The fact is then sufficiently established, that distilled water has the property of dissolving lead—Does the same hold true in relation to waters in ordinary use? In the year 1809, it was first announced by Guyton Morveau, that the salts which are held in solution by some natural waters, destroy their property of acting on lead, and that of these modifying circumstances none are more remarkable in their action than the neutral salts. Dr. Christison has pursued this investigation with great success, and has proved that this preservative power exists in the case of sulphates, muriates, carbonates, hydriodates, phosphates, nitrates, acetates, tartrates, arseniates, &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 preservative.
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 deposit 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 of 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 nearly so, for 24 hours in a glass of water, the water may be safely conducted through lead-pipes.

4. Water which contains less than about an 8000th of salts in solution, can not be safely conducted in lead pipes without certain precautions.

5. Even this proportion will prove insufficient to prevent corrosion, unless a considerable part of the saline matter consists of carbonates and sulphates, especially the former.

6. So large a proportion as a 4000th part, probably even a considerably larger proportion, will be insufficient, if the salts in solution be in a great measure muriates.

7. In all cases careful examination should be made of the water after it has been running a few days through the pipes; for it is not improbable that other circumstances, besides those hitherto ascertained, may regulate the preventive influence of the neutral salts.