THE THEORY O F DYEING, IV BY WILDER D. BASCROFT
In the first paper of this series tables were given1 showing that the amounts of tannin taken up by wool2 and by cotton3 vary continuously with the concentration of the aqueous solution, no definite compound being formed. Wool takes up more tannin from hot solutions than from cold ones; but the reverse appears to be true for cotton.? Since tannin is an acid mordant, the amount adsorbed should be less in alkaline solutions and greater in acid solutions if no other factor comes in. Addition of alkali cuts down the amount of adsorbed tannin almost to zero. Addition of acetic acid5 increases the adsorption which, however, passes through a maximum6 when the concentration of the acid becomes high. Sulphuric acid decreases the adsorption of tannin by cotton, and hydrochloric acid has practically no effect a t all. These differences with different acids are undoubtedly connected with the relative adsorptions of these acids by cotton and we cannot hope for a complete understanding of the matter until somebody secures data with special reference to this point. The increased adsorption due to salts seems to depend more upon a decrease in the apparent solubility of the tannin than upon any effect due to adsorbed ions, though here again satisfactory data are entirely lacking. I have been unable t o find any quantitative data in regard to the adsorption of oil mordants by cotton. In view of what we know about the adsorption of hydrochloric and sulphuric acids by cotton, there is no reason for assuming the existence of any compounds in the case of oleic acid or sulphonated Turkey red oils. Bancroft: Jour. Phy-s. Chem., 18, 4 (1914). Pelet-Jolivet: “Die Theorie des Farbeprozesses,” 79 (1910). Sanin: Zeit. Kolloidchemie, IO, 82 (1912). Knecht and Kershaw: Jour. Soc. Dyers, 1892,40;Ganswindt: “Theorie und Praxis der modernen Farberei,” 2 , 216 (1903). Knecht, Rawson and Loewenthal: “A Manual of Dyeing,” I, 188(1910). Dreaper: “The Chemistry and Physics of Dyeing,” 161 (1906).
The Theor31 of DyeiHg
51
As yet only a few lakes have been studied carefully from the viewpoint of colloid chemistry; but these few cases are enough to clear up matters very much. Biltzl has studied the behavior of alizarine with hydrous chromic oxide and hydrous ferric oxide to determine whether chromic and ferric alizarates are formed. In Table I are given the data for alizarine red SW and chromic oxide. To 5.460 cc of chromium hydroxide gel ( = 0.1106 g Cr203) there were added 2 0 0 cc aqueous alizarine solution, containing 0.8 percent XaOH ; the mixture was boiled for an hour and a half. TABLEI Conc. solution glliter
Grams dye adsorbed per gram oxide
0.00034
0 . I75
0.0031 0.0052 0.0078
0.306 0 358 0.402
Grams dye adsorbed per gram oxide
g/liter
0.0188 0 034'
'
0.565 0 740 0.904 1 50
0.0500 0
417
There is a continuous increase in adsorption with increasing concentration, and the data can be represented fairly well by an exponential formula ( ~ , r n = ) ~ 2.1 c where ~ , ' mis the amount of alizarine per gram of oxide and c is the equilibrium concentration in the solution. Biltz, therefore, concludes very properly that no chromium alizarate is formed. The data for alizarine and ferric oxide are given in Table 11. To 2 . 2 2 0 cc ferric oxide gel ( = 0.1141g FeOa) there were added 2 0 0 cc of varying amounts of alizarine dissolved in 0.8 percent NaOH. The mixture was shaken for 6-8 hours. TABLEI1 _ _ ~ __ _ _ __
~
~
~
Conc. solution gjliter
Grams dye adsorbed per gram oxide
0.067; 0.0964 0 . I34 0.00234 0.00242 0.308 .~ ~ _ _ _ _ ~ 0.0011~ 0.00201
Grams dye adsorbed per gram oxide
Conc. solution g/liter
0.002 6 I 0.0028 I 0.00326 0.00369
Ber. deutsch. chem. Ges., 38, 4143 (1905).
