt 
 formed simply by the combination of sulphuric 
 acid and alumina ; whence Bergman recommend- 
 ed to saturate the excess of sulphuric acid which 
 is usually found in the lixivium of alumed earth 
 with a pure clay, instead of the potash or putrefied 
 urine (naturally charged with ammonia), which 
 is commonly added. But Chaptal observed, * 
 that if the acid lixivium be boiled with baked or 
 raw clay, the solution is but slowly made, and after 
 a long ebullition. If the lixivium be filtered, when 
 it appears to be saturated, it lets fall, on cooling, a 
 large proportion of the clay which it had dissolved; 
 and if in this state the solution be concentrated, the 
 clay separates, forming a precipitate which prevents 
 all crystallization. From this observation we may 
 conclude, that potash or ammonia must enter 
 into the composition of alum. Descroizilles as- 
 serted, that the potash did not contribute to the 
 crystallization of alum by the saturation of the 
 acid, but by its combination ; and he found, on 
 trial, that sulphate of potash could produce the 
 same effect. Chaptal had come to the same re- 
 sult, and established this practice in his factory. 
 Lastly, Vauquelin made an exact analysis of 
 alum, and discovered that it contained, neces- 
 sarily for its crystallizing, sulphate of potash or 
 
 * M6m. de l'Academie, 1788. 
 VOL. I. Z 
 
354 SULPHATE OF ALUMINA. 
 
 ammonia, or both at the same time. He esti- 
 mated the amount of sulphate (of potash) present 
 in alum, drawing from his observations this infer- 
 ence, that whenever crystals of alum are obtained 
 from an earthy or stony substance, by means of 
 sulphuric acid, that substance contains potash. 
 It has been seen, that the ore of Tolfa naturally 
 contains carbonate of potash. Some other ores 
 may be in the same condition. The wood-ashes 
 formed in their roasting, supply them likewise 
 with potash and sulphate of potash. Hence it is 
 not surprising that alum may be obtained with- 
 out the addition of potash, or putrefied urine, to 
 furnish the ammonia. Bergman remarks, that 
 the latter addition gives rise to an alum which 
 alters the colours. It is not known whether it 
 be by too large a proportion of sulphate of am- 
 monia, or by the mixture of some other hurtful 
 substance, that alum may acquire this bad qua- 
 lity. 
 
 It may be remarked, that Bergman had himself 
 discovered,* after his first work, not only that it 
 was not for the absorption of the excess of acid 
 that potash or ammonia was necessary to the for- 
 mation of alum, but that they were still effica- 
 cious when in the state of sulphate. 
 
 It ought not, however, to be thence concluded, 
 that the effect is entirely the same, whether pot- 
 ash be employed, or sulphate of potash. By the 
 first, the requisite saturation of the acid, when it 
 
 * De Platina, § Opusc. vol. ii. 
 
SULPHATE OF ALUMINA. 355 
 
 is in excess, is greater, and consequently the pro- 
 duction of alum ought to be more considerable, 
 if enough of alumina be present. Whenever, 
 therefore, there is an excess of acid, but a defect 
 of potash or alumina, the advice of Bergman may 
 probably be followed with advantage, namely, to 
 add alumina, and at the same time a sufficient 
 quantity of potash. To accomplish this twofold 
 object we may employ, as Vauquelin points out, 
 the residuum of the distillation of nitrate of pot- 
 ash by clay, which may be particularly adapted 
 to the fabrication of alum by means of sulphuric 
 acid. 
 
 In the prices of the alums of commerce there 
 is a considerable difference, and that of Rome is 
 generally preferred for colours that are to be 
 lively and clear. By analysis, therefore, must be 
 discovered what are the differences which dis- 
 tinguish alums from one another. 
 
 Vauquelin has brought to the analysis of alum 
 the precision and accuracy which characterize his 
 researches.* On decomposing alum by potash, 
 its ammonia is disengaged. On the other hand, 
 by decomposition with ammonia, evaporation of 
 the liquid, and drying the residuum strongly, the 
 sulphate of potash is obtained by itself. By this 
 means Vauquelin has ascertained, that alum con- 
 tains nearly 7 per cent of the sulphate of potash 
 or of ammonia ; and this quantity is usually 
 divided between both of these sulphates. (Note 
 Y.) 
 
 f Annal. de Chim. torn. xxii. 
 
356 SULPHATE OF ALUMINA. 
 
 He has recently examined five kinds of alum, 
 taken from different factories. He determined 
 the proportion of acid which each contained, by 
 precipitating the sulphuric acid with barytes, and 
 comparing the weights of the precipitates. He 
 had previously precipitated the alumina by am- 
 monia, and subjected it to a strong desiccation. 
 
 It results from his experiments, that these five 
 kinds of alum, among which was the alum of 
 Rome, afforded proportions almost rigorously the 
 same ; and that the quantity of iron which is 
 found, for example, in that of Liege, of good 
 quality, is nearly the same as what he obtained 
 from Roman alum. Hence he is led to believe, 
 that it is only from a prejudice that the last con- 
 tinues to be preferred ; and if a proportion of 
 iron which can do harm be present, he recom- 
 mends to get rid of it by prussiate of potash. 
 
 We shall deviate a little from the consequences 
 to which the experiments of this great analyst 
 seem to lead. 1. We have, examined alums, par- 
 ticularly factitious ones, (ceux defabriquej, which 
 contained undoubtedly a pretty considerable ex- 
 cess of acid, for they left, after, their crystalliza- 
 tion, a very acid liquor. What Vauquelin has 
 found in the five specimens, four of which had 
 been sent by the manufacturers themselves, and 
 were consequently choice samples, does not au- 
 thorize the conclusion, that all the alums in the 
 market have a like proportion of acid. 
 
 2. We have mixed with a solution of the alum 
 of Liege, which appeared to be very pure, a little 
 
"" 
 
 1 
 
 SULPHATE OF ALUMINA. 357 
 
 gallic acid ; and a similar test was applied to the 
 Roman alum. The first assumed a black hue, 
 and the second did not change. Analysis would 
 probably have pointed out but a slight difference j 
 but this slight difference is sufficient to produce 
 an alteration on lively colours, for which, espe- 
 cially, a severe choice is requisite. 
 
 After submitting this alum to crystallization, 
 in which the first formed crystals were taken, 
 the solution of these crystals was no longer af- 
 fected by the gallic acid, so that it then present- 
 ed properties completely analogous to those of 
 Roman alum. Bergman had already observed 
 this effect of a careful crystallization which he 
 recommended. 
 
 With regard to the iron present in alum, and 
 which may exist in considerable proportion when 
 it is crystallized with little care, Monnet had for- 
 merly observed, that the sulphate of iron could 
 be entirely separated by crystallization j on the 
 other hand, Leblanc has made mixed crystals of 
 sulphate of iron and sulphate of alumina (sulfate 
 d'alun). These facts would seem to be recon- 
 cileable, by the consideration of the state in 
 which the iron exists. When highly oxidized, 
 as it undoubtedly is in the lixivia of alum ore, it 
 requires a great excess of acid to be susceptible 
 of solution, and the oxide must precipitate, as 
 we shall afterwards see, during the evaporation 
 and crystallization, or be retained in the uncrys- 
 tallizable residuum. But if a little oxidized sul- 
 phate be mixed with the sulphate of alumina, 
 
358 SULPHATE OF ALUMINA. 
 
 and if crystallization take place immediately, the 
 iron no longer requires in this case an excess of 
 acid. It may thus be placed in circumstances 
 which allow it to form a combination. 
 
 To recapitulate : We conceive that, in the ma- 
 nufacture of alum, matters should be so managed 
 as to leave no excess of acid, and to avoid those 
 additions of uncrystallizable residuums, which it 
 is proper to treat separately, according to Berg- 
 man's advice, whether it be for extracting their 
 salts, or for making an alum out of them, which 
 afterwards requires more care for its purification, 
 or an alum intended for purposes where it is not 
 needed to be pure. In the second place, The 
 crystallization should be so conducted that the 
 purity of the salt shall not be affected. Conse- 
 quently, it should not be suffered to condense in 
 great masses, but have a residuary liquid that 
 may retain what would affect the qualities requir- 
 ed in the combination. To accomplish this ob- 
 ject, the crystallizations might be reiterated, and 
 all the residua treated separately. 
 
 It appears to us that this art is improving pro- 
 gressively, as the manufacturers are becoming 
 more enlightened in the conduct of their opera- 
 tions, and that there will soon be no need of hav- 
 ing recourse to Roman alum. 
 
 Those who require alum need not make a 
 selection in employing it for sombre hues ; but 
 they should be very nice with regard to lively 
 and clear colours. Instead of analysis, which 
 requires time and practised skill, we propose to 
 
■*»■!'■ ' 
 
 SULPHATE OF ALUMINA.. 359 
 
 i 
 
 them, 1. To crystallize a portion of the aluin 
 which they are to use ; if the residuum be per- 
 ceptibly more acid, this alum might modify the 
 colours by its excess of acid : 2. To mix a little 
 of the infusion of gall-nuts with the solution of 
 alum ; although, by its own colour, this infusion 
 may be less proper for this trial than pure gallic 
 acid, it will point out sufficiently well if the alum 
 contains an injurious quantity of iron. In this 
 case, the alum may be purified by one crystalli- 
 zation, leaving a sufficient (liquid) residuum. 
 
 When an exact analysis of alum is wished to 
 be made, we must not lose sight of the difference 
 which, according to the means employed, exists 
 in the insoluble precipitate, from which the pro- 
 portion of alumina is to be determined. 
 
 If the precipitate be made by means of a car- 
 bonate, it retains a considerable proportion of the 
 acid, and even of the alkaline base ; for on dis- 
 solving it in nitric or muriatic acid, alum is ob- 
 tained by crystallization. The best agent is am- 
 monia ; but it is difficult to deprive this preci- 
 pitate sufficiently of sulphuric acid, so as not to 
 produce a precipitate of sulphate of barytes, when 
 its solution in nitric or muriatic acid is mixed 
 with a solution of a barytic salt. 
 
