BODIES GENERALLY EXISTING AS GASES. 161 



I have not yet resolved this irregulanty, but believe there are two or more sub- 

 stances, physically, and perhaps occasionally chemically different, in olefiant gas ; 

 and varying in proportion with the circumstances of heat, proportions of ingredients, 

 &c. attending the preparation. 



The fluid affected the resin of the gauge graduation, and probably also the resin 

 of the cap cement, though slowly. 



Hydriodic acid. — This substance was prepared from the iodide of phosphorus by 

 heating it with a very little water. It is easily condensable by the temperature of a 

 carbonic acid bath : it was redistilled, and thus obtained perfectly pure. 



The acid may be obtained either in the solid or liquid, or (of course) in the gaseous 

 state. As a solid it is perfectly clear, transparent, and colourless ; having fissures 

 or cracks in it resembling those that run through ice. Its solidifying temperature is 

 nearly —60° Fahr., and then its vapour has not the pressure of one atmosphere ; at a 

 point a little higher it becomes a clear liquid, and this point is close upon that which 

 corresponds to a vaporous pressure of one atmosphere. The acid dissolves the cap 

 cement and the bitumen of the gauge graduation ; and appears also to dissolve and 

 act on fat, for it leaked by the plug of the stop-cock with remarkable facility. It 

 acts on the brass of the apparatus, and also on the mercury in the gauge. Hence the 

 following results as to pressures and temperatures are not to be considered more 

 than approximations : — 



At 0° Fahr. pressure was 2*9 atmospheres. 

 At 32° Fahr. pressure was 3*97 atmospheres. 

 At 60° Fahr. pressure was 5-86 atmospheres. 



Hydrohi^omic acid. — This acid was prepared by adding to perbromide of phos- 

 phorus* about one-third of its bulk of water in a proper distillatory apparatus 

 formed of glass tube, and then applying heat to distil off the gaseous acid. This 

 being sent into a very cold receiver, was condensed into a liquid, which being rec- 

 tified by a second distillation, was then experimented with. 



Hydrobromic acid condenses into a clear colourless liquid at 100° below 0°, or 

 lower, and has not the pressure of one atmosphere at the temperature of the carbonic 

 acid bath in air. It soon obstructs arid renders the motion of the mercury in the air- 

 gauge irregular, so that I did not obtain a measure of its elastic force ; but it is less 

 than that of muriatic acid. At and below the temperature of —124° Fahr. it is a 



ments of ice which formed on it in the air conducted, for when touched it preserved its electric state. Believing 

 as yet that the account I have given of the cause of the electric state of an issuing jet of steam and water (Phil. 

 Trans. 1843, p. 17) is the true one, I conclude that this also was a case of the production of electricity simply 

 by friction, and unconnected with vaporization. 



* The bromides of phosphorus are easily made without risk of explosion. If a glass tube be bent so as to 

 have two depressions, phosphorus placed in one and bromine in the other ; then by incHning the tube, the 

 vapour of bromine can be made to flow gradually on to, and combine with, the phosphorus. The fluid proto- 

 bromide is first formed, and this is afterwards converted into solid perbromide. The excess of bromine may be 

 dissipated by the careful application of heat. 



MDCCCXLV. Y 



