458 DR LYON PLAYFAIR AND MR J. A. WANKLYN ON A MODE OF 
Thus it appears that great dilution with hydrogen does not hinder the specific 
gravity from attaining to nearly 4:1 at low temperatures. 
Acetic acid vapour at low temperatures is chemically different from acetic 
acid vapour at high temperatures. Two modes of representing the change at 
once suggest themselves—viz., 
The former equation is more in accordance with our results than the latter, 
requiring that acetic acid having (at high temperatures) a vapour density of 
2°073, should double on cooling, so as to have a vapour density of 4:146. The 
second equation requires a change of 6 vols. into 4, or an increase of vapour 
density to 3:112—a number which is considerably exceeded in our experiments. 
Further experiments are needed to decide between these different modes of 
representation. Ata future opportunity we hope to have the honour of laying 
before the Society the results of a further enquiry, embracing different members 
of the Acetic Acid series. In particular, the results of a diffusion-analysis applied 
to these vapours, as it has been already by Bunsen and FRANKLAND, to certain 
permanent gases, promise to throw much light upon the subject. 
The following supplement contains some examples of vapour densities taken 
upon bodies which, from their proneness to decomposition, have not hitherto 
been attempted. 

Supplement containing instances of the employment of the foregoing methods. 
(Read 29th April 1861.) 
Nitrate of Ethyl. 
Among the nitrates, the nitrate of methyl alone has been made the subject of 
a vapour-density determination. Bodies of this kind become explosive on being 
raised only a few degrees above their boiling points, and hence are difficult to treat — 
by the usual methods. 
We have deemed it interesting to estimate the vapour-density of nitrate of 
ethyl. 
The nitrate of ethyl used in our experiments had been prepared by the action 