 Another circumstance impairs the precision of 
 these comparative determinations. When the 
 solution of alum is very dilute, the alumina retains 
 water, which it does not give entirely up at a very 
 strong heat ; but when it is concentrated, the 
 precipitate which it affords abandons the water 
 
360 SULPHATE OF ALUMINA. 
 
 much more easily, according to the observation 
 of T. de Saussure.* Hence, from the circum- 
 stances of the precipitation, and the degree of 
 heat at which the precipitate is dried, there may 
 exist great differences in its valuation. 
 
 According to Bergman, 100 parts of sulphate 
 of alumina (alum) contain 18 parts of alumina. 
 T. de Saussure reduces this quantity to 0.09, and 
 Vauquelin, in his last analysis, to 0.085. 
 
 Lime and the alkalies, mixed in certain pro- 
 portions with the solution of alum, cause this salt 
 to take a cubical form. Sieffert appears to have 
 first described this variety of alum.t Leblanc 
 has made interesting observations on the crystal- 
 lization of this salt, not yet analyzed by chemists. 
 It must have the acid properties in a less degree 
 than ordinary alum, as Vauquelin thinks, and it 
 would appear, that from the stronger action of 
 the alkaline base on the acid, this salt would give 
 up the alumina more readily to the colouring par- 
 ticles, since alkali is commonly added to the solu- 
 tion of alum for precipitating their lakes. 
 
 According to Bergman, 30 parts of water are 
 required for dissolving one of alum ; 3 parts of 
 boiling water are sufficient. 
 
 * Journ. de Physique, torn. liii. 
 
 f Sieffert's versuche mit einheimischen farbe materien, &c. 
 1775. Sieffert quotes a dissertation on cubical alum, which 
 he printed in the Edinburgh Magazine. For obtaining this 
 alum, he prescribes the mixture of 12 parts of alum with one 
 part of quicklime slaked in the atmosphere, dissolving this 
 mixture in boiling water, and evaporating gently. 
 
"*m 
 
 SULPHATE OF ALUMINA. 361 
 
 We have remarked, that in several woollen 
 dyes tartar was added, which had the property 
 of moderating the action of alum on the filaments, 
 without attempting to explain how it impaired its 
 energy. Bancroft observes, that the dyers indeed 
 frequently omit the tartar, diminishing at the 
 same time the usual proportion of alum. 
 
 Linen and cotton have less disposition to com- 
 bine with alumina than animal substances. Hence, 
 a small proportion of soda or potash is commonly 
 added, which must favour, as has been said, the 
 decomposition of the alum. 
 
 This method is not sufficient for qualifying 
 alum to become a mordant on printed goods. 
 The solution which contains the alumina must be 
 concentrated, without having crystals formed in 
 it. The acetate of alumina has not only this ad- 
 vantage, but it possesses likewise another, depen- 
 dent on the acetic acid, which serves as the sol- 
 vent. This acid acts only by a weak affinity, 
 and consequently retains the alumina more feebly 
 than the sulphuric acid ; and in the drying, to 
 which goods impregnated with the mordant are 
 subjected, its volatility makes it fly off, so that 
 these goods do not carry into the bath an acid 
 which might injure the colour. These advanta- 
 ges render the acetate of alumina a very fit sub- 
 stitute for the ordinary aluming in several cot- 
 ton dyes, accommodated to the improved pro- 
 cess of calico printing ; but acetic acid scarcely 
 effects the dissolution of alumina, as it exists in 
 clays. Their force of cohesion is too great an 
 
362 SULPHATE OF ALUMINA. 
 
 obstacle for the weakness of the acid to overcome. 
 It is by means of the acetate of lead that an 
 exchange of bases is produced, which we shall 
 have occasion to examine. Hence the prepara- 
 tion of acetate of alumina amounts to a price 
 which does not permit its use in several dyes, till 
 a mode be got of preparing this combination less 
 expensively. The properties of acetate of alu- 
 mina led us to believe, that it might be substituted 
 with success for alum in the dyeing of wool. 
 We have made trials with madder ; but the cloth 
 took a less intense colour, without our being able 
 to point out the cause of this result, dependent 
 probably on some circumstance which we over- 
 looked. (See Note C.) 
 
 Alumina dissolves pretty copiously in potash 
 and soda, especially by calcination. Macquer 
 was much occupied with this solution, in order to 
 employ it in dyeing. But as the alkalies possess 
 the property of dissolving colouring substances, 
 and of abstracting them from the stuffs on which 
 they are fixed, they do not seem fit to serve as 
 solvents of alumina. The experiments of Hauss- 
 man. however, prove that this mordant may 
 be employed in some circumstances with advan- 
 tage. (Note Z.) 
 
IP 
 
 mm 
 
 m^~* 
 
 SULPHATE OF IRON, &c. 
 
 363 
 
 CHAPTER III. 
 
 Of the Sulphate, and some other Combinations 
 
 of Iron. 
 
 The sulphate, or vitriol of iron, martial vitriol, 
 green copperas, is not an uniform and identical 
 combination. It varies, not only by the admix- 
 tures which may be present, but also by the state 
 of the oxide of iron, whence very different effects 
 may result from its action. 
 
 The sulphate of iron may be directly made from 
 iron and sulphuric acid, diluted with a certain 
 quantity of water; and a combination may there- 
 by be obtained, possessing determinate qualities. 
 But the low price of this article rarely allows of 
 this manufacture being conjoined with that of 
 sulphuric acid. 
 
 Sulphate of iron is found native in coal-mines, 
 in the cavities or" pyritous mines, and in schists. 
 But the most part of what is employed comes 
 from the martial pyrites, or natural sulphurets of 
 iron. 
 
 These substances are composed of iron, sul- 
 phur, alumina, siliceous earth, and sometimes cal- 
 careous earth, in different proportions. The for- 
 mation of the sulphate of iron in these minerals, 
 is effected by exposing them for a long time to 
 the action of air and moisture, or by roasting them 
 in the open air, and leaving them afterwards ex- 
 posed to its action. This operation must somc- 
 
 
 
V 
 
 I 
 
 36l« SULPHATE, AND OTHER 
 
 times be reiterated. The sulphate that is formed 
 is extracted by lixiviation and evaporation. 
 
 The iron in the native suTphurets of pyrites is 
 oxidized, for when they are exposed to the action 
 of fire in a retort, sulphurous acid is evolved, 
 which does not happen with the sulphurets formed 
 with the metal. It is disoxidized in this opera- 
 tion, and the residuum is a true sulphuret. 
 
 Sulphate of iron is also formed in the mineral 
 waters which hold copper in solution, after it is 
 precipitated by iron. This solution, which re- 
 tains a little copper, is thereafter crystallized. 
 
 The sulphate of iron of Goslar contains com- 
 monly a little zinc, and that of Hungary and Sax- 
 ony a little copper.* The sulphates of England 
 and France are purer. They contain, however, 
 sometimes alum, especially those of France. 
 
 Sulphates free from copper or alum would be 
 formed, if the precaution were taken of keeping 
 fragments of iron in the boiler, which serves for 
 evaporation, as Monnet recommends;! for iron 
 slightly oxidized has the property of precipitating 
 copper and the base of alum. The superiority of 
 English vitriol seems to be owing to this precau- 
 tion. The same practice is also observed in two 
 manufactories in the neighbourhood of Alais.t 
 The zinc alone would not be precipitated. But 
 
 * Mineralogy of Kirvvan. 
 f Trait6 de Vitriolisation. 
 % Elemens de Chimie de Chaptal, torn. iii. 
 
mmm^^am^ 
 
 I 
 
 
 COMBINATIONS OF IRON. 365 
 
 it is rarely found, and only in small quantity, in J 
 
 the sulphates of iron. ] 
 
 The copper which exists in several kinds of 
 sulphate of iron is not injurious to the black 
 dyes, in which this metallic salt is principally em- 
 ployed; but for other purposes, it must be got 
 rid of. This is easily effected, by keeping for 
 some hours in a cold solution of this salt plates 
 of iron, on which the copper precipitates. But 
 this operation could not be performed by crystal- 
 lization, because, according to the observation 
 of Monnet, the sulphate of iron and that of cop- 
 per form a compound salt that cannot be thus 
 separated. \ 
 
 Alum is probably more injurious to black than 
 copper is ; for when a black stuff is boiled with 
 
 alum, it destroys the colour by dissolving it. 
 The sulphate of iron varies in its properties 
 
 according to its state of oxidation. 
 
 It is almost colourless when its metal is very 
 
 slightly oxidized, or in the condition of black 
 
 oxide. It assumes a red colour when the iron is 
 
 much oxidized, constituting a red oxide. Proust, 
 
 who directed our attention particularly to the two 
 
 states of iron, and to their distinctive properties, 
 
 regards them as two fixed terms of oxidation, 
 
 between which there is nothing intermediate. 
 
 We cannot adopt, in this respect, the opinion of 
 
 this chemist, whose delicate and numerous obser- 
 vations have contributed so much to the advance- 
 ment of the science. As the causes, however, 
 
 which may produce the oxidation or disoxidation 
 
366 SULPHATE, AND OTHER 
 
 of this iron, make it usually pass from a very ad- 
 vanced degree of oxidation to another adjoining 
 the lowest degree, we neglect this consideration, 
 and conform usually in our explanations with the 
 opinion of Proust. (Note AA.) 
 
 ' When the solution of slightly oxidized iron is 
 
 exposed to the air, it becomes gradually turbid, 
 and lets fall a yellow precipitate. If the effect be 
 complete, crystals are no longer obtainable by 
 evaporation, but an extract is got, which has a 
 great excess of acid. Highly oxidized iron then 
 
 j requires an excess of acid for its solution ; and 
 
 when it is in this state, the sulphuric acid has 
 much difficulty to dissolve a smaller quantity of 
 it, than if it is in the metallic form. By the de- 
 composition of water which occurs in the latter 
 case, it can take only the state of black oxide. 
 If the crystals of the sulphate of iron be left ex- 
 posed to the air, they lose their green colour, be- ' 
 coming dull and yellowish. Their solution now 
 yields only a salt with excess of acid, and an in- 
 soluble yellow substance remains. It is obvious, 
 therefore, that in order to preserve the sulphate 
 of iron or its solution in its primitive state, air 
 must be excluded. 
 
