adds, when the quantity does not exceed a 600,000th or a millionth part of the water, as in these instances, it is ridiculous to imagine that any harm can result to man from the constant use of it for domestic purposes.
Another fact of some practical consequence, which flows from the experimental conclusions stated above is, that although it may be perfectly safe to keep some waters in leaden cisterns, it may be very unsafe to use covers of this metal, because the water which condenses on the covers must be considered as pure as distilled water. It has been found that white lead forms in much larger quantity on the inside of the covers of cisterns than on the cisterns themselves, where both are constructed of lead. A remarkable illustration of this is mentioned in a paper read before the Academy of Sciences at Paris in 1788 by the Comte de Milly. About a year after getting two leaden cisterns erected in his house, to keep the water of the Seine for general domestic purposes, he was attacked with severe and obstinate colic; which led him to examine his cisterns. He found that the sides, where they were occasionally left exposed by the subsidence of the water, and more especially the leaden cover, were lined with a white liquid, which was constantly dropping from the lid into the cistern, like the drops in caverns where stalactites are formed. The water was in consequence so strongly impregnated with lead as to give a dark precipitate with liver of sulphur.[1] The reason of this occurrence is, that the water in the cistern is a solution of preventive salts, but what reaches the lid is in a manner distilled. In Edinburgh the lids of the cisterns are invariably made of wood, whether on account of its superior cheapness merely, or because a leaden cover had been found perishable, I have not been able to discover.
It may be well to conclude these remarks on the action of spring waters on lead with a general summary of the chief circumstances to be adverted to in using lead for keeping or conveying water; to which may be added a few hints for preventing action where it is found to have taken place.
The general results of the preceding inquiries are that rain or snow-water for culinary use should not be collected from leaden roofs, nor preserved nor conveyed in lead;—that the same rule applies to spring waters of unusual purity, where for example the saline impregnation does not exceed a 15,000th of the water;—that spring water which contains a 10,000th or 12,000th of salts may be safely conveyed in lead pipes, if the salts in the water be chiefly carbonates and sulphates;—that lead pipes cannot be safely used, even where the water contains a 4000th of saline matter, if this consist chiefly of muriates;—that spring water, even though it contain a large proportion of salts, should not be kept for a long period in contact with lead;—and that cisterns should not be covered with lids of this metal.
Where action is observed to take place in the instance of particu-*
- ↑ Rozier. Observations sur la Physique, xiii 145.
