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, 
id duces less heat in combining with the acids 
mieh an le onfa 
n ahenrn 
than the oxide of zinc. The salts of li p P 
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 requis 
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 CcoM- 
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 necess@- 
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 ine 
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 2 
influence of the light of the sun, is one of the most remarkable facls : 
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 
