340 SOLID PARTS OF ANIMALS. 



dens into a thread, and is then distinguished by the name of raw- 

 silk. There is another liquid which exudes from the silk at the 

 same time, and which, by solidifying, covers the thread with a kind 

 of varnish. The raw-silk as spun by the worm is rather brittle. 

 It acquires flexibility and softness by boiling it with soap and 

 some other processes, through which it passes before it is manu- 

 factured into silk cloth or ribbons or thread. 



Roard in 1807 published an elaborate set of experiments on 

 silk.* He examined the action of water, alcohol, acids, alkalies, 

 and soap upon silk, and extracted from it various substances, 

 which he distinguished by the names of gum, colouring matter, 

 and wax. His paper was valuable ; but organic chemistry had 

 not at that time made sufficient progress to enable him to make 

 a satisfactory analysis of silk. The subject was taken up by 

 Mulder in 1836.f 



To analyze silk Mulder weighed out 7 7 '2 grammes of raw 

 yellow silk, and 59*55 grammes of white raw-silk. Being wash- 

 ed in cold water that liquid was rendered yellow by the yellow 

 silk. It had dissolved the substance which constitutes the differ- 

 ence between yellow and white raw-silk. From this it would 

 appear that this substance is soluble in cold water. 



1. Both kinds of silk were now boiled in distilled water, re- 

 newed repeatedly till the water ceased to be thrown down by 

 the infusion of nut-galls. Long boiling and much water was ne- 

 cessary to free the silk from every thing soluble in that liquid. 

 By this treatment the yellow silk was rendered lighter coloured ; 

 but the white was not altered. Both had acquired a softer feel. 

 Being dried the white silk hadjost 16*75 grammes of its weight, 

 and the yellow 22-2S. Or the white silk lost 28-12, and the 

 yellow 28-86 per cent. 



The decoctions being evaporated to dry-ness over the water 

 bath, a brittle greenish coloured matter remained, not altered 

 by exposure to the atmosphere. This is the substance which 

 Roard distinguished by the name of gum. 



2. The silk was now boiled in absolute alcohol. The yellow 

 silk lost its colour. The treatment was continued as long as the 

 alcohol acquired any colour from the yellow silk. The alcoho- 

 lic solutions from both silks were distilled till only four ounces 



* Ann. de Chim. Ixv. 44. 



f Poggendorf's Annalen, xxxvii. 594, andxl. 260. 



