354 ME. E. T. GiJUTHEE ON THE 



depth, and it is doubtful whether the average sounding- 

 would be as much as half this; indeed, it seems to me to be 

 probable that 15 feet would more nearly represent the mean 

 depth. As in other salt lakes the height reached by the water is 

 liable to considerable seasonal variation ; the difference of level 

 seems to bear such a large proportion to the average depth of the 

 lake that the composition and specific gravity of the water must 

 undergo very considerable alteration during the change from the 

 dry-season level to that of the wet-season. It might be quite 

 possible to compute the lotal volume of the lake from the data 

 supplied by gravimetric measurements considered in relation 

 to the easily measurable increase of volume after the rainy 

 season. 



The specific gravity of a sample of water obtained on. Sep- 

 tember 16, 1898, was 1'1138 at 15° C. Its salinity was equal to 

 about |- of that of the Dead Sea (sp. gr. 1'2225 at 120 metres, 

 Lartet). 



A chemical analysis of the filtered water, undertaken for me 

 by my friend Mr. J. J. Manley, gave the following proximate 

 results, calculated in parts by weight in 100 grammes of the 

 solid salts : — 



Sodium chloride 86-203 



Magnesium chloride 6"816 



Magnesium sulphate 3"915 



Calcium sulphate 1*151 



Potassium sulphate 1*741 



99-826 



•017 per cent, of free carbonic acid gas was also present, as welt 

 as an unweighable trace of barium. The weight of the total 

 solids came to 14'893 parts in 100 of the water*. 



The average temperature of the water during the month of 

 August was about 80° E. at the surface and some two degrees- 

 lower at the bottom (depth 25 feet). The very shallow water 

 very near the shores was of course heated up to a higher tem- 

 perature (82° E.), and was far more concentrated by evaporation 

 than the open lake-water : in many places along the margin the 



* Por further details concerning the chemical and physical characters of 

 the water, see a paper by R. Giinther and J. J. Manley, " On the Waters of the 

 Salt Lake of Urmi," in Proc. Eoyal Society, 1899, vol. Ixv. pp. 312-318. 