0.6jj I .OI ~
I
.6gj
2.j7
11-ilder D . Baiiuojt
52
While the concentration in the solid is increasing from 0.134 to 6.01 the concentration of the solution \-aried only from 0.00234 to 0.00281. Biltz was of the opinion that this was really to be considered as a constant concentration, so he ran another set of experiments with 1 . 0 2 j cc ferric oxide gel ( = o . O g S I j g Fe,O,). The data are gil-en in Table 111. TABLE I11 Conc. solution gl liter 0 00313 o 00314 o 003jj o 00417
-
Grams dye adwrbed per gram oxide
Coiic. solution
o 236 0 579 1 425
o 0125 0
0708
2.44
0
I59
g!liter
0 OOj2
gram oxide
3 27 4 73 6 16 6 57
From these experiments, Biltz concluded that we really have a ferric alizarate consisting of one molecule Fe203t o three molecules alizarine. He accounts for the fact that the concentration of the solid phase continues to rise by postulating that the amorphous, hypothetical ferric alizarate adsorbs alizarine. This might be legitimate if the amount of adsorption were small; but it runs to an excess of forty percent of alizarine, stopping there merely because no more experiments were made. The only proper deduction to be made from these experiments is that there is no evidence of the formation of ferric alizarate and that we are dealing with a con’tinuously varying adsorption. This is confirmed by the fact that gelatinous ferric oxide takes up six times as much alizarine as a granular oxide. If we had a definite compound, the granular oxide should have shown it clearly. Of course, I do not intend to deny the possibility of ferric alizarate and chromic alizarate existing under certain conditions but merely that they are not formed under the conditions described. For instance, we do not get any hydrate of ferric oxide under ordinary conditions of precipitation; but van Bemmelenl has shown that a monohydrate can be prepared from sodium ferrite. 1
“Die Absorption.” 174 (1910)
53
The experiments of Liechti and Suidal on ferric alizarate are not convincing either waq7. They mixed solutions of ferric chloride and ammonium alizarate together according to the equation Fe2C16 3C14H604(KH4)? = Fe2iC1,Hi,O4)? 6T\;H,C1, and a brownish black precipitate of ferric alizarate was thrown down. This in itself means nothing because the precipitate would have to have this composition unless the solution were to become acid or alkaline. If the solution had become either acid or alkaline, some of the alizarine or of the iron would have been dissolved. “If the precipitate is well washed, dried, and extracted with ether, a moderately large amount of alizarine dissolres out and the residue, on re-drying, forms a black powder which, on analysis, gives the formula Fe203(C14H603)2.5.” The extraction of alizarine by ether is not proof that we have or have not a compound. Alcohol will take cupric chloride out of the definite compound CuCl2.zH20.zKC1and will extract adsorbed iodine from charcoal. If the extraction was carried on long enough, the ether ought to have taken out all the alizarine in excess of the next compound supposing there to be any. On that basis the system is behaving like one in which we have adsorption and no compounds. “If pure ferric hydrate, freshly prepared and well washed, is stirred up with a quantity of alizarine paste and water in proportions corresponding to the formula Fe203.3C14Hs04, and the mixture gradually heated to IOO’, and then boiled five hours, the water lost by evaporation being replaced, a precipitate is produced which is soluble to some extent in distilled water, giving a violet solution. If this is washed, dried, and then extracted with ether, the ether dissolves out a large quantity of alizarine. The residue, redried and analyzed, has the formula (Fe203)3(C14H603)?. It is more than probable that by the long-continued boiling, a part of the ferric hydrate loses some of its hydroxyl groups as water, thus forming only a very basic compound, which may also be regarded as
+
Jour. Soc Chem. I d . , 5 , 523 (1S86)
+
Wilder D. Bancroft
54
a mixture of a less basic compound with ferric oxide.” Since there is no such compound ordinarily as ferric hydroxide, the non-existent hydroxyl groups cannot be lost. If this were ferric alizarate and ferric oxide, both sets of experiments on extraction with ether are grossly inaccurate. We do not have to question the accuracy of Liechti and Suida’s experimental work if we postulate adsorption. On heating for five hours, the hydrous ferric oxide coagulated somewhat and had less adsorbing power. Consequently, more alizarine was extracted with ether. Pelet-Jolivetl has made some experiments on the dyeing by crystal ponceau of wool mordanted with alum. The data are given in Table IV. TABLEIV 2 grams wool mordanted with alum Volume of solution = 2 0 0 cc A = crystal ponceau (sodium salt) B = crystal ponceau 0.25 g NazS04.IoHzO Time = j days at room temperature
+
I
Total dye milligrams
Dissolved dye A milligrams
Adsorbed dye A milligrams
~
1
___.__
113.8 189.8 303.6 4’7.5 569.3
37.8 107 . 4 214.8
76 82.4 86.8
-
-
-
I
-
~
Dissolved dye B milligrams __ -~
42.2 116.4 220.8 329.3 479.9
1
,
Adsorbed dye B milligrams
71.6 73.4 82.8 88.2 89.4
These results are perfectly normal. It is a clear case of adsorption and the sodium sulphate cfits down the amount of dye taken up, which is what it should do. Quite different results were obtained at 90’. The data are given in Table V. I n this case the amount adsorbed is practically independent of the concentration in the bath and it seems probable that a definite compound is formed, though one would have liked to have seen some experiments made with less than 140 milligrams of crystal ponceau. Pelet-Jolivet succeeded in preparing ___._
-~
-
“Die Theorie des Farbeprozesses,” 2 1 3 (1910)
a crystalline aluminum salt of crystal ponceau. It is evidently a definite compound and it may very likely be formed under the conditions of the experiments at 90'. TABLE V grams wool mordanted with alum zoo cc solution of crystal ponceau Time = 2 hours a t 90' 2
-
~~-
~~~
~~~
Total dbe milligrams
182.7 292.3
40' , 9
548.I 730.8
.
