UC-NRLF 
 
 SB 32 331 
 
 A POPULAR TREATISE 
 
 ON 
 
 THE COLLOIDS IN THS 
 INDUSTRIAL ARTS 
 
 A&NDT--K 
 
A POPULAR TREATISE ON 
 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
Published by 
 
 The Chemical Publishing Company 
 
 EASTON, PA. 
 
 Publishers of Scientific Books 
 
 Engineering Chemistry Portland Cement 
 
 Agricultural Chemistry Qualitative Analysis 
 
 Household Chemistry Chemists' Pocket Manual 
 
 Metallurgy, Etc. 
 
A Popular Treatise on 
 The Colloids in the Industrial Arts 
 
 BY 
 
 PROF. DR. KURT ARNDT 
 
 Privat-Dozent at the Technuche Hochschule, Berlin, Germany 
 Translated from the Second Enlarged German Edition by 
 
 NAHUM E. KATZ, B.Sc. 
 
 Chemist to Eagle Cotton Oil Company. Meridian, Miss. 
 Member of the American Chemical Society 
 
 EASTON, PA.: 
 
 THE CHEMICAL PUBLISHING CO. 
 1914 
 
 LONDON, ENGLAND : 
 
 WILLIAMS A, NORGATE 
 
 14 HENRIETTA STREET, COVENT GARDEN, W. C. 
 
TT1 
 
 A 
 
 COPYRIGHT, 1914, BY EDWARD HART. 
 
TABLE OF CONTENTS. 
 
 Translator's Preface iv 
 
 Preface v 
 
 Preface to the Second German Edition vi 
 
 Definition of the Term "Colloid" i 
 
 Colloidal Solutions 2 
 
 Colloidal Solutions of Metals 4 
 
 Flocculation of Colloidal Solutions 8 
 
 Reversible and Irreversible States of Aggregation 12 
 
 General Remarks on Dispersed Systems 14 
 
 Suspension- and Emulsion-Colloids 16 
 
 Ruby-Glass 18 
 
 Milky- White Opaque Glass. Troostite. Phosphorus 21 
 
 Colloids in the Mineral Kingdom 23 
 
 Silver- and Gold-Mirrors 25 
 
 Manufacture of Tungsten Lamps 26 
 
 Colloids in the Ceramic Industry 32 
 
 Colloids in the Hydraulic-Cement Industry 35 
 
 Colloids as Adhesives and Glues 38 
 
 Usefulness of the Colloids in the Absorption of Liquids 39 
 
 Dehydration of Peat by Electro-Osmosis 40 
 
 Colloids as Diaphragms and Filters 41 
 
 Adsorption 42 
 
 Varnish-Making 44 
 
 Dyeing 44 
 
 Tanning 47 
 
 Soap Manufacture 50 
 
 Brewing Industry 52 
 
 Lubricating Greases 53 
 
 Sewage Purification 55 
 
 Colloids in Agriculture 57 
 
 Index 61 
 
 300345 
 
TRANSLATOR'S PREFACE. 
 
 The warm reception and great approval with which 
 the little volume of Prof. Dr. Kurt Arndt's "Die 
 Bedeutung der Kolloide fur die Technik" met in Ger- 
 many make it very desirable that it becomes accessible 
 also to the English-speaking chemists. It will be es- 
 pecially welcomed by those busy works-chemists who do 
 not have the time to make a special study of the chem- 
 istry of the colloids, but who desire to keep abreast with 
 the development of their science and the application of 
 its various theories in the different industries. 
 
 This translation has been made from the second Ger- 
 man edition which has been revised and considerably en- 
 larged by the author. It was thought advisable to add 
 an Index, which is missing in the German edition. 
 
 I feel it a pleasant duty to express here my thanks 
 to the publisher of this translation, Prof. Dr. Edward 
 Hart, proprietor of the Chemical Publishing Company, 
 for his revision of my manuscript and for the great care 
 in the preparation of the book for publication. 
 
 NAHUM E. KATZ. 
 
 MERIDAN, Miss., January, 1913. 
 
PREFACE. 
 
 The present treatise originated from a lecture, which 
 I delivered before the "Verein zur Befoerderung des 
 Gewerbefleisses," in Berlin. Since this short lecture was 
 favored with a very detailed abstract in the "Chemiker- 
 Zeitung," and, since it found otherwise more attention 
 than expected, I willingly complied with the request of 
 the energetic publisher of the "Kolloid-Zeitschrift" to 
 make my lecture accessible to larger circles, and to pre- 
 sent a popular treatment of the subject of the intimate 
 relation between colloidal chemistry and the Arts and 
 Manufactures, in a separately issued volume. The 
 chemist, who makes a special study of colloidal chem- 
 istry, will naturally find in the present unassuming 
 treatise little which is new to him. 
 
 Since the purely scientific problems of colloidal chem- 
 istry were treated in the "Introduction To Colloidal 
 Chemistry" by Poschl, 1 I was in the position to limit 
 myself to short introductory remarks in explanation of 
 the most important ideas and terms, after which I entered 
 into a more thorough discussion of technical matters. I 
 have brought together a large quantity of material, which 
 I have taken from technical magazines (preferably, 
 from the "Zeitschrift fur Chemie und Industrie der Kol- 
 loide"), partly from the book by A. Miiller, "Allgemeine 
 Chemie der Kolloide," (Leipzig, 1907), partly from my 
 own book, "Technische Anwendungen der physikalischen 
 1 This book has been translated into English. 
 
VI PREFACE 
 
 Chemie," (Berlin, 1907), but I have not striven after 
 completeness, but endeavored, to give the reader a Vivid 
 Picture of the Great Significance, which the colloids have 
 in numerous important processes. K. ARNDT. 
 
 Charlottenburg, New- Year, 1909. 
 
 PREFACE TO THE SECOND GERMAN EDITION. 
 
 In the two years, since the first edition of this treatise 
 appeared, colloidal chemistry has rapidly developed. 
 Numerous treatises, preferably, in the "Zeitschrift fur die 
 Chemie und Industrie der Kolloide" and their "Chem- 
 ische Beihefte," have brought forth much which is 
 of interest, and some which is of value to the indus- 
 tries. I have endeavored to do justice to all these devel- 
 opments within the scope of my treatise, by changes and 
 considerable additions. The chapters on Dispersed 
 Systems, Suspension- and Emulsion-colloids, in which I 
 duly considered the new classification of colloidal chem- 
 istry and its terms, and, the chapter on the Colloids in 
 the Mineral-kingdom, and in the Brewing-Industry are 
 new. 
 
 To those who desire further information about scien- 
 tific colloidal chemistry, the "Grundriss der Kolloid- 
 chemie" by W. Ostwald, (Dresden, 1911), the second 
 edition of which has just appeared, may be recom- 
 mended. 1 
 
 K. ARNDT. 
 
 Charlottenburg, Easter, 1911. 
 1 A third edition of this book has already appeared. 
 
1. Definition of the Term "Colloid." The name 
 "Colloid" is connected with the Greek word KoAAa = 
 glue, and means "glue-like"; it was first used by Th. 
 Graham half a century ago. This English chemist 
 termed as Colloids various substances, which, indeed, 
 chemically, have nothing to do with glue, but which re- 
 semble in appearance the soaked-up cabinet-maker's glue^ 
 as, for instance, the gelatinous precipitate which is ob- 
 tained when muriatic acid is added to a concentrated 
 solution of waterglass. From sodium silicate, hydro- 
 chloric acid separates a voluminous jelly, which, by wash- 
 ing, we can free almost completely from the salt. By 
 heating, we gradually expel the large quantity of water 
 which is absorbed by the jelly, and at last obtain a pul- 
 verulent mass which gives off the last traces of its water 
 only when it is strongly ignited. Heated over an oxy- 
 hydrogen flame the silicic acid melts and on cooling con- 
 geals to a transparent glass, quartz glass. But if we let the 
 mass cool extremely slowly, then the quartz-glass trans- 
 forms into small crystals. So we have for one and same 
 substance, silicic acid, three different states: the col- 
 loidal, the glassy and the crystalline state. In a 
 strict sense, silicic acid has several crystalline states, 
 since it is found in several crystalline forms, of which 
 rock-crystal presents an especially beautiful example. 
 One of these states, the hexagonal crystalline form of 
 
2 THE COI^OIDS IN THE INDUSTRIAL ARTS 
 
 rock-crystal, is, at the ordinary temperature, the state 
 of rest of silicic acid into which the other forms tend to 
 change. 
 
 The glassy state forms a continuation of the liquid 
 state; the glasses are considered as liquids which have a 
 very great internal friction. The colloidal state, on 
 the contrary, may be defined as the solid non-crystal- 
 line state; we really cannot call it amorphous, form- 
 less, because, as was shown by C. Biitschli, colloidal 
 silicic acid presents a very fine cell-structure. It 
 has a honey-comb (wabige) structure, and therefore, like 
 a sponge, it is able to absorb liquids. Such a cell-struc- 
 ture of great surface development is shown by numerous 
 inorganic and organic jellies, particularly the cells of veg- 
 etable and animal bodies, and of substances which are 
 obtained from them: wool, and other textile fibers, 
 leather, glue, caoutchouc, cellulose and celluloid, pro- 
 teins; all come under the term colloid. How infinite 
 the field. 1 The reader will anticipate that the industrial 
 arts as well, have much to do with "Colloids," although 
 up to the present time they have generally not made use 
 of this name. 
 
 2. Colloidal Solutions. If we add muriatic acid to a 
 dilute solution of waterglass, no jelly separates, but after 
 
 1 It is accepted at present that all substances are able, under 
 appropriate conditions, to assume the colloidal state. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 3 
 
 evaporating the solution, it congeals suddenly with sep- 
 aration of silicic acid. In spite of the fact that from 
 the dilute solution no silicic acid visibly separates, the 
 sodium silicate and the hydrochloric acid have neverthe- 
 less entered into a chemical inter-action; this can be 
 proven by physical measurements. For instance, by 
 measuring the electrical conductivity of the solution. 
 We have in this case a colloidal solution. We can re- 
 move the salt from this solution by transferring the latter 
 into a vessel, the bottom of which is formed of a parch- 
 ment membrane, and placing it in pure water. The salt 
 diffuses through the membrane, while the colloidal silicic 
 acid does not. In this way, by Dialysis, we are able, if 
 we renew the water from time to time, to obtain a col- 
 loidal solution of silicic acid which contains only traces of 
 salt. By evaporation we can concentrate it to a certain 
 degree. But the more concentrated the solution becomes 
 the easier it congeals. We can coagulate it, for instance, 
 immediately, by adding to it a minute quantity of soda, 
 or by passing into it only a few bubbles of carbonic acid 
 gas. This colloidal solution of silicic acid manifests 
 besides its remarkable instability, still other very impor- 
 tant differences from a true solution, for instance, that 
 of common salt. While a solution of salt boils only 
 above 100 C. and freezes below o C., the boiling and 
 freezing points, the vapor tension and electrical conduc- 
 
4 TH COIvLOIDS IN THE) INDUSTRIAL ARTS 
 
 tivity of the colloidal solution are not much different 
 from those of pure water. 
 
 For colloidal solutions Graham introduced the name 
 Sol; 1 when water is the solvent, the name became 
 Hydrosol. Correspondingly there are Alcosols, etc. 
 The precipitated colloid on the contrary was a Gel. 2 
 
 Like the hydrosols of silicic acid, the hydrosols of iron 
 hydroxide, aluminium hydroxide, stannic acid, tungstic 
 acid, arsenious sulphide, Berlin blue, etc., can be obtained 
 by chemical transformation in dilute solutions and puri- 
 fied by dialysis. 
 
 3. Colloidal Solutions of Metals. Metals may also be 
 obtained in the condition of colloidal solutions, when 
 their salts in very dilute solution are reduced to metals. 
 In this way, the great physicist M. Faraday, as early as 
 1857, obtained a colloidal solution of gold when he 
 treated a very dilute solution of gold-chloride with yel- 
 low phosphorus. A very good method for the prepara- 
 tion of colloidal solutions of gold is given by R. Zsigmon- 
 dy, who studied these solutions very thoroughly, and even 
 devoted to them a special book. 3 He employs formalde- 
 hyde as the reducing agent and by a small addition of 
 potash increases the stability of the colloidal solution. 
 
 1 From "Solution." 
 
 2 From "Gelatine." 
 
 8 R. Zsigmondy, Zur Erkenntins der Kolloide (Jena 1905). 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 5 
 
 If the water employed in this process is sufficiently free 
 from impurities, a colloidal solution of gold is obtained 
 which has a magnificent deep-red color and which will 
 keep for years. In reflected light, on the contrary, this 
 solution has a dirty brown color. This turbidity is an 
 indication that in this case we do not have a true solu- 
 tion, but that in the water solid particles which reflect 
 the light are suspended. If the colloidal solution is illu- 
 minated by a very bright light, then the separate gold- 
 particles can even be seen under a microscope. v 
 
 H. Siedentopf, of Jena, constructed for this purpose 
 the following appliance: strong arc-light, or still better, 
 sun-light is condensed by lenses to a light-cone with a 
 perpendicular axis, the point of which falls into the solu- 
 tion to be tested. The microscope is focused on the point 
 of the light-cone, the place where the greatest brightness 
 prevails. In pure, dust-free water the vision field re- 
 mains dark ; in the colloidal solution of gold, on the con- 
 trary, numerous brilliantly variegated red, yellow, and 
 green discs are seen, which restlessly fly to and fro in a 
 constant zig-zag movement. 1 
 
 If the visible gold-particles in a limited space are 
 counted and the quantity of gold in this space is deter- 
 1 The brightness of the ultra-microscopic vision was consider- 
 ably enhanced by the introduction of the Paraboloid- and Kardioid- 
 Condensers. Now even very small quantities of solution are 
 sufficient. 
 