 The precipitate now spoken of, is a salt with 
 excess of oxide. By means of an alkali, the acid 
 may be abstracted, when merely a red oxide re- 
 mains. 
 
 If iron be put into a solution of the highly oxi- 
 dized sulphate, a yellow precipitate is deposited, 
 which is also a salt with excess of oxide, and the 
 
■^ 
 
 
 COMBINATIONS OF IRON. 367 
 
 solution resumes the state of green sulphate. 
 Hence appears the utility of adding iron in the 
 preparation of the sulphate. It is thus obtained 
 in the state for forming crystals, and those un- 
 crystallizable residuums called mother waters are 
 avoided. 
 
 The sulphate which contains the black oxide 
 is in a much greater state of saturation, and we 
 have seen that gallic acid could not separate and 
 precipitate this oxide from the sulphuric acid. It 
 is not to be doubted, then, that it exerts a far 
 more energetic action on the acid, than when it 
 is much oxidized. 
 
 In the precipitates produced by the alkalies, 
 from the solutions of both sulphates, characters 
 appear which depend on this difference of action. 
 The little oxidized sulphate affords with the al- 
 kalies greenish precipitates, which retain a greater 
 proportion of acid in like circumstances ; and 
 even when the sulphate is highly oxidized, its 
 precipitates are red, and do not retain any acid. 
 If we treat with a concentrated alkali the green 
 precipitate obtained from the slightly oxidized 
 sulphate, its acid is removed, and it becomes grey 
 or black. On exposing it to the air, it continues 
 to oxidize, passing to yellow. It then grows red, 
 by the action of an alkali which seizes its acid. 
 
 What we have now advanced concerning the 
 difference which distinguishes the green sulphate 
 from the red sulphate, must be applied to all the 
 solutions of iron in the acids. The whole of them 
 form a more intimate combination with the black 
 
368 SULPHATE, AND OTHER 
 
 oxide than with the red. They exhibit, besides, 
 differences dependent on the energy of the acid. 
 Thus, muriatic acid dissolves highly oxidized iron 
 more easily than the other acids. It is true, that 
 if it contains an excess of oxygen, a portion of 
 the acid forms oxygenated muriatic acid, accord- 
 ing to the observation of Fourcroy. Iron pro- 
 duces also in the precipitation of highly oxidized 
 muriate, a yellow precipitate, which owes this 
 colour to the acid remaining combined with it. 
 But it may be supposed, that highly oxidized 
 muriate of iron would be less proper for black 
 dyes than the sulphate, because it would retain 
 with more force the oxide which must enter into 
 the formation of the black molecules. 
 
 Acetate of iron is employed for printed cali- 
 coes, and in general for black colours in linen 
 and cotton, for the same reasons which make 
 acetate of alumina be preferred. But we need 
 not have recourse to so costly a process. Acetic 
 acid dissolves iron directly ; and to have it in the 
 most oxidized state, fragments of the metal must 
 be kept a long time in good vinegar. The ob- 
 ject would not, however, be accomplished, were 
 the solution left always over the iron. For we 
 have seen, that in the metallic state it precipi- 
 tates a highly oxidized salt. The liquor, then, 
 is to be decanted, and kept in a vessel where it 
 may have contact of air, so as to pass to the 
 highly oxidized state. This decantation ought to 
 be made whenever the solution is completed. 
 
 Bi 
 
COMBINATIONS OF IRON. , 369 
 
 For the ordinary black dyes, where there is no 
 need of so concentrated a solution, vinegar is not 
 employed, but a less expensive acid is frequently 
 formed with different vegetable substances, for 
 example with the bark of the birch tree. To 
 the vessel in which this operation is executed, 
 the name of tonne au noir (black cask) is given. 
 This object would be better accomplished, if the 
 precaution were taken to keep the solution, after 
 it is made, out of contact of iron. 
 
 In explaining the action of astringents, we 
 have mentioned the observation of Proust, who 
 found, that the highly oxidized sulphate was 
 brought back to the state of the little oxidized, 
 by the action of astringents, and even of other 
 colouring substances ; whence he concludes, that 
 it is right to employ in dyeing only the highly 
 oxidized sulphate. This conclusion appears to 
 us just, when black dyes are -in question, with 
 the exception, perhaps, of the dyeing of silk. It 
 should even be applied to all solutions of iron 
 used for this purpose. But the same thing does 
 not hold true when solutions of iron are made 
 use of for other colours. For example, in the 
 manufacture of printed goods, in order to obtain 
 the colour called rust yellow, sulphate of iron 
 is made use of, or, still better, the little oxidized 
 acetate, formed by the decomposition of acetate 
 of lead with sulphate of iron. The salt with 
 excess of oxide, which is formed in the cloth, has 
 an agreeable yellow colour, which, by the con- 
 
 vol. i. a a 
 
 
370 SULPHATE OF IRON. 
 
 tact of alkalies, passes to grey ; after oxidizing in 
 the air, it becomes red. 
 
 The shades of yellow which may be given to 
 cotton by means of iron, with which we shall be 
 elsewhere occupied, prove that it is not the oxide 
 of iron alone which serves to give colour in this 
 instance, but that the precipitate retains a por- 
 tion of the acid ; for it is always to an acid that 
 the oxide of iron owes this colour. 
 
 The changes of colour must never be lost sight 
 of, which result from the different oxidations of 
 iron in the dyes, where it is used for other co- 
 lours besides black, as Chaptal has shewn. Thence 
 the precautions which must be taken, in order 
 that this oxidation shall go on uniformly during 
 the operation itself, and that the stuff be exposed 
 to it in an uniform manner. 
 
 There is one operation for which the iron 
 should be, on the contrary, at the lowest stage of 
 oxidation : This is the solution of indigo, by 
 means of the sulphate of iron, precipitated by an 
 alkali. Slightly oxidized iron gives solubility to 
 the indigo, by carrying off' the oxygen, which 
 renders it insoluble. The oxide of copper pro- 
 duces a contrary effect, affording oxygen to in- 
 digo deprived of it. This renders the sulphate 
 and acetate of copper proper for the reserves, 
 that is to say, for preserving the parts of the ' 
 cloths to which they are applied, from the fixa- 
 tion of the indigo, which by resuming oxygen 
 can no longer combine with the stuff. 
 
 ■— 1>> immmwrnuuMim I 1 1 
 
■^^■■^■■Wli 
 
 SULPHATE OF COPPER. 371 
 
 The differences of oxidation of the metallic 
 substances employed in dyeing, and the effects 
 flowing from them, merit the greatest attention ; 
 and by observing them with more care than has 
 hitherto been done, several operations will be 
 rendered methodical (regularisees), whose results 
 are 1 regarded as capricious, becoming at the same 
 time more uniform and more advantageous. 
 
 CHAPTER IV. 
 
 Of Sulphate of Copper. 
 
 The sulphate of copper, blue vitriol, vitriol of 
 Cyprus, blue copperas, is not much employed in 
 dyeing ; but it is of great service for forming 
 the colours used particularly for painted papers ; 
 and hence its fabrication, and the means of ob- 
 taining it pure, have become interesting to the 
 arts. 
 
 Different methods are employed for making 
 sulphate of copper. The native sulphuretj or 
 copper pyrites, or mate, resulting from the fu- 
 sion of copper ore, which is a combination of 
 copper and sulphur, is calcined, and the pro- 
 duct of the calcination is left to effloresce. The 
 copper thus deprived of a portion of its sulphur 
 oxidizes, and the sulphur is converted into sul- 
 phuric acid. The salt that forms is then ex- 
 tracted, and crystallized. A second process, 
 analogous to the preceding, consists in calcining 
 
72 SULPHATE OF COPPER. 
 
 a mixture of copper and sulphur, in exposing the 
 sulphuret in like manner to effloresce, lixiviating 
 the salt, and crystallizing it. 
 
 Since the (modern) fabrication of sulphuric 
 acid has allowed it to be employed for several 
 purposes to which its former price was an ob- 
 stacle, sulphate of copper has been formed, by 
 dissolving the metal, or its oxide, in sulphuric 
 acid. To this sulphate it is objected, that for 
 some purposes it contains an excess of acid ; 
 but it would be difficult to avoid this incon- 
 venience. 
 
 There are some native waters which contain 
 sulphate of copper. 
 
 The principles to be attended to in purifying 
 the sulphate of copper deserve to fix our atten- 
 tion, because they are applicable to all the me- 
 tallic solutions, and may explain several pheno- 
 mena observed in the chemical action of different 
 bodies. 
 
 The insolubility of any compound that is form- 
 ed, should be considered as a cause of its forma- 
 tion,* whenever the elements that can produce it 
 are brought together. Thence may be deduced, 
 as we have said, the cause of the precipitations 
 and changes of base, which occur in the recipro- 
 cal action of the acid and alkaline substances. 
 
 The same effect takes place in the reciprocal 
 action of metallic oxides and acids. The oxides 
 can seldom produce neutralization in combining 
 with the acids, when their combination retains 
 solubility j but these combinations require a 
 
- *"PUU*- Ml 
 
 WW^s 
 
 SULPHATE OF COPPER. 373 
 
 greater or less excess of acid, a condition which 
 varies according to the state of oxidation. Thus 
 we have seen, that the highly oxidized sulphate 
 of iron requires a considerable excess of acid, 
 which the little oxidized sulphate does not. If 
 the excess of acid be removed, the highly oxi- 
 dized salt, which is insoluble, precipitates. 
 
 It thence results, that when a metal is in solu- 
 tion, and when it needs an excess of acid in order 
 to preserve this state, the addition of another 
 oxide, which shall require a less considerable ex- 
 cess of acid, will cause the first to fall down in 
 the form of an insoluble salt ; and if the second 
 needs an excess of acid, although less consider- 
 able, it will be precipitated in its turn by an oxide 
 which is soluble without excess of acid, or which 
 requires less of it. 
 
