BLEACUING. 129 



hand, but every trace of weaver's gum must have been pre- 

 viously removed by boiling with water. The fibres are laid 

 on a plate of glass, and oil of vitriol dropped on it. A single 

 lens is sufficient, to obsei've the eifect. In a short time the 

 cotton fibre is dissolved, the flax unaltered, or only the finest 

 fibres attacked. 



The oil test is also a good one, and convenient in execution. 

 When flaxen fibres are rubbed up with olive-oil, they appear 

 transparent, like oiled paper, while cotton, under similar cir- 

 cumstances, remains white and opake. Dyed goods exhibit 

 the same, if previously bleached by chloride of lime. 



Eisner's method consists in putting the fibres for a few 

 minutes into a tincture of various red dyes, of which cochineal 

 and madder give the most striking results. The tincture is 

 made by putting 1 pt. madder, &c. into 20 pts. common alcohol 

 for 24 hours. In the cochineal tincture, cotton is colored bright- 

 red ; flax, violet ; — in madder, cotton becomes light-yellow ; 

 pure flax, yellowish-red. 



It is better to employ several of these tests, the mieroscopic, 

 oil, sulphuric acid, and combustion, rather than to rely upon 

 a single test. 



Tanning Cotton and Linen. — English and French fisher- 

 men have been long in the habit of tanning their sails, &c. in 

 bark liquors, in order to render them more durable. Millet 

 states that pieces of linen, treated for 72 hours with an oak- 

 bark liquor at 150°, and stretched on frames, remained unal- 

 tered in a damp cellar for 10 years ; while untanned linen in 

 the same place and for the same time had entirely rotted. 

 The one frame, also tanned, was perfectly preserved, and ihe 

 other, untanned, had rotted. It was further shown that linen, 

 which had begun to moulder, might be preserved from further 

 change by being tanned. It seems to be only necessary that 

 the articles should be kept 2 or 3 days in a warm solution of 

 tannin. Sponge may be similarly tanned. 



2. BleacJiing. — The oldest process of employing sun and 

 dew is still resorted to, but has been almost supplanted by the 

 use of chlorine or chloride of lime. The new and singular 



