SIR B. C. BRODIE ON THE CALCULUS OE CHEMICAL OPERATIONS. 
59 
naturae,” which cannot be generated by any known process of generation. Without 
venturing to impose any limit on the powers of nature, we yet should think twice about 
the evidence before committing ourselves to belief in a mermaid ; and I must confess 
that I feel a similar hesitation in believing in the existence of any chemical substance 
made out of hydrogen, oxygen, and nitrogen which cannot be made by the operations 
a, and v. We are not, however, driven into this corner. 
First, we may notice in regard to one of these two substances, namely, hyponitric 
acid, that the observed density of the gas is not a constant, but varies with the tempe- 
rature at which the observation is made. This point has been observed in three inde- 
pendent sets of experiments by Playfaie and Wanklyx, by Mullee and by Deville, 
the results being in the main concordant. When the density is taken at a low tempe- 
rature, it approximates to, although it does not reach, the number corresponding to the 
symbol av 2 ^ ; thus we have : — 
Density 
Density 
Observer. 
Temperature. 
(Air 1). 
(Hyd. 1). 
Deville 
261 
2-65 
38-24 
Mullee 
20 
210 
38-96 
Playfaie and Wanklyn . 
24-5 
2-52 
36-39 
55 55 
11-3 
2-64 
3819 
55 55 
4-'2 
2-59 
The density corresponding to the symbol av 2 ^ is 46’0, showing a difference between 
this number and the lowest observed density of about 1 5 per cent. 
As the temperature of the gas increased the density diminished, until the observed 
density (in the observation made) attained a numerical value of 1*57, after which the 
observations ceased. 
In the following Table these densities are calculated on the hydrogen scale, and also 
in the usual manner, the density of air being assumed as 1 : — 
Density 
Density 
Temperature. 
(Air 1). 
(Hydrogen 1). 
100°-1 
1-68 
24-24 
111-3 
1-65 
23-80 
121-5 
1-62 
23-35 
135-0 
1-60 
2314 
154-0 
1-58 
22-80 
183-2 
1-57 
22-60 
Now the theoretical density of the tetroxide of nitrogen symbolized as av 2 | 4 is on the 
hydrogen-scale 46, and on the air-scale 319. Half this density, therefore, is on the 
hydrogen-scale 23, and on the air-scale 1-59. The conclusion to be drawn from these 
numbers, therefore, is that the gas undergoes a gradual expansion with the increase of 
temperature until at about 150° this limit is attained, so that the constitution of the 
MDCCCLXXVII. K 
