398 Proceedings of the British Association. 



the decomposition of the salts of the oxide of zinc ; but the heat extracted 

 by the former was about twice as great as that extracted by the latter, 

 because the oxide of copper produces less heat in combining with the acids 

 than the oxide of zinc. The salts of lime furnish an example of an absorp- 

 tion of heat when their solutions are decomposed by potash, — a circum- 

 stance easily explained by the fact before established, that the hydrate 

 of lime, when combining with the acids, develops more heat than the 

 hydrate of potash. But, in accordance with the principle above stated, 

 the diminution of temperature is the same with equivalents of all the 

 salts of lime. In an inquiry of this kind many precautions are requi- 

 site, in order to obtain accurate results. Among the most important 

 may be mentioned, the exact neutrality of the salt to be decomposed, a 

 perfect equality of temperature in the solution before mixture, and the 

 precipitation of the oxide in the state of a pure hydrate, and not of a 

 subsalt. — Prof. Kane thought it highly probable that the law propounded 

 by Dr. Andrews will eventually be judged by chemists to be the most 

 important communication made to this Section. He also observed, that 

 if we mix an atom of oil of vitriol with an atom of water, a con- 

 siderable degree of heat is developed. Now, the concentrating of this 

 dilute acid was not simply a case of evaporation, but one of decompo- 

 sition ; and it would appear that the same quantity of heat was necessa- 

 ry to effect that decomposition as was developed during the combination. 



Mr. West read a paper " on a remarkable case of Corrosion of Lead 

 by Spring Water, after passing through an Iron Pipe.'''' The water of 

 a spring, which had flowed into and from a leaden reservoir for sixty 

 years without injury to either, and which passed through leaden pipes 

 without metallic impregnation, when further conveyed a long distance, 

 through iron pipes, contained lead in solution, and was so destructive to 

 the bottoms of the leaden cisterns, into which it next flowed, that some 

 of them had to be renewed in five or six years. Mr. West stated the 

 analyses of the water in question, which, except as to the lead, were the 

 same when taken from all the three situations : he imputes the mischief 

 to contact with oxides of iron from the pipes, and considers that the 

 remedy must be mechanical, by coating the iron pipes or the leaden 

 cisterns with some other substance, so as to preserve the lead itself from 

 contact with peroxide of iron. 



" On the Decomposition of Carbonic Acid Gas, and the Alkaline Car- 

 bonates, by the Light of the Sun," by Prof. Draper of New York. The 

 decomposition of carbonic acid gas, by the leaves of plants under the 

 influence of the light of the sun, is one of the most remarkable facts 

 in chemistry. Dr. Daubeny, in a very able paper in the Transactions 

 of the Royal Society for 1836, came to the conclusion, that the decom- 

 position in question was due to the rays of light, a result obtained by 



