muriates, carbonates, hydriodates, phosphates, nitrates, acetates, tartrates, arsenates, &c. These salts, however, do not possess an equally protective influence, the carbonates and sulphates being most, the chlorides the least energetic of those saline substances commonly met with in waters. As a general rule, it appears that those whose acid forms with the lead a soluble salt of lead, are the least energetic ; while those whose acid forms an insoluble salt of lead, are most energetic. The variable quantity of salts necessary to prevent the action of water on lead, may be seen from

the following results obtained by actual experiment.

Of acetate of soda a 100th part of the water is a prese: rvative. Of arseniate of soda 12,000th " Of phosphate of soda 30,000th " Of hydriodate of potash 30,000th " Of muriate of soda 2,000th Of sulphate of lime 4,000th " Of nitrate of potash 100th

,

The sulphates of soda, magnesia, lime, and the triple sulphate of alumina and potash, possess about the same preservative power ; which appears to depend on the acid, not on the base of the salt. The general results of Dr. Christison's investigations, appear to be, that neutral salts in various, and for the most part minute ,

proportions, retard or prevent the corrosive action of water on lead --allowing the carbonate to deposite itself slowly, and to adhere with such firmness to the lead as not to be afterwards removed by moderate agitation, -- adding subsequently to this

crust other insoluble salts of lead, the acids of which are derived from the neutral