40 



THE SALTON SEA. 



the normal carbonate of calcium and the hydrated carbonate of magnesium. Consequently 

 the carbonate, and not the bicarbonate radicle, is given in the table of results. All con- 

 stituents are stated in parts per 100,000. 



DISCUSSION OF RESULTS. 



In order that a comparison may be made of the increase in concentration which has 

 taken place in the total constituents from year to year, correction must be made for the 

 fact that the samples were not collected on the same date each year. When applying this 

 correction to the total constituents, in order to give them the values which they would 

 have if the samples were collected on June 3 of each year, it was assumed that the daily 

 evaporation from the lake during the last week in May is 1.5 times as great as the average 

 daily evaporation for the whole year. 



With the exception of the first year period, the yearly percentages of increase of the con- 

 stituents are seen to increase progressively. This result is to be expected, for as the volume 

 of the lake becomes smaller an equal loss of water by evaporation will produce a greater 

 increase in concentration of the constituents. 



The high result found for the increase of the constituents during the first year period 

 may be explained on the assumption that the water had not yet reached a state of equi- 

 librium with respect to the salts in the bottom of the lake. 



Table 7. — Percentage yearly increase of total constituents. 



Table 8. — Annual fall of surface of the lake. 



The rate at which the surface of the lake is lowering, as a result of evaporation, is 

 shown in table 8. The surface altitudes of the lake as observed from year to year were 

 taken from the gage readings at Salt Creek trestle, maintained for a time jointly by the 

 Southern Pacific Railway and the United States Weather Bureau. 



Since the fall of the surface of the lake was greater during the first year period than 

 for any equal period since then, it might at first sight appear that the high result found 

 for the increase of the constituents during the first year period was due to a greater evapo- 

 ration during that time, or to a smaller volume of inflowing water, or to both. The difference, 

 however, in the fall of the surface of the lake between the first and second year periods is 

 not great enough to correspond to the difference found between the total constituents for 

 the same periods, and it may therefore be concluded that the high value found for the first 

 year increase of the constituents was largely caused by leaching of salts from the bottom 

 of the lake, as already stated. 



When the composition of the residue is expressed in percentages of the total anhy- 

 drous inorganic solids, as is done in table 9, it will be seen that the concentrations of the 

 principal constituents with respect to the water must have increased each year in almost 

 the same proportion as the total constituents, since the percentage which each forms of 

 the latter has remained fairly constant. 



Although the composition of the salts in solution has remained fairly constant when 

 considered as a whole, yet some slight variations have taken place. Thus, the calcium 

 and carbonate ions have decreased, as will be discussed later, while both the sodium and 

 chlorine ions have increased slightly. The magnesium and sulphate ions, however, have 



