An EJJaj on Blfacbing. 307 



Which might be occafioned by the extraordinary 'effort of the 

 fleam ; an event much to be apprehended. The door, which 

 was moveable, was fattened by ten bars and as many fcrews, 

 which preffed it againft the rabbet (already faced with tow or 

 moiftened leather) until it was fo clofe that none of the fteam 

 could efcape. For the greater convenience it ought lo be 

 furnimed with two iron handles, in order that it may be taken 

 off with more eafe. 



The boiler E,E,E, which forms the bottom of this cham- 

 ber, and in which the alkalino-cauftic ley is boiled, is 18 

 inches in depth : its other dimenfions are four inches lefs 

 than thofe of the chamber. This diminution is deftined for 

 receiving the edges of the boiler, which thus ferve to fupport 

 it, as well as a wooden grate, over which the workmen pafs 

 during the manipulation. In the middle of this chamber are 

 placed two reels, A and B, on which are rolled up from i3 

 to 20 pieces of cloth. The axes of thefe reels pafs through 

 leather collars, which prevent the efcape of the fteam, and 

 the cloth is rolled up and unrolled by handles fixed on the 

 outride. A regulator, H, which communicates with the in- 

 fide of the boiler, indicates the height of the ley and the ftate 

 of its exhauftion. The boiler is heated in the ufual manner, 

 or by Count Rumford's plan. 



I caufed to be conftru&ed at Troves another apparatus 

 deftined fojr bleaching hoftery. As thefe articles cannot be 

 unrolled, and as heaping them together might impede the 

 action of the vapour, I employed frames covered with cloth, 

 and placed at the diftance of four inches above each other. 

 On thefe the hoftery was depofited in fuch a manner, that 

 the vapour, in rifing from the boiler, might penetrate it in 

 every part, deftroy the colouring matter, and bleach it com- 

 pletely. 



Some new obfervations induced me to propofe for the 

 winding of cloth a roller, which might be immerled at plea- 

 fure in the boiler in order to moiften the cloth from time to 

 time. All thefe kinds of apparatus will be explained here- 

 after. 



Having thus fpoken of the inftruments employed in this 

 new art, I {hall examine the principles on which it is found- 

 ed, and delcribe the bed method of bleaching by this procefs. 



The bleaching of vegetable fubftances depends on the de- 

 ftru&ion of their colouring principle by the combined action 

 of the air, moifture, and light, or rather, by the united in- 

 fluence of thefe principles to alter their natural colour. 



Alkalies have on the colouring matter of vegetables an 

 a&ion which produces the effecl; of a real combuftion. Were 



V 2 we 



