420 JOSEPH STRUTHERS 



is crushed and treated with hydrochloric acid, the resultant 

 pasty mass is dissolved in boiling water and the solid material 

 separated and removed by filtration or decantation; the clear 

 solution is then crystallized in iron tanks, yielding pure crys- 

 tals of boric acid. The chemical reaction involved is (2Mg3B8 

 O15), MgCl3+12HCI+18H20 =7MgCl2+16H3B03. 



In the sulphuric acid process calcium borate is treated 

 with sulphuric acid, the reaction yielding soluble boric acid 

 and precipitated calcium sulphate. The boric acid is obtained 

 by leaching with hot water, the solution so produced being 

 concentrated by evaporation until the cr3^stals of boric acid 

 separate out from the solution. In California the process is 

 slightly modified. The borate mud is boiled in huge tanks of 

 water containing sulphurous acid, which decomposes the cal- 

 cium borate, thereby liberating the boric acid in the solution 

 and leaving the calcium in the form of insoluble calcium sul- 

 phate. As before, the boric acid is dissolved by leaching with 

 hot water, which, however, extracts also a small quantity of 

 other soluble salts. For this reason fractional crystallization 

 is necessary in order to obtain a fairly pure product. In a few 

 works the insoluble calcium sulphate is separated and removed 

 by passing the muddy solution from the tanks through filter 

 presses. 



The sulphuric acid process is sometimes used to decompose 

 the boracite of the Stassfurt deposits, and in this case Epsom 

 salt is obtained as a by-product from the magnesium sulphate 

 contained in the mother liquor, according to the following 

 chemical reaction: (2Mg3BA5), MgCl2+7ffS04+18H20=7Mg 

 S4O+ 2HCI+I6H2BO3. 



Boric acid is produced by heating in a closed vessel 100 

 parts of colemanite and 150 parts of ammonium sulphate. 

 The product of the first reaction is ammonium borate, which 

 is later decomposed into ammonia and boric acid. The am- 

 monia is condensed and collected, and the boric acid is dis- 

 solved from the residuum by leaching with water and concen- 

 trating the resultant aqueous solution until crystals of boric 

 acid are formed. The crystals are then removed, washed 

 with water until free from adhering mother liquor, dried, and 

 packed for shipment to the market. At times the crystals are 



