FREE AND PERFECTLY ELASTIC MOLECULES IN A STATE OF MOTION. 
63 
The length of that portion of it intercepted between the point of contact and the 
axis of the curve, is equal to three times the length of the abscissa. 
The tension given being e, and the corresponding absolute temperature r being 
required, assume any absolute temperature as near to r as may be guessed roughly; 
then, by the formula for the given vapour, t ———) = e, compute e. The value of 
r may then be found directly, with all necessary precision, by the following equation : 
f 4H -f 3G yt 
T= \vt^ +S ^ 
From this value of r subtract 461, and we have the temperature required on Fahr. 
scale that corresponds to the elastic force e. 
J. J. Waterston. 
December 15, 1845. 
Explanation of Table of Gases and Vapours. 
Received February 19, 1846. 
Having found the following Table useful to refer to while studying the subject of 
gases and vapours, I have been led to hope that it might be made available, so far as 
it goes, in shortening the labour of drawing up a complete view of their physical 
constants. That such a condensed view of their physical character and constitution 
is a desideratum will probably be generally admitted, and principally with reference 
to theoretical chemistry does it seem to be of importance to have their molecular 
characteristics placed before the eye in a clear and concise manner. 
The tables of this description that are usually inserted in chemical treatises do not, 
perhaps, give to the arithmetic of volumes all the clearness that it is susceptible of. 
This is a consequence of employing the chemical equivalent or lowest combining 
proportion as the unit, whether or not it happens to correspond with the specific 
gravity of the gas, and it is generally either half this ratio or, as in the case of 
sulphur, of phosphorus, and of arsenic, even a smaller fraction of it. 
Thus we have H + 0 the symbol for water. In Dr. Turner’s ‘Chemistry’ its 
constitution is thus defined : 1, or one equivalent of hydrogen, -j- 8; or one equivalent 
of oxygen, = 9 the equivalent of water; and, by volume, 100 of hydrogen combines 
with 50 of oxygen to form 100 of steam. If we take 16 as the equivalent of oxygen, 
which corresponds with its specific gravity, then HOj expresses distinctly the consti¬ 
tution of steam both by weight and volume. Another objectionable point may some¬ 
times be remarked though it has now almost disappeared, the combining ratio by 
volume is inserted before any determination of the fact has been made : thus 