6 THE COLLOIDS IN THE: INDUSTRIAL ARTS 
 
 mined by analysis, then the average size of these par- 
 ticles can be calculated. If it be assumed that these par- 
 ticles are spherical, it is found that their diameters in 
 different solutions of gold range from about 10 to 40 /A/*. 1 
 This size is far under the limit of visibility under an 
 ordinary microscope. For this reason H. Siedentopf 
 named his appliance Ultra-microscope and termed the 
 particles which are made visible by it, ultra- or submi-> 
 croscopic From the fact that the gold-particles appear 
 as small discs nothing can be concluded as to their real 
 form ; this is due only to the imperfections of our vision. 2 
 
 In light red solutions of gold, R. Zsigmondy was able 
 to point out still smaller particles, down to 6 /A/U,. In 
 others he found also larger particles, up to 200 /*/&; these 
 solutions already began to disintegrate, the gold particles 
 clumped together to larger complexes and were gradually 
 sinking to the bottom. 
 
 In two interesting graphical descriptions, in his above- 
 mentioned book, R. Zsigmondy compared the magnitude 
 of these ultra-microscopical gold particles, on the one 
 hand, with microscopically small objects, such as blood 
 corpuscles, starch particles, suspensions of porcelain 
 clay, bacteria, on the other hand, with the still smaller 
 (calculated) dimensions of the molecules of chloroform, 
 
 1 /A is the sign for one millionth part of one millimeter (micron). 
 
 2 The stars also appear to us, not as points, but as small discs. 
 
THE: COLLOIDS IN THE: INDUSTRIAL ARTS 7 
 
 alcohol, etc. We learn from this comparison that, in 
 general, the molecules are still very much smaller than 
 the ultra-microscopical gold-particles, but that very 
 large molecules, which comprise very many atoms, such 
 as, for example, the molecule of soluble starch (accord- 
 ing to C A. Lobry de Bruyn) are much like them. The 
 ultra-microscope has considerably shifted the limits be- 
 tween visible and invisible. In several pink-colored solu- 
 tions of gold the existence of mass-particles even still 
 smaller than 6 ftp. must be assumed. Indeed, these par- 
 ticles can no more be seen separately by means of the 
 ultra-microscope, but their presence is detected by a 
 feeble glittering of the light; R. Zsigmondy terms these 
 particles amicroscopic. 1 If a few drops of the usual 
 colloidal solution of gold are added to such an amicro- 
 scopic solution of metallic gold, the flocculation of the 
 latter is considerably accelerated. 
 
 Another way of preparing the hydrosols of metals, 
 worked out by G. Bredig, is the following: an electric 
 arc or strong sparks are formed under water between 
 two wires of the respective metal; the metal then evap- 
 orates and partially remains in the water as a colloidal 
 
 1 The lower limit of visibility of metallic particles is especially 
 favorably located because these particles reflect the light rays very 
 strongly. The molecule of soluble starch, despite its large size, 
 will be invisible under the ultra-microscope, because it does not 
 shine sufficiently bright. 
 
 2 
 
8 THE COIAOIDS IN THE INDUSTRIAL ARTS 
 
 solution; another part clumps together and sinks to the 
 bottom. The solution of gold, obtained in this way, is 
 usually colored violet blue. Most of the metals have 
 been prepared in this second way in the condition of 
 colloidal solutions in water and in other liquids. So, 
 for instance, Th. Svedberg prepared a blue colloidal solu- 
 tion of metallic sodium in ligroin. But none of these 
 numerous solutions can be compared in beauty of color- 
 ation with that of the solution of gold. A colloidal solu- 
 tion of platinum, for example, appears yellowish brown 
 in transmitted light and almost black in reflected light. 
 The hydrosol of silver has a brick-red color. Most of 
 the colloidal solutions of metals are very instable and 
 soon precipitate the metal. 
 
 4. Flocculation of Colloidal Solutions. Since the col- 
 loidal solutions do not correspond to any condition of 
 equilibrium and their particles tend to clump together, 
 the colloid flocculates by itself in a longer or shorter 
 period ; boiling usually accelerates this decomposition. 
 
 A small addition of an alkali to the water considerably 
 increases the keeping qualities of the metallic Sols. The 
 Sol of silicic acid, on the contrary, becomes more stable 
 by the addition of some hydrochloric acid. Some in- 
 vestigators assert that, in general, the presence of cer- 
 tain small quantities of "electrolytes" is needed for the 
 existence of colloidal solutions. At any rate, it is a fact, 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 9 
 
 that most of these solutions are very sensitive towards 
 any change in the quantity of electrolytes, which they 
 contain ; for example, the red solution of gold is colored 
 blue by the addition of one drop of hydrochloric acid, 
 and the gold gradually separates. 
 
 The quantity of the addition, which causes the change 
 in the coloration, or the beginning of precipitation, varies 
 with the nature of the solution and that of the addition. 
 Quantities of electrolytes, which remain below this limit, 
 the swelling value (Schwellenwert), will not cause 
 the flocculation of the hydrosol even in a longer period. 
 The explanation of this phenomena at present preferred, 
 is based on the fact, that colloids, as, in general, all solid 
 particles, move in the field of an electrical current. If 
 we send a current, having a pressure of about no Volts, 
 or more, through a colloidal solution, it is observed, that 
 the solution is almost a non conductor, but that the col- 
 loidal particles collect at one pole. 1 Colloidal metals 
 
 1 While the mass particles of the colloid migrate together 
 towards one and the same pole, in solutions of "electrolytes," one 
 part of the molecules migrates toward one, and the other part 
 towards the other pole ; for example, the chlorine of hydrochloric 
 acid migrates towards the positive pole (Anode), and the hydrogen, 
 towards the negative pole (Kathode). In accordance with this, 
 the ionic theory assumes that the hydrochloric acid is split into 
 negatively charged chlorine-ions and positively charged hydrogen- 
 ions. Potassium hydroxide (caustic potash), when dissolved in 
 water, is split into positive potassium-ions and negative hydroxyl- 
 ions. 
 
IO THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 usually migrate towards the positive pole, the Anode; 
 therefore they are negatively charged ; since (as is known 
 from friction electricity) opposite electricities attract 
 each other. Iron hydroxide and aluminium hydroxide, 
 on the contrary, migrate towards the cathode, and are 
 therefore positively charged. More accurate observa- 
 tions revealed the fact, that, "migration-sense" (Wander- 
 ungssinn) is not so much dependent on the kind of the 
 colloid, but that it is determined mostly by the small 
 quantities of electrolytes, which are found even in very 
 pure solutions. A very small increase of the hydrogen- 
 ions in the water electrifies the hydrosol positively so 
 that its particles migrate towards the negative pole; a 
 minute increase of the hydroxyl-ions electrifies it, on the 
 contrary, negatively so that its particles migrate towards 
 the positive pole. 
 
 An addition of ions, which carry a charge opposite to 
 that of the colloidal particles, causes their precipitation; 1 
 so a negatively charged colloid is coagulated by positively 
 charged ions. Similarly charged ions cause no precipi- , 
 tation, or have a slight protective action. ^^^^^ 
 
 Hydrosols which carry opposite charges precipitate 
 each other; so, for example, colloidal solutions of gold 
 
 1 The precipitating power of the respective ion is the greater 
 the higher its chemical valence ; a bivalent ion acts more than 
 one-and-a-half times as strongly as a univalent one. But hydro- 
 gen- and hydroxyl-ions possess the greatest precipitating power. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS II 
 
 and of stannic acid give a purple precipitate which corres- 
 ponds to the well known purple of Cassius. If a larger 
 quantity of the oppositely charged colloid is added to the 
 solution, often no precipitation occurs, on the contrary 
 the solution becomes more stable. Especially organic 
 colloids, such as gelatine and proteins, increase the sta- 
 bility of colloidal metals; therefore these are termed 
 protective colloids. The pharmaceutical industry is 
 making use of these colloids in the manufacture of col- 
 loidal silver and mercury. 1 We have seen in the example 
 of hydrosol of gold, which becomes more stable by the 
 addition of a little alkali (i. e., hydroxyl-ions) that sim- 
 ilarly charged ions also make a colloidal solution more 
 stable, if they are added in a sufficiently small quantity. 
 
 The flocculation processes are of paramount impor- 
 tance in physiological chemistry; here belongs, for in- 
 stance, the mutual precipitation of toxins and antitoxins 
 ( Immuno-serum ) . 
 
 Singular is the behavior of solutions of proteins. If 
 the protein solution is purified from salts, as much as 
 
 1 This protective action is manifested also in very fine mechan- 
 ical suspensions, as, for example, in a suspension of soot in water. 
 Despite its very fine division, soot can be prevented from precipi- 
 tating only by a protective colloid (lime), which fact is taken into 
 consideration' in the manufacture of water colors. In a similar 
 manner Acheson was able, by treating his graphite with tannic 
 acid and water, to bring it into such a condition that it could be 
 permanently suspended in water and oils, and in this way become 
 useful as a lubricating material. 
 
12 THE: COLLOIDS IN THE INDUSTRIAL ARTS 
 
 possible, by long dialysis, it does not coagulate, when 
 heated, but it does so when salts are subsequently added 
 to it. Complete coagulation ensues only when the solu- 
 tion reacts slightly acid. When milk, for example, cur- 
 dles, proteins which have been chemically changed by 
 ferments are precipitated ; the curdling represents an in- 
 termediate step ; the curdled protein is completely coagu- 
 lated by the subsequent heating. 
 
 When the precipitated colloid changes to the form of 
 a Gel, it still does not completely separate from the 
 water, but forms, as I have mentioned before, a peculiar 
 honey-comb-like structure, which contains enclosed 
 water. 
 
 5. Reversible and Irreversible States of Aggregation. 
 
 When pure hydrosols of metals are precipitated, no real 
 Gel- formation results, but a sort of metallic sponge is 
 produced. In the case of precipitated gold a light pres- 
 sure with the burnisher is sufficient to transform the 
 dried powder into coherent metal. If it should be desired 
 to bring this gold again into the condition of a colloidal 
 solution, this could be accomplished only in a round- 
 about way, probably by dissolving it in aqua-regia and 
 reducing the solution with formaldehyde. But colloidal 
 silver, which is prepared by the method of C. Lea 1 and 
 
 1 C. Lea reduces the solution of silver-nitrate with iron sul- 
 phate in the presence of sodium citrate. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 13 
 
 which contains organic impurities, easily dissolves in 
 water; it can even be precipitated from the colloidal 
 (blood-red) solution by ammonium nitrate, and then 
 again dissolved in water. Such Sols used to be desig- 
 nated as reversible (umkehrbar) and the hydrosol of 
 gold was considered as an example of another class, the 
 irreversible Sols. This difference in behavior is, how- 
 ever, not so much due to the nature of the respective sub- 
 stance, as to the treatment which is accorded to it. For 
 this reason, in a strict sense, it can be spoken only of 
 reversible and non-reversible states of aggregation of 
 the colloids. 
 
 Colloidal silicic acid, which in the process of evapora- 
 tion has lost but little water, can be liquefied by an addi- 
 tion of water ; even in a somewhat later stage of the pro- 
 cess of evaporation the silicic acid can be brought into 
 solution by treating it with a solution of caustic soda; 
 according to Th. Graham one part of sodium hydroxide 
 in 1,000 parts of water is sufficient to convert into hydro- 
 sol 200 parts of silicic acid when the whole is cooked for 
 one hour. This liquefaction process used to be termed 
 peptisation ; by this term it was compared with the 
 process of transformation of protein into pepton which 
 goes on in the intestines when food is digested. 
 
 Reversible states of aggregation are caused by change 
 of temperature in lime, agar-agar, and fish-glue, which, 
 
14 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 when they have a certain composition, congeal in the 
 cold to a semi-solid Gel that liquefies again on being 
 warmed. 
 
 6. General Remarks on Dispersed Systems. The term 
 dispersed systems, has recently been introduced to 
 designate compositions in which one substance is very 
 finely divided within another one. The finely divided 
 substance is termed the dispersed phase, while the 
 other, which is mostly in very large excess, is not termed 
 the "solvent," but, in a more general way, the dispers- 
 ing medium. From these dispersed systems, which 
 come under the term colloidal solutions, are distinguished, 
 on the one hand, suspensions, or aggregated dispersed 
 systems (grob disperse,) and, on the other hand, true 
 solutions, or molecular dispersed systems. A sharp 
 dividing line cannot be drawn between either of these 
 systems; in reality, all such dispersed phases, the par- 
 ticles of which measure between one ten thousandth to 
 one five hundred thousandth of a millimeter, have to be 
 considered as colloidal solutions. 
 
