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

salts in solution, --and thus at length forming a permanent and impermeable screen in the form of a film over its surface, through which the action of the water cannot

any longer be carried on. These films are composed of the carbonate of lead, with a little of the muriate, sulphate, arseniate, or phosphate of lead, according to the nature of the acid in the alkaline salt, which is dissolved in the water. The following general conclusions may therefore be considered as sufficiently established.

1. Lead pipes ought not to be used for the purpose of conducting water, at least where the distance is considerable, without a careful examination of the water to be transmitted.

2. The risk of a dangerous impregnation with lead is greatest in the instance o f the purest waters.

3. Water, which tarnishes polished lead when left at rest upon it in a glass vessel

for a few hours, cannot safely be transmitted through lead-pipes without certain precautions ; and conversely, it is probable, that if lead remain untarnished, or