 For the same reason, different effects will be 
 obtained, by varying the oxidation of a metal, 
 and thereby the solubility of its combinations. 
 Thus we have seen, that iron precipitated the 
 highly oxidized sulphate, forming a combination 
 which preserves its solubility without excess of 
 acid. In these circumstances two combinations 
 are produced, one which remains in solution, and 
 another which is insoluble. The action even of 
 the alkalies is usually limited to the production of 
 a similar effect on metallic solutions. 
 
 Gay Lussac, who established this point of 
 theory,* supported it by several interesting facts. 
 
 * Annales ilc Chimie, torn. xlix. 
 
374 SULPHATE OF COPPER. 
 
 We shall confine ourselves to an account of the 
 observations which relate to the preparation of 
 the sulphate of copper and the sulphate of iron. 
 
 " When the iron is highly oxidized, it is preci- 
 pitated by the oxide of copper ; when slightly so, 
 the reverse takes place. Here are two conse- 
 quences of great importance, because they are 
 susceptible of frequent applications to the arts : 
 the first is, that the whole iron can be separated 
 from a solution of copper ; the second, that the 
 whole copper in a green solution of iron may be 
 removed. 
 
 " Several colours are prepared with the sul- 
 phate of copper, but the iron which it always 
 contains, and which has not hitherto been com- 
 pletely separated, alters their shade. If, for ac- 
 complishing this object, the iron be strongly oxi- 
 dized by means of nitric acid, or, still better, by 
 oxygenated muriatic acid, it will be precipitated 
 entirely from the sulphate of copper, by pouring 
 into it a sufficient quantity of potash, heating and 
 agitating the liquor very well. 
 
 " The green sulphate of iron is pretty fre- 
 quently employed in the arts, and in several cases 
 it is of consequence to free it from all the copper. 
 Iron has indeed the property of separating it, but 
 it appears to do so but very imperfectly, and in a 
 long time. It will be undoubtedly more advan- 
 tageous to employ potash, pouring a little of it 
 into the green sulphate. The precipitate of black 
 oxide of iron will soon return into solution by 
 agitation ; and it will throw down at once the 
 
ACETATE OF COPPER. 3^5 
 
 oxide of copper, and the red oxide of iron, if 
 either exist in the green sulphate," 
 
 CHAPTER V. 
 
 Of VerdigriSy or the Acetate of Copper. 
 
 Formerly verdigris was prepared only in Mont- 
 pellier and its neighbourhood. The process fol- 
 lowed there consisted in causing the stalks of 
 grapes to ferment along with the vinasse (wine- 
 lees), then plates of copper were arranged stratum 
 super stratum with these stalks, and the whole was 
 left together for some time. On withdrawing 
 them, they were set aside ( au relai) in a corner 
 of the cellar, where they were further sprinkled 
 with wine-lees ; and lastly, the verdigris formed 
 by this operation was scraped off. 
 
 This process has been improved and rendered 
 more economical in these latter times, by substi- 
 tuting for the stalks the squeezed husks of grapes, 
 previously subjected to the acetous fermentation, 
 thus suppressing the vinous matter with which 
 they had formerly bedewed the stalks. Chaptal 
 has described the details of this process.* 
 
 At Grenoble, ready made vinegar is employed, 
 with which the plates of copper are moistened. 
 The verdigris prepared in these two methods 
 differs in some of its properties. 
 
 • Memoircs de l'lnstit. vol. ii. 
 
37 O ACETATE OF COPPER. 
 
 Chaptal has made a comparison of them.* The 
 first is unctuous, pasty, little soluble in water ; it 
 is preferred for the purposes of painting. The 
 second is drier, of a more decided greenish blue 
 colour, and more soluble in water. It produces 
 better effects in dyeing ; giving more vivacity to 
 the colours, and requiring a smaller quantity to 
 compose the mordants. 
 
 This difference depends upon their composi- 
 tion. The first contains, in particular, uncom- 
 bined oxide of copper, or carbonate of copper, 
 and the second approaches to the state of an 
 acetate. 
 
 In either preparation of verdigris the copper is 
 reduced to an oxide by the concurrent actions of 
 atmospheric air, and the acetic acid employed or 
 formed. But as copper vessels are much used, 
 it will be proper to dilate a little further on the 
 manner in which the acids act on this metal. 
 
 For dissolving copper in the acids, it must, 
 like other metals, be combined with oxygen or 
 reduced to an oxide. Hence it must either at- 
 tract oxygen from the atmosphere, or obtain it 
 from the acids, or from the decomposition of 
 water by the co-operation of another force ; for 
 it has not this property of itself. 
 
 The vegetable acids cannot yield oxygen to 
 copper ; but the action which they exercise upon 
 it so favours its combination with oxygen, that it 
 attracts it speedily from the atmospheric air, and 
 
 * Memoires do l'lnstit. vol. i. 
 
ACETATE OF COPPER. 377 
 
 is reduced to an oxide so as to become soluble in 
 the acid liquid. This must not be hot, in order 
 that the copper ma) 7 attract oxygen from the at- 
 mosphere. The vegetable acids do not attack cop- 
 per while they are hot, and the same thing takes 
 place with oils and other substances which act 
 on this metal, unless there be a portion of copper 
 already oxidized ; for in this case it dissolves 
 readily, whatever temperature the liquor may 
 have. Hence we perceive the necessity of never 
 allowing liquors that can corrode this metal to 
 cool in copper boilers, and of taking care to keep 
 them always very clean, so that no oxide is form- 
 ed on their surface. 
 
 Nitric and nitro-muriatic acids, though diluted 
 with water, afford oxygen to copper, especially at 
 a boiling heat. Hence they must dissolve a por- 
 tion of this metal in the baths into which, for ex- 
 ample, solution of tin enters, unless the boiler be 
 tinned with care. This effect may be diminished, 
 however, in consequence of the nitric acid exert- 
 ing its action on the vegetable, and more parti- 
 cularly the animal, substances present in the 
 bath, and from its being saturated by the am- 
 monia that is generated. 
 
 In verdigris, copper is reduced to the state of 
 oxide, and is combined with a more or less con- 
 siderable proportion of acetic acid. When the 
 oxide is completely saturated with this acid, it is 
 wholly soluble in water, and forms by evapora- 
 tion rhomboidal crystals of a blue colour, which 
 attaching themselves to little wooden rods, give 
 
 \ 
 
I / 
 
 ) 
 
 ) 
 
 378 ACETATE OF COPPER. 
 
 origin to those groups called crystallized verdigris, 
 or crystals of Venus. There is this difference, 
 then, between this salt and verdigris, that in the 
 first the oxide of copper is completely saturated 
 with acetic acid, forming an acetate of copper ; 
 while, in verdigris, there is but a variable propor- 
 tion of the oxide of copper in the condition of an 
 acetate. This saline portion can be separated by 
 solution in water. There remains, in this case, 
 only an oxide of copper, or a salt with excess of 
 oxide, which dissolves readily in acetic acid, and 
 thus is converted to the saline state. Sometimes 
 the verdigris contains but very little acetate ; 
 sometimes, on the contrary, it contains scarcely 
 one-fourth of its weight of oxide of copper un- 
 combined , in which circumstances consists, as we 
 have said, the difference which distinguishes the 
 verdigris manufactured at Grenoble from that of 
 Montpellier. (Note BR) 
 
 Clegg, in attempting to substitute for verdigris 
 in the black dye an ingredient less expensive, 
 says, that he observed that the copper of verdi- 
 gris threw down, in the state of an oxide, the iron 
 of the sulphate of iron held in solution along with 
 astringent matters. Regarding verdigris, there- 
 fore, as a precipitant of iron, he sought to substi- 
 tute for it other substances capable of precipitat- 
 ing this metal from its solvents. He first tried 
 the alkalies ; and his experiments, which on the 
 small scale appeared to succeed, had no success 
 on the great. In fact, the alkalies do not preci- 
 pitate the combination of iron and the astringent 
 
If 
 
 ACETATE OF COPPER. 
 
 379 
 
 principle ; but they unite along with it, giving it 
 a reddish hue. He next ascertained, by several 
 trials, that the verdigris might be perfectly re- 
 placed by a mixture of sulphate of copper and 
 potash. He prescribed the dissolving the sul- 
 phate of copper, and adding to it solution of pot- 
 ash, till the blue colour disappeared, that is to say, 
 till the whole of the copper was thrown down. 
 For this purpose a nearly equal weight of sul- 
 phate of copper and of alkali is required. He 
 asserts, that the weight of the two together is a 
 substitute for an equal weight of verdigris ; and 
 that this process may be put in practice, especi- 
 ally for hats, the dyeing of which consumes a 
 great deal of verdigris. 
 
 We shall remark on this process, that the oxide 
 of copper produces in reality a precipitate in a 
 solution of iron blackened by an astringent ; but 
 this precipitate is not solely oxide of iron j it is 
 owing to the black molecules which result from 
 the combination of the oxide with the astringent 
 principle. This precipitation may, indeed, be 
 one mode in which oxide of copper contributes 
 to dyeing of black; but it is probable that the 
 principal way in which it is useful to this dye 
 consists in forming a blue with logwood, which 
 also enters into it, or a shade between green and 
 black, which results from its combination with 
 the astringent ; for we have observed, that it was 
 advantageous for deepening the black to derive 
 it from different colours. It is thus obvious how 
 a verdigris which contains much acetate of cop- 
 

 380 ACETATE OF LEAD. 
 
 per, may produce better effects than one which 
 has a larger proportion of unsaturated oxide, or 
 carbonate. 
 
 CHAPTER VI. 
 
 Of the Acetate of Lead, or Salt of Saturn. 
 
 The acetate of lead is a combination of lead 
 reduced to oxide, and of acetic acid. It is usu- 
 ally crystallized in slender confused needles. 
 
