PROFESSOR CHRISTISON ON THE ACTION OF WATER UPON LEAD. 267 



ordinary purity was not without foundation. Accordingly, it afterwards appeared 

 from analysis to be very unusually pure. Oxalate of ammonia occasioned a white 

 haze, and slowly a very scanty white precipitate, shewing a trace of lime. Phos- 

 phate of ammonia had no effect at first, on being added to the water after removal 

 of the lime ; but in the course of some hours, a few microscopic shining crystals 

 formed on the glass, thus indicating a trace of magnesia. Nitrate of baryta, 

 however, did not affect the water in the slightest degree, proving the extreme 

 scantiness of sulphates. And nitrate of silver caused only a faint opalescent 

 whiteness ; so that even the muriates were present in unusually small quantity. 

 On concentrating the water it was found that the salts existing in it were hydro- 

 chlorates, sulphates, and carbonates of lime, magnesia, and soda, and that the 

 hydrochlorates greatly predominated. A minute estimate of the several ingre- 

 dients was not attempted, because unnecessary. But their total amount proved 

 to be only 0.554 of a grain in 11,860 grains, or gdbsth-* Water taken direct from 

 the pipe, and kept for some days well corked in a bottle, was quite transparent 

 when first poured out ; but, on being slightly concentrated by boiling, a few white 

 shining crystals of great delicacy were formed. These, when detached and washed 

 with distilled water, disappeared in water acidulated with nitric acid ; and on this 

 solution being evaporated to dryness, there was obtained a trace of crystalline 

 powder, which, when re-dissolved, gave a fine yellow precipitate with bichromate 

 of potash, and a black one with sulphuretted hydrogen, clearly proving the pre- 

 sence of lead dissolved in the water. , 



On referring to what has been stated in my account of my first experiments 

 respecting the action of water on lead, it will readily appear why this water 

 should have oxidated and dissolved the metal of the pipe. The spring is not only 

 one of very great purity, but the protective salts contained in the water likewise 

 consist chiefly of those whose preventive power is the feeblest of all the natural 

 ingredients of springs. For in my experiments on the small scale, it did not ap- 

 pear that the hydrochlorates effectually prevented the action of distilled water, 

 unless present in the proportion of a 2000th at least. 



It remains to take notice of the remedy applied in this case. When a similar 

 instance happened at Tunbridge, in 1814, with the additional circumstance that 

 its nature was not discovered till lead-colic began to appear among the irunates 

 of the houses supplied with the water, the only satisfactory remedy which could 

 be thought of, was the expensive one of removing the pipes and replacing them 



* On again lately analyzing the water, I found the solid residuum to be exactly one grain in 17,500. 

 Nitrate of baryta, after twenty-four hours' rest, occasioned an exceedingly scanty deposite of sulphate ; 

 and the residuum left, on evaporating 17,000 grains, effervesced very slightly with diluted nitric acid. 

 The sulphates and carbonates were thus again proved to exist in very minute proportion. In this water 

 a stick of polished lead became tarnished in an hour ; and in four days a little white powder formed on 

 the bottom of the vessel under the lead. 