 The suspensions differ in their behavior from the col- 
 loidal solutions in that they can be separated from the 
 solvent by sedimentation, or more rapidly, by centrifu- 
 galizing; by stirring up the separated slime the suspen- 
 sion is mostly restored. When filtered, the slime is re- 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 1$ 
 
 tained by the filter paper, while colloids usually pass 
 smoothly through the paper. 
 
 From the molecular dispersed systems, the true solu- 
 tions, colloidal solutions are distinguished in that in re- 
 flected light they appear turbid, and that they exhibit 
 the so-called Tyndal-.Effect. If a bundle of bright light- 
 rays, condensed by lenses to a cone, is thrown (as in 
 an ultra-microscope) into a colloidal solution, thejight- 
 cone shines with a more or less bright light, 
 on the size and the reflective-power of the 
 ticles, while a true solution, on the 
 dark. In that special case, xvhen the true solution con- 
 tains a fluorescent substance, (for example, a water ex- 
 tract of chestnut-bark) it will, indeed, also emit light, 
 but this peculiar bluish or greenish light is not polarized 
 like that of the Tyndall-effect, i. e., when observed 
 through a Nicol-prism, it does not change its brightness 
 on turning the prism. A second very characteristic 
 property of colloidal solutions is their very small diffu- 
 sion power. Colloids cannot permeate membranes 
 which let true solutions pass through; this difference 
 was made use of to purify the colloidal solution of silicic 
 acid from salt by dialysis by means of a parchment skin. 
 On account of this great difference in the diffusion, it 
 is possible to conveniently examine the nature of, for 
 example, solutions of dyes, by pouring same on gelatine : 
 
16 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 if the dye penetrates the gelatine, there is a true solution ; 
 but if the separating surface remains, then we have a 
 colloidal solution. 
 
 7. Suspension and Emulsion-Colloids. Lately the col- 
 loids have been very properly divided into two classes. 
 The distinction is between those colloidal solutions in 
 which the finely divided substance is liquid, here the 
 dispersed phase consists of ultra-microscopical fluid par- 
 ticles, the emulsion-colloids, and those in which the small 
 
 : "' 
 
 particles are solid, which are termed suspension-colloids. 
 In the colloidal solution of gold we have an excellent 
 example of the suspension-colloids, or shorter the sus- 
 pensions. To the emulsion-colloids belong, in the first 
 place, gelatine, and protein-solutions. Suspension-col- 
 loids are flocculated even by a small addition of an elec- 
 trolyte; emulsion-colloids are much more stable. Sus- 
 pension-colloids scarcely influence the mobility of the 
 solvent, but emulsion-colloids make the solvent more vis- 
 cous, and, in general, the viscosity (the internal friction) 
 of emulsions increases very much upon cooling. These 
 differences disappear inasmuch as they depend on the 
 solvent, and very diluted emulsoids may behave like sus- 
 pensoids, while the latter, on the contrary, at higher con- 
 centrations, resemble the first. The upper concentration 
 limit of the suspensoids is mostly small; R. Zsigmondy 
 was able to prepare colloidal solutions of gold with the 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 17 
 
 highest content of only o.i per cent, of gold, and G. 
 Bredig was able to obtain, by electrical spraying, not 
 more than 0.014 per cent. Indeed, W. R. Whitney and 
 J. C. Blake prepared, in roundabout ways, more concen- 
 trated gold-sols, but there is no assurance that we do not 
 have to do in this case with a suspension. Emulsoids 
 have no upper limit of concentration. 
 
 To the emulsions belong also the foams. That, for 
 example, of the white of an egg, which is beaten to a 
 foam, is a mixture of two liquids, and does not probably 
 consist of skins filled with liquid. This becomes evident 
 when the foam settles in the cold : it melts then to a clear 
 solution, which can easily be freed from the impurities 
 of the white of an egg (threads, coagulums). 
 
 Common to all colloids is the very fine division and, 
 therefore, the, in comparison with the mass, enormous 
 surface-development. 1 The more the surface is devel- 
 oped, the more come into the foreground the actions of 
 the surface energy, which endeavor to reduce the surface, 
 and for that purpose strive to clump the small particles 
 together to a larger structure. On the other hand, all 
 
 1 The total surface increases in the same proportion as the 
 diameter of the separate particles decreases. For example, a clay 
 ball of one centimeter in diameter has a surface of 3 square centi- 
 meters (in round figures); if this mass is divided into 100,000 little 
 balls, the total surface is then equal to more than 30 square meters. 
 
1 8 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 bodies endeavor to draw from their surroundings and 
 to accumulate on their surface gases, liquids, and solid 
 particles. In the colloids, with their very much devel- 
 oped surface, this endeavor, likewise, comes to the fore- 
 ground. In the following chapters we shall see of what 
 value these general properties of the colloids are to the 
 technics, and which special part certain colloids play in 
 technical processes. 
 
 8. Ruby Glass. The magnificent color of the colloidal 
 solution of gold we find reproduced in the gold ruby 
 glass. Genuine ruby glass is obtained when gold- 
 chloride is added to the glass-mass. If the mixture is 
 cooled off quickly, a colorless glass is obtained, which, 
 when subsequently heated to the softening-point, sudden- 
 ly becomes tarnished by a splendid ruby-red. The quan- 
 tity of gold which is contained in ruby glass is minute, 
 only 0.05 to 0.06 per cent. In the red glass H. Sieden- 
 topf and R. Zsigmondy were able to distinctly discern 
 the ultra-microscopical particles of gold. Their follow- 
 ing experiment is very instructive: They heated to the 
 melting-point one end of a strip of colorless, very slowly 
 cooled ruby-glass, while the other end remained cold. 
 The hot end of the glass became shining red, the red 
 coloration weakening towards the cold end, while the lat- 
 ter unheated part of the glass remained entirely color- 
 less. The ultra-microscope showed in the shining red 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS IQ 
 
 part of the glass brilliant-green particles in very short 
 distances from one another; in the weakly red one there 
 was but a symmetrical green light-cone, which was weak- 
 ening towards the colorless end. 
 
 When a strip of poor ruby-glass was heated in a 
 similar manner unilaterally, its hot end was colored blue, 
 the coloration becoming weaker towards the cold end, 
 being, first violet, and then light pink, while the cold end 
 again remained colorless. In this case the ultra-micro- 
 scope showed brighter single particles, which were sep- 
 arated from one another by much longer distances, and 
 which shone copper red in the blue part of the glass, 
 yellow further on, and green in that part of the glass 
 which appeared pink in the transparency. The average 
 distance from one particle to another was, however, as in 
 the good ruby-glass, about the same in the entire strip 
 The brightness of the particles diminished from the blue 
 toward the colorless end ; in this case feebly lighted par- 
 ticles could be discerned also in the cold part of the 
 strip. 
 
 These entangled phenomena can be interpreted in the 
 following manner: On cooling, gold particles separate, 
 which, however, are too small to give the glass any color- 
 ation. These gold germs ( Goldkeime ) , when heated again, 
 grow and produce the beautiful ruby-red; they grow 
 the quicker the hotter the glass, therefore, the time of 
 
2O THE COLIXHDS IN THE INDUSTRIAL ARTS 
 
 heating being equal, the largest particles of gold are to 
 be found in those places which were exposed to the 
 greatest heat. This separating of the gold can last only 
 until the supersaturation-point of the respective kind of 
 glass and temperature is reached. 
 
 Under the ordinary conditions of work only a part 
 of the total gold separates in the ruby-glass as the color- 
 ing matter in the form of ultra-microscopic particles. 1 If 
 the red ruby-glass is remelted at a white heat, the gold 
 goes again into solution and the fusion remains colorless 
 when cooled, but by reheating it may again be colored red. 
 
 Some kinds of ruby-glass are tarnished red already 
 upon cooling; in these glasses the conditions for the 
 formation and growth of crystallization center-points 
 upon cooling are more favorable. 
 
 The reason why the edges of a pressed ruby-glass re- 
 mained colorless on heating are also of interest : the edges 
 cooled in the press more rapidly and on reheating 
 warmed up more rapidly and hotter than the center. In 
 the ultra-microscope the edges showed much less but 
 considerably larger green particles of 1 10 to 145 /*/* than 
 the rest of the glass-mass. The edges had to pass 
 through the temperature of the germ-formation too 
 rapidly, so that only few germs could develop which on 
 
 1 This has been proven by colorimetrical experiments. See: R. 
 Zsigmondy, Zur Erkenntniss der Kolloide (Jena 1905), pp. 128-135. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 21 
 
 reheating rapidly grew to a considerable magnitude. 
 But the center of the glass upon cooling had enough 
 time to develop a large number of germs which on heating 
 were less strongly warmed and therefore did not grow 
 as rapidly. 
 
 In spoiled ruby-glass the germ formation and growth 
 are disturbed; there are less germs developed and these 
 grow slower than in good ruby-glass. R. Zsigmondy as- 
 sumes that instead of simple crystals, crystalline germs 
 were formed. 
 
 The coloration process in copper ruby-glass may be 
 similar to that in gold ruby-glass. Copper ruby-glass 
 upon cooling is colored greenish, and only on being gently 
 heated it becomes red. 1 
 
 9. Milky- White Opaque Glass. Troostite. Phosphorus. 
 
 Milky-white opaque glass, which has been prepared by 
 the addition of fluor-spar, contains, according to A. Lot- 
 termoser, 2 calcium fluoride in the condition of a colloidal 
 solution. The fact that such glass appears turbid in re- 
 
 1 H. Siedentopf explained in a similar manner the blue color- 
 ation, which at times appears in rock salt. In this case the ultra- 
 microscopical crystals of metallic sodium are the coloring matter. 
 H. Siedentopf was able to prepare artificially such colored sodium- 
 chloride crystals, by treating them in vacuum with vapors of 
 sodium or potassium. When reheated the color changes, because 
 the ultra-microscopical particles undergo a similar change as those 
 of ruby-glass. 
 
 8 A. Lottermoser, Zeitschr. f. angew. Chemie, 1906, 19 : 369-377. 
 
22 THE COLLOIDS IN THE) INDUSTRIAL ARTS 
 
 fleeted light and allows transmitted light to pass through 
 clearly with a yellowish color, speaks in favor of the ac- 
 ceptance of this theory. The glaze-colorations, which 
 are formed by metals, may also be considered as colloidal 
 solutions. 1 
 
 Colloidal solutions occasionally appear also in metal- 
 alloys. So, C. Benedicks 2 considers the structural-ele- 
 ment (Gefiigebestandtheil) of slowly cooled steel, the 
 Troostite (an intermediate stage between Martensite and 
 Pearlite), discovered by F. Osmond, as a colloidal solu- 
 tion of cementite (iron-carbide). If this Troostite is 
 heated to 150 degrees for a sufficiently long period, the 
 ultra-microscopical germs grow and needles of cementite 
 become visible. 3 
 
 Colloidal intermediate forms do not seem to be rare in 
 other transformations. H. Siedentopf found that when 
 white phosphorus changes into the red form, a colloid 
 is obtained at first. 
 
 He observed that when a piece of white phosphorus 
 was placed tinder the Kardioid-Ultra-microscope at a 
 magnification of 1,500 times, he noticed in the phos- 
 
 1 Just as the colorations of the borax- and sodium-phosphate 
 glasses so useful to the analyst. 
 
 2 C. Benedicks, Zeitschr. f. physikal. Chem., 1905, 52 : 733. 
 
 3 Sufficient information as to the value of Martensite, etc., can 
 be found in my book, "Technische Anwendungen der phy- 
 sikalischeu Chemie" (Berlin 1907), p. 235. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 23 
 
 phorus, right after the illumination, small white points, 
 which rapidly grew to radiant brightness, and then turned 
 red. In a solution of phosphorus in carbon bisulphide 
 the process is the same. 
 
 10. Colloids in the Mineral Kingdom. The costliest 
 members of the mineral kingdom, the precious stones, 
 owe their magnificent color, often, to minute quantities 
 of a colloidally dissolved coloring substance. C. Doelter 
 includes in this class, among others, the smoky (yellow) 
 topaz and most of the sapphires, the beautiful blue color 
 of which is due to colloidal cobalt oxide; in ruby, how- 
 ever, he assumes the coloring substance to be a true solu- 
 tion of chromium oxide in alumina. A very beautiful 
 artificial ruby, which belongs to me, appears indeed 
 in reflected light turbid and dark, just like a colloidal 
 solution of gold on heating, it turns green; upon cooling 
 it is again colored red. 
 
 Of the semi-precious stones, the opal is to be consid- 
 ered as a colloid, and in fact as a Gel. According to F. 
 Cornu, 1 the Gels are in general far more numerously 
 represented in minerals than was hitherto supposed ; they 
 are the typical products of all normal disintegration pro- 
 cesses. So, for example, bauxite (aluminium-hydrox- 
 ide) and the already mentioned opal (hydrated silica) 
 are such colloidal products of the disintegration of 
 
 1 F. Cornu, Koll-Zeitschr., 1909, 4 : 15, and in other places. 
 3 
 
24 THE: COLLOIDS IN THE: INDUSTRIAL ARTS 
 
 rocks. Numerous Gels appear also in the oxidation zone 
 of the ore-beds, for example, Psilomelane in the man- 
 ganese ores. The Gels of the mineral kingdom are dis- 
 tributed, according to F. Cornu, in the groups of the 
 hydroxides, the sulphates, the hydrated phosphates, the 
 arsenates, the antimonates (Bleiniere), the silicates, and 
 the salts, which contain organic acids (Dopplerite of the 
 moss-worts) ; they are entirely absent in the other groups, 
 for example, in the sulphides, the carbonates, and the 
 anhydrous silicates, etc. ; that, indeed, is to be expected, 
 if the mode of their formation as disintegration products 
 is taken into consideration. 
 
