924 General Notes. [November, 



3. Common Salt. The deposit of gypsum ceases when .88 

 of the original volume of water has evaporated, and that of salt 

 commences when only one-tenth of the volume remains, and 

 continues till that quantity has been reduced one-half. 



4. Sulphate of magnesia. A still further evaporation causes 

 the deposition of this salt, mingled however, with chloride of 

 sodium. When the only three parts- out of a hundred remain, 

 the quantities of sulphate of magnesia and common salt are 



5. Carnallibe, or double chloride of potassium and magnesium. 

 This is deposited when the water has been reduced to a little less 

 than one-fiftieth of its original volume. 



Spontaneous evaporation goes no further; a bitter mother 

 liquor is left that never dries at the ordinary temperature of the 

 hottest regions of the globe. This liquor contains much chloride 



Taking these facts in their order, and applying them to the 

 saline beds found in different parts of the earth, it is evident that 

 the substances last deposited must be rarest, since at each stage 

 the evaporation is more advanced, and the chances favorable to 

 further deposition diminished. This is borne out by the facts, 

 since gypsum is most common, chloride of sodium next. We 

 may also predicate that if one of the substances last deposited in 

 artificial evaporation be found in the crust of the earth, beds of 

 all those substances which are previously deposited will be found 

 around it. This is always the case, gypsum occurs without com- 

 mon salt, but never common salt without gypsum. At Strass- 

 furth, Prussia, all these substances occur, with, in addition, boracic 

 acid combined with magnesia. Chemists have been of opinion 

 that since "borate of magnesia is almost insoluble in water, it 

 ought to have been deposited in the inferior beds," and have 

 appealed to volcanic agency to explain its occurrence. Analysis, 

 however, shows that boracic acid exists in the mother liquor left 

 after evaporation, and in such quantity that spectral analysis, or 

 the flame of hydrogen, reveals its presence in a single drop. 



Thus boracic acid, occurring abundantly in the midst of the 

 deliquescent salts of the mother liquor, Ceased to be a rare sub- 

 stance, and may be expected to be found where deposits of gyp- 

 sum and salt occur, and there only. M. Dreulefait goes on to 

 state that he has proved his deductions by observations carried 

 on throughout a considerable portion of Southern Europe ana 

 Northern Africa, and has come to the conclusion that the pre- 

 sence or absence of volcanic agencies makes no difference to tne 

 quantity of boracic acid found in saliferous districts. Ihesau. 

 springs of the non-volcanic parts of the south of France, bw> - 

 xerland, and Germany are as rich in boracic acid as those of tne 

 ophitic districts of Engadine or the Pyrenees. . 



The lecturer then treated of the salt pools formed in the aeu* 