 This salt has a sweet taste, mixed with a little 
 astringency, which has caused it to get the im- 
 proper name of sugar ofsaturn. 
 
 Acetic acid out of contact of air does not at- 
 tack lead in the metallic state. But if the air 
 touches its surface, the lead is gradually oxidized 
 by means of the oxygen which it attracts, and 
 thereby becomes soluble in the acid. As this 
 manner of preparing the acetate of lead would 
 be disadvantageous, both because it would take 
 much time, and a large portion of the acid would 
 evaporate, other processes are had recourse to. 
 
 White lead is an oxide of lead combined with 
 carbonic acid. To form it, the metal in plates is 
 suspended over vinegar in earthen vessels, which 
 are covered with horse dung, to afford heat for 
 evaporating the vinegar, which exhaling, reduces 
 the lead to an oxide by means of the air, and 
 then dissolves it. Carbonic acid is evolved at 
 the same time, which precipitates the lead in a 
 
ACETATE OF LEAD. 381 
 
 carbonate. This carbonate, pulverized with much 
 care, constitutes white lead. But a portion of 
 the oxide is retained by the vinegar, forming 
 acetate of lead, which is merely to be evaporated 
 and purified by a second crystallization. 
 
 The greater part of the acetate of lead is pre- 
 pared with distilled vinegar, obtained from beer 
 or wine, and with white lead, which being re- 
 duced to a very subtile powder, is in the most 
 favourable state for dissolving. 
 
 If no acetate of lead be at hand, it is easy to 
 manufacture it one's self, by dissolving an oxide 
 of lead in distilled vinegar, and evaporating the 
 solution to the proper point of crystallization. 
 Different oxides of lead may be employed. White 
 lead dissolves more easily than the others, except 
 ceruse ; but we must avoid the latter, because it 
 is a mixture of white lead and chalk. Litharge, 
 or semi- vitrified oxide of lead, may be substituted 
 for white lead j minium dissolves with more diffi- 
 culty. 
 
 It would probably be sufficient to dissolve the 
 oxide of lead in white (pale) vinegar, whose ex- 
 tractive part, by which principally it differs from 
 distilled vinegar, would do no harm ; but it must 
 be remarked, that the acetate of lead is a com- 
 pound not uniform in its proportions. Thenard 
 has observed, that the ordinary acetate of lead 
 can still dissolve a quantity of oxide almost equal 
 to what it already contains, and then it assumes 
 a different form of crystallization. But the new 
 
7 
 I 
 
 1 
 / 
 
 / 
 
 \ 
 l 
 
 ! I 
 
 I 
 
 9 
 
 1 
 
 / 
 
 382 ACETATE OF LEAD. 
 
 crystals are decomposed by simple exposure to 
 air, and a portion of the oxide is converted into 
 carbonate. On being dissolved in water, they 
 likewise abandon a portion of the Oxide, forming 
 an abundant precipitate ; after which the soluble 
 | combination is restored to the ordinary state. 
 
 ) On repeating this experiment, we have observ- 
 
 ed that the acetate of lead which we used, red- 
 dened the vegetable colours, acting on paper 
 stained with turmeric like feeble acids ; but after 
 being surcharged with oxide of lead, its solution 
 reddened the tincture of turmeric like alkalies, 
 so that there is here an indication of the alka- 
 line properties which the oxides exercise on the 
 acids. 
 J The crystals of acetate of lead usually afford a 
 
 slight precipitate when they are dissolved in dis- 
 tilled water ; which precipitate is owing to car- 
 bonate of lead formed at their surface. But they 
 I J produce, with the waters of rivers and wells, a 
 
 much more abundant precipitate, arising from 
 the sulphates and the muriates which are present 
 in these waters, the quantity of which is propor- 
 tional to that of these salts. The muriate of lead, 
 however, has a certain degree of solubility. 
 
 The acetate of lead is not employed directly 
 as a mordant in dyeing, although it produces an 
 abundant precipitate with the greater number of 
 the solutions of colouring matters j but its preci- 
 pitates have sombre and dead hues. The chief 
 use that is made of it, is to procure acetate of 
 
ACETATE OF LEAD. 383 
 
 alumina. Since the force of cohesion of this 
 earth is opposed to its direct solution in the ace- 
 tic acid, a mixture of sulphate of alumina is made 
 with acetate of lead. Thus (acetate of) alumina 
 is procured in the liquid state. But the elements 
 of these combinations being placed together, and 
 the oxide of lead possessing the property of af- 
 fording an insoluble combination with sulphuric 
 acid, this compound is formed and precipitates, 
 while the alumina remains dissolved in the acetic 
 acid. (See Note C.) 
 
 Accident made known this combination, so 
 important in the printing of calicoes ; several 
 useless substances indeed were added to it, till 
 chemistry determined the essential ingredients. 
 
 Certain expert manufacturers imagined, that 
 they should preserve among the ingredients a 
 given proportion of chalk and potash, with the 
 view of absorbing an excess of acid ; but this 
 addition does nothing but throw down, uselessly, 
 a portion of the oxide of lead, and introduce into 
 the acetate of alumina foreign salts, which may 
 injure the effects that it ought to produce. Ex- 
 perience has proved, that without these mixtures 
 a good preparation was obtained ; hence the only 
 thing to be determined is, the proportions which 
 effect the exchange of base most completely. 
 
 Haussman employed an acetate of tin, formed 
 by decomposing the acetate of lead by the muri- 
 ate of tin ; but this preparation has some disad- 
 vantages : 1. ft retains a little muriate of lead ; 
 for this salt has a slight solubility j 2. A triple 
 
/ 
 
 j 
 
 I 
 
 I ( 
 
 
 / 
 
 384 OF THE ALKALIES. 
 
 salt is formed, which contains a great proportion 
 of lead, if the necessary proportion of acetate of 
 lead be used. 
 
 CHAPTER VII. 
 
 Of the Fixed Alkalies. 
 
 Magnesia, lime, barytes, strontites, and glu- 
 cina, might indeed be regarded as fixed alkalies, 
 since the whole of them, and some more than 
 potash or soda, possess the property of saturating 
 the acids, and forming with them neutral combi- 
 nations. They are distinguished, however, by 
 the name of earths, or alkaline earths, in consi- 
 deration of the solidity and pulverulency which 
 give the idea of an earth ; and the name of fixed 
 alkalies is reserved for potash and soda, which 
 being of great use in dyeing, should be well 
 studied. 
 
 As for ammonia, although it be the most power- 
 ful of the alkalies, since, in equal quantity, it 
 exercises in a higher degree the alkaline proper- 
 ties on the acids, its volatility is an obstacle to its 
 use in most part of the operations of dyeing. 
 
 Article I. 
 
 Of Potash. 
 
 Potash, named vegetable alkali, because it is 
 derived from the combustion of vegetables, is an 
 
OF POTASH. 385 
 
 identical substance. But the state of saturation 
 in which it exists, and the mixtures confounded 
 with it, considerably diversify its effects and 
 value." 
 
 When its whole alkaline power is to be exerted, 
 it must be deprived of the carbonic acid, with 
 which it is combined in greater or less proportion, 
 and which gives it the property of effervescing with 
 such acids as expel its carbonic acid. With this 
 view it is dissolved and treated with quicklime* 
 which, seizing its carbonic acid, precipitates in 
 the form of an insoluble salt. What is called pure 
 or caustic potash, is thus obtained. It still re- 
 tains, however, a portion of carbonic acid, to free 
 it from which it must be treated with alcohol. 
 In this case two combinations are formed, the one 
 an alcohol of potash, and the other, which remains 
 dissolved in a portion of water, or which separates 
 in crystals, is carbonate of potash. On expelling 
 the alcohol from the former combination, we have 
 pure potash. But this preparation is not wanted 
 in dyeing, except for experiments of research. 
 
 The watery solution of ordinary potash con- 
 tains also foreign salts, which it may be worth 
 while to separate, as is done for the manufacture 
 of fine glass. For this purpose, the potash is dis- 
 solved in as little water as possible, and the solu- 
 tion is allowed to settle. The salts less soluble 
 than potash, separate in a great measure, and fall 
 down. 
 
 Potash, not saturated with carbonic acid, at- 
 tracts the humidity of the air, and thereby dis- 
 
 vol. i. b b 
 
386 OF POTASH. 
 
 solves, forming a liquor called oil of tartar, per 
 deliquium. It also attracts carbonic acid, and in 
 a long period of time acquires the property of 
 crystallizing. Bonn and Monnet had observed 
 this crystallization before its cause was known. 
 
 It should be observed, that carbonate of potash 
 has the property of crystallizing, before getting 
 the quantity of carbonic acid which can combine 
 with it. When this is the case, it attracts mois- 
 ture from the air. In the solution, the portion 
 which remains liquid, acts sufficiently on the water 
 to permit the other portion to crystallize. When 
 this water is removed, the crystals exert sufficient 
 force on the water of the atmosphere, and attract 
 enough to be reduced to a liquid. It would 
 seem, that the carbonate of potash can assume 
 variable quantities of carbonic acid, even when 
 it has no longer the property of attracting humi- 
 dity. 
 
 These different states of saturation of the car- 
 bonic acid demand attention, when potash is 
 employed in dyes whose colours may be affected 
 by it, or in which the texture of the stuffs can 
 suffer alterations j for, in the caustic state, the 
 alkali exerts a greater power of combination with 
 other substances. 
 
 Different names have been given to potash, 
 according to the substance from which it is ex- 
 tracted. It is called salt of tartar, when obtained 
 from the acidulous tartrate of potash, or tartar. 
 To make this preparation, the tartar is wrapped 
 up in paper cones, and is thus exposed to com- 
 
 7 
 
MM 
 
 OF POTASH. 
 
 387 
 
 bustion. After dissolving the residuum in water, 
 the solution is concentrated by heat, the foreign 
 salts are separated in proportion as they fall down, 
 and by desiccation the potash is procured, which 
 retains much carbonic acid, formed by the de- 
 struction of the tartaric acid, at a sufficiently mo- 
 derate heat for a great deal of it to remain in 
 combination. This potash is very rich in alkali; 
 but it is very costly. 
 