 The external characteristic of the mineral Gels is the 
 conchoidal fracture, presupposing that they have not 
 lost any water; they often stick to the tongue. 
 
 Many mineral colloids have their crystalline antitypes. 
 So, for example, opal has an antitype in Calcedony, 
 which appears as a crystalline transformation product of 
 the colloidal form. 
 
 As especially important colloids of the mineral king- 
 dom, I will also mention kaolin, anthracite and bog-iron- 
 ore. 
 
 In the soil there are present in the form of colloids 
 iron oxide, silicic acid, amorphous silicates, and the 
 humus substances; as non-colloidal ingredients there 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 25 
 
 are quartz, fragments of crystalline silicates, and the 
 simple salts, such as calcium carbonate, phosphates, 
 chlorides, and sulphates. The humus substances form 
 an amorphous complex of decomposition products of the 
 sugars and proteins; they are agglomerated with the 
 colloidal silicates and adhere also to the crystalline par- 
 ticles. 1 
 
 11. Silver and Gold Mirrors. The flocculation of hy- 
 drosols of metals is made use of in the preparation of 
 silver and gold mirrors on glass. Under certain con- 
 ditions, the silver separates from the colloidal solution 
 on the glass plate as a brilliant mirror. The whole pro- 
 cess lasts few or several minutes, according to which 
 formula is employed in the preparation of the silver- 
 mirror (all are based on the reduction of a silver salt in 
 a dilute solution by formaldehyde, sugar, or Seignette- 
 salt, etc.) ; as an intermediate stage there appears a 
 brick- red colloidal solution of silver. If the process is 
 conducted incorrectly, instead of a coherent brilliant 
 metallic layer, a grayish-yellow skin and a slimy or gran- 
 ulated powder separate. The fact, that the slightest de- 
 viation from the formula is so fatal, is not surprising 
 if the sensitiveness of colloidal solutions is taken into con- 
 sideration. As it is well known, the preparation of the 
 glass, which is to be silvered, is also important; the sep- 
 1 Gedenkboek, J. M. van Bemmeln (Haider), 1910, p. 62. 
 
26 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 aration is facilitated if the surface is already overlayed 
 by a silver coating, even if this is an invisible one. In 
 the analogous process of gilding the preliminary pro- 
 duction of an invisible gold layer is even necessary. The 
 ultra-microscopical particles rapidly attach themselves 
 to the already separated metallic particles. The metallic 
 mirror can be reinforced as desired by the addition of 
 a fresh quantity of the colloidal solution. 
 
 Since the silver-mirror, in spite of its exceedingly 
 small thickness, is a good conductor of the electrical cur- 
 rent, it is possible to electro-deposit on it a thick layer 
 of copper and then on the latter a thin layer of palladium. 
 S. Cowper-Coles manufactures hollow metallic mirrors 
 on a large scale by producing them on curved glass- 
 molds in the way described, and then separating the 
 metallic layer by heating. 
 
 12. Manufacture of Tungsten Lamps. While in the 
 preparation of metallic mirrors the separation of the col- 
 loid in the form of a coherent metallic layer is desired, 
 and that part which is flocculated as an invisible powder, 
 is considered as an inconvenient waste; in the manufac- 
 ture of tungsten lamps, on the contrary, we desire to 
 obtain the metal in the form of a Gel, because this Gel 
 is sufficiently plastic to be pressed into thin filaments. 
 One would wonder why the compact tungsten metal is 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 2/ 
 
 not rolled out and squirted into filaments directly, as it 
 is done with the tantalum metal for tantalum-lamps. Un- 
 fortunately, metallic tungsten is much too brittle to be 
 drawn into wire, not to mention filaments of less than 
 0.05 millimeter in diameter, as those that are used as 
 metallic filaments in incandescent lamps. 1 On the other 
 hand, tungsten, which melts only at about 2,900 (1,000 
 higher than platinum and 500 higher than tantalum), 
 by the reason of its cheapness, is especially fitted for 
 the preparation of filaments for lamps on account of its 
 exceedingly high melting-point. The aspiration of the 
 lighting industry is concentrated in an endeavor to heat 
 the illuminative body to the highest temperature possible, 
 because the light-radiation increases extraordinarily rap- 
 idly with the increase of temperature. The higher the 
 temperature of the illuminative body, the larger the part 
 of energy, with which it is supplied, is transformed into 
 light. Carbon, indeed, does not melt, but the carbon 
 filament, in general, cannot be heated over 1,800 degrees 
 without deteriorating. The metallic filament lamps are 
 able to glow so much brighter, since such lamps consume 
 for each normal candle-power only about one volt, i. e., 
 
 1 The metals are better conductors than carbon ; for that rea- 
 son the lamps, which are intended for the use with the current of 
 the usual pressure of 1 10 volts require long metallic filaments, in 
 order to furnish the necessary electrical resistance. 
 
28 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 only about one-third of the electrical energy, which is 
 consumed by the old carbon filament lamps. 
 
 The filaments for osmium lamps, made from metallic 
 osmium, which cannot be drawn into threads, can be 
 prepared in a chemical way, by igniting carbon threads in 
 an atmosphere of the vapors of osmic acid, a very vola- 
 tile oxygen compound of osmium. At this high heat, 
 the osmic acid is decomposed into osmium and oxygen, 
 the osmium is deposited on the thread, while the carbon 
 and oxygen burn off, so that a thread of metallic osmium 
 results at last. 
 
 The common method, however, was to pulverize the 
 metal, as finely as possible, mix it with a binding material, 
 such as dextrin, gum-solution, sugar-syrup, to a thick 
 mush and squirt this under high pressure through fine 
 holes to form filaments of the desired thickness and form. 
 These filaments were heated strongly, whereby the or- 
 ganic binding material was carbonized ; in this way fused 
 filaments were obtained, which conducted well and which 
 contained the carbon in the form of carbide or as a 
 solid solution. 
 
 The same methods can also be applied to tungsten, 
 when either the volatile tungsten-oxy-chloride is em- 
 ployed, or the pulverized tungsten is worked to a dough 
 with some binding material. But the second method, 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 2Q 
 
 which hitherto was employed by preference, has its de- 
 fects. The squirting requires very high pressure and, 
 further, the carbon in the finished filament is often un- 
 equally distributed and forms knots; the cross-section 
 of the filament is in other ways also not uniform through- 
 out the whole length. The thin section offers to the cur- 
 rent more resistance, is heated stronger, and, in conse- 
 quence soon burns through. 1 Binding materials were 
 tried which volatilize at moderate temperatures, for ex- 
 ample, paraffin and camphor mixed with alcohol. Fin- 
 ally H. Kuzel has given up the use of any artificial bind- 
 ing materials and made the tungsten extraordinarily 
 plastic in the way indicated above, by converting it into 
 the form of a Gel. The above mentioned binding ma- 
 terials are, indeed, themselves colloids. If the tungsten 
 metal is pulverized very finely in a ball-mill and is pul- 
 verized further again and again for weeks and months, a 
 powder is obtained, which, being mixed with water, gives 
 a ductile mass. But, when this mass is pressed to thin 
 filaments in a stamping press, it is noticed that the ductil- 
 ity of the mass is not yet sufficient, that the filaments 
 break; they are too brittle for further treatment. It is 
 
 1 More information can be found in the valuable article of A. 
 Lottermoser : Einige Bemerkungen ueber die Herstellung von 
 Metallfaeden fuer elektrische Gluehlampen, besonders aus kolloid- 
 en Metallen, Chem. Ztg., 1908:311-313. See also Roll. -Zeitshr., 
 1908 : 2, 347. 
 
30 THE: COLLOIDS IN THE INDUSTRIAL ARTS 
 
 possible, however, to bring the mechanically extraordin- 
 arily pulverized tungsten into the colloidal condition, in 
 fact, into a comparatively concentrated solution, by 
 treating it alternately with alkalies and acids, and giving 
 it, intermediately, plentiful washing. If the tungsten is 
 precipitated from this solution, a viscous mass of an ex- 
 ceedingly fine division is obtained, which has all the de- 
 sirable properties, and which can be drawn out to fila- 
 ments of 0.03 millimeters in cross-section, through very 
 fine holes bored in rubies, without the use of great power. 
 
 At first, these filaments conduct the current badly, 
 but the small current, which passes through them, is suf- 
 ficient to heat the filament. In the heat the small par- 
 ticles combine to larger ones; the filament allows a 
 stronger current to pass through and at last at a white 
 heat the tungsten fuses to a solid, good conducting metal- 
 lic filament, which meets all the requirements in mechan- 
 ical and electrical respects. 
 
 Instead of gradually heating the unfinished filament 
 by the electrical current in the lamp, the filaments, as 
 they come from the press, and after they are dried, are, 
 preferably, ignited in an atmosphere of nitrogen, or in 
 vacuo (because the ignited tungsten is oxidized by the 
 oxygen of the air). The desired metallic filaments are 
 at last obtained at a white heat. They are then cut into 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 31 
 
 the proper length, and are cemented to the current-lead- 
 ing-in-wires in the lamp socket by means of tungsten 
 Gel; by heating also this cement is transformed into a 
 coherent metal. After that the glass globe is placed over 
 the filaments and fastened to the socket, finally the lamp 
 is evacuated, or filled with nitrogen gas, and sealed. 
 The siriuscolloid lamps, which are manufactured in 
 Germany by J. Pintsch, are claimed to withstand a cur- 
 rent of considerable overpressure, without being deter- 
 iorated. 
 
 The Auer-Gesellschaft manufactures its osra-lamps 
 by a different process, the details of which have not been 
 made public. 
 
 With reference to the theoretical explanation of the 
 Kuzel process, A. Lottermoser assumes that the grains 
 of the already exceedingly fine ground tungsten powder 
 are etched by the alternating treatment with alkalies and 
 acids, and in this way they are finally reduced to the 
 diameter of ultra-microscopical particles. Further, the 
 chemicals applied in this process introduce into the solu- 
 tion certain ions which make the metal-hydrosol stable 
 when they are present in a definite small concentration 
 (for this reason the plentiful washings between the sep- 
 arate etchings are employed) ; these ions are, probably, 
 
32 THE: COLLOIDS IN THE INDUSTRIAL ARTS 
 
 the hydrogen-ions of the acids, on the one hand, and the 
 hydroxyl-ions of the alkalies, on the other hand. 1 
 
 It has been found lately that perfectly pure tungsten 
 is ductile and can be drawn out to threads of 1 / 50 mil- 
 limeter thickness, such as are used in metal-filament 
 lamps. This discovery will, probably, overturn the whole 
 industry, and will do away with colloidal tungsten. 
 
 13. Colloids in the Ceramic Industry. As in the 
 younger tungsten-lamp industry, so, from ancient times, 
 in the ceramic industry the Gel formation is utilized in 
 order to make the pliant ceramic mass more plastic. The 
 noblest material of the ceramic industry, porcelain clay, 
 which consists of almost pure aluminium silicate, is first 
 freed from the heavier and coarser particles by very 
 careful washing, and is then mixed with "diluting-mater- 
 ials" (Magerungsmitteln), Feldspar and quartz, which 
 are also very finely ground and washed. In spite of the 
 painful mechanical preparation, this mass, after being 
 freed from the superfluous water in a filter-press and 
 wedged in a wedging machine, is, (like the powdered 
 tungsten), not yet sufficiently plastic to be subjected to 
 further treatment at once; it must be previously stored 
 for a long period. During the storing in a damp cellar 
 the porcelain mass becomes black and evolves gases, car- 
 bonic acid, ammonia, hydrogen-sulphide, which originate 
 1 A. Lottermoser, loc. cit. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 33 
 
 in the decomposed organic ingredients that were intro- 
 duced into it partly by the raw materials, partly by the 
 water. 1 This process is termed "mellowing/' or "cur- 
 ing" (Faulen, Mauken). The longer the mass is mellow- 
 ing the more pliant it becomes ; usually the mass is stored 
 at least for three months. According to P. Rohland the 
 success of the mellowing consists in the formation of 
 a colloid which is peptised under the influence of the 
 alkali present in the mass. The acid fermentation of the 
 organic substances causes the binding of the alkali and 
 therewith the coagulation of the colloidal solution. 
 
 Kaolin also, which is by itself more plastic than the 
 porcelain mass, must be mellowed previous to being sub- 
 jected to further treatment. 
 
 A very interesting application of the peptisation of 
 the colloids is the process, discovered by E. Weber for 
 the manufacture of glass melting-pots by casting. By 
 the addition, according to the nature of the fire-resistant 
 clay, of a small, accurately measured, quantity of soda 
 and a little water, under constant vigorous stirring, he 
 transforms the finely ground slip into a thin mush, which 
 is then run out from the mixing vessel into the pot molds 
 placed below. If the slip were mixed with water only, 
 it would soon settle to the bottom of the mold, while 
 in the Weber's process the whole mush gradually hard- 
 1 R. Dietz, Das Porcellan (Halle), 1907 : 41. 
 
