^I,E ACHING. 163 



dilated t.ogethei' by this resiijoijs matter. To sepa- 

 rate these filaments from eacli otlier, and to destroy 

 entirely the resinous colouring matter, is ^a process 

 of some difficulty. Solutions of alcalies rendered 

 caustic *5 called alcaline leySy have the property of 

 dissolving resins ; hence they have been used for 

 this purpose in bleaching. The linen is boiied in 

 water containing a quantity of ca'.:::;tic potash, 

 which acts upon the resiil of the external filaments, 

 and loosens them a little irom each Qther. The 

 cloth is then spread upon the grass, and exposed to 

 the action of the air, sun, and dew; and is also 

 occasionally watered. It is then returned again 

 into the bucking vat ; and the alkaline solution is 

 poured over it : by this another layer of the fila- 

 ments is opened, and the resin dissolved. It ds 

 then carried again to the field, and ti'eated as 

 before. In this manner, the ibucking and spreading 

 on the grass are repeated alternately, for 15 oi' 16 

 times, according to the weather and other circum- 

 stances, until the clotli is whitened. Were the 

 alcaline ley go strong as to dissolve xill the resin at 

 once, it would injure the texture of the fabric. 



This alternate bucking and. exposing on the grass 

 is the old manner of bleaching, and was universally 

 used, till Scheele discovered the properties of the 

 oxygenated muriatic acid in destroying vegetable 

 colours. M. Bertholiet first applied this property 

 to the purposes of bleaching, and he, with great 

 liberality, communicated his observations to the 

 public. For this purpose, he immersed the cloth 

 into diluted oxygenated muriatic acid, between the 

 operations of the alcaline leys, which produced .the 



* Common potash is rendered sufficiently.c^usdcfor the pur- 

 pose of bleaching, by adding to it quickhme, which nas a stronger 

 affinity for the carbonic acid than potash. 



M S 



