Dr. Bolley on the Theory of Dyeing. 507 



estimated, as sufficiently appears from the foregoing short histo- 

 rical summary. 



2. It must be attributed to an oversight that, in Erdmann's 

 essay, no mention is made of the experiment the particulars of 

 which I communicated on a former occasion, " On the Dyeing 

 of Amorphous Cotton*/' Mittenzwey has, it is said, investi- 

 gated the beliaviour of disorganized cellulose towards mordants 

 especially alum, in order to decide the question " whether the 

 structure of cotton fibres is essential to the process of dyeing, 

 as is assumed in W. Crum's theory among others." This ques- 

 tion is rightly answered in the negative, as, however, it had 

 already been by myself as early as the spring of 1858t. The 

 passage which touches on this subject is as follows : — " I can, in 

 the present communication, only shortly mention that from this 

 behaviour the conclusion maybe drami,that the structure of cotton 

 fibres has no connexion with their power of taking a dye. This 

 view, as is well known, is opposed to several theories which have 

 been advanced concerning the dyeing process (to W. Crum's for 

 example)." 



3. The result, that cotton (amorphous or organized) neither 

 unites with alum nor separates alumina nor a basic salt from it, 

 is confirmed by my experiments on the behaviour of fibres 

 towards that salt. 



4. In Erdmann's treatise it is said, "An alum solution is 

 chosen, not only because it is one of the commonest mordants, 

 but especially because it is not decomposed by heat.''' The last 

 reason may stand ; but to the first we must say that alum is by 

 no means one of the commonest mordants employed in cotton-dyeing. 

 On the contrary, the mordants employed, almost without excep- 

 tion, in the operations of the cotton-dyer, are either the so-called 

 neutral alum (that is, alum partly decomposed with soda), or 

 acetate of alumina, or sulphate of alumina, or a soap-bath after 

 alum, &c. This circumstance is indeed noticed in another part 

 of Erdmann's treatise ; but then it is added, " This explanation 

 does not, however, serve (that is, the deposition of a basic salt 

 from the aluminous mordant employed) when cotton is prepared 

 for dj'cing with a mordant of common alum, which does not yield 

 any basic salt to the fibre, and which can be completely washed 

 out again." If, however, it never, so to speak, occurs in prac- 



* Ann. der Chem. und Pharm. vol. cvi. p. 235, and thence transcribed in 

 O. L. Erdmann's Journ.fiir Prakt. Chemie, vol. Ixxiv. p. 381. 



t In sujiport of tliis view, I have since, just as Professors Erdmanu and 

 Mittenzwey liave done, mordanted and dyed with different decoctions 

 of dye-woods, sulphate of baryta and other pulverulent mineral bodies, and 

 exliiljited the preparations at the sitting of the Ziu'ich Society of Natural 

 Philosophy. 



