S74 



Analyses of Books* 



[Mat, 



The opinion that heat is -a body is so consonant to the corarooii 

 sense of mankind, that 1 defy any man to explain the pheoo- 

 inena of heat without using a language which implies it, how 

 hostile soever his own notions may be to this opinion. In this 

 respect it agi ees with the Newtonian doctrine of light. As the 

 opinion that heat is a body was universally embraced by chemi- 

 cal philoi^ophers for about 40 years, it is not surprising that the 

 love of novelty, or the discovery of new facts, should induce 

 modern philosophers to incline to the contrary opinion. This 

 vacillation 1 conceive to be of great service to the knowledge of 

 the subject;, by inducing the pioneers of science to neglect no 

 part of the subject, but to break up the ground in every quarter, 

 and thus to throw together a much greater mass of important 

 facts than could otherwise be collected. But the knowledge of 

 the subject is not yet far enough advanced to bear the conclu- 

 sions of Count llumford and Sir Humphry Davy ; perhaps it 

 may never reach such a point, for some subjects are so much 

 beyond the reach of the human faculties that the more they are 

 discussed the iiiore obscure they become. 



Sir Humphry Davy next takes a general view of the pheno- 

 mena of chemical ahuiity. This part of the work is chiefly 

 calculated for those who have made some progress in chemistry ; 

 and will be read with most interest by those who are best ac- 

 quainted with the science. The following are the general heads 

 stripped of all their illustrations. , Some bodies, as oil and 

 water, do not unite together ; while others, as salt and water, 

 do. \¥hen substances combine, the Gjualities of the new com- 

 pound differ very much from those of its constituents. Bodies 

 before they unite chemically must be in apparent contact; but 

 it is not necessary that one of them be in a state of liquidity. 

 Substances vary io the intensity of their afiinity. Hence one 

 substance is capable of displaci'Dg another, and these decompcsi- 

 tioos are facilitated 6y the mutual action of four bodies, or what 

 are called double decompositions. All chemical compounds 

 consist of bodies united in definite and constant proportions. 

 Sir H. Davy is happy io the numerous illustrations which he has 

 addiiced in proof of this fact. The most beautiful are those of 

 the combinations of the gases. The respective weights of bodies 

 that unite may be represented by numbers and their multiples, 

 and the following are the numbers belonging to the elementary 

 , bodies which he notices in this part of his work : — 



Hydrogen 1 



Oxygen 15 



Azote , 26 



Chlorine , .67 



Potassium 7^ 



These numbers would require some animadversions; but the 