 The cendres gravelees, which are the product 
 of the combustion of wine lees and vine branches, 
 are also rich in alkali, although the potash is here 
 less pure than that obtained from tartar. 
 
 The potash, known by different names in com- 
 merce, comes chiefly from the North of Europe, 
 and the United States of America. It is the 
 product of combustion in vast forests, for the 
 wood of which no better use can be found. But 
 this operation not being every-where made with 
 the same care, is the main cause of the great dif- 
 ferences in the product. According to Linnaeus, 
 the birch or alder is burned with a slow fire; with 
 the ashes and water a kind of paste is made ; with 
 this paste a range of billets of the pine or fir is 
 covered ; over this range another is laid trans- 
 versely, covered in like manner with the same 
 paste ; and in this manner the layers of wood and 
 paste are continued, till the pile acquires a con- 
 siderable height. Fire is now put to it, and when 
 the ashes begin to flow, the pile is overturned, and 
 the ashes in scmifusion are beat with flexible 
 
38(8 OF POTASH. 
 
 rods. They are incrusted by this operation on 
 the logs, and become as hard as stone. 
 
 It is obvious, that by this process the potash 
 must contain a great deal of foreign earth ; but it 
 appears that lime is sometimes mixed with it. 
 Home found some of it, chiefly in a species of 
 potash called cassoude, much used by the bleach- 
 ers in Belgium, and the neighbouring depart- 
 ments. 
 
 So defective a process as the above is not fol- 
 lowed every-where ; but in some places the ashes 
 are lixiviated, by covering them with water in 
 casks. After some hours, the liquid is run off, 
 new water is poured on, and the operation is re- 
 peated, till the water conies off nearly insipid. 
 The last waters are employed for new leys, as 
 in the lixivia of the plaster rubbish from which 
 saltpetre is extracted. The waters are subse- 
 quently evaporated ; the result is black and car- 
 bonaceous. It is called salin. This substance, 
 calcined in a furnace, becomes white, and yields 
 a good potash. 
 
 Ashes which have undergone no preparation are 
 also made use of, and principally for leys. What 
 has been said of potashes, may be applied to 
 them. 
 
 The vegetables from which potash is extracted 
 differ much from one another, both in the quan- 
 tity of ashes which they yield on combustion, and 
 in the proportion of potash found in their ashes. 
 We shall give an outline of the observations which 
 have been made on this subject, because they 
 
i^WM^nK*" 
 
 —*m 
 
 OF POTASH. 389 
 
 may guide us in the art of preparing potashes, 
 and in their different applications to the arts. 
 
 It results, from the experiments of Pertuis in 
 particular,* that the herbaceous plants furnish 
 in equal weight, after their drying, much more 
 ashes than ligneous (woody) plants, and that the 
 first contain a larger proportion of alkali ; that 
 the trunks of trees yield less than the branches, 
 and the branches less than the leaves ; but on 
 this subject, as well as on several others relating 
 to vegetation, much more extensive and exact 
 researches than the above are to be found in a 
 work just published by Theodore de Saussure.t 
 
 * Ann. de Chimie, torn. xix. 
 
 f Recherches Chim. sur la Vegetation. We find in this ex- 
 cellent work, observations which occasion some modifications 
 in the explanations which we have given on the change pro- 
 duced by the air on the colouring particles, and the vegetable 
 substances which suffer its action. The author has deter- 
 mined in a more positive manner the circumstances of this 
 alteration. 
 
 Saussure, on exposing extracts and*other vegetable sub- 
 stances to the action of the air in closed vessels, found that 
 the volume of the air was not diminished, but that its oxygen 
 was changed into carbonic acid, extracting its carbon, and com- 
 bining with it. At the same time, a production of water takes 
 place, by the more intimate combination of the hydrogen con- 
 tained in this substance with the oxygen which was equally 
 contained in it, and, of consequence, the substance contains a 
 larger proportion of charcoal. The effect is therefore compar- 
 able, in this respect, to that of a slight combustion. 
 
 His observations, however, even prove that the fact is not 
 general ; the oils absorbed some oxygen. It would appear, 
 that the action of oxygen does not produce uniform effects 
 
390 OF POTASH. 
 
 His experiments have placed beyond doubt,, 
 that potash, and the other salts which are found 
 in the ashes of vegetables, are not a product of 
 vegetation, but that they proceed from the soil 
 from which they are absorbed, and even from the 
 atmosphere. Consequently, the same vegetables 
 which grow in different soils yield in their com- 
 bustion a different proportion of ashes, which 
 have different proportions of saline or earthy sub- 
 stances, either soluble or insoluble. The parts 
 of vegetables leave more ashes, as they are sub- 
 ject to a greater transpiration ; because these 
 ashes proceed from the substances which were 
 held in solution in the vegetable juice. Thence 
 the leaves afford more than the bark ; this more 
 than the alburnum j and the alburnum more 
 than the timber. 
 
 For the same reason, herbaceous plants yield 
 much more of it than the woody plants. 
 
 The proportions of the alkalies, or rather of the 
 soluble part, vary in these ashes. The seeds 
 contain most ; the leaves come next ; but when 
 they are young they contain more. The bark 
 has the smallest quantity of it. This quantity is 
 seen to diminish, according as the rain water has 
 dissolved and carried it away. 
 
 The phosphates, which the ashes of vegetables 
 contain, form an important consideration. Saus- 
 
 even on the substances which are not oily. But it will be 
 necessary to distinguish, by new observations, the cases differ- 
 ent in the mode, but uniform in the result, which is a predo- 
 minance of carbon. 
 
OF POTASH. 391 
 
 sure has found, that all vegetables contain the 
 following phosphates : Phosphate of potash ; phos- 
 phate of potash and lime, soluble like the preced- 
 ing ; and phosphate of lime, insoluble. As they 
 usually contain carbonate of lime, changes of 
 combination take place during incineration. The 
 phosphate of potash is decomposed by the car- 
 bonate of lime j and there is found in the ashes 
 only phosphate of lime, or a smaller quantity of 
 the first two combinations, than what existed in 
 the vegetable. If different vegetable parts be 
 incinerated, a result will be obtained, which is 
 not the mean that would have been got by 
 making the incineration separately. Thus the 
 bean contains phosphate of potash, without car- 
 bonate of lime, and no phosphate of lime is 
 found in its ashes. But if it be burned along with 
 the stem, which contains carbonate of lime, there 
 is obtained, instead of phosphate of potash, a 
 much larger portion of phosphate of lime than 
 the incineration of the stem alone would have 
 given. 
 
 From these observations, some results may be 
 drawn useful to our subject, which we abridge 
 with regret. 
 
 1. For the fabrication of potash, it is more 
 advantageous to collect herbaceous plants, leaves, 
 and small sprigs of trees, than to burn the trunks 
 themselves. 
 
 2. When the ashes are boiled into a condensed 
 ley, in order to extract their potash, the alkali 
 must convert a part of the insoluble phosphate 
 
39# OF SODA. 
 
 of lime into phosphate of lime and potash ; and 
 the portion of the alkali which enters into this 
 combination becomes inactive, by reason of the 
 saturation which it experiences. 
 
 We shall not dwell on the other substances 
 which enter into the composition of the ashes, 
 and of ordinary potash ; because the only mat- 
 ter which is useful and of importance to estimate 
 is the alkaline. We have described, in treating 
 of bleaching, the most exact means of arriving 
 easily at this valuation. If there be an intention, 
 however, of employing potash as an alterative or 
 auxiliary, it may be proper to ascertain if it con- 
 tains much carbonic acid, which its effervescence 
 with acids points out. But a solution of it must 
 be previously made to separate the effect of the 
 potash from that of the carbonate of lime. The 
 quantity of carbonic acid which escapes may be 
 ascertained by verifying the loss of weight expe- 
 rienced by the mixture of potash and acid, whose 
 separate weights had been determined before- 
 hand. 
 
 Article II. 
 
 Of Soda. 
 
 Chemists have given the name mineral to this 
 alkali, because it is often found at the surface of 
 the earth, or in subterraneous cavities. Thus a 
 great quantity of it may be gathered in Egypt 
 
 i 
 
OF SODA. 
 
 393 
 
 in the neighbourhood of lakes, called natron; a, 
 name also given to the soda obtained from them. 
 In several parts of Barbary, Syria, Persia, in the 
 West Indies, China, and even in our climates, it 
 is likewise found. 
 
 The conditions which determine this produc- 
 tion, are, judging from the observations made 
 near the natron lakes,* a mixture of muriate of 
 soda and carbonate of lime, in a moist ground, 
 not too clayey, and a pretty hot temperature. In 
 this case, a slight solution of carbonate of. lime 
 is effected, and the causes which favour the ef- 
 florescence peculiar to carbonate of soda, deter- 
 mine its separation, while a corresponding portion 
 of muriate of lime infiltrates into the earth. 
 
 'The soda thus collected in Egypt is not pure," 
 but contains variable proportions of carbonate of 
 soda, muriate of soda, sulphate of soda, and of 
 earth, mingled,, even when different specimens are 
 taken on the same grounds. 
 
 The greatest part of the soda, however, which 
 is made use of, is the product of the combustion 
 of plants which grow on the sea-shores, and par- 
 ticularly of the salsola soda, Linn. 
 
 The most esteemed comes to us from Alicant. 
 Some is also extracted from the same plant on 
 our maritime coasts, as well as on others. To 
 these sodas, according to the countries and plants 
 from which they are got, different names are 
 given j such as, Rochette, Varech, Salicor. Julia 
 
 
 * Memohe sur l'Egypte. 
 
S94< OF SODA. 
 
 has lately given an interesting description of the 
 culture of the salsola, established in the environs 
 of Narbonne, from which a soda comes, known 
 under the name of Salicor.* 
 
 These sodas differ much from one another in 
 the proportion of carbonate of soda. There are 
 ashes of Varech which contain hardly any of it ; 
 but it is useless to dwell on these differences, be- 
 cause confidence can only be put in the chemical 
 proof, which should be the same as for potash. 
 A good soda, or a carbonate of soda, should be 
 assumed for a term of comparison ; because a 
 larger proportion of acid is required to saturate 
 a quantity of soda than an equal weight of potash. 
 
