UELATION OF LAKES TO CLIMATIC CMNDITIONS. 4O 



111 the natural eva})oration of water in enclosed Ijasins the succession 

 will seldom l)e as reg-ular as described a1)ove. for the reason that the j)rocess 

 is apt to he iuterru})ted hy the additinn of tivsli supplies of ^^•ater, and the 

 succession Ijegun anew, or else chemical changes initiated which will vaiy 

 tlie resiilts. In this connection it is to be noted also that changes of tem- 

 l)erature, as from summer to winter, may modify the succession of salts 

 deposited. 



The se})aration of sodium sul})hate, potassium chloride, and common 

 salt from the mother li(pior derived from the concentration of sea-water, 

 l)y alternate evaporation and cooling, is the *i)rinci[)le of Iialard's well- 

 known process largely used for obtaining salt from sea-water in the soutli 

 of Europe. In ^Nlesel's modification of this process, a low temperature is 

 obtained artificially. When sea-water is concentrated until its specific 

 gravity is 1.24 (28° of Beaume's hydrometer) it de})osits about four-fifths 

 of the common salt it originally contained ; after adding 10 per cent of 

 sea-water to the mother liquor remaining, it is passed through a refriger- 

 ating machine and its temperature lowered to — 18° C. The low tempera- 

 ture causes double decomposition to take place between the magnesium 

 sulphate and the sodium chloride, sodium sulphate being deposited and 

 the magnesium chloride remaining in solution. ^ 



A i)rocess similar to that just described occurs in nature, as is shown 

 by the precipitation of large quantities of sodium sul})hate from the Avaters 

 of Great Salt lake, during cold weather. This anticipation of Balard's 

 process is noticed in advance in connection with other features of Great 

 Salt lake. 



The correspondence l)etween the succession of salts formed by the 

 evaj)oration of sea-water, and the succession found in many saline deposits 

 decjily buried in the earth's crust, is of great interest and no doubt 

 ex})lains the genesis of some natural accumulations of this character. It 

 is not always necessary, however, in seeking an explanation of the origin 

 of beds of common salt, gyjisum, etc., four)d in Iciiticulai- masses among 

 stratiiied rocks, to assume tliat they wvn: prccij)itated from isolated bodies 

 of sea-water. On the contrary, tlie study of saline lakes has shown that 

 similar dejjosits may result from the long concentration of ordinary 

 river Avaters. So far as we are at ))resent conreiiied. however, the 

 process in either case is the same, since the waters of the ocean itself 

 owe their salinity in a great degree to the concentration of the Avaters 

 of streams. 



1 Hcprn-t of .Furies: Iiitcniatiimal KxliiMtinii. ISO-J. Class IL i>\). 4H-;J4. 



