TRANSACTIONS OF SECTION B. 623 



colourless rosaniline base can only give rise to the fuchaine-red colour by formatiou 

 of a salt. 



Since this time, however, the author has shown that in dyeing chemically 

 indifferent substances, such as glass and china-clay, which cannot play the part of 

 acids, the acid of the basic colour remains quantitatively in the dye-bath ; he has 

 further shown that the rosaniline base exists in a coloured form. The full force of 

 this contradiction of the chemical theory is not admitted, it having been objected 

 that many kinds of glass are slightly attacked by water, and are thus not chemi- 

 cally indifferent. The author showed many years ago, however, that this objection 

 is founded upon a total disregard of the fact that the results are of a quantitative 

 nature. 



The author remarks that whilst the attack has been directed against the strong 

 part of his work, its weak point — which is as follows — has not hitherto been 

 noticed. The fact that in the dyeing of chemically indifferent substances with 

 basic colours the acid part of the latter remains quantitatively in the bath is only a 

 proof that one has to deal with the same phenomenon which is observed in the 

 dyeing of silk and wool, and is not an indication that salt formatiou has taken 

 place between the colour base and the fibre substance ; the dyeing of glass and 

 china-clay is, at any rate, a process of absorption, and its external similarity with 

 the dyeing of silk and wool with the same colours is not necessarily a proof of the 

 identity of the two processes. The author's work was directed solely against the 

 validity ascribed to the argument repeatedly brought forward in support of the 

 chemical theory, and still leaves open the question of the nature of the processes 

 concerned in the dyeing of animal fibres with basic colours. Should it ever be 

 possible to prove the existence of chemical compounds between colour and fibre, it 

 will be most probably done in the case just referred to, but such information could 

 certainly not be obtained in the manner only lately attempted by Knecht. 



Knecht boiled out with alcohol wool and silk dyed with night-blue, and believed 

 himself forced to the conclusion that the extract contained chemical compounds of 

 the night-blue base with keratin or fibroin respectively. If the conclusion were 

 correct, it would be possible, by prolonged repetitions of the operations of dyeing 

 and extraction with alcohol, to bring about a gradual destruction of the fibre. 

 The improbability of this is obvious, and the author clearly proves the incorrect- 

 ness of Knecht's final conclusions by repetition of the work upon which they are 

 based. After precipitating the colour base and eliminating the alcohol, Knecht 

 prepared aqueous solutions from the above-mentioned alcoholic extracts, which, 

 according to his statement, possessed the property of precipitating magenta and 

 night-blue, and which he therefore supposes to contain keratin or fibroin respec- 

 tively, or chemical compounds formed from these two substances during the pro- 

 cess of dyeing. On repeating these experiments the author finds that the solutions, 

 if perfectly pure fibre material purified with alcohol has been used, precipitate 

 solutions of magenta only, and that but very slightly indeed. The same preci- 

 pitate may, however, be obtained if wool and silk are entirely left out of the experi- 

 ments ; he finds that, by precipitating the colour base from an alcoholic solution 

 of night-blue with barium hydrate and by afterwards removing the latter from 

 the solution, a liquid is finally obtained which has the property of precipitating a 

 solution of magenta. 



In this instance it is naturally quite out of the question that keratin or fibroin 

 play any part in the precipitation. 



The second principal support upon which the chemical theory rests has also 

 been given by Knecht. It was observed at an early date that molecular propor- 

 tionality between colour and fibre seems non-existent in dyeing trials ; the results 

 thus differ from those obtained in cases of ordinary chemical combination. By 

 dyeing wool in very concentrated solutions of picric "acid and similar acid colours, 

 Knecht supposed that he had established the existence of chemical compounds 

 formed in definite molecular proportions. The repetition of these experiments by 

 Perger and Ulrich has, however, shown that Knecht, in his desire to make the 

 fibre take up as large a quantity of the colour as possible, used such an excess of 

 colour that part of it was deposited as crystals upon the dyed fibre. It is therefore 



