TAKING THE DENSITY OF VAPOUR OF VOLATILE LIQUIDS. 461 
E, 
Determination of Vapour-density of Nitric Acid at 68-5° C. 
Cubic Centimeters 
at 0° C. and 760 m.m. Grm. 


Vol. of Air+ Vapour = 394:60 weighing °7255 
ay aud = 262:48 4 3395 
132°12 *3860 
Hence 132-12 cub. cent. of nitric acid vapour weighs ‘3860 grm. Vapour- 
density = 2:258. In the above experiment the bulbs, when sealed up, were per- 
fectly colourless. 
ine 
Determination of Vapour-density of Nitric Acid at 40°5° C. 
Cubic Centimeters 

at 0° C. and 760 m. m. Grm. 
. fare ee . . 
Vol. of Air+ Vapour, 31762 weighing ‘4664 
at ies < 5 286:38 55 3705 
31:24 "0959 
Hence 31:24 C. C. of nitric acid vapour weigh 0959 grm. Vapour density 
=2-373. In this instance the bulbs were very faintly tinged with peroxide of 
nitrogen. Possibly this may be the real reason why in this case the number is a 
little higher than in the former experiment. 
¢: Vapour Densities. 
Obs. 1 at 68°5° , , ; F 2°258 
oD yp 40°5 2-373 
The formula | O, requires eS x 0691 =2-1766. 
It thus appears that nitric acid vapour is pretty nearly normal, even at many 
degrees below the boiling point, under ordinary atmospheric pressures. 
Here the remark may be made, that one of the sources of uncertainty belonging 
to Dumas’ method is avoided. 
_ Several grammes of substance are generally taken for a Dumas’ vapour-density 
determination. Fractional distillation takes place in course of the operation, so 
that unless the substance be of extreme purity, the specific gravity obtained is 
liable to depart widely from the mean specific gravity of the sample. 
The method which we have described completely avoids this. Only a small 
quantity of substance is necessary, and even that need not be completely evapo- 
rated, since the portion of the apparatus containing the substance is afterwards 
separated from the portion filled with gas and the vapour. 
Peroxide of Nitrogen, N O,. 
Peroxide of nitrogen offers one of the examples of physical and chemical pro- 
VOL. XXII. PART III. 6c 
