444 DR LYON PLAYFAIR AND MR J. A. WANKLYN ON A MODE OF 

with a view to questions of chemical constitution, it may be desirable to show 
that a vapour partially saturating a gas deposits itself like a gas, although the 
temperature is lower than that requisite for its condensation if alone and under 
ordinary barometric pressure. 
The researches of REGNAULT on aqueous vapours, undertaken with a view to : 
meteorological inquiries, have shown that the vapour of water at a temperature : 
even so low as 0° C. behaves as if it were a true gas. Its ratio of expansion 
closely approximates to that of air; its vapour density, when mixed with air, is 
‘622, or the theoretical numbers. The evidence in this case is satisfactory, that 
aqueous vapour, held as such in air, follows the laws which regulate uncondensible 
gases; but the mode in which the results were obtained is quite special, and appli- 
cable only to water itself.* The tension of water at low temperatures having 
been determined, RecNaULT caused a measured volume of air, saturated with | 
moisture at a known temperature, to pass through a weighed tube containing sul- | 
phuric acid. The increase in weight of the drying-tube gives the amount of : 
aqueous vapour present; and as the quantity of moist air and the tension of water 
were known, the data were sufficient to calculate the volume of the aqueous 
vapour which occasioned the increment in weight. 
By employing permanent gases to take up volatile liquids, we have examined 
whether other vapours comport themselves like gases, as aqueous vapour does. 
Our experiments embrace alcohol and ether: the former we have employed in a 
slightly moist state, and also absolutely anhydrous. | 
For this inquiry we have found a slight modification of Gay-Lussac’s process 
to be most convenient. <A carefully dried graduated tube is filled with warm mer- 
cury, and inverted in the mercurial trough. Next, dry hydrogen is introduced. 
The gas is then measured, adopting the precautions which are requisite in measure- 
ments for a gas analysis. The liquid to be operated upon, of which a weighed 
portion is contained in a small glass bulb, is subsequently passed up to the hydro- 
gen contained in the graduated tube. The tube, with its contents, is then lifted 
out of the mercurial trough by means of a small iron cup, and transferred to the 
bath in which it is to be heated, and which contains some mercury, occupying 
about an inch of its interior. An adjustment of the graduated tube having been 
made, water is poured into the bath, and heat applied, until the boiling-point of 
the liquid under examination has been passed. After all the liquid contained in 
the bulb has evaporated, the bath is allowed to cool very slowly, being stirred up 
constantly, so as to keep its temperature uniform throughout. Before each obser- 
vation, great care was taken to ensure uniformity of temperature. 
The following minute corrections were made :— 
1. A correction for meniscus equal to 0°3 cubic centimeter. 









* Reenavtt, Ann. de Ch. et Phys., 3™° séries, p. 158. 

