On Chemical Equi talent a. 107 



that the ratio of their union is that of 1 to 1, of 1 to 2, or of 

 1 to 3, by volume. It is important to observe, that when we 

 consider the weights, there is no simple and definite relation 

 between the elements of a first combination ; it is onlv when 

 there is a second between these same elements, that the new 

 proportion of that body which has been added, is a multiple of 

 the first. Gases, on the contrary, in such proportions as can 

 combine, give rise always to compounds whose elements are in 

 volume nmltiples the one of the other. 



" Not only do the gases combine in very simple propoftions, 

 as we have just seen, but moreover the apparent contraction of 

 volume which they experience by combination, has likevvise a 

 simple relation with the volume of the gases, or rather with the 

 volume of one of them." 



By supposing the contraction of volume of the two gaseous con- 

 stituents of water to be only equal to the whole volume of oxvgen 

 added, he found the ratio of the density of steam to be to that 

 of air as 10 to 16; a computed result in exact correspondence 

 with the experimental result lately obtained in an independent 

 method, by the same excellent philosopher. "Ammoniaca! gas 

 is composed in volume," says he, " of 3 parts of hydrogen and 

 1 of azote, and its densitv, compared to that of air, is 0*595* ; 

 but if we suppose the apparent contraction to be one-half of 

 the total volume, we find 0-591 for its density. Thus it is de- 

 monstrated by this nearly perfect accordance, that the apparent 

 contraction of its elements is precisely one-half of the total 

 volume or rather double the volume of azote." M. Gay-Lussac 

 subjoins to his beautiful memoir a table of gaseous combination, 

 which, with some modifications derived from subsequent re- 

 searches, will be inserted under the article Gas. 



The same volume of the Memoires ])resents another import- 

 ant discovery of M. Gay-Lussac, on the subject of equivalent 

 proportions. It is entitled. On the relation which exists between 

 the oxidation of metals, and their capacity of saturation for 

 the acids. He here proves by a series of experiments, that the 

 quantity of acid which the different metallic oxides require for 

 saturation, is in the direct ratio of the quantity of oxygen which 

 they respectively contain. " I have arrived at this principle," 

 says he, " not bv the comparison of the known ])roportions of 

 the metallic salts, which are in general too inexact to enable us 

 to recognise this law, but by observing the mutual precipitation 

 of the metals, from their solutions in acids." 



When we precipitate a solution of acetate of lead, by a plate 



of zinc, there is formed a beautiful vegetation known under the 



;iame of the tree oj Saturn; and which arises from the rcduc- 



O 2 tion 