34 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 ens to a solid mass, which is uniform in structure and 
 thick in the fracture, for which reason the pots do not 
 suffer any longitudinal cracks, even at more considerable 
 fluctuations of temperature in the glass furnace. 
 
 Besides the greater durability in comparison with the 
 pots which were formed by hands, the casting process 
 means also a considerable saving in time and labor. The 
 production of one pot, which holds 220 to 225 kilograms 
 of glass, requires from the time when the mixture is 
 measured up to the time when the filled mold is carried 
 away not more than one hour. After 24 hours of stand- 
 ing still the pot has hardened so much that the core of 
 the mold can be taken out; after a further 24 hours the 
 mantel is taken off and at the same time the upper edge 
 of the casting is cut off. Further treatment is not re- 
 quired. This process has been employed since 1905 in 
 the glass works of Aug. Leonhardi in Schwepnitz (Sax- 
 ony). 
 
 Clays, which cannot be liquefied by soda only, as J. 
 Keppeler 1 found, can be brought into that condition by 
 the addition of humic acid. 
 
 In drying in the kiln the colloidal ingredients distin- 
 guish themselves in that they, in correspondence with 
 their large surface development, tend in a large measure 
 
 1 See the lecture by J. Keppeler, Zeitschr. f . angew. Chemie, 
 1909, 22 : 526. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 35 
 
 to diminish their surface by shrinking. Crystalline sub- 
 stances do not manifest such fire-shrinking properties at 
 all. Due to the fine division of their mass, the colloids 
 are usually at the head also in respect to the rapidity with 
 which they change into other states of aggregation. 
 While, for example, quartz crystals, even at a white 
 heat change but very slowly into the crystalline form, 
 tridymit, which is stable at temperatures above 1,000 
 degrees, and also quartz-glass transforms only slowly, 
 the colloidal silicic acid forms tridymit rapidly even at 
 1,000 degrees. 
 
 14. Colloids in the Hydraulic- Cement Industry. Just 
 as, according to the theory of P. Rohland, in kaolin and 
 porcelain, so also in cement does the colloidal condition 
 play an important part. 
 
 According to W. Michaelis 1 in the first stage of the 
 hardening process of Portland cement, in that stage, 
 which is called setting (Abbinden), there are formed, 
 with absorption of water, colloidal calcium hydro-silicate 
 and -aluminate, and colloidal calcium hydroxide. The 
 crystals of calcium hydroxide and calcium aluminate, 
 which are formed gradually, find in the yielding, jelly- 
 like colloid-mixture room for their development; in 
 separating out these crystals petrify more and more the 
 
 1 W. Michaelis, Jahresbericht der chemischen Technology, 
 1906 : 109, ff. 
 
36 TH COLLOIDS IN THE INDUSTRIAL ARTS 
 
 first perfectly elastic colloid, which, moreover, on drying 
 becomes by itself hard as a stone, thus cementing by it- 
 self the sand-grains or the crystals, which are embedded 
 in it. The colloidal cement, this "mineral Gel," as W. 
 Michaelis calls it, protects the iron in the iron-ore-cement 
 from rusting, by surrounding it in the form of a thick 
 protecting layer. The hardening of the hydraulic ce- 
 ment is based on the gradual setting free of the swelling 
 water, the continued hardening of the colloids, the bind- 
 ing of water as water of crystallization, and the continued 
 formation of crystals of calcium hydroxide. The larger 
 cement grains are protected from the absorption of 
 water by the jelly-like calcium -hydro-silicate and calcium- 
 hydro-aluminate, which are not permeable to water, so 
 that when a pure cement, which has hardened under 
 water years ago, is pulverized, it hardens anew and, in- 
 deed, the more, the coarser the original powder was. 
 Thus, in the hardening of the cement, we have to do with 
 the combined action of colloidal and crystalline sub- 
 stances; the water, which is contained in the colloid, 
 compels us to make additions of "diluting-materials" 
 (Magerungs-mitteln) in order, that the cement on hard- 
 ening, may not shrink too much. 
 
 E. Stern, 1 indeed, does not accept this theory wholly, 
 but also thinks that the formation of jelly-like substances 
 1 Chem. Ztg., 1908 : 85. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 37 
 
 in the period of the setting of the cement is very prob- 
 able. To prove the presence of colloids, he carried out 
 the following experiment: when hydraulic cement (or a 
 pure aluminate) is mixed up with water, the lime and 
 alumina go into solution. If a finely pulverized alumin- 
 ate is dialysed, in the dialysate can be found only lime, 
 alumina is not found at all, or is present in traces only. 
 
 E. Stern studied the setting and hardening processes 
 more closely under the microscope, retarding these pro- 
 cesses by the addition of gelatin. He spread coarse- 
 grained cement on the object-plate and covered it with 
 a few cubic centimeters of a two per cent, solution of 
 gelatine. After drying, the gelatine preparation was 
 immersed in water (100 cc.). At the end of 24 hours 
 the cement grains were superfically attacked by the 
 water, but no crystals were to be seen there; the larger 
 part of the lime had diffused out, while aluminium hy- 
 droxide and calcium carbonate were formed, which sur- 
 rounded the cement grains. When the access of air was 
 perfectly excluded, instead of carbonate, crystals of 
 calcium hydroxide were formed. 
 
 According to Stern, the cement grains, in setting, are 
 surrounded by a colloidal layer; in hardening, crystals 
 (sodium carbonate and hydroxide, aluminate and sili- 
 cate) separate out and, indeed, in the interior of the ce- 
 
38 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 merit block chiefly calcium hydroxide, and on the exter- 
 nal part calcium carbonate. 
 
 According to P. Rohland, the colloids are of especial 
 importance in the hardening of cement in sea-water, 
 because they are impermeable to all salts of magnesium, 
 which would be detrimental to the mortar. 
 
 15. Colloids as Adhesives and Glues. According to the 
 above given explanation, we may consider the colloidal 
 elementary mass of the hydraulic cement as a binding 
 material. In a very general way the colloids, indeed, 
 are employed for glueing and cementing purposes. 
 While in soldering the liquid solder forms an alloy with 
 the metallic thread which is to be soldered, in glueing 
 such a mutual dissolving process does not take place, 
 but, so to say, intimate interlacing of two cell-structures 
 is produced. In glueing of wood and other substances 
 of a cellular structure, the glue, owing to its great plas- 
 ticity, penetrates the pores of the wood and on solidify- 
 ing unites well glued pieces with such force that they 
 can be separated only with great trouble and damage. 
 Being interposed between flat surfaces such as metallic 
 and glass, the glue fills up the slightest depressions and 
 cracks, even if such are not visible to the naked eye; in 
 this way it forms in a manner, a uniform whole. 
 
 If the adhesive power, as it is often assumed, were 
 the result only of the elimination of all the air between 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 39 
 
 the two surfaces, which are glued together, and the air 
 pressure alone were holding these surfaces together, then, 
 first, the adhesive would bind best only as long as it re- 
 mains moist; adhesives, however, bind well only on dry- 
 ing, and many of these attain their full adhesive power 
 only after a long period. Second, the adhesive power 
 could not be any greater than that which corresponds to 
 the air pressure, i. e., one kilogram to each square centi- 
 meter of the surface to be glued ; but it is usually several 
 times greater. For instance, the adhesive strength of 
 good joiner's glue is 150 kg. to I sq. cm. 1 Prom this 
 example we may see how great a tensile strength may be 
 manifested by this delicate colloidal structure. 
 
 16. Usefulness of the Colloids in the Absorption of 
 Liquids. In consequence of their peculiar porosity the 
 colloids are able to absorb large quantities of liquids and, 
 indeed, often, by being swelled at the same time, much 
 more than the original volume of their pores. The 
 absorption-ability is made use of, for example in electro- 
 technics in the preparation of dry batteries; besides 
 plaster of Paris, gelatine, agar-agar, blotting-paper, 
 saw-dust, cellulose, cotton and other organic substances 
 are used ; of the inorganic colloids, in the case of acidic 
 
 1 See F. Knieger, Kleben und Klebbstoffe, Verhandlungen 
 des Vereins zur Befoerderung des Geverbefleisses, 1905 : 132. 
 4 
 
4O THE COLLOIDS IN THE: INDUSTRIAL ARTS 
 
 liquids, the Gel of the silicic acid, and in the case of 
 alkaline liquids, iron-oxy-hydrate are used. 
 
 This absorption power of the colloids is also made 
 use of in order to remove disagreeable liquids ; Peat- 
 molds (Torf-mull), for example, are readily employed 
 for the absorption of liquid fecal matters. 
 
 This water absorption plays an important part also 
 in nature. The richer a soil is in colloidal ingredients, 
 the more water it is able to retain. Cultivated peat soil, 
 for example, which is superficially dried and is still some- 
 what moist to the touch, contains, according to the deter- 
 minations of P. Khrenberg and H. Pick, 1 no per cent, 
 of the weight of the dry substances in water; in humic 
 garden soil (fresh and moist) it is 38 per cent. ; In air 
 dried, ground Dollart-clammy-soil it is 1 1 per cent. ; in air 
 dried loess it is 3 per cent.; and in fine sand (containing 
 0.3 per cent, of organic substances) it is, according to 
 my own determinations, but 0.2 per cent. 
 
 17. Dehydration of Peat by Electro-Osmosis. The 
 
 large quantity of liquid which is absorbed by peat is a 
 great obstruction to its employment as a fuel. Simple 
 pressing removes the water from the peat just as inef- 
 fectively as it does from, for example, the Gel of silicic 
 acid. If it is not desired to leave to the air and sun the 
 1 Gedenkboek, J. M. van Bemmeln (Helder 1910), pp. 201-204. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 4! 
 
 tedious job of drying the peat, and it is attempted to 
 evaporate the water ballast rapidly by heating, one ex- 
 periences difficulties due to the comparatively high cost 
 of this process. Several years ago a process for the 
 dehydration of peat, which was invented by Prince 
 Botho Schwerin drew considerable attention; it is based 
 on the following : an electrical current of several hundred 
 Volts pressure is conducted through a thick mush of 
 ground peat and water; the peat is then forced towards 
 the positive pole and the water towards the negative one ; 
 in this interesting way he succeeded in removing from 
 the peat-slime a good portion of its water. 
 
 18. Colloids as Diaphragms and Filters. The applica- 
 tion of the Gels as porous "diaphragms" and as filters is 
 based on the cell structure of the Gels. Water, and 
 substances which are really dissolved in water, pass 
 through the pores without great difficulty, but colloids 
 diffuse only very slowly, or not at all. 1 In nature, such 
 colloidal diaphragms are the cell-walls of plants. Their 
 impermeability toward colloids is made use of in the beet- 
 sugar manufacture, in the process of leaching the beet 
 slices, the sugar passes out while the colloidal ingred- 
 ients of the cell-juice remain. Of the artificial dia- 
 
 1 The diffusion appears to go on mainly through the liquid, 
 which is present between the cell-walls, while the walls them- 
 selves do not allow any passage. 
 
42 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 phragms we have mentioned parchment paper, which is 
 employed in the dialysis of the Sols of silicic acid. On 
 the other hand, how great the permeability is in the case 
 of electrolytes, is illustrated, for example, by the follow- 
 ing: In storage batteries diaphragms are sometimes 
 used made from sulphite-cellulose pasteboard. In order 
 to make them more durable, these diaphragms are soaked 
 in rosin. In a short time, after they are immersed in 
 the storage battery, these diaphragms, in spite of the fact, 
 that they have been soaked with the non-conducting 
 rosin, absorb so much of the sulphuric acid, that they 
 conduct the current very well. 
 
 When the particles of the colloidal solution are very 
 small, they also will go through very fine filters. Usual 
 filter paper still retains particles measuring about 5 /*; 
 hardened filters permit the passage of particles measur- 
 ing up to 2 ju, and Pukal-filter-candles, indeed, only up 
 to 0.3 /u. If the pores of a filter paper are made smaller 
 by the addition of jellies of different concentrations, ac- 
 cording to the process of H. Bechhold, a mixture of 
 different colloids may be subjected to fractional filtration, 
 and for example, colloidal silver (Lysargin) may be 
 separated from Haemoglobin (the coloring ingredient of 
 blood). 
 
 19. Adsorption. It is incorrect to consider the process 
 of filtration only as a kind of percolation ; here comes to 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 43 
 
 the foreground another property of the colloids, based 
 on their cell structure, namely, the adsorption-power, 
 which is based on their enormous surface development. 
 By the name adsorption is designated the remarkable 
 phenomenon that gases, liquids, and finely divided sub- 
 stances adhere, often with great force, to the surface of 
 many materials. Each window pane, for example, is 
 covered with a not insignificant layer of water and gases, 
 from which it can be completely freed only by heating 
 for several hours in an evacuated room. The adsorption 
 power increases with the surface and depends, not only 
 on the nature of the adsorbing, but also on the nature of 
 the. adsorbed substance. Colloids are preferably ad- 
 sorbed again by colloids. So, for example, the ultra- 
 microscopical particles of gold, despite their small size, 
 are retained, in filtering, by the filter and clog up the 
 pores. 
 
