32 Proceedings of the Royal Physical Society. 



to 56*28 per thousand.^ The evaporation goes on, however, 

 on the greatest scale in the Kara-Boghaz, which is a shallow 

 diverticulum from the eastern part of the middle basin. It 

 is possibly a basin into which the Oxus emptied itself in 

 former times. It is about 3000 square miles in extent, and 

 is separated from the Caspian proper by a narrow channel 

 not more than 150 yards wide, and only seven or eight feet 

 in depth. This basin, being exposed to every wind, and to 

 a most intense summer heat, is subject to the loss of an 

 enormous quantity of water by evaporation, and as there is 

 practically no inflow from rivers to balance this loss, it is 

 made good by a steady influx from the Caspian. Hence a 

 current of water runs inward to the Kara-Boghaz during the 

 summer months with a speed of two to three and a half miles 

 per hour, according to the wind and the season. Hence the 

 saline constituents are concentrated, and layers of both 

 chloride of sodium and gypsum are continually being de- 

 posited, while the magnesia salts contained in the mother- 

 liquor flow back into the Caspian. Von Baer ^ has calculated 

 that the Kara-Boghaz alone receives from the Caspian the 

 enormous quantity of three hundred and fifty thousand tons 

 of salt per diem. 



Another well-known example of an inland lake which 

 receives the rainfall of a large area, and concentrates its 

 dissolved contents by excessive evaporation, is Elton Lake, 

 which is about two hundred miles from the northern border 

 of the present Caspian, in the Kirghis Steppe. This yielded 

 annually as much as 220,550,000 lbs. of chloride of sodium, 

 but the Eussian government have ceased to work it, and 

 obtain salt instead from Lake Baskounchak, which is dry in 

 summer, and has its bed covered with salt (F. W. Rudler). 

 " Towards the end of the summer, the waters of Lake Elton 

 become reduced to a mother-liquor in which the salts amount 

 to 271 '3 per thousand, and consist of more than 60 per cent, 

 of chloride of magnesium, with much sulphate of magnesia, 

 and a little chloride of sodium. During the winter, a large 

 quantity of sulphate of magnesia crystallises out, and is again 



1 Justus Roth, Cont. Rev., Aug. 1880, p. 245. 



2 "Kaspisclie Studien," Bull. Acad. Sc. St Petersburg, 1865-56. 