 Soda is in the state of a carbonate, or most 
 part of it at least is in that state, when plants are 
 incinerated. It crystallizes, retaining much wa- 
 ter of crystallization ; but it parts with this easily 
 to the air, and falls thereby into efflorescence, 
 with the loss of nearly one-half its weight. 
 
 This difference distinguishes it from potash, 
 which naturally retains, after incineration, only a 
 part of the carbonic acid necessary to its crystal- 
 lization ; and which, till it be saturated with it 
 to this point, attracts, on the contrary, the humi- 
 dity of the air ; a difference apparently depend- 
 ing on the stronger affinity which soda exercises 
 on the acids, and on the greater condensation 
 which it produces, particularly on those that are 
 naturally elastic. 
 
 * Ann. de Chimie, torn. xlix. 
 
OF SODA. 395 
 
 Although the native carbonate of soda crystal- 
 lizes and dries in the air, it retains, however, 
 weak alkaline properties, arid greens the colours 
 that characterize them. But it may take a larger 
 proportion of carbonic acid. The celebrated 
 Klaproth has observed in a species of carbonate 
 of soda, or natron, a proportion of carbonic acid, 
 nearly double of that obtained from the ordinary 
 carbonate. Hence its alkali is in a different state 
 of saturation. Probably it would not afford marks 
 of alkalinity. It might be found perhaps acidu- 
 lous. It does not effloresce. 
 
 As soda contains, not only a good deal of 
 foreign salts, but a greater or less proportion of 
 sulphuret, it is right to employ it for certain ope- 
 rations of dyeing in the state of a pure carbonate. 
 It is then called salt of soda (crystals of soda). 
 
 In order to free soda from the foreign sub- 
 stances, it is to be dissolved in water, and the 
 different salts are to be separated as they precipi- 
 tate or crystallize. The crystals of carbonate of 
 soda form last of all. 
 
 When this salt is used, it is essential to pay at- 
 tention to the state in which it exists ; for when 
 it is in crystals it contains one-half (fully 3-5ths) 
 its weight of water of crystallization. Hence, 
 when it has effloresced, one part produces as 
 much effect as two parts of crystals. 
 
 Lime acts on this salt in the same manner as 
 on carbonate of potash ; that is to say, it robs it 
 of the greater portion of its carbonic acid, ren- 
 dering it caustic. In this state it is pure soda, 
 
396 op soap. 
 
 (for the small quantity of carbonic acid which it 
 retains may be neglected), the soda of chemists, 
 the ley of the soap-boiler. 
 
 Sometimes the name of strong water, or strong 
 liquor of the soap-boilers, is given to a solution of 
 caustic soda. 1 Such a denomination may easily 
 lead to mistakes, making this alkaline solution be 
 confounded with nitric acid, called also eau forte, 
 (strong water, or aquafortis). Hellot tells us that 
 he was deceived in this way, in the preparation of 
 a vat of indigo, which had been suggested to him. 
 
 Since soda exerts on acids a stronger action 
 than potash, it may probably produce also a 
 greater effect on colouring substances when it is 
 pure; but its alkaline action is much more mo- 
 derate when it is in the state„of carbonate/ for it 
 is then in a high degree of saturation, and pos- 
 sesses uniform properties. From this circum- 
 stance it should therefore be preferred to potash, 
 which has less carbonic acid, containing variable 
 quantities of it, in the state in which it is ex- 
 tracted. 
 
 CHAPTER VIII. 
 
 Of Soap. 
 
 Soap is the combination of an alkali with an 
 oil. Alkali deprived of carbonic acid must be 
 employed for its formation ; for this acid may 
 eliminate its oil in combining with the alkali. 
 
=S3!B 
 
 of soap. 397 
 
 We must begin, therefore, with stripping it of its 
 combined carbonic acid. In the work-shops the 
 name soap-ley is then given to it. 
 
 To make this ley, the soda which is used for 
 hard soap is treated with a suitable proportion of 
 lime, usually two of lime for one of soda. A 
 succession of waters is passed through the same 
 mixture. The last, which are least charged, are 
 employed the first in the boiling with oil ; be- 
 cause the coagulation which would be formed at 
 first with too strong a ley, would obstruct the 
 uniformity of the combination. 
 
 We have remarked, that the caustic alkali, pre- 
 pared with quicklime, retained a portion of its 
 carbonic acid ; which, on treating the caustic ley 
 with oil, converts a part of the alkali into a car- 
 bonate that cannot enter into the compound. 
 Whenever the formation of the soap is advanced, 
 the portion of ley converted into carbonate, which 
 may serve anew to make a caustic ley with quick- 
 lime, is run off by a stopcock placed in the lower 
 part of the boiler. Strong ley is then added. 
 When it is ascertained from samples that the 
 consistence of the soap is sufficient, it is drawn out 
 and run into a species of wooden moulds, where 
 it cools, and takes the form adapted to commerce. 
 But before this last operation, a certain quantity 
 of muriate of soda is added, which facilitates the 
 separation of the soap from the aqueous liquid, 
 (spent ley). 
 
 This preparation maybe made in the cold, but 
 it is longer and less easily finished. 
 
398 of soap. 
 
 Recent soap contains a great deal of water, 
 which it loses by desiccation. Fraudulent dealers 
 endeavour to sell it with all this weight ; and to 
 preserve it in this state, they keep it in a moist 
 place, even in water saturated with sea-salt. This 
 brine does not dissolve it, but merely confines in 
 it the whole water that it can hold. For separat- 
 ing, by this property, the soap from its solution 
 in the boiler, the muriate of soda was added to- 
 wards the end, as we have stated. The redun- 
 dancy of water is discovered by keeping the soap 
 in a dry and warm place, where it soon loses what 
 is superfluous. Starch, or other foreign substances, 
 are sometimes mixed with soap, in order to aug- 
 ment its weight. 
 
 Marbled veins are given to soap by adding, 
 before it has assumed consistency, a little sul- 
 phate or red oxide of iron, which probably forms 
 some metallic soap, that is unequally mixed with 
 the paste. Soap becomes harder by this means, 
 and retains less water. 
 
 The general properties of compounds are re- 
 cognized in soap. Thus soda, which produces, 
 as we have seen, a greater effect with the acids, 
 comports itself in the same way with the oils, 
 thereby forming soaps, harder and less soluble 
 than those which have potash for their base. In 
 consequence of this greater insolubility, if muriate 
 of soda be added to a solution of soap made with 
 potash, the soda takes the place of the potash, 
 and it is a soap with base of soda which coa- 
 gulates and separates, as Darcet, PelJetier, and 
 
-*~^ 
 
 OF SOAP. 399 
 
 Lelievre observed, to whom we owe a very good 
 description of the preparation of soap.* 
 
 The oils contribute, on the other hand, to the 
 qualities of the combination which they form 
 with the alkalies : thus the fatty substances na- 
 turally solid, such as tallow, lard, and butter, 
 form solid and firm compounds ; olive oil, which 
 has a tendency to become solid whenever its tem- 
 perature is lowered, affords a hard soap, which 
 makes it be preferred, for this species of soap, (to 
 which, in other respects, it communicates no dis- 
 agreeable smell or colour), to the other oils, which 
 being less consistent, yield softer soaps, common- 
 ly coloured. 
 
 If oils be combined with bases naturally dis- 
 posed to take the solid state, such as lime, mag- 
 nesia, barytes, metallic oxides, insoluble soaps 
 are formed ; but this insolubility is an obstacle 
 that prevents the combination from being direct- 
 ly formed with accuracy. The solution of an 
 alkaline soap must be taken, and lime, barytes, 
 or strontites water poured into it. These alkaline 
 earths take a portion of the oil from the soluble 
 alkalies to form an insoluble soap, which sepa- 
 rates. Instead of the aqueous solution of these 
 bases, their solution in an acid mav be taken. 
 In this case an exchange of base occurs, and the 
 earthy combination is more completely formed. 
 The latter method must be employed for the 
 
 * Mdmoires de Chimie, torn. xix. (Annalcs ?) 
 
 7 
 
400 OF SOAP. 
 
 bases insoluble in water, such as magnesia, and 
 the metallic oxides. 
 
 The uses for which soap is employed lead some- 
 times to the preference of a hard, and sometimes 
 of a soft soap. The first is prepared with soda 
 and olive oil. It ought to be white. This soap 
 is used in the ungumming (scouring) of silk. 
 
 To make soft soap, oil of colza, turnip seed, or 
 fish oil, is employed. The cheapest at the place 
 of the manufacture is generally chosen. But as 
 softness is the quality now desired, potash is used 
 instead of soda. Whiteness is of no consequence 
 to this soap ; and the oils made use of commonly 
 impart a greenish or even blackish colour, whence 
 the article is called green or black soap. 
 
 This soap is chiefly used in the bleaching of 
 cloths and raw yarns ; and in the operation of 
 fulling woollens. 
 
 For the latter purpose, a less costly combina- 
 tion may be employed, possessing the detersive 
 properties of soap ; this is the solution of an ani- 
 mal substance in potash. Chaptal observed,* 
 that potash which has been saturated with frag- 
 ments of wool formed this species of soap, which 
 might be advantageously substituted for ordinary 
 soap. The odour which it communicates to cloth 
 is dissipated by washing, and exposure to the air. 
 
 * M§moires de l'lnstit. torn. i. 
 
OF SULPHUR. 
 
 401 
 
 CHAPTER IX. 
 
 Of Sulphur. 
 
 Sulphur exposed to a certain heat volatilizes, 
 and then resumes the solid state by the contact 
 of cold bodies. Thus it is reduced to subtile 
 molecules, called flowers of sulphur. This pre- 
 paration is made in the small apparatus of the 
 laboratory ; or on the great scale, in a kind of 
 chimnies or chambers, where it attaches itself to 
 the cool walls. 
 
