VOLUMES OF ATOMS IN THE GASEOUS STATE. 127 



<jases combine by measure, was first observed by Humboldt 

 and Gay-Lussacin 1805. The subject was pursued by the latter 

 chemist, who established the simple ratios in which gases gene- 

 rally combine, and published the laws observed by him, or his 

 Theory of Volumes, shortly after the announcement of the 

 Atomic Theory by Dalton. They afforded new and indepen- 

 dent evidence of the combination of bodies in definite and also 

 in multiple proportions, equally convincing as the observed 

 proportions by weight in which bodies unite. Gay-Lussac 

 likewise observed that the product of the union of two gases, 

 if itself a gas, sometimes retains the original volume of its 

 constituents, no contraction or change of volume resulting from 

 their combination; thus one volume of nitrogen and one vo- 

 lume of oxygen form two volumes of deutoxide of nitrogen ; 

 one volume of chlorine and one volume of hydrogen form two 

 volumes of hydrochloric acid gas ; and that when contraction 

 follows combination, which is the most common case, the vo- 

 lume of the compound gas always bears a simple ratio to the 

 volumes of its elements. Thus two volumes of hydrogen and 

 one of oxygen form two volumes of steam, one volume of ni- 

 trogen and three of hydrogen gas form two volumes of ammo- 

 niacal gas, one volume of hydrogen and one-sixth of a volume 

 of sulphur- vapour form one volume of sulphuretted hydrogen 

 gas. In these and all other statements respecting volumes, 

 the gases compared are supposed to be in the same circum- 

 stances as to pressure and temperature. 



The uniformity of properties observed among gases in 

 compressibility and dilatability by heat, has appeared to many 

 chemists to indicate a similarity of constitution, and to favour 

 the idea that they all contain the same number of atoms in 

 the same volume. May not equal volumes of oxygen and hy- 

 drogen gases, for instance, be represented by an equal num- 

 ber of atoms of oxygen and hydrogen respectively placed at 

 equal distances from each other, and the difference of sixteen 

 to one in the densities of the two gases arise from the atom of 

 oxygen being really sixteen times heavier than that of hydro- 

 gen? Equal volumes of gases would then contain an equal 

 number of atoms, and one, two or three volumes would be 

 an equivalent expression to one, two or three atomic propor- 

 tions, the terms volume and atom becoming of the same import, 

 or expressing equal quantities of bodies. But such a view is 



