ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 43 
to an insoluble form. He, however, in 1895, admits that with animal 
fibres dyeing is a chemical process. The researches of P. Richard °° into 
the nature of wool and silk led him to assert the existence of an amido 
_ group in these substances which can be diazotised and the resulting diazo 
compound coupled with phenols &c. At the same time, by decomposition 
of the diazo compound, a hydroxy group is formed which can be coupled 
with diazo compounds. 
Champion’s discovery of lanuginic acid being published, Knecht ?? now 
turned his attention to this in a long series of researches that have finally 
confirmed his position as leader of the purely-chemical faction. In 1888 he 
showed that, having prepared lanuginic acid either by Champion’s method 
or by dissolving wool in barium hydrate solution, precipitating the barium 
with carbon dioxide and from the filtrate precipitating the acid with lead 
acetate, then removing the lead with sulphuretted hydrogen and evaporat- 
ing the filtrate, the resultant substance gave brightly coloured precipitates 
with dye solutions of acid and basic dyes and also with solutions of metallic 
salts. Comparing this with the facts observed: that wool and silk absorb and 
hold with a tenacity which will not yield even on boiling acids and alkalies ; 
that they also absorb dye-bases from neutral baths, leaving the whole of the 
acid from the dyestufi in the bath as ammonium salt; he deduces that 
definite chemical compounds must be formed between the colour-base (or 
under given conditions colour-acid) with some break-down products of the 
wool or silk of the nature of lanuginic or sericinic acid. With acid colours, 
the action of the acid produces in the fibre a substance capable of forming 
lakes with the acid colouring-matter. The behaviour of the fibre in 
presence of great excess of substantive dye in some experiments even 
shows the probability of combinations according to the law of multiple 
proportions. Knecht?* undoubtedly proved that in dyeing wool with a 
series of acid colours belonging to the same homologous series the amount 
of colour taken up was in exact proportion to their molecular weights ; 
hence the laws of chemical combination are obeyed. 
These convictions of Knecht have been continuously combated by 
yon Georgievics and the physicists, but a series of investigators reported 
experiments which corroborated Knecht’s observations. L. Vignon *® 
tested for the amount of heat evolved in the absorption of acids (sulphuric, 
hydrochloric, stannic) and alkalies respectively by silk, wool, and cotton, 
and found that the first fibre evolves the greatest heat, even during absorp- 
tion of salts. Cotton only evolves heat with strong acids or alkalies, and 
then only feebly ; this he explains by the fact that cotton has no nitrogen 
(citing empirical formule), 
silk = C41 Hoa2N4g056 3 wool = CygHi4oNo753 5 cotton = C,H,00;; 
and that cotton previously treated with ammonia will react evolving 
heat. He obtains a substance by treating cotton with ammonia, which 
contains nitrogen, and this substance possesses greater dyeing powers, but 
in the opinion of the writer this compound is far more likely to be a 
degradation product of cotton. Wool and silk he knows to be capable of 
3 m 1884, Soc. Ind. de Mulhouse, ‘ Aufklirung der chemischen Konstitution de 
olle.’ 
*7 Journ. Soc. Dyers and Col. 1888, p. 72; 1889, p. 71. 
*8 Tbid., 1904, p. 242. 
*° Comptes Rendus, 1890. 