 How peculiarly adsorption acts can be seen, for ex- 
 ample, in the fact that R. Zsigmondy was able to prevent 
 adsorption on the filter by adding white of an egg, or 
 another protective colloid, to the hydrosol of gold; gold 
 particles measuring 30 ^ smoothly passed through 
 Maassen-filter-candles and Pukal-filters. In this case 
 probably, also chemical combinations assert themselves. 
 The usual proteins, in general, appear to be quite indif- 
 
44 THE; COIXOIDS IN THE INDUSTRIAL ARTS 
 
 ferent to the material of the filter, while ferments and 
 toxins enter into combination with it. 
 
 20. Varnish-Making. Varnish-making is largely based 
 on the adsorption properties of the colloids. Just as 
 freshly precipitated aluminium-hydroxide takes up the 
 gold from a colloidal solution of gold and produces a 
 beautiful red varnish, so the Gel of aluminium-hydrox- 
 ide causes other coloring matters to adhere to it. The 
 well-known receipt for the making of a varnish consists 
 in the following : A solution of coloring matter is mixed 
 with a solution of alum and the aluminium-hydroxide, 
 which takes up the coloring matter, is precipitated by 
 soda. This process, formerly used to be explained as 
 the producing of a chemical combination, while, accord- 
 ing to the modern views, there is, in the first place, a 
 case of adsorption. 
 
 21. Dyeing. Adsorption plays a great part also in the 
 dyeing of textile-fibers. Many dye solutions, when in- 
 vestigated by L. Michaelis under the microscope, proved 
 to be colloids, as, for example, carmine, naphthol-yellow, 
 induline, violet-black, aniline blue, congo-blue, bavarian- 
 blue in a water solution, scarlet dissolved in alcohol, etc. 
 
 Fluorescin, eosin, toluidine blue, nile-blue, methylene 
 blue, and other fluorescent substances do not show any 
 ultra-microscopical particles, but do show a light-cone. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 45 
 
 The suspensions of chrom-yellow and of ultramarin 
 contain comparatively very coarse particles. In the deep 
 blue "solution" of ultramarin, which appears clear to the 
 eye, which can be filtered through paper, and which, 
 often, does not settle for months, small points can be seen 
 even under an ordinary microscope with a magnification 
 of 1,200. 
 
 L. Michaelis makes the following interesting conclu- 
 sions from his ultra-microscopical studies : those coloring 
 matters, which form colloidal solutions in water, can be 
 employed as elementary coloring matters, and as such, 
 which possess a diffusive power. 
 
 Numerous coloring matters cannot readily be fastened 
 on the textile-fiber, the material to be colored must prev- 
 iously be subjected to the process of mordanting. For 
 this purpose it is mostly impregnated with colloidal 
 aluminium hydroxide, which effects a wash-proof union 
 between the coloring matter and the fiber. 
 
 Dyeing was considered from the point of view of 
 colloidal chemistry first of all by Otto N. Witt, who two 
 decades ago pointed out the colloidal character of the 
 textile-fibers. 1 Later the theory of dyeing was devel- 
 oped by P. S. Zacharias and by W. Biltz. 
 
 The solid fibers behave like the Gels ; they have a cell- 
 
 1 See, for instance, the treatise by O. N. Witt, "Zur Theory 
 des Faerbeprocesses;" Faerber-Zeitung, 1890-91, No. I. 
 
46 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 structure and are swelled on "steaming." By the alkali 
 and acid "fulling," as well as by the previous preparation, 
 the fibers are brought, according to Ed. Justin Miller, 
 into a jelly-like condition, and by the mechanical action 
 of the fulling they are cemented and felted together. 
 According to P. S. Zacharias, each direct dyeing takes 
 place in two steps: first, absorption, in which the color- 
 ing matter penetrates the swelled up fiber, second, fixa- 
 tion, in which the penetrated coloring matter is made 
 insoluble by chemical reaction or by coagulation. 
 
 The fiber as W. Biltz states, takes up comparatively 
 more substantive coloring matter from a dilute solution, 
 than from a concentrated one. He showed further that 
 in the case of dyes, which are of the type of benzopur- 
 purin, the textile-fiber may be substituted by an inorganic 
 colloid, as aluminium hydroxide, without causing a quan- 
 titative change in the adsorption. 
 
 The laws of adsorption have been especially investi- 
 gated by the thorough researches of H. Freundlich. 1 
 He discovered that the ratio between the adsorbed quan- 
 tity and the concentration of the solution is expressed 
 by an exponential equation ; the constants of this equation 
 are different in different cases. 
 
 1 A grouping of these investigations is made by H. Freundlich 
 in his book, * * Kapilarchemie " (I/eipzig 1909). 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 47 
 
 22. Tanning. 1 The animal hide represents a mixture 
 of protein-like substances, which are in the form of a 
 Gel. The vegetable tannins, which are used in the indus- 
 try, are also in the condition of colloidal solutions ; con- 
 sequently, tanning represents a reaction, which takes 
 place between colloids. The precipitation processes, 
 which are caused in colloidal solutions by electrolytes, 
 assert themselves even in the process of the extraction of 
 tannin from the tannin raw materials by water; distilled 
 water extracts considerably more tannin than raw water ; 
 the losses are the heavier, the more impurities contained 
 in the water, which is used in the process. The hide, 
 which, by soaking and treatment with lime, was de-haired 
 and freed from flesh, and which, by treatment with acid, 
 was de-limed, absorbs from the tanning materials, pre- 
 ferably, colloids. 2 These colloidal tanning materials 
 (tannin, etc.,) are absorbed more or less rapidly, accord- 
 ing to their nature, being taken up, preferably, by the 
 upper parts of the hide, or penetrating also to its interior. 
 Since from leather which was tanned by vegetable tan- 
 nins, more tannin can be washed out immediately upon 
 
 1 A fuller treatment of the subject is given by E. Stiasny 
 in Koll.-Zeitsch., 1908, 2 : 257-263. 
 
 8 An important part is played thereby by the "swelling up" of 
 the fiber. As J. v. Schroeder found in his research work, "Zur 
 Kenntniss der Gerbprocesse" (Dresden, 1909), hide-powder, in 
 order to be able to take up tannins, must first, be soaked in water. 
 
48 THE: COLLOIDS IN THE: INDUSTRIAL ARTS 
 
 the finishing of the tanning process, than after the leather 
 has been stored, it is to be assumed, that, in time, the 
 adsorbed tannin changes from the reversible-, into the ir- 
 reversible- Gel-form, a process, which is catalytically 
 accelerated by the fibers of the hide. But the tannin, 
 which is taken up by the hide, is surely changed also 
 chemically; oxydation, anhydration, and polymerisation 
 are presumed to be these chemical transformations. 
 Since, further, diffusion and capillarity are determining 
 factors of the penetration of the hide by the tannins, the 
 process of tanning appears to be a very complicated one, 
 the theory of which is still obscure. 
 
 In mineral-tanning chromium salts (chrom-tanning) 
 and alum are used. The real tanning material is the col- 
 loidally dissolved basic salt. Since the alum splits up 
 less basic salts, than the chromium sulphate, the alum- 
 inium salts penetrate the hide more rapidly, indeed, but 
 their tanning action is weaker. While chrom-tanned 
 leather resists the action even of hot water, a larger por- 
 tion of the aluminium hydroxide can again be washed 
 out from alum-tanned leather; the longer the leather is 
 stored, the more of the aluminium hydroxide becomes 
 insoluble. 
 
 The fact, that the iron salts, which are closely related 
 to those of chromium and aluminium, are not well fit for 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 49 
 
 tanning purposes (the leather is made brittle), E. 
 Stiasny traces back to the iron hydroxide, which does 
 not diffuse sufficiently and is too easily precipitated. By 
 the addition of blood (as a protective colloid) the iron 
 tanning can be improved. 
 
 In fat-tanning the colloidal fat (Tran, etc.,) is ad- 
 sorbed by the fiber and then transformed into insoluble 
 oxydation products by the oxygen of the air. Also in 
 this case we find the general principle of the tanning, 
 the colloidally dissolved tanning material is first adsorbed, 
 then it is changed into an insoluble form, so that the tan- 
 ning cannot retrocede. 
 
 The essence of any tanning process consists, accord- 
 ing to the conception of P. S. Zacharias, 1 in the follow- 
 ing: the hide is transformed into leather by the coagula- 
 tion of the swelled up hide fiber, and by the nullifying 
 of its ability to take up water through an appropriate 
 deposition of the tannins. 
 
 The processes which take place in pickling have 
 lately been studied more closely by Henry R. Procter. 2 
 In pickling, the hide is treated with a very diluted solu- 
 tion of sulphuric acid, whereby the fibers of the binding 
 tissues swell up strongly; they are then immersed in a 
 
 1 Lecture at the Fifth International Congress of Applied Chem- 
 istry, Berlin, 1903. 
 
 2 Kolloidchemische Beihefte, 1911, 2 : 243-284. 
 
5<3 THE) COLLOIDS IN THE INDUSTRIAL ARTS 
 
 concentrated solution of salt which causes contraction, 
 the fiber is strongly dehydrated and becomes leather-like. 
 The saturated solution of salt is not able to dehydrate a 
 hide, which has not been subjected to a preliminary 
 treatment with acid. 
 
 Gelatine, which, owing to its formless structure, offers 
 simpler conditions for investigation than the hide sub- 
 stance, and, which in other respects behaves similar to 
 the hide substance, according to the observations made by 
 H. R. Procter, is able to take up, in strongly diluted solu- 
 tions of muriatic acid, more than fifty times its weight 
 of water, while in pure water it takes up only seven or 
 eight times its weight of water. Very dilute acids exert 
 only a slight swelling action. Neutral salts (i. e., salts, 
 which have neither an acid, nor an alkaline reaction), 
 when in a neutral solution, increase the swelling, but, 
 when in presence of a trace of muriatic acid, they effect, 
 on the contrary, a considerable contraction. H. R. Proc- 
 ter assumes, that gelatine, which acts as a weak base, 
 forms with the acid a salt-like compound. 
 
 23. Soap-Manufacture. Soap represents by its spongy 
 consistency the typical structure of a Gel. The large 
 quantities of water, which are contained in soap, in 
 storage, are gradually given off. But, if, on the contrary, 
 dried soap is placed into water, it swells up and dissolves 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 51 
 
 to a jelly. This liquefaction process takes place more 
 rapidly when, according to F. Goldschmidt, some alkali 
 is added to the water; this is the reason why the soap- 
 maker remelts his scrap not with water, but with weak 
 lye. 
 
 The salting out (graining) of the soap, i. e., the sep- 
 aration of the soap from the aqueous solution, by the 
 addition of a mixture of common salt, soda, and caustic 
 soda, has hitherto been considered as an "ion-reaction" ; 
 now this process is considered as the flocculation of a 
 colloid. That concentrated soap solutions are of a 
 colloidal nature, is proven by the fact, that they boil at 
 1 00, just as pure water, while the boiling-point of a 
 true solution is higher than that of the solvent. The 
 electrical conductivity of a strong soap solution is also 
 very small at room temperature, while otherwise the 
 alkali salts are very good conductors. But, in order to 
 avoid misunderstandings, I wish to emphasize, that soap 
 solutions are by no means always colloidal, and that 
 there are various differences. 
 
 Owing to its great porosity, the soap-Gel is able to 
 absorb much water without appearing moist, which 
 property is made use of by manufacturers. For adul- 
 terating purposes, various cheap fillers, such as common 
 salt, potash, and sodium-silicate may be added. The 
 soft soaps, which, as is known, are not solid, but have a 
 
52 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 jelly-like consistency, are "filled" with potato-Hour, 
 which is, indeed, in its turn perfectly well gelatinized by 
 the action of alkalies. The potato-flour is mixed with 
 potash and a solution of soap, the mixture is added to 
 the soft soap, and the whole is crutched till it is uniform, 
 when, finally, a solution of caustic potash is added. A 
 product is then obtained, which, despite its high water 
 content, has, owing to the flour-gelatine, the firmness of 
 a good article. 
 
 24. Brewing-Industry. The observation, made by H. 
 Bechhold, that colloidal solutions are clarified by filters, 
 the pores of which have been reduced by jellies, has been 
 made use of by F. Emslander to explain certain pro- 
 cesses in the brewing-technic. From the wort (malt 
 extract), to which hops have been added, and which was 
 boiled with the hops for several hours, a sediment sep- 
 arates upon cooling, the so-called malt-residuum (Kuehl- 
 gelaeger), which settles to the bottom of the cooling 
 vessel and consists mostly of coagulated albumen. 
 The malt-residuum can be easily separated from the 
 wort by filtering through coarse linen cloth. On the 
 other hand, the so-called keg-residuum (Fassgelaeger) 
 which separates in mellowing of the beer in keg storage, 
 is not easily separated by filtration, because its solid par- 
 ticles are very small, and contain very many bubbles of 
 carbonic acid, which clog the pores of the filter. But 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 53 
 
 if the beer be passed through a filter, which already con- 
 tains the malt-residuum, a perfectly clear filtrate may be 
 obtained, and time is also saved. 
 
 Soluble proteins may act in the beer as protective col- 
 loids, and prevent the flocculation of the yeast; in such 
 case the beer remains turbid. 
 
 The remarkable influence of water on the quality and 
 kind of the beer can be explained, in some respects, by 
 colloidal chemistry. Water which contains much iron 
 acts harmfully because the flocculated iron hydroxide 
 carries away with it taste- and extractive matters; the 
 beer is not matured (Vollmundig). Water, which con- 
 tains lime, has, on the contrary, a favorable influence, 
 because it improves considerably the yield from the 
 malt, and helps the maturing. 
 
