great ravages. Tronchin very properly ascribed its increase to lead entering the body insidiously along with the water, which for culinary purposes was chiefly collected from the roofs during rain. He farther attempts to account for the rain-water having acquired the power of corroding the lead, by supposing that it was rendered acid in consequence of the roofs having been covered with decaying leaves from trees which abounded in the city; and without a doubt this explanation accords with the season at which the lead colic was observed to be most frequent,—namely, the autumn. But he does not seem to have been aware that rain-water itself possesses the corroding property, independently of any extrinsic ingredient except the gases it receives in its passage through the atmosphere.[1]—Mérat has referred to a Dutch author, Wanstroostwyk, for an account of a similar incident which happened at Haarlem.[2]
The co-operating effect of acid emanations in the atmosphere is well exemplified by an interesting incident which occurred this year in Manchester, as detailed in some documents put into my hands by Dr. Hibbert Ware. A gentleman being seized with symptoms, which in the opinion of his medical adviser were owing to the insidious introduction of lead into the body, it was found by Mr. Davies that the rain-water from a leaden roof, which had been used in the family for nine years, contained a considerable impregnation of lead. At first this excited some surprise, because the roof was an old one. But on farther inquiry it was found, that the rain in descending contracted an impregnation of hydrochloric acid from the vapours which escaped from an adjoining manufactory. A portion of the water which was sent to me contained so much lead dissolved that it became dark-brown on the addition of hydrosulphuric acid, and a considerable black precipitate was slowly deposited.
Spring-Water.—Most spring-waters, unlike rain or snow-water, have little or no action on lead, because they generally contain a considerable proportion of muriates and sulphates.
As an example of a spring water which does not act on lead at all, the mineral water of Airthrey, near Stirling, may be mentioned. In four ounces of water from the strongest spring at Airthrey, I kept for thirty-five days three bright rods of lead weighing 47·007 grains; and at the end of that period the rods were very nearly as brilliant as when they were first put in, and weighed 47·004 grains. This result is easily explained on considering the nature of the water. It contains no less than a seventy-seventh part of its weight of saline matters, which are chiefly muriates, and partly sulphates.
Another good illustration occurred to me lately, which contrasts well with some instances of an opposite description to be mentioned presently. The house of Phantassie in East-Lothian was supplied with water by a lead pipe from a distance of a mile. About a year afterwards, when I had an opportunity of examining into the circum-*
