174^ BLEACHING. 



insect inhabits warm climates, and cannot be reared 

 in this country without difficulty, nor in sufficient 

 quantity for the purpose of procuring silk. The 

 south of Europe and Asia are its proper countries. 



The silk is spun by the silk-worm in the form of 

 threads of a semi-transparent matter, which it winds 

 up round itself when it passes into the crysalis 

 state. The threads, when formed, are connected 

 together by a viscous substance, from which they 

 must be separated before they can be wound off, 

 by putting them into hot water. 



The silk itself is covered with a yellow varnish, 

 which is soluble in alcaline leys ; and as this varnish 

 conceals the lustre of the silk, it is necessary to 

 detach it. Silk is itself soluble in strong alkaline 

 leys ;| care must be taken, therefore, not to injure 

 the silk in taking off the varnish. Water at a boil- 

 ing heat has no action on silk ; but steam dissolves 

 its varnish. 



In France they proceed as follows. They fill a 

 boiler with a very weak solution of caustic soda, 

 and place in a chamber connected with tlie boiler, 

 the skeins of raw silk, wound on frames ; then they 

 close the door of the chamber, and make the solu- 

 tion in the boiler boil. Having continued the 

 ebullition for twelve hours, they slacken the fire, 

 and open the door of the chamber. The steam, 

 which is always above 250° Fahr., will have dis- 

 solved the gum of the silk. The skeins are then 

 washed in warm water, wrung, and boiled a second 

 time ', then washed again several times with soap, 

 till they have acquired the necessary whiteness and 

 softness. 



It is not possible, however, to give to silk all the 

 necessary splendour by this process alone ; to com- 

 plete it, the silk must be exposed to the action of 



