BODIES GENERALLY EXISTING AS GASES. 



169 



The mixed solid and liquid substance yields a vapour of rather less pressure than 

 one atmosphere. In accordance with this result, if the liquid be exposed to the air, 

 it does not freeze itself as carbonic acid does. 



The liquid tends to distil over and condense on the cap cement and bitumen of 

 the gauge, but only slightly. When cyanogen is made from cyanide of mercury 

 sealed up hermetically in a glass tube, the cyanogen distils back and condenses in 

 the paracyanic residue of the distillation, but the pressure of the vapour at common 

 temperatures is still as great, or very nearly so, as if the cyanogen were in a clean 

 separate liquid state. 



A measured portion of liquid cyanogen was allowed to escape and expand into gas. 

 In this way one volume of liquid at the temperature of 63°Fahr. gave 393*9 volumes 

 of gas at the same temperature and the barometric pressure of 30*2 inches. If 100 

 cubic inches of the gas be admitted to weigh 55*5 grains, then a cubic inch of the 

 liquid would weigh 218-6 grains. This gives its specific gravity as 0"866. When 

 first condensed I estimated it as nearly 09. 



Cyanogen is a substance which yielded on different occasions results of vaporous 

 tension differing much from each other, though the substance appeared always to be 

 pure. The following are numbers in which I place some confidence, the pressures 

 being in atmospheres of 30 inches of mercury, and the marked results experimental ='<'. 



Ammonia. — This body may be obtained as a solid, white, translucent, crystalline sub- 

 stance, melting at the temperature of 103° below 0°; at which point the solid sub- 

 stance is heavier than the liquid. In that state the pressure of its vapour must be 

 very small. 



Liquid ammonia at 60° was allowed to expand into ammoniacal gas at the same 



temperature ; one volume of the liquid gave 1009*8 volumes of the gas, the barometer 



being at the pressure of 30*2 inches. If 100 cubic inches of ammoniacal gas be allowed 



to weigh 18-28 grains, it will give 184-6 grains as the weight of a cubic inch of liquid 



ammonia at 60°. Hence its specific gravity at that temperature will be 0'731. In 



the old experiments I found by another kind of process that its specific gravity was 



0-76 at 50°. 



* See Bunsen's results, Biblioth^que Universelle, 1839, xxiii. p. 185. 



MDCCCXLV. Z 



