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preservative power as would be inferred from Dr. Christison's 

 remarks. Even rain water, in the ordinary modes of collec- 

 tion, acquires occasionally, according to his observations as 

 well as my own, sufficient saline matter to be quite preserva- 

 tive. But it may be unsafe to trust to this as sanctioning the 

 use of rain water conducted from leaden roofs, or its preser- 

 vation in leaden cisterns, when intended in either case for 

 culinary uses. He points out, too, a mode in which leaden 

 cisterns, when kept covered, may be and have been acted on 

 while storing water in itself preservative. It is that such 

 water will give out vapour to the atmosphere above ; when 

 the cistern is only partially full, this vapour, on any accidental 

 reduction of temperature, condenses as pure or distilled water 

 on the uncovered portion, acts on this, and trickles down to 

 the saline or preservative water beneath. He describes some 

 cisterns the upper parts of which had been corroded in 

 this manner. Minute, accurate, and systematic as were the 

 experiments of Dr. Christison, to which the above ab- 

 stract does but feeble justice, he has not exhausted the sub- 

 ject. He found the presence of much carbonic acid in the 

 water to counteract somewhat powerfully the defensive effect 

 of the salts. With me this has been less remarkable than with 

 him. I think that I have observed lead partially immersed to 

 be, apart from any condensation of water, more acted on than 

 when wholly immersed. I impute this to a galvanic action 

 between the wet and the dry lead. The question, very ma- 

 terial in a practical point of view, how far slight impurities of 

 certain kinds in the lead itself render it more or less readily 

 acted on? has not been scientifically investigated. Dr. C. does 

 not touch upon it. I find Chinese tea lead, which contains 

 tin, to remain bright in such distilled water as rapidly acts on 

 plumber's English lead ; but on the other hand plumber's 

 solder, which contains a much greater proportion of tin, was 

 in one cistern more generally attacked than the lead itself. 



