the Eastern Portion of the Basaltic District of India. 563 



ing up baskets of the black mud, at a season when there was much more water in the lake*, was 

 also formed under the surface of the mud in lamellar spiculi radiating in every directionf. The 

 salt accumulates slowly, and is collected only once in several years, the quantity having diminished 

 in consequence of the mounds erected above the edge of the crater to regulate the supply of water, 

 having been neglected ; but it is evident, from the great beauty of the specimens obtained, that 

 the quality is not affected by this cause. The salt is collected at the end of the dry season, when 

 the water is low ; and I observed mounds of the black mud on the banks, covered with an efflo- 

 rescence of tabular crystals. The salt is used for washing and dying chintzes, &c., and is ex- 

 ported to considerable distances. I imagined that the water of the lake in which such large quan- 

 tities of salt were deposited, was saturated ; but I found its specific gravity to be only 1027 "65, a 

 solution of the salt itse'f obtained from the bottom at the same time being 1148-4 ; and the water ra- 

 pidly dissolved the crystals thrown into it. On analysis, the salt was found to consist in 100 parts : 

 of carbonic acid, 38; soda, 40*9 ; water, 20"6 ; insoluble matter, "5, and a trace of a sulphate. 

 This nearly corresponds to the composition of the trona or striated soda from the lakes of Fezzan, 

 examined by Mr. R. Phillips J ; but approaches somewhat nearer to the equivalent numbers of 

 the sesquicarbonate established by that analysis, which is to be ascribed to the greater purity of 

 the Lonar salt. The water of the lake contained besides, a little potash, muriate of soda 29 

 grains, sesquicarbonate of soda 4-2 nearly, and sulphate of soda '1 ofa grain in 1000 grains of the 

 water. No lime could be detected in it, nor did I discover any magnesia. These facts confirm 

 Berthollet's theory of the formation of carbonate of soda in the natron lakes of Egypt, viz. that 

 ofa mutual decomposition of the muriate of soda and carbonate of lime when in a pasty state. 



The striated soda of Fezzan and of this lake, containing half an equivalent more of carbonic 

 acid than can be furnished by carbonate of lime, renders some modification of his theory necessary ; 

 and the most probable explanation appears to be, that the carbonic acid by which the lime is held 

 in solution in the mud, furnishes the acid, and perhaps indicates the existence of an unstable 

 sesquicarbonate of that substance ; which is not improbable from other facts in the history of the 

 union with that acid. This was suggested by my friend Captain Smith of the Madras Engineers, 

 and explains the circumstance sufficiently. 



Like most points in physical science, these observations have other and more extensive applica- 

 tions than that of affording an explanation of the production of natron in this lake. Carbonate of 

 soda is extensively distributed over the surface of the soil in various countries, more especially in 

 the basaltic portion of Central and Western India, and in the limestone districts of the south ; the 

 Teal relations of which have been a subject of discussion amongst Indian geologists, and inferences 

 unsupported by fact have been drawn from it. In all the places where I have met with it, or of 

 which detailed information has been obtained, muriate of soda and carbonate of lime existed in 

 the soil, and the natron was found on the surface of the moist earth or mud. Near Gundycottah 

 on the banks of the Pennar, common salt is interstratified with the upper schistose strata of the 

 argillaceous limestone on which the sandstone rests ; and on the surface of the neighbouring soil, 

 natron, contaminated with much muriate of soda, is collected and used in washing and in glass- 

 making. The salt associated with the limestone, and the water of a saline well dug through it, 

 having the specific gravity of 1002-5, contain common salt and a little sulphate without any car- 

 bonate of soda, which is no doubt produced in the same manner as the Lonar salt. I did not 

 ascertain whether it was also a sesquicarbonate, but I have examined a portion of native carbo- 

 nate of soda from another part of India, with which Mr. Faraday had the kindness to furnish me, 

 and I found it to be composed ofa mixture of that salt with muriate of soda and a little sulphate. 

 The same is probably true of the carbonates found in other countries in similar situations §. A 



* July, 1824. 



+ The natron of a lake near Maracaybo in South America occurs in the same way, the Indians 

 .breaking up the layers of salt with long poles ; and then, by diving, they remove it from under 

 a bed of mud which covers it, and they place it in small canoes, as is done at Lonar. Journal of 

 the Royal Institution, vol. i., p. 188. 



X Journal of the Royal Institution, vol. vii., p. 294. 



§ The carbonate of soda formed by the incineration of saline plants in the deserts of Northern 

 India, and by the deflagration of nitrate of soda and charcoal in the south of the Penuisula, must 

 not be confounded with the natron found in the soil. 

 VOL. V. — SECOND SERIES. 4 D 



