An Effajt o?i Bleaching. 



Of Si/L 



Silk is a diaphanous matter fpun by a -caterpillar, and 

 formed of a fubitance contained in its Body, which becomes 

 hard in the air. This infect inhabits warm climates, being 

 indigenous in Alia : it was naturalized in Europe about the 

 time of the downfal of the Roman empire. 



The filaments prepared by the filkworm are rolled up in a 

 cod or ball. In the flate in which we find it, it is covered 

 with a yellow varnifh, which deftroys its brilliancy and ren- 

 ders it rough. Silk by chemical analyfis gives carbonate of 

 ammonia and oil ; water at a boiling heat produces no efFe£t 

 upon it ; alcohol makes it experience no change, but con- 

 centrated alkaline leys attack and diffolve it. 



To give fplendour to filk, it mutt be freed from its varnifh. 

 This covering is foluble in alkaline leys. Silk is fcoured by 

 means of foap, which ought always to be cholen of a good 

 quality for fear of framing it, and fometimes with diluted 

 muriatic acid. Silk by being fcoured with foap lofes a 

 fourth of its weight. The matter difengaged from it is ex- 

 ceedingly foetid : if a fkain of filk be not warned in abundance 

 of water after being fcoured, it will become hot in a few 

 days, putrid fermentation will take place, and fmall white 

 worms will be produced, which will devour the glutinous 

 and faponaceous matter that remains in the filk. The liquor 

 in which it is boiled putrefies, and becomes ufclefs. Macquer 

 has very properly obferved, thnt if the yellow varnifh can be 

 precipitated to the bottom of the foapy liquor before putrefac- 

 tion takes place, the foap may be recovered, and the dyer 

 will thus make a confiderable laving. 



Even when the beft foap is ufed, it is generally fufpecled 

 that it injures the whiten el 8 of the filk. The fplendour of 

 the Chinefe filks is brighter than that of the European, and 

 the Chinefe employ no foap in their operations. We i re- 

 member that the Academy of Seiences propofed a prize for 

 a method of fcouring without foap, which was gained by 

 Rigaud, who performed it by a (light alkaline iblution. 

 Colomb even diilblved the varnifh of filk in water, notwith- 

 standing the opinion entertained of its infallibility in that 

 liquid. He expofed the raw filk for nine hours to ebullition, 

 and freed it from the varnifh with the lols of a fourth of its 

 weight. 



iSiotwith (landing the whitenefs which filk acquires by 

 thefe different operations, it mult be carried to a higher de- 

 cree of fplendour by expofing it to the action of fuiphurous 



U 4 acid 



