TRANSACTIONS OF THE SECTIONS. 
O i O 
spheric air at 60°, barom. 30 inches, are found by experiment 
to weigh 31*0117 grs.; but if we wish to know from this datum 
what the same bulk of air will weigh at 32°, Gay-Lussac’s for¬ 
mula will give us 32*8206 grs. instead of 32*7900 grs., being an 
error of no less than *0306 gr. in weight, and nearly one tenth 
of a cubic inch in volume. 
The experiments on moist air are expected to throw consi¬ 
derable light on the law of the tension of vapour; but for want 
of leisure principally they have not yet been completely investi¬ 
gated. For similar reasons also, some observations on the spe¬ 
cific gravities of hydrogen, oxygen, azote, and carbonic acid 
gases are deferred till a future opportunity. In conclusion, it 
may be remarked, that the fluctuating weight of atmospheric 
air renders it a very improper unit of comparison for gaseous 
bodies : quite as improper, for example, as sea water would be 
for fluids. 
A letter w 7 as read from James Apjohn, M.D., Prof, of Che¬ 
mistry in the Royal College of Surgeons, Ireland, communica¬ 
ting A Formula by which a 'proper correction for Vapour 
may be applied to the specific Gravities obtained by Expe¬ 
riments on Gases saturated with Moisture. 
In this letter, the writer expresses his opinion that it was 
with great propriety the Association had directed the attention 
of chemists to a reinvestigation of the relative densities of the 
principal elementary gases. He had, in consequence, projected 
a course of experiments on this subject, which, however, had 
been interrupted by more urgent duties. The method of oper¬ 
ating by a comparison, in two successive experiments, of the 
weights of equal volumes of the gas, and of atmospherical air, 
is recommended by the circumstance of its being independent 
of all knowledge of the volume of the gas or of the weight of a 
given bulk of atmospheric air; but it requires either artificial 
desiccation, which is extremely troublesome; or if the gas and 
air are saturated with moisture, then, for rigorous exactness, it 
requires the correction for vapour ; to furnish which, Dr. Ap¬ 
john proposes the following formula. 
If the specific gravity of dry atmospherical air at any tempe¬ 
rature t, and pressure p, be represented by 1, it will become, 
rp 
when the air is charged with vapour, 
f+’ 6 ~ 5 p> / beill g the 
tension belonging to vapour at the temperature t. For similar 
reasons, if x represent the specific gravity of any other gas, at 
the same pressure and temperature, oc:—p~ 4"'625^ will be its 