 25. Lubricating Greases. If lime soap (15-23 per 
 cent.) be dissolved in heavy mineral oils, to which is 
 added a little water (1-4 per cent.), a lubricating grease 
 is obtained, which has a salve-like consistency, and is 
 used especially for lubricating inaccessible bearings. 
 Without water, the solution of lime soap in mineral oil is 
 liquid; under the ultramicroscope it appears turbid. A 
 solution of lime soap in pure benzene also shows a 
 bluish light-cone. The black, non-transparent mineral 
 oils also appear under the ultra-microscope as colloidal 
 solutions. 
 
54 THE; COLLOIDS IN THE: INDUSTRIAL ARTS 
 
 Reddish-yellow lubricating oils give an amicroscopic 
 bluish light-cone, likewise white paraffin oil. Crystal- 
 lized paraffin, which is dissolved in benzene in smaller 
 quantities, does not show a distinct light-cone, but, after 
 a considerable quantity of paraffin is dissolved, a light- 
 cone appears consisting of beautifully flashing sub-mi- 
 croscopical particles. 
 
 The solution of asphalt in benzene appears dark under 
 the ultra-microscope; but, if plenty of alcohol is added 
 to it, sub-microns appear, which are, evidently, precipi 
 tated asphalt. To the naked eye this solution appears 
 clear. 
 
 Resin also, when in an alcoholic solution, exhibits sub- 
 microscopical particles. 
 
 If the water-free solution of lime soap in mineral oil 
 be intimately mixed with only three-fourths of one per 
 cent, of water, it becomes salve-like in consistency; its 
 viscosity often increases with time. From the view- 
 point of colloidal chemistry, this transformation can be 
 explained as a process of coagulation. 
 
 In concluding these observations D. Holde suggests 
 that the ultra-microscope be employed in the examination 
 of mineral oils, paraffin, ceresin, rosins, etc. 
 
 Under the ultra-microscope, Russian, almost paraffin- 
 
THE: COLLOIDS IN THE INDUSTRIAL ARTS 55 
 
 free, petroleum oil, for example, can immediately be dis- 
 tinguished from the American. 
 
 26. Sewage Purification. The sewage of cities con- 
 tains a large quantity of organic substances, and, indeed, 
 the larger part of these in the condition of colloidal solu- 
 tions. The sewage can be purified from these harmful, 
 putrescible substances, by the addition of suitable chemi- 
 cals (chemical purification). Since the putrescible 
 sewage substances migrate in the electric current to- 
 wards the positive pole, and are negatively charged 
 towards water, positively charged colloids are adapted for 
 their precipitation, as, for example, the hydrosol of iron 
 hydroxide. The iron hydroxide, which is obtained by 
 the decomposition of iron chloride, in flocculation, car- 
 ries down with it the major part of the putrescible sub- 
 stances. Drinking water also may be purified in the 
 same manner, by the addition of measured quantities of 
 iron chloride and sodium carbonate. L. Schweikert 
 recommends, instead of these additions, a colloidal solu- 
 tion of iron hydroxide, which he prepares from freshly 
 precipitated iron hydroxide, by washing with water until 
 it goes into solution. With one litre of this solution 
 (which costs about 3 Pfennige less than i cent) 
 Schweikert was able to purify i cm. of water, taken 
 from the river Elbe. 
 
 Colloidal aluminium hydroxide is also adapted for use 
 5 
 
56 THE} COLLOIDS IN THE) INDUSTRIAL ARTS 
 
 as a clarifying agent, for example, of waste waters from 
 starch manufacturing plants. 1 
 
 When these clarifying agents are applied, it must be 
 taken into consideration that they, indeed, carry down 
 the organic putrescible substances, but they do not de- 
 stroy them. If these organic substances are carried away 
 by running water soon, this clarification is sufficient, but, 
 if the precipitate remains in the same place, putrefaction 
 sets in. In order to avoid this, in such cases, a purifi- 
 cation agent is to be employed, which oxidizes and de- 
 composes, as, for example, ozone. 
 
 In the chamber process of sewage purification, the 
 gradual flocculation of the organic substances is made 
 more rapid by the putrefaction, which sets in. The walls 
 of the chamber are covered with sediments consisting 
 of rolled together colloids; the gases, which are evolved 
 during the process of putrefaction, stir up the sludge, and, 
 from time to time, bring it to the top, or hold it suspend- 
 ed in the liquid. These sludge particles adsorb on their 
 surfaces further quantities of colloids; as soon as the 
 gas escapes, the sludge sinks again to the bottom. By 
 frequently repeating this movement, the sewage becomes 
 continually clearer. 
 
 1 According to P. Rohland, also the highly plastic kaolins of 
 Striegan, in Schlesien-Germany, thanks to their richness in col- 
 loids, can be used for clarification of waste waters. Koll.-Zeitschr. , 
 1908, 2 : 177-179. 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 57 
 
 After this clarification, the sewage is conducted 
 through tubes or through sprinkling filters; these are 
 filled with materials having a large surface, which adsorb 
 the colloidal, refuse substances, as well as a part of the 
 ammonia and the salts. 
 
 If the purification mass is coarse, and the air has free 
 access to the tubes, the jelly-like sediment gradually 
 becomes granular and may easily be rinsed out. 
 
 When filters are employed for the purpose of purify- 
 ing water, their action is based primarily on the adsorp- 
 tion-power of the filtering-medium, be it sand, carbon, 
 wood-wool, or the like; by depositing themselves on the 
 filtering medium, the colloids enlarge still more the ef- 
 fective surface, and therewith improve the adsorption. 
 As is known, filters mostly do not work well at the be- 
 ginning, they must, first, be worked up. 
 
 Along with these colloidal reactions, the transforma- 
 tions brought about by bacteria, especially in the Biologi- 
 cal process of purification of sewage are, however, the 
 most essential feature. 
 
 27. Colloids in Agriculture. The inventive man un- 
 consciously derives benefit from the colloids, which are 
 present in the fertile soil, as well as those in the numerous 
 trades. That very process of reducing and etching, 
 which H. Kuzel employed in order to obtain tungsten in 
 a colloidal condition, is practiced by nature on a large 
 
58 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 scale. The influence of the disintegration process, which 
 results in the formation of colloids, has been mentioned 
 on page 23. In addition to that, there are other power- 
 ful forces. The rivers, the Elbe, for example, in flow- 
 ing, carry with them rocks and soil; on the way to the 
 sea, the soil becomes ever more finely divided, partly 
 mechanically, partly by putrefaction processes (in the 
 same manner as in the process of mellowing of kaolin), 
 and at last the viscous silt is deposited in the sea between 
 the alluvial land and the shore; this deposit is, owing, 
 probably, to its extraordinary fine division, an exception- 
 ally fertile soil, so that the cost of building dams is cov- 
 ered by the sale of this land with profit. A hectar 
 (about 2 1/2 acres) of this land costs at present about 
 3,000 Marks (about $710). 
 
 Even usual soil manifests a large binding capacity for 
 the nourishable materials, which are contained in irri- 
 gating waters, and, in general, in the manures. Accord- 
 ing to J. M. van Bemmeln 1 , the ability of soils to take up 
 salts of the alkalies and alkaline-earths from their solu- 
 tions is based on their content of basic, soluble in hydro- 
 chloric acid, silicates, which contain lime, magnesia, 
 potash and soda, and which are able to exchange these 
 bases with the salts contained in the water. It is seen, 
 that also in this case, as in many others, which were con- 
 1 J. M. van Bemmeln, Die Absorption (Dresden 1910). 
 
THE COLLOIDS IN THE INDUSTRIAL ARTS 59 
 
 sidered before, the chemical transformations enhance 
 the adsorption action. 
 
 The silt of the Nile also contains a considerable quan- 
 tity of hydrated silicates, suitable for the colloid forma- 
 tion, which take up from the Nile-water every year, 
 during the innundations, potash, nitrogen, and phosphoric 
 acid and transfer these stored up nourishing materials 
 to the plants after the waters recede. In this manner Ef" 
 
 -<" 
 
 Pohl explains the astonishing, inexhaustible fertility oft 
 the Nile-land. 
 
 The great water absorption ability of soils rich in col- 
 loids, which prevents a too rapid drying out of the soil 
 during dry periods, and which in this way is useful to 
 the plant-growth, was already mentioned on page 40. 
 
 It would be easy to find in literature as well as in 
 practice other cases, in which the colloids play an im- 
 portant part. 1 However, I believe that the birds-eye- 
 
 1 For example, in the photographic technics we find the re- 
 markable fact that the bromo-silver gelatine plates, at first, are not 
 fit for use ; they must be previously stored. In storing, the plates, 
 which are transparent at the beginning, become very turbid ; the 
 ultra-microscopical bromo-silver particles clump together into 
 somewhat larger particles, which are now especially light-sensitive. 
 In general, the colloidal forms of the silver halogens, their adsorp- 
 tion further the tanning and adsorption of the gelatine play a 
 weighty part in the photography. I only wish, in a few words, 
 to call attention to the work of Luppo-Cramer, "Kolloidchemie 
 und Photography (Dresden 1908). 
 
60 THE COLLOIDS IN THE INDUSTRIAL ARTS 
 
 view of the colloids, which I have here presented, is in 
 a quantitative way satisfactory, in a qualitative way 
 there is as yet much to be desired. In most of the cases 
 we know very little of the real essentials of the phenom- 
 ena. But we may cherish the conviction, that colloidal 
 chemistry, which is yet more than one hundred years 
 behind the chemistry of crystalline substances, in the 
 future may be able to give the desired enlightment. 
 Each step forward in this dark field is, directly or in- 
 directly, of importance and value also to the arts and 
 manufactures. 
 
INDEX 
 
 PAGE 
 
 Absorption power of colloids, utilization of the 
 
 in the preparation of dry batteries 39 
 
 in the removal of disagreeable liquids 40 
 
 importance of the, in nature (soil) 40 
 
 Acheson 1 1 
 
 Acid, silicic, colloidal 2, 13, 35 
 
 silicic, hydrosol of 4 
 
 stannic, hydrosol of 4 
 
 tungstic, hydrosol of 4 
 
 tannic u 
 
 Adhesi ves, colloids as 38 
 
 Adhesive power 38, 39 
 
 Adsorption 42, 43, 44 
 
 power of colloids 43 
 
 properties of the colloids in varnish making 44 
 
 properties of the colloids in dyeing 44 
 
 laws of 46 
 
 prevention of 43 
 
 Aggregated dispersed system (See also : Suspension) 14 
 
 Aggregation, irreversible state of 13 
 
 reversible state of 13 
 
 Agriculture, colloids in 57 
 
 Alcosol 4 
 
 Aluminium hydroxide, hydrosol of 4, 10 
 
 Amicroscopic particles 7 
 
 Arsenious sulphide, hydrosol of 4 
 
 Batteries, diaphragms in storage 42 
 
 Bechhold, H 52 
 
 Beer, protective colloids in 53 
 
 influence of water on the quality of 53 
 
 Bemmeln, J. M. van 40, 58 
 
62 INDEX 
 
 PAGE 
 
 Benedicks, C 22 
 
 Berlin blue, hydrosol ot 4 
 
 Biltz, W 45, 46 
 
 Blake, J. C 17 
 
 Bredig, G 7, 17 
 
 Brewing industry, colloids in the 52 
 
 Casting glass-melting pots, Weber's process of 33 
 
 Cell-structure 2 
 
 Cell walls, plant, as colloidal diaphragms 41 
 
 Cement, colloidal 36 
 
 hardening of, in sea-water 38 
 
 Michaelis' theory of the hardening process of hydraulic 35 
 
 Stern's theory of the setting of 35 
 
 Ceramic industry, colloids in the 32 
 
 Clarifying agents in the purification of water and sewage.... 56 
 
 Clay, liquefaction of 34 
 
 Coloration, glaze 22 
 
 interpretation of the process of, in gold ruby glass 19 
 
 in copper ruby glass 21 
 
 Colors, protective colloids in the manufacture of water n 
 
 Colloid, definition of the term I 
 
 Colloids, emulsion 16 
 
 protective 16 
 
 protective, in beer 53 
 
 protective, in fine mechanical suspensions n 
 
 suspension 16 
 
 as adhesives 38 
 
 as diaphragms 38 
 
 as filters 41 
 
 as glues 38 
 
 adsorption power of 43 
 
 adsorption, utilization of, in the preparation of dry bat- 
 teries 39 
 
INDEX 63 
 
 Colloids (continued) 
 
 adsorption, utilization of, in the removal of disagreeable 
 
 liquids .......................................... 40 
 
 surface development of .............................. 17 
 
 in agriculture ......................................... 57 
 
 in the absorption of liquids ........................... 39 
 
 in the ceramic industry .............................. 32 
 
 in mineral kingdom .................................. 23 
 
 in photographic technic ............................... 57 
 
 peptisation of ........................................ 33 
 
 Colloidal cement .......................................... 36 
 
 Colloidal character of textile fibers .......................... 45 
 
 diaphragms, plant cell walls as ........................ 41 
 
 silicic acid .......................................... 2 
 
 solutions ....................................... 2, 3, 7 
 
 solutions, clarification of ............................. 52 
 
 solutions, flocculation of .............................. 8 
 
 solutions of metals ................................... 4 
 
 solutions of platinum ................................. 8 
 
 solutions of silver, preparation of, by method of Lea... 12 
 
 solution of sodium ................................... 8 
 
 Concentration limit, of emulsoids ........................... 17 
 
 of suspensoids ...................................... 16 
 
 Condenser, kardioid ....................................... 5 
 
 paraboloid ........................................... 5 
 
 Copper ruby glass .......................................... 21 
 
 interpretation of the coloration process in ............ 21 
 
 Cornu, F ................................................ 23, 24 
 
 Cowper-Coles, S ........................................... 26 
 
 Crystalline antitypes ...................................... 24 
 
 forms ............................................... i 
 
 state ................................................ i 
 
 Curdling of milk ........................................... 12 
 
 Curing, see: Mellowing of porcelain clay. 
 
