OF GASEOUS BODIES. 123 



vapour, in accordance with the law of multiples 

 as shown in hydrochloric acid, ammonia, &c. 



The same principle applies to the various com- 

 binations of hydrogen with the vapours of bro- 

 mine, cyanogen, arsenic and mercury, as in its 

 combinations with the vapours of sulphur, iodine, 

 &c. (See Table III. of the preceding Chapter.) 



When 3, 4, or 5 volumes of oxygen combine 

 with 2 of nitrogen, the aggregate bulk and elastic 

 force of the resulting compounds diminish with 

 every additional dose of oxygen. Nitrous and 

 nitric acid may be liquefied by moderate degrees 

 of cold without pressure. Yet they contain nearly, 

 if not quite as much caloric as the oxygen and 

 nitrogen of which they are composed, when in a 

 separate state. It was long ago observed by 

 Higgins, that during those combinations no ca- 

 loric is given out and that during the union of 

 nitric acid with potass, very little heat is disen- 

 gaged.* 



That this is really true, would appear from the 

 immense quantity and intensity of the heat evolved 

 by the deflagration of nitrate of potass with char- 

 coal and sulphur, as in gunpowder and other de- 

 flagrating mixtures formed of nitre, phosphorus, 

 naphtha, turpentine, and various combustibles. It 

 is generally known, that during their combustion 

 with nitre, nearly as much caloric is given out, 



* It is also known that when nitrous acid is passed through a 

 red hot iron tube, it is decomposed into its constituent elements, 