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.

8. Where the water is of sufficient purity to act on lead, a remedy may b e found, either, in leaving the pipes full of water and at rest for three or four months

or by solution of phosphate of soda ; in the proportion of about a 25,600th

part.*

Dr. Kane, however, seems to differ from Dr. Christison in opinion on this

subject ; for after having mentioned the crust which gradually forms on the interior of the cistern, and assists in protecting it from the oxidizing action of the air, he remarks, " no danger is therefore to be apprehended from the supply of water to a city being conveyed through leaden pipes, and preserved in leaden cisterns ; for all water of mineral origin dissolves, in filtering through the layers of rocks in its passage to the surface, a sufficiency of saline matters to serve for its protection."

Now, to apply these results to the water of the Croton ; as this holds in solution

only about one 18,000th part of salts, it must, according to Christison, exert a corroding influence on the lead-pipes. Dr. Dana, of Lowell, has lately investigated

this subject and detected lead in the water which had passed through the leadenpipes for the distribution of water in the city of Lowell. The first examination was made from a sample of water taken from the source or spring-head before it had entered the leaden pipes, when the specific gravity was found to be 1,000,18. The pint, on evaporation to dryness, yielded 2.37 grains of solid matter.