1525.] (]f Claude-Louis Bertholkt. 163 



emphatic words of Cuvier, Je serai avec vous ; and never was 

 there a more perfect proof of esteem and affection given, by the 

 tiniversal assent of men of science, to any individual, than those 

 distino-uished associates now freely accorded to Berthollet, in 

 pledo-ilio- themselves to encomiter those dangers of which they 

 knevv nothing, but that he was to share them. But for the 

 existence of such a man as Berthollet, who possessed at once 

 the entire confidence of the General, and the perfect e&teem and 

 re^rard of men of science, it must have proved whoUy impossible 

 to'^unite on this occasion the advancement of knowledge with 

 the progress of the French arms. . , ,, -^ t n .. .i 



One of the most important essays furnished by Berthollet to the 

 Institute of Egypt, resulted from an investigation into the nature 

 of certain phenomena presented by the Natron Lakes in the 

 neighbourhood of Cairo, situated on the borders of the Desart, 

 and living name to the Valley of the Six Lakes. The beds of 

 these bodies of water appear to be generally composed of calca- 

 reous rock, and the water itself is more or less brackish, in con- 

 sequence of the presence of a saUne matter almost entirely 

 consistino- of common salt. These lakes, although extensive, 

 are generally shallow ; and although annually filled to overflow- 

 ing, they are rapidly dried up again to a large extent, in conse- 

 quence of the high temperature and remarkable dryness of the 

 climate. As the water retires, it deposits over the whole surface 

 of the country an inexhaustible supply of a hard, compact, saline 

 concretion, consisting of a mixture of cai-bonate and muriate of 

 soda. This substance contains so much of the former of these 

 salts, that it is extremely valuable for every purpose to which 

 that alkali can be separately applied. Accordingly, immense 

 quantities of it are annually collected under the superintendence 

 of o-overnment, and it is not only distributed over the country m 

 caravans, but was at one time exported in great quantities to 

 France, England, Italy, and other parts of Europe. Theorigm 

 of this carbonate of soda was a question of much interest, but 

 one the resolution of which was attended with no small diffi- 

 culty-. . ,• 1 1 1 • * 



The water in its original state contains little else than muriate 

 of soda : during evaporation, a quantity of this salt disappears, 

 and is replaced by carbonate of soda. What is the cause of this 

 change? It should seem that it must be the result of a decom- 

 position of part of the dissolved muriate of soda; yet what is the 

 manner in which this decomposition is effected ? 



It was to attempt the solution of this interesting problem that 

 Berthollet accompanied Andieossy, in the survey which that 

 officer was taking of the Natron Lakes and of the adjacent 

 country. Upon examining carefully the bed of the Lakes, in the 

 hope that some light might thereby be thrown on the object ot 

 his research, M. Berthollet made the important observation that 



m2 



