310 M. Beketoff on the Displacement of some Elements by others. 



iodide of silver is the most stable, because here the ratio of the 

 equivalents is nearest unity. Hence it is that AgO so readily 

 decomposes with KI, and in like manner AgCl with KBr and 

 KI. But potash decomposes Agl and AgBr only with diffi- 

 culty, but AgCl much more easily. The elements have there- 

 fore a tendency to form compounds with equal equivalents ; and 

 it is not surprising that the author could liberate barium from 

 BaO, but not from BaCl by aluminium. 



This, however, forms no exception to the influence of the 

 specific gravity of the elements upon the course of the reaction. 

 According to Wohler, aluminium can readily liberate Ag from 

 Agl, and the author succeeded in doing the same with manga- 

 nese. But at a very high temperature aluminium and, especi- 

 ally, magnesium will probably be set free from their respective 

 iodides by silver, as in fact Deville has set potassium free from 

 KI by silver. 



The author thinks that all these phenomena, taking into 

 account Dulong and Petit's law, may be deduced from the me- 

 chanical theory of heat. He finds a confirmation of his views 

 in the composition of the earth's crust itself. Al and Se, whose 

 equivalents and specific heats are almost equal, are for the most 

 part found combined with oxygen and with one another. Fluorine 

 is mostly combined with Ca, CI mostly with Na, Ag frequently 

 with I. But the phenomena of the so-called elective affi- 

 nity remain unexplained. If it is intelligible why, for instance, 

 AgO decomposes with KI, it is also inexplicable why K unites 

 with CI, Br^ and even I, but not Ag or Zn. 



The compounds which chemically dissimilar elements form 

 are stable, and take place in few ratios ; while the compounds of 

 analogous elements (for instance CI and Br) can take place in 

 several ratios, and have but little stability. In the first case the 

 combination always takes place with more or less disengagement 

 of heat, in the second case seldom or never. If the heat is trans- 

 muted into motion, the conclusion is obtained that the elemen- 

 tary, motions of one kind of elements (K, Na, &c.) interfere with 

 the motions of the other elements, but not with those of each other. 

 The reason of this peculiar deportment of the elements could only 

 be deduced from hypotheses, upon which the author will not at 

 present enter. 



In the thermal phenomena of chemical reactions, the quantity 

 of heat which is used in a change of volume of the compounds 

 must be taken into account. The quantity of heat which becomes 

 free in the union of two bodies is T = X + B, in which X is the 

 heat which becomes free in the combination or neutralization of 

 properties, and B is the heat used up in the change of volume. 



As T is known from experiment, and B may be calculated, X 



