279 COTTER: SODA INDUSTRY OF SIND. 



is due to reactions between calcium bicarbonate, salt, and gypsum, 

 the last two substances reacting to form calcium chloride and sodium 

 sulphate ; the sodium sulphate thus formed is supposed to exchange 

 with calcium bicarbonate to produce alkali. Lastly a view put 

 forward by E. Sickenburger may be mentioned. In a paper dealing 

 with the alkaline lakes of Egypt, 1 be suggests that the carbonates 

 are derived through the reduction of sulphates by organic matter 

 such as algae, which are abundant in the Egyptian lakes. 



I have had little time to investigate this question. Nevertheless 

 I Bhould like to put forward tentatively the conclusions to which 

 I have come. I feel difficulty in accepting W. Center's hypothesis 

 for several reasons, first because, there are no rocks in the immediate 

 neighbourhood of these alkaline lakes of Rind, and the nearest 

 roc k — the limestones of Eohri and Sukkur — cannot be supposed to 

 contain any appreciable quantity of alkaline silicates. Secondly the 

 alkaline region is very limited in extent, and is surrounded by a 

 saline region ; if however the alkali was really due to the decom- 

 position of more distant rock-masses such as the Himalaya, or the 

 Archaean complex of Kajputana, how are Ave to explain the peculiar 

 limited geographical distribution of the alkaline lakes ? 



These considerations, as well as the fact that there are very large 

 quantities of salt both in association with the alkali and in the 

 country immediately surrounding the alkaline area, 2 lead me to 

 suppose that a hypothesis such as that of Sickenburger is prefer- 

 able in the case of the Sind dhavds. I think however that the fact 

 that the efflorescences from the xim or percolating water contain 

 lar^e quantities of carbonate shows that the conversion of sulphates 

 to carbonates cannot be produced by the decomposition of algae 

 in the lakes, but has taken place before ever the salts reached the 

 lakes, and while they were actually dissolved in the percolating 

 water. The decomposition is of course carried on by bacterial 

 action, and it seems reasonable to suppose that the carbonates 

 derive their carbon from the decomposition of organic matter, as 

 has been suggested by Sickenburger. I see no necessity for the 

 hypothesis put forward by some authorities that the carbon is 

 derived from the breaking down of calcium carbonate. 



i Chem. Zcit., 1892, pp. 1045— 1601. 



* See Blanford, Mcc. Qeol Sur. lnd. t X, p. 10; also La Totcho, ** ©eckgj 

 of Western Rajputana," Mem. Qwt. Svr. Ind., XXXV. 