 Dehydration of peat by electro-osmosis ................... 40, 41 
 
64 INDEX 
 
 PAGE 
 
 Dialysis 3, 12, 42 
 
 Diaphragms, artificial , 41,42 
 
 in nature. See: Plant cell walls. 
 
 in storage batteries 42 
 
 Diffusion 41 
 
 power of colloidal solutions 15 
 
 Dispersing medium 14 
 
 phase 14, 16 
 
 Dispersed systems 14 
 
 Doelter, C 23 
 
 Ductility of pure tungsten 32 
 
 Dyeing 44, 45 
 
 theory of, by Zacharias and Biltz 45 
 
 Electro-osmosis, dehydration of peat by 40, 41 
 
 Emslander, F 52 
 
 Emulsion-colloids 16 
 
 Emulsions, viscosity of 16 
 
 Emulsoids 16 
 
 Energy, surface 17 
 
 Faraday, M 4 
 
 Fibers, colloidal character of textile 45 
 
 Filaments 26 
 
 Kuzel's process for the manufacture of metallic 29 
 
 Filters 42 
 
 gels as 41, 57 
 
 Flocculation process, importance of the, in physiological chem- 
 istry . . _ ii 
 
 Flocculation, of an amicroscopic solution of gold 7 
 
 of colloidal solutions 8, 9, 51 
 
 of hydrosols of metals 25 
 
 of suspension-colloids 16 
 
 Foams 17 
 
 Freundlich, H 46 
 
 Fulling 46 
 
INDEX 65 
 
 PAGE 
 
 Gel ^ 4, 12, 14, 23, 24, 26, 29, 32 
 
 Gels, as diaphragms 41 
 
 as filters 41 
 
 distribution of, in mineral kingdom 24 
 
 mineral. See also : colloidal cement 24 
 
 soap 51 
 
 solid fibers as 45 
 
 Germs, formation of gold 19, 20 
 
 in spoiled ruby glass 21 
 
 Glass-melting pots, Weber's process for the manufacture 
 
 of, by casting 33 
 
 Glass, milky-white opaque 21 
 
 quartz I, 35 
 
 ruby 18 
 
 Glassy state I, 2 
 
 Glaze-colorations 22 
 
 Glue i, 2 
 
 fish 13 
 
 Glueing 38 
 
 Glues, colloids as 38 
 
 Gold, colloidal solution of 4, 5 
 
 flocculation of an amicroscopic solution of 7 
 
 preparation of colloidal solutions of, by the method of 
 
 R. Zsigmondy 4 
 
 ruby glass 18 
 
 ruby glass, interpretation of the coloration process in.. 19 
 ruby glass, discernment of the ultra-microscopical gold- 
 particles in, by Siedentopf and Zsidmondy 18 
 
 ruby glass, preparation of genuine 18 
 
 Goldschmidt, F 51 
 
 Graham, Th I 
 
 Graining of soap 51 
 
 Graphite, protective colloids in the preparation of, as a lubri- 
 cating material 1 1 
 
66 INDEX 
 
 PAGE 
 Greases, lubricating 53 
 
 Hardening, Michaelis' theory of the, process of hydraulic 
 
 cements 35 
 
 of cement in sea-water 38 
 
 Hide, animal 47 
 
 fiber, swelling up of 47 
 
 Holde, D 54 
 
 Honey-comb structure 2, 12 
 
 Hydrosol, of aluminium hydroxide 4 
 
 of Berlin blue 4 
 
 of gold ii 
 
 of iron hydroxide 4 
 
 of iron in the purification of water and sewage 55 
 
 of metals, Bredig's method of preparation of 7 
 
 of metals, flocculation of, in the preparation of gold 
 
 and silver mirrors 25 
 
 of silver 8 
 
 of stannic acid 4 
 
 of tungstic acid 4 
 
 Ions, precipitating power of 10 
 
 Iron carbide 22 
 
 Iron salts in tanning 48, 49 
 
 Iron tanning 49 
 
 Jelly i, 2 
 
 inorganic 2 
 
 organic 2 
 
 Kaolin, Putrefaction process in 32 
 
 Kardioid-condenser 5 
 
 Ultramicroscope 22 
 
 Keg residuum 5 2 
 
INDEX 67 
 
 PAGE 
 
 Keppeler, J 34 
 
 Kuzel, H 29, 57 
 
 Lamps, incandescent 27 
 
 metallic filament 27 
 
 osmium 28 
 
 osra 31 
 
 tantalum 27 
 
 tungsten 26 
 
 tungsten, manufacture of 26 
 
 siriuscolloid 31 
 
 Lea, C " 12 
 
 Leather, chrom-tanned 48 
 
 Lighting industry, aspiration of 27 
 
 Liquefaction of clay 34 
 
 of soap 51 
 
 Liquid state 2 
 
 Lottermoser, A 21, 31, 32 
 
 Lubricating greases 53 
 
 Luppo-Cramer ^ 59 
 
 Magnitude of ultra-microscopical gold-particles. 6 
 
 Malt-residuum 52 
 
 Martensite 22 
 
 Medium, dispersing 14 
 
 Mellowing of porcelain clay 33 
 
 Membrane, parchment 3 
 
 Mercury, colloidal 1 1 
 
 Metal alloys 22 
 
 Metals, colloidal solutions of, in the preparation of gold and 
 
 silver mirrors 25 
 
 preparation of hydrosols of, by the method of Bredig. . 7 
 
 Michaelis, L 44, 45 
 
 Michaelis, W 35, 36 
 
68 INDEX 
 
 PAGE 
 
 Micron 6 
 
 Microscope, ultra- 5, 6 
 
 Migration-sense 10 
 
 Milk, curdling of 12 
 
 Miller, E. J 46 
 
 Mirror, gold 25 
 
 hollow metallic 26 
 
 hollow metallic, manufacture of, by the method of Cow- 
 per-Coles 26 
 
 silver 25 
 
 Molecule of chloroform 6 
 
 of soluble starch 7 
 
 Molecular dispersed system. See also : True solutions 14 
 
 Nicol-prism 15 
 
 Nile, silt of the 59 
 
 Opal 23 
 
 Organic jellies ^ 2 
 
 Ore-bed 24 
 
 Osmium lamps, preparation of filaments for 28 
 
 Osmond, F 22 
 
 Oxy-hydrogen flame I 
 
 Paraboloid condenser 5 
 
 Parchment membrane 3 
 
 Particles, amicroscopic 7 
 
 starch 6 
 
 ultra-microscopic 6, 16 
 
 Pearlite 22 
 
 Peat, dehydration of, by electro-osmosis 40, 41 
 
 molds 40 
 
 pressing of 40 
 
INDEX 69 
 
 PAGE 
 Peptisation of colloids 13, 33 
 
 Weber's application of the, in the manufacture of glass- 
 melting pots by casting 33 
 
 Percolation 42 
 
 Permeability 42 
 
 Pharmaceutical industry, protective colloids in the u 
 
 Phase, dispersed 14, 16 
 
 Phosphorus, yellow 4 
 
 change of white, into red 22 
 
 Protographic technic, colloids in the 59 
 
 Physiological chemistry, importance of flocculation process in. n 
 
 Pickling 49 
 
 Plant cell walls as colloidal diaphragms 41 
 
 Platinum, colloidal solution of 8 
 
 Pohl, E 59 
 
 Porcelain clay 32 
 
 storing of 32 
 
 Potato-flour as a soap filler 52 
 
 Power, adhesive 38, 39 
 
 diffusion, of colloidal solutions 15 
 
 Procter, H. R 49, 50 
 
 Protective-colloids 1 1 
 
 in mechanical suspensions n 
 
 Protein, coagulation of 12 
 
 solution of II 
 
 Psilomelane 24 
 
 Purification of water and sewage 56 
 
 Putrefaction processes , 58 
 
 in kaolin 32 
 
 Quartz-glass I, 35 
 
 Receipt for making a varnish 44 
 
 Rock-crystal I 
 
7O INDEX 
 
 PAGE 
 
 Rock-salt, Siedentopf's explanation of the coloration of 21 
 
 Rohland, P 33, 35, 38, 56 
 
 ruby-glass 18 
 
 gold 18 
 
 preparation of genuine 18 
 
 copper 21 
 
 Salt, Siedentopf's explanation of the coloration of rock 21 
 
 Salting, see : graining of soap 
 
 Sapphires 23 
 
 Schweikert, L 55 
 
 Schwerin, Prince Botho 41 
 
 Setting of cement, Stern's theory of 37 
 
 Sewage-purification 55 
 
 biological 57 
 
 chamber process of 56 
 
 chemical 55 
 
 Shrinking of colloids in the drying kiln 35 
 
 Siedentopf, H 5, 6, 18, 21, 22 
 
 Silicic acid, colloidal 2 
 
 Silt of the Nile 59 
 
 Silver, hydrosol of 8, 1 1 
 
 preparation of colloidal, by the method of C. Lea 12 
 
 Slime 14 
 
 Soap, gel 51 
 
 fillers 51 
 
 manufacture, colloids in the 50 
 
 Sodium, blue colloidal solution of 8 
 
 silicate I, 3 
 
 Soil, binding capacity of, for nourishable materials 58 
 
 colloids in the 24 
 
 importance of the water absorption ability of colloids 
 
 in 40, 59 
 
INDEX 71 
 
 PAGE 
 
 Sol 4 
 
 irreversible 13 
 
 keeping qualities of metallic 8 
 
 reversible 13 
 
 Soldering 38 
 
 Solution 4 
 
 colloidal 2, 3 
 
 colloidal, of metals 4 
 
 colloidal, of gold 8 
 
 Solvent 14 
 
 Soot, suspension of, in water 1 1 
 
 Spar, fluor 21 
 
 Spraying, electrical 17 
 
 Sprinkling filters 57 
 
 Stannic acid, hydrosol of 4 
 
 Starch-particles 6 
 
 State, amorphous 2 
 
 colloidal I, 2 
 
 crystalline T 
 
 glassy I 
 
 liquid 2 
 
 solid non-crystalline 2 
 
 of aggregation, irreversible 13 
 
 of aggregation, reversible 13 
 
 of rest of silicic acid 2 
 
 Stern, E 36 
 
 Stiasny, E 47, 49 
 
 Stones, precious 23 
 
 Structure, cell 2 
 
 honey-comb 2, 12 
 
 Sub-microscopical particles 6 
 
 Sugar, beet, manufacture 41 
 
 Surface development of colloids 17 
 
 Surface energy 17 
 
 6 
 
72 INDEX 
 
 PAGE 
 
 Suspension 14 
 
 colloids 16 
 
 colloids, flocculation of 16 
 
 mechanical 1 1 
 
 porcelain clay 6 
 
 Suspensoids 16 
 
 concentration limit of 16 
 
 System, aggregated dispersed. See also : Suspensions 14 
 
 dispersed 14 
 
 molecular dispersed. See also : True solutions 14 
 
 Swedberg, Th 8 
 
 Swelling value 9 
 
 Tannic acid 1 1 
 
 Tanning 47 
 
 essence of any, process 49 
 
 fat 49 
 
 iron 49 
 
 iron salts in 49 
 
 mineral 48 
 
 Tannins, extraction of 47 
 
 vegetable 47 
 
 Tantalum 27 
 
 lamps 27 
 
 lamp, preparation of filaments for 28 
 
 Textile-fibers 2 
 
 fibers, colloidal character of 45 
 
 Topaz, smoky, yellow 23 
 
 Toxins ii 
 
 Tridymit 35 
 
 Troostite 22 
 
 True solutions 3, 14, T 5 
 
 Tungsten 27, 32 
 
 ductility of pure 3 2 
 
 oxy-chloride 28 
 
INDEX 73 
 
 PAGE 
 
 Tungstic acid, hydrosol of 4 
 
 Tyndal effect 15 
 
 Ultra-microscope 5, 6 
 
 in the examination of mineral oils, etc 54 
 
 Ultra-microscopic particles 6, 16 
 
 of gold, Siedentopf and Zsigmondy's experiment to dis- 
 cern, in gold ruby glass 18 
 
 Varnish, receipt for making of a 44 
 
 making, adsorption properties of the colloids in 44 
 
 Viscosity of emulsions 16 
 
 Visibility, limit of, of metallic particles 7 
 
 Waterglass, (See Sodium silicate.) 
 
 Weber, E 33 
 
 Whitney, W. R 17 
 
 Witt, O. N 45 
 
 Zacharias, P. S .45, 46, 49 
 
 Zsigmondy, R 4, 6, 7 16, 18 
 
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