Dissolved dye milligrams
Adsorbed dye milligram?
42.3 154.7 261, I 413.7 592.4
130.4 137.6 140.8 134.4 138.4
A somewhat similar phenomenon seems to have been observed by Baylissl with alumina and Congo red. "If to a solution of Congo red an excess of hydrochloric acid be added, the blue free acid is precipitated; but if the precipitate be suspended in water and dialysed, a deep blue colloidal solution is formed, as described in a previous paper.? Freshly precipitated and well-washed aluminum hydroxide is suspended in water, and a small quantity of the blue acid colloid is added. A dark blue precipitate falls, which can be washed by decantation, best with the aid of the centrifuge, and again suspended in water. It remains dark blue, and might hastily be supposed to be merely an aggregated portion of the acid colloid. That this is not so, and that the body contains also aluminum hydroxide, is shown at once by its beha\ 'lor on warming. When this is done, a red solution is rapidly formed, which, on cooling, deposits flakes of a red substance, while the solution itself becomes pale in color. The same change occurs at room temperature, but very slowly. It is evident that we have here, in the adsorption compound formed a t first, acid and base existing side by side but uncombined. Proc. Roy. SOC.,84B, 81 (1911). Ibid., SIB,2 7 0 (1909).
56
W i l d e r D. Bancrojt
On heating, chemical combination takes place with the formation of the aluminum salt of Congo red, which, like all the salts of this acid, is of a red color. Congo red is a convenient body for the present purpose, since the salts are of a color which is so different from that of the acid. “The precise manner in which combination is caused to take place by the action of heat does not immediately concern us; the most important fact is that a body can be prepared containing acid’and base uncombined. The mode of formation of the adsorption compound is, it will be noticed, t o all intents and purposes a case of the mutual precipitation of electropositive and electronegative colloids, in this case, aluminum hydroxide and Congo-red acid, respectively. “ The dry preparation of aluminum hydroxide supplied b y Kahlbaum can be used, but, owing to the large size of the grains, it is not very effective. It is important that, whatever preparation be used, no free caustic alkali must be present, otherwise the red salt of the dye with this alkali is formed a t once. The adsorption compound, if formed at all, only exists for an infinitesimally short time, owing to the rapidity of the chemical reaction. “ I n order to obtain as large a relative surface of the hydroxide as possible I have made various hydroxides in colloidal solution, prepared by dialysis of solutions of salts which are hydrolytically dissociated. Ferric chloride, aluminum acetate, zirconium and thorium nitrates have been treated in this way. With ferric hydroxide, although the result of the experiment is quite distinct, the change of color on heating is not so obvious as with a colorless hydroxide. Aluminum hydroxide is good, but is unstable when sufficiently dialysed. The best of all those with which I have worked are the colloidal hydroxides of zirconium and thorium, which are beautifully clear and colorless solutions. The clearness is of course an indication of the minute size of the suspended particles. Like all solutions prepared in the way described, they still contain, even after prolonged dialysis, traces of the original acid. If this is present in too large a proportion, no red salt is formed
The Theory
OJ
Dyeing
57
even on heating the adsorption compound. This fact was shown in a striking way in my first preparation of zirconium hydroxide, which had been insufficiently dialysed. In this case, although the adsorption compound was duly precipitated, it did not become red on heating. When the adsorption compound was suspended in water and subjected to further dialysis, it was noticed to be turning slightly reddish a t room temperature; on boiling, the change to the red salt is immediate. The compound with thorium hydroxide seems to require heating for a longer time before combination occurs than do the others; but this may be merely owing to the presence of more acid in the particular preparation.” It is clear that the blue lake is not a definite compound. Bayliss assumes that the red lake is the aluminum salt adsorbed by alumina but the only proof of this that he offers is the color-presumably because it did not occur to him that anybody would question the conclusion. On the assumption of the formation of an aluminum salt, I do not see why the presence of a trace of free acid should have so much effect. As long as there is a sufficient excess of alumina, one would expect a portion of the excess to combine with the Congo red. This difficulty disappears if we assume, as Blucher and Farnaul do that “the red Congo acid, although instable in aqueous suspension, is stabilized by the hydrous aluminum oxide.” This is in accord with the stabilization of rosaniline and other color bases by wool or silk.* Gilbert3 has recently made a study of the copper lakes of eosine. He found that a definite, crystalline copper eosinate could be prepared; but that it was a different substance from the so-called copper eosinate prepared by a metathetical reaction between sodium eosinate and copper sulphate. Although the lake is fairly constant in composition when prepared in this way, it always contains an excess of copper when an excess of copper salt is employed. LThen hydrous copper Jour.Phys Chem, 18,634 (1914). I b i d , 18, 128 (1914) Jour.Phys Chem , 18,586 (1914).
