256 On the Manufacture of Salt in India. 



As the quantity of sulphate in the Calcutta bittern is 

 proportionally small, sulphuric acid, or some sulphate, must 

 be added to form the sulphate of magnesia. 



I first thought of sulphate of iron, which ought to be 

 the cheapest substitute for sulphuric acid. And although it 

 has been stated in the Coal Reports, 1838, p. 52, that sulphate 

 of iron may be made at a nominal price from pyritous or 

 refuse coal, such as that of Kyuk Phyu, yet impure sulphate 

 of iron is sold in the bazar at eight rupees per maund, a 

 price which must prohibit its use in chemical manufactures. 

 To separate the muriate of magnesia from the other salts, 

 let the bittern be boiled down to one-half or two-thirds, 

 according to its specific gravity, and set it aside to crystallize, 

 decant the liquor, and remove the crystals of muriate of mag- 

 nesia before they deliquesce. 



The muriate of magnesia is then to be placed in a vessel 

 to which receivers are attached, and sulphuric acid added gra- 

 dually till no more muriatic acid vapour is disengaged, then 

 remove the adopting tube, and add carbonate of magnesia 

 to take up the excess of sulphuric acid as long as carbonic 

 acid gas is disengaged, and set the neutralized solution aside 

 to crystallize in flat shallow vessels. The muriatic acid re- 

 covered in this process, is equivalent to the sulphuric acid 

 expended in making the sulphate. 



For carbonate of magnesia, treat the bittern as for the 

 sulphate, and dissolve the muriate of magnesia in thrice 

 its bulk of water ; dissolve the same quantity of carbonate of 

 soda prepared from sajee muttie in the same proportion of 

 water, mix the solution, and boil for a quarter of an hour ; 

 allow the carbonate of magnesia to fall to the bottom, decant 

 off the water, and dry the magnesia. The carbonate of 

 magnesia thus prepared, is of a lighter and finer quality than 

 that which is imported. Other experiments are in progress, 

 from which it will appear, that the first part of the process, 

 that of boiling the bittern, may be dispensed with. It has been 



