MANUFACTURE OF SODA. 



are rolled with considerable pressure upon both 

 sides with a fluted board fastened to the operator's 

 hand by a strap ; by this means, and by repeating 

 the rolling, a grain is given to the leather. 



After the skins are curried, it may be required 

 to colour them. The colours usually given to 

 them are black, white, red, green, yellow, &c. 



If the skins are to be blacked, the process varies 

 according to the side of the skin to be coloured. 

 Leather that is to be blacked on the flesh side, 

 which is the case with most of the finer leather 

 intended for shoes and boots, is coloured with a 

 mixture of lamp black, oil, and tallow, rubbed into 

 the leather. And what is to be coloured on the 

 grain side is done over with chamber lye, and then 

 with a solution of sulphate of iron, which turns it 

 black. 



MANUFACTURE OF SODA. 



Soda, or the mineral alcali, (described above, 

 under Chemistry) is sometimes found in a native 

 state, as in the lakes of Natron in Egypt, which are 

 dry in the summer season ; the water leaving after 

 evaporation a bed of soda, or, as it is there called, 

 natron, of two feet in thickness. 



A marine plant, called the Salsola soda, which 

 grows among the cliffs on the sea coast, seems to be 

 endowed by nature with the property of decom- 

 posing the salt water, that is, of separating the 

 muriatic acid from the soda, which latter it absorbs. 

 This plant is collected by the Spaniards with great 

 care, and burnt for the manufacture of barilla, 

 which is a carbonate of soda mixed with various 

 impurities. 



Soda is also procured in a still more impure 

 state, by the burning of the sea weeds on our own 



