104 An Ejfay on Bleaching. 



acid gas in a clofe chamber, or by immerfing it in that acid 

 in a liquid Mate. 



Of the Bleaching of Silk. 



. To obtain the complete bleaching of filk it is fubjecTed to 

 feveral operations. The firft tends to deprive it of the gum 

 and colouring matter which externally cover its filaments; 

 the ftcond, to give it a jutt decree of whitenefs: fometimes 

 the fconring is federal times repeated ; it is then baked, 

 blued, and fulphured. 



It is freed from the gum by a ley of foap and foft water, in 

 the proportion of from twenty-five to thirty pounds of the 

 finefl kind of foap for a hundred pounds of filk. The boiler 

 is then expofed to the action of the fire, and the heat is fo 

 far kept down by a little cold ley, a3 to maintain, as uni- 

 formly as pu-ffible, the temperature of about 90 degrees of 

 Fahrenheit. The filk is turned, to expofe all the parts of the 

 fkains to the action of the bath. The fkains are then twitted 

 on the w ringer to free them from the ley. They are put into 

 bags of coarfe cloth in packets of about twenty-five pounds. 



The baking, as the workmen term it, though a boiling, is 

 performed by throwing all thefe bags into a kettle of frelh ley 

 compofed as the preceding, making it boil for two or three 

 hours, and ftirring it often with a batton left the filk (hould 

 adhere to the bottom : it is then taken from the bags, after 

 which it is opened and fpread out. When the fkains have 

 been fuffered to drain thev are again wrung, and then rinled 

 in a ftream of water. When they have Deen well wafhed 

 and beat in the running water, they are examined, to fee 

 whether there be any fpots not diflblved which may render 

 it neceflfary to repeat the operation. 



To give it whitenefs, a foapy ley is prepared of four ounces 

 of foap for each pound of filk, diluted with water till it form 

 a good lather when well ftirred and beaten. The fame heat i$ 

 maintained as in the preceding operations, and never that of 

 boiling water; the filk is preffed for half an hour at leaft, and 

 after being turned for another half hour it is removed ; and, 

 not unfrequently, it is baked before it is fubjectcd to the ope- 

 ration of fulphuring. 



This tu bite baking is performed in a ley fimilar to that 

 above defcribed, and in bags like thofe employed for boiling 

 the filk in its raw (rate. This baking finifhes the bleaching 

 with foap. The filk being taken from the bags is wrung, and 

 rinfed in running water. If an azured white be required, 

 it is made to puts through blue; after being azured, and 



when, 



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