 When sulphur is exposed to a more elevated 
 temperature, it combines with oxygen, passing 
 thereby to the state of an acid ; but this acid 
 differs according to the elevation of the temper- 
 ature, or the vivacity of the combustion. When 
 the temperature is not sufficiently high, sulphur- 
 ous acid is obtained. 
 
 Sulphurous acid differs from sulphuric, 1. From 
 the oxygen in it being less condensed, so that 
 the combination retains a pretty great elasticity, 
 and dissolves in only a small quantity in water : 
 2. From the proportion of its oxygen being small- 
 er than in sulphuric acid, but, at the same time, 
 this element experiences a much weaker action 
 on the part of the sulphur ; a circumstance which 
 has great influence on its characteristic proper- 
 ties. 
 
 vol. r. c c 
 
402 OF SULPHUR. 
 
 The oxygen is retained, therefore, much more 
 feebly in sulphurous than in sulphuric acid. 
 Hence several substances, which do not take 
 oxygen from sulphuric acid, decompose- the sul- 
 phurous. It inclines, in this respect, to the pro- 
 perties of oxygenated muriatic acid, although it 
 does not give up its oxygen so easily, but, on 
 the contrary, carries off that of the oxygenated 
 muriatic acid, in order to pass to the state of sul- 
 phuric acid. In like manner, it inclines to the 
 properties of nitric acid. 
 
 Sulphurous acid, or the combination of the 
 sulphurous gas with water, is not employed in 
 the processes of dyeing ; but the vapour formed 
 directly by the combustion of sulphur is used. 
 In this state of gas, it exercises a more lively ac- 
 tion, for it whitens the flowers, which, in its liquid 
 state, it reddens like the other acids. It would 
 be wrong, therefore, to substitute liquid sulphu- 
 rous acid for the fumes of burning sulphur, as 
 has been proposed. There are circumstances, 
 however, where a different or more moderate 
 effect might be wished for, in which it would be 
 advantageous to employ it in the liquid state. We 
 have seen one example of this, in the process of 
 Giobert for bleaching raw silk. 
 
 For obtaining it in this state, there is a more 
 convenient and easier means than by the com- 
 bustion of sulphur ; that is, merely to mix with 
 sulphuric acid a vegetable substance containing 
 hydrogen, as sugar, and to distil, receiving the 
 
^r-r 
 
 OF SULPHUR. 
 
 403 
 
 vapour that is disengaged into the bottom of a 
 receiver, by means of a tube. Heat, which tends 
 to produce elastic combinations, determines a 
 formation of water, at the expense of the hydro- 
 gen of the sugar, and a production of sulphurous 
 acid, which issues to combine with the cold water. 
 But there is formed at the same time a little car- 
 bonic acid, of no importance to the operations 
 for which the liquid acid is intended. Besides, 
 when the sulphurous acid acquires a certain con- 
 densation, it expels the carbonic acid from the 
 water. 
 
 Sulphuring, or exposure to the fumes of burn- 
 ing sulphur, is employed to give the utmost white- 
 ness to silks and woollens intended for white stuffs. 
 
 For the sulphuring process an insulated cham- 
 ber, having no chimney, is made choice of, through 
 which, on occasion, a current of air may be sent. 
 
 For 50 kilogrammes of silks stretched on 
 perches, placed at a height of rather more than 
 two metres, nearly one kilogramme of sulphur, 
 reduced to a coarse powder, is put into an 
 earthen or iron pot, at whose bottom there is a 
 little ashes. This powder is set fire to in several 
 places. The chamber is well closed, to prevent 
 the dissipation of the sulphurous fumes. Next 
 day, the windows are thrown open to let them 
 escape, and to dry the silk. But in winter, after 
 the smell of the sulphur has gone away, the win- 
 dows are re-shut, and burning charcoal is intro- 
 duced, in chafingdishes, to make the silk dry. 
 
404 OF SULPHUR. 
 
 This operation gives the silk not merely a great 
 whiteness, but, at the same time, creakiness or 
 rustling in handling, (du cri ou du maniement), 
 that is to say, a species of tremulous elasticity, 
 which is perceived on pressing it between the 
 fingers. 
 
 As the maniement gives a certain stiffness to 
 silks, those must not be sulphured which are to 
 be watered, (destinees a faire de la moire), be- 
 cause they would give too much resistance to 
 the impressions of the calender, under which the 
 silks are passed to give them the undulations. 
 
 In like manner, sulphuring cannot be applied 
 to silks intended for felt, (bonneterie), because 
 they would corrode the iron and steel of the tools 
 with which they are to be worked, and occasion 
 rust. 
 
 Sulphured silk takes on most colours badly ; 
 and, therefore, previously to dyeing, it must be 
 freed from sulphur, (desoufree), by repeated 
 soaking and shaking over in hot water. 
 
 When silk is sulphured, if it be thought not to 
 have sufficient azure for the wished-for shade, it 
 must be azured a second time in clear water, 
 without addition of soap, and then again sul- 
 phured. 
 
 These properties of the sulphured silk are 
 owing to the sulphurous acid which has com- 
 bined with it, whose presence may be made per- 
 ceptible by means of sulphuric acid, which im- 
 mediately disengages sulphurous vapours from it. 
 
--'-*=- 
 
 OF WATERS. 405 
 
 The sulphuring of woollen cloth is executed in 
 nearly the same manner as that of silk ; but it is 
 to be remarked, that if this operation be not per- 
 formed with precaution, and that if the combus- 
 tion of the sulphur takes place with too much 
 rapidity, sulphuric acid is formed, which falling 
 down in drops, corrodes the cloth, — an inconve- 
 nience not easily avoided. 
 
 CHAPTER X. 
 
 Of Waters. i 
 
 i 
 
 The qualities of waters is an essential object 
 in dyeing ; but it is perhaps less important to I 
 
 make known the injurious effects which they may ^ 
 
 produce, than to destroy the prejudices to which J 
 
 they have often given rise. Thus peculiar pro- | 
 
 perties have been ascribed to the water of the I 
 
 Bievre, which supplies the manufactory of the 
 Gobelins ; but Guillaumot remarks, that when 
 this little river is too low, the water is drawn 
 from the Seine, without seeming to render the 
 dyes less beautiful. 
 
 It is superfluous to say, that the waters used 
 in dyeing must not be muddy, or contain putrid 
 substances ; that waters so much charged with 
 foreign matters, as to be ranked among mineral 
 waters, easily distinguishable by the taste, must 
 not be employed. With these exceptions, waters 
 
406 OF WATERS. 
 
 act on the colouring particles principally by the 
 earthy salts they contain, which render the co- 
 lours in general deeper and more dull. 
 
 The carbonates of lime and magnesia have, 
 moreover, the inconvenience of being thrown 
 down during the ebullition, which expels the 
 excess of carbonic acid that held them in solu- 
 tion. Thus these earths applied to the stuffs 
 darken them, and hinder the colouring particles 
 from penetrating. 
 
 It is of importance, therefore, to ascertain these 
 species of waters, called hard or crude, in order 
 to avoid them -in most dyes. Chemists possess 
 methods, not only of determining the different 
 principles contained in waters, but even of as- 
 signing with precision the quantity of each ; but 
 the precautions requisite for this analysis, in ge- 
 neral demand a profound knowledge and experi- 
 mental dexterity, which persons engaged in dye- 
 ing cannot be presumed to possess. Happily a 
 trivial and easy test is sufficient to shew whether 
 a water contains an injurious quantity of these 
 salts. This is, the solution of soap. 
 
 All the salts having an earthy base decompose 
 soap by an exchange of bases. Their earth unites 
 to the oil, while their acid combines with the 
 alkali of the soap ; and from the combination of 
 the oil and the earth, a soap with earthy base 
 results, which being insoluble in water, forms the 
 clots, (or mottling), which are in that case ob- 
 servable. 
 
■MBMVMBM^^^W^^^^^— 
 
 OF WATERS. 407 
 
 Whenever, therefore, a water is limpid, when 
 its flow is constant, when it has no sensible taste, 
 and dissolves soap well, it may be regarded as 
 very proper for dyeing j and all such as possess 
 these qualities are equally suitable. 
 
 But since a choice of waters is not always 
 equally at command, methods have been sought 
 for correcting such as were bad, at least to a cer- 
 tain degree, particularly for the purpose of dye- 
 ing delicate colours. With this view, water in 
 which bran has been fermented, called sour wa- 
 ter, is principally used. 
 
 It appears that sour water acts by decomposing 
 the carbonates of lime and magnesia, its acid ex- | 
 
 pelling the carbonic acid. The earthy sediment 
 which forms during ebullition is thus obviated. 
 
 Mucilaginous plants are also boiled along with 
 the water to be corrected, when a froth forms, 
 that is skimmed off. The mucilage coagulates, 
 carrying with it the earths which separate on 
 the volatilization of the carbonic acid, as well as 
 such as are merely mixed with the water, and 
 which render it turbid. 
 
 The salts with an earthy base, which are in 
 general injurious to dyeing, may in certain cases 
 be useful, serving to modify the colours when our 
 object is to obtain deep shades. 
 
 As the water of a river may contain more or 
 fewer salts with an earthy base, according as its 
 bed is higher or lower, it happens sometimes that 
 on following exactly the same process the same 
 
 c 
 
408 OF WATERS. 
 
 shade is obtained only at certain periods ; or 
 some modifications are required to be made in 
 the process to obtain the same result, according 
 to the state of the river. 
 
 The waters which decompose soap, and form a 
 [ soap of lime, are disadvantageous to bleaching, 
 not merely by the waste of the soap uselessly de- 
 composed, but principally because the calcareous 
 soap, which is insoluble in water, fixes on the 
 stuff, gives it a greasy feel, renders it at the same 
 time yellow, and shakes off in small scales. This 
 inconvenience is obviated by decomposing the 
 earthy salts with a little carbonate of soda or 
 potash. 
 
 END OF THE FIRST VOLUME. 
 
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