* Bancroft
58
Wilder D. Bancroft
oxide is treated with ether solutions of eosine in varying amount the typical adsorption curve is obtained and there is no indication of a definite compound. Under these conditions the total amount of eosine taken up is only about one-tenth of the amount necessary to form copper eosinate. A wider range of concentrations was obtained by starting with colloidal hydrous copper oxide and colloidal eosine (free acid). The ratio of copper to eosine was varied between two molecules of copper to one of eosine and two molecules of eosine to one of copper. All these lakes behave like the lake with the copper and eosine in equivalent quantities and all can be carried into colloidal solution. In presence of ether small amounts of certain salts cause decomposition of the lake into hydrous copper oxide and eosine. This seems to be analogous to Bayliss’ results with Congo red and alumina where small amounts of acid prevent the development of the red color. With magnesia and eosine solutions the typical form of adsorption curve is obtained. The evidence is convincing that none of the ordinary eosine lakes are compounds at all and that lead eosinate, for instance, does not exist under the ordinary conditions of precipitation. Davisonl found that the acid dyes, Fast Green, Acid Green, Acid Violet, Croceine Orange, Alizarine Yellow, and Fast Blue were adsorbed less by alumina when sodium sulphate was present in the bath than when it was not. This is what happens when wool is substituted for alumina and has been discussed in detail in the first paper of this series. Pelet-Jolivet2 has shown that methylene blue is adsorbed by silica, the amount taken up varying with the previous treatment of the silica in a manner quite similar to that observed by Liechti and Suida with iron and alizarine. Dreaper3 believes that magenta and tannin form a definite compound; but he gives no proof for this and he admits that one hundred parts of the alleged magenta tannic acid compound will adJour. Phys. Chem., 17, 748 (1917). “Die Theorie des Farbeprozesses,” 71,205 (19x0). a “The Chemistry and Physics of Dyeing,” 244 (1906).
T h e Theory of Dyeing
59
sorb at least up to 160 extra parts of tannic acid if the latter be present in excess. It is, therefore, safe to consider the case of magenta and tannin as one of adsorption. Saninl considers that the basic dyes form definite compounds with tannin when the dye is in excess, but admits that tannin is adsorbed when the tannin is in excess. He gives no proof for the existence of a definite compound a t any time except the fact that he can write a formula for the product and Gilbert’s work with the copper-eosine lakes shows how little reliance is to be placed on that test. The mordanting of basic dyes with acid dyes and Yice rersa is of course nothing but a case of adsorption. Though the data are not as complete as one would like, it seems to me that they are sufficient to justify the conclusion that in general the dye is adsorbed by the mordant and does not form any definite compound with it. We have next the problem of the fixing agents. Sodium phosphate is used for fixing alumina, sodium arsenate for iron, lime for alizarine and alumina, tartar emetic for antimony. Putting it more broadly we can say that phosphates, arsenates, silicates, oleates, and tannin are used as fixing agents for the metallic mordants while the metallic mordants act as fixing agents for tannin and the oleates. Are we dealing with definite compounds in these cases or do we have the precipitation of a positive by a negative colloid and eice versa? Mecklenburg has studied the case of tin phosphate? and ferric a r ~ e n a t e . ~He found that a regular adsorption curve was obtained when stannic acid was treated with phosphoric acid and that there was no evidence of any formation of stannic phosphate under the conditions of the experiment. He also found that different samples of stannic acid took up different amounts of phosphoric acid from which he was inclined to deduce the existence of five stannic acids; but that of course was absurd. It would have been easy to have preZeit. Farbenindustrie, IO, 97 (1911);Zeit. Kolloidchemie, 13, 305 (19x3). (1912). Zeit. phys. Chem., 83, 609 (1913).
* Zeit. anorg. Chem., 74, 2 0 7
Wilder
60
D.Bancrojt
pared twenty stannic acids if this were the only test. This is merely another instance of the general phenomenon that the degree of the adsorption varies with the conditions under which the adsorbing agent is prepared. Exactly similar results were obtained with ferric oxide and sodium arsenate. I n all cases adsorption curves were obtained, but the degree of adsorption varied with the previous history of the ferric oxide preparation. In these two cases, which have been studied, we find that tin phosphate and ferric arsenate are not formed. I t is, therefore, probable that when a corresponding study of aluminum phosphate, stannate, and silicate1 shall have been made, it will appear that these are also cases of adsorption. This does not preclude the formation of these substances as definite compounds under certain conditions. As a matter of fact crystallized aluminum orthophoschate has been prepared by de Schulten2 and crystallized ferric arsenate by Hautefeuille and h l a r g ~ t t e t . ~Wislicenus and Muth4 have studied the action of tannin solutions on fibrous alumina. They find that the amount of tannin taken up increases rapidly at first with the concentration of the solution and then reaches a practically constant value. They deduce from this the existence of an aluminum tannate, but this is hardly justifiable. They have merely found what others have found in undoubted cases of adsorption that the adsorption apparently reaches a limiting value. Experiments with differently prepared samples of alumina would undoubtedly have given different figures. It is not possible a t present to account satisfactorily for the action of lime in the case of alizarine with iron or alumina mordant. Liechti and Suida6 believe that definite compounds are formed; but their experiments were done a t a time when
?
Cf. Stremme: Jour. Chem. SOC.,94 11, 1041 (1908); IOO 11, 406 (1911). Comptes rendus, 98, 1853 (1884). Ibid., 106,135 (1888). Zeit. Kolloidchemie, 2, XVIII (1908). Schmidt: Zeit. phys. Chem., 74, 699 (1910). Jour. SOC.Chem. Ind., 5 , 52j (1886).
The Theory o j Dyeing
61
that was the only possible explanation. If normal calcium alizarate is mixed with perfectly clear lime-water in a closed vessel, and allowed to stand for some time, a portion of the calcium alizarate dissolves, forming a ruby-red solution. If this solution is then boiled for only a short time, a brownish red precipitate separates, whilst the supernatant liquid becomes quite colorless, and contains much free lime. This precipitate is soluble on continued washing with water, forming a violet solution. On analysis, it proves to be a basic calcium alizarate, having the formula CaO.CI4H6O3.Ca0. “This is the compound originally dissolved in the limewater, the behavior of which solution, on warming, points to the existence of a much more basic calcium alizarate in the cold solution. Experiment shows, indeed, that about 5 ~ 0 1 s CaO can hold in solution I mol of the basic calcium alizarate.” There is nothing in this to show that we do not have a peptonization by lime with coagulation on boiling. The statement that the precipitate is soluble on continued washing with water sounds as though peptonization were taking place as the coagulating agent was washed out. The compound (A1203.CaO(C14H603)4) is readily produced as a fine dark red precipitate by the action of calcium acetate and aluminum acetate on ammonium alizarate. This lake is soluble on continued washing with water, and is also partially soluble in ammonia. The ammoniacal s o h tion, when filtered and evaporated to dryness, leaves a residue which, according to analysis, possesses the formula A1203(C14H603)4, while the portion insoluble in ammonia is found to have the formula A1203.CaO(C14H603)3, the original lake having the formula A1203.CaO(C14H603)4. It appears, therefore, that ammonia dissolves out alizarine and normal aluminum alizarate, leaving behind an aluminum calcium alizarate, which is more basic than the normal alizarin red.” These experiments are open to the same criticisms that were made to the experiments on the iron alizarates. In their present form they are of no value whatsoever. It is also not quite clear how aluminum alizarate can be removed from an
Wilder D. Bancroft
62
aluminum calcium alizarate and leave the ratio of alumina to lime the same as before. It has been noticed’ that caustic alkalies do not redissolve hydrous aluminum oxide or hydrous chromium oxide if the precipitation has been made in presence of a magnesium salt. There is nothing to show whether a similar result is obtained in presence of a calcium salt; but it seems to me that experiments along this line would be profitable. Sanin2 has made some measurements on the reaction between tannin and antimony salts. He claims to find three different salts depending on the conditions of the experiment. I n dilute solutions with no excess of potassium antimony tartrate, there is precipitated the salt (Cl4H90&Sb0H. If an excess of the antimony salt is taken the salt has the composition CI4H9O9.Sb0.At 8oo-9o0 the precipitate analyzes to (C14H9(Sb0)09)2SbOH.It is admitted that it is difficult to obtain any of these salts pure, but Sanin prefers to consider the products as mixtures of two of these definite compounds rather than as substances of continuously varying composition. He considers that the first of these three salts is one that is formed in the fabric. In a later paper Sanin3 rather weakens on this point. He admits that adsorption does occur when tannin and potassium antimony tartrate are mixed and all that he claims now is that it is also possible to get definite compounds if one observes certain conditions. One cannot object to this though one would like more definite proof that compounds are formed at all. The difficulty is that Sanin claims that the technical conditions for dyeing cotton with basic dyes are exactly those which lead to the formation of definite compounds and that is by no means proved. It seems to me that Sanin’s experiments are precisely analogous to those of Gilbert where he found that a lake of fairly constant Knecht, Rawson and Loewenthal: “A Manual of Dyeing,” (1910).
* Zeit. Farbenindustrie, 9, 2 ,
1 7 , 49 (1910). Zeit. Kolloidchemie, 13, 305 (1913).
2, 2 2 2 , 240.
The Theory o j Dyeing
63
composition is obtained when copper sulphate and sodium eosinate are mixed. There seems to be no sufficient reason for the present for denying the existence of definite oleates though it is possible that these substances exist only on sufferance. Knecht, Rawson and Loewenthall say that “ t h e amount of iron which is taken up by the fiber depends less on the strength of the mordanting liquor than on the amount of oil that has already been fixed in the material; the oil attracts the oxide of iron with great energy, so that it is not readily stripped from the fibre, even by comparatively concentrated sulphuric or hydrochloric acid.” This is more the behavior that one could expect in case of adsorption than in case we had ferric oleate present. It would not surprise me at all to find that no definite compounds are formed under ordinary conditions between oleic acid and alumina or iron oxide. The general conclusions are as follows: I . Tannin is adsorbed by wool and cotton, forming no definite compounds with either. Oil mordants are adsorbed by cotton. 2 . Alizarine is adsorbed both by chromium mordant and iron mordant. 3 . Alumina adsorbs crystal ponceau, Fast Green, Acid Green, Acid Violet, Croceine Orange, Alizarine Yellow, and Fast Blue. 4. Alumina adsorbs the blue form of Congo red and perhaps stabilizes the red form of the free acid. 5. The eosine lakes are cases of adsorption though definite crystalline compounds can be prepared under certain conditions. 6 . Tannin adsorbs basic colors. 7 . Silica adsorbs methylene blue. 8. Color lakes are generally cases of adsorption. Definite compounds are formed only under special conditions. 9. The mordanting of basic colors by acid colors and vice versa are cases of adsorption. “A Manual of Dyeing,”
2,
597 (1910).
W i l d e r D. Bamroft
64
IO. In most cases fixing agents act because they are colloids of the opposite sign from the mordants. 1 1 . Ferric arsenate and tin phosphate are not'formed under ordinary conditions of precipitations though both compounds are known. It is probable, though not yet proved, that aluminum phosphate, silicate, oleate, etc., are also not formed under ordinary conditions. 12. No definite statement can be made as to the action of lime on alizarine in alumina mordant; but it seems probable that the lime prevents the peptonization of the alumina. 13. There is certainly adsorption when tannin and antimony salts are brought together and the evidence as to the formation of three definite salts is not satisfactory. 14.The behavior of iron salts with oil mordants appears, to indicate adsorption though it is not safe to deny the formation of definite oleates in some cases. 15. The formation of definite compounds plays no important part in the practice of dyeing.
Cornell Unzverszty
