MANUFACTURE OF SODA. 213 



shores, particularly in Scotland, from which is pro- j 



duced a substance called help. 



But the demand for a pure carbonate of soda 

 having become very considerable of late years, from 

 its great utility in many arts and processes, various 

 means have been tried for procuring it by decom- 

 posing the salts, in which it exists, combined with 

 acids. Muriate of soda has been decomposed for 

 this purpose. The following method is described 

 in Nicholson's Journal. 



Solutions of 500lbs. of sulphate of soda*, and 

 560lbs. of American potash, are made to boil, and 

 are then mixed. As soon as the mixture boils, it 

 is conveyed into a cistern of wood, lined with lead, 

 half an inch thick, which is fixed in a cool place. 

 Sticks of wood are then placed across the cistern, 

 from which slips of sheet lead, two or three inches 

 wide, are hung into the fluid, at four inches distance 

 from each other. When all is cool, the fluid is let 

 off, and the chrystallized salt is detached from the 

 slips of lead, and the bottom of the trough. The 

 salt is then washed, to free it from impurities, after 

 which it is transferred again into the boiler, dis- 

 solved in clear water, and evaporated by heat. As 

 soon as a strong pellicle is formed, it is suffered to 

 cool so far that the hand may be dipped into it 

 without injury, and the heat is kept at that temper- 

 ature as long as effectual pellicles continue to be 

 formed over the whole surface of the boiler, and 

 then fall to the bottom. When no more are formed, 

 the fire is withdrawn, and the fluid ladled out into 

 the cistern to crystallize. The sulphate of potash, 

 &c. which had been deposited, is then taken out of 



* Sulphate of soda is sold cheap by the bleachers, who save 

 it as the residue in decomposing common salt by sulphuric acid 

 with manganese. 



p 3 



