Integral Weights in Chemistry. 319 



each being in a simple relation of volumes, the weight of this 

 unit-volume of any species has also been called its propor- 

 tional weight or combining weight. 



These relative weights of equivalent volumes become, in the 

 language of the atomic hypothesis, atomic or molecular weights. 

 Since, however, a gas or vapour, whether it be of a so-called 

 elemental species, or one known to be formed by homogeneous 

 or by heterogeneous integration, is a unit or integer the spe- 

 cific gravity of which, at standard temperature and pressure, 

 varies directly as its equivalent or combining weight ; and, 

 further, since this weight is nothing else than the specific 

 gravity of the gas or vapour, hydrogen being unity (H 2 = 2), 

 it may, dispensing with all hypothesis, be designated the 

 weight of the integer, or, in other words, as the integral weight 

 of the gaseous or vaporous species. 



3. From the time of Gay-Lussac, the fact that all chemical 

 reactions, so far as regards gaseous or vaporous species, are 

 subordinated to a simple relation of volumes, and that the 

 specific gravity of such species is but a function of the equi- 

 valent or integral weight, has been well understood; the 

 volume at standard temperature and pressure being invariable. 

 The attempts made to establish a similar relation between the 

 specific gravity and the integral weights of liquid and solid 

 species have, however, hitherto been unsuccessful for the 

 reason that the law of volumes was lost sight of, and the 

 volume for such species, instead of being regarded, as in the 

 case of gaseous bodies, as a constant unit, was assumed to be 

 an arbitrary and a variable quantity ; the so-called atomic or 

 molecular volume being conceived as conditioned, not only by 

 crystalline form, but by various other circumstances. That 

 the law of volumes, as proclaimed by Gay-Lussac, applies not 

 only to gaseous species, but to liquids and solids also, was, 

 however, maintained by the present writer in 1853, " as lead- 

 ing the way to a correct understanding of the equivalent 

 volumes of the latter;" although the constantly affirmed tra- 

 dition of the subordination of the so-called molecular volume 

 of solid species to the variations of crystalline form prevented 

 him, for many years afterw r ard, from arriving at the simple 

 solution of the problem embodied in the assertion made at the 

 same time, that " the doctrine of chemical equivalents is that 

 of the equivalency of volumes ; " or, in other words, that the 

 law of volumes is universal, and that for all species — solid, 

 liquid, or gaseous — the volume, under proper conditions of 

 pressure, is the same. 



4. Hydrogen, as the lightest known species, is the unit of 

 integral weight in Chemistry; and a litre of this gas at 0°and 



