454 DR LYON PLAYFAIR AND MR J. A. WANKLYN ON A MODE OF 
In neither of these determinations did the weight of aqueous vapour reach 10 
milligrammes. 
Hitherto substances supposed to be normal in regard to their vapour-densities 
have been examined. We next proceed to examine an abnormal case of con- 
siderable interest. Acetic acid, as is well known, is very irregular in its vapour- 
density. Canours, who has made many experiments upon it, gives its vapour 
density at different temperatures as follows :— 
At AO59 CIN. 3180 | AG BUOVCs OS 2:248 
130° we 3:105 220° res 2-132 
140° “eg 2-907 240° ie 2-090 
150° ae PA bi) 270° a3 2:088 
160° 7 2-604 . 310° ig 2:085 
170° ae 2-480 | 320° 2 2083 
180° 3 2°438 336° ae 2-083 
190° he 2-378 | 

Chemists seem to be divided as to the true explanation of this irregu- 
larity, some referring it to abnormal physical properties inherent in acetic 
acid vapour; others, on the other hand, to a change in composition taking 
place during alteration of temperature. Some experiments of BrneEav’s, to 
which we have previously referred, are decidedly in favour of the latter 
view. At ordinary temperatures, and at extremely reduced pressures, BINEAU 
finds for the vapour-density of acetic acid a number nearly approaching 4:00. 
It would seem from their being so rarely quoted that these results of BINEAU’s 
have not met with the credit which they deserve; and, indeed, the method 
employed is not altogether free from objection. Binrau 
made an imperfect barometer containing a chamber 
nearly void of air, and about 5 litres in capacity. He 
observed the temperature and the height of the column 
of mercury, comparing the latter with the height of a 
perfect barometer. A small weighed quantity of acetic 
acid, contained in a little bulb open at one end, was then 
introduced, a contrivance being used to prevent egress 
of the acid before the summit of the mercury was 
reached. As the capacity of the 5-litre dilatation was 
almost infinite compared with the capacity of a few 
millimetres length of the tube, it is evident that the volume of vapour could be 
directly measured by the depression caused in the column.* One of the causes — 
of uncertainty in these experiments is the great accuracy with which the readings — 
of the mercurial column must be made, in order to attain to even rough approxi- 
mate values of the vapour-density. This will be at once understood when we 
quote from Binrau’s memoir :— 











* Bineav, Ann. de Ch, et Phys., 3™e série, xvili. p. 236. 

