CHEMICAL SCIENCE. 177 



small doses of arsenious acid, a fact well known to horse-dealers. 

 That quantity of fat, and of albumen, which corresponds to the 

 depression in the secretion of carbonic acid and urea, remains in the 

 body ; and if the animal receive adequate nourishment, its weight 

 increases. 



CONTAMINATION OF WATER BY LEAD. 



A letter having appeared in the Times from Professor Faraday, 

 explaining a very simple mode of treating Water that was contami- 

 nated by receptacles of Lead in the neighbourhood of the sea (a 

 matter of great interest at military posts), Sir John Burgoyne 

 requested Dr. Faraday to favour him with a note on the subject, with 

 the addition of any simple practical remedies, if such there were, for 

 the presence of lead in water arising from other combinations. The 

 following answer was returned by that eminent chemist : — 



" Royal Institution. 



" ATy dear Sir John, — I consider your request relating to the leaded 

 water an honour, and in replying may add an observation or two to 

 the original matter. The case at first was simply that of certain 

 waters, which, having been collected from rain, by roofs, gutters, 

 pipes, or cisterns of lead, were contaminated more or less with the 

 metal. All water so obtained has not been found thus affected, and 

 there is much difference and uncertainty about the mutual action of 

 lead and water in different cases. When rain water falls upon 

 surfaces of lead it is apt to act on them ; and the water thus con- 

 taminated, by standing exposed to air generally clears itself from the 

 dissolved lead, the metal separating as a carbonated precipitate, and 

 falling to the bottom. But when the sea spray has access to the 

 leaded surfaces, the action of the rain water is such that the dissolved 

 lead does not separate in this way, or if it does, only after a much 

 longer time.* It is such water as this that I recommend to be 

 treated with carbonate of lime. Enough whitening or levigated 

 chalk is to be mixed with the fluid to make it of the consistency of 

 good milk (though more will do no harm), and the whole is either to 

 be filtered or to stand until clear. I have never yet found any 

 sample of water poisoned as above, that was not freed from the lead 

 by this process ; and from the actions that occur in the laboratory, I 

 have no doubt, that if two or three pounds of such powdered chalk 

 were put into a cistern, and stirred up occasionally after rain, it 

 would keep the water free from lead. Now, my consideration was 

 entirely confined to cases of the above kind, and to the service of 

 the Trinity House. I might say much more to you about the modes 

 of testing for lead in water, so as to discover its presence, aud, 

 within certain limits, its proportion, and also about the clearance of 

 lead from all domestic waters by filtration, or otherwise ; but I have 



* Professor Faraday, in his letter to the Editor of the Times, stated that "the 

 salt of the sea spray, which often reaches the roofs of buildings, even when they 

 are half-a-mile or more from the shore, causes the rainwater to dissolve aporiiou 

 of the lead, which is larger or smaller under different circumstances, and at times 

 rises up to a quantity injurious to health, and poisonous." 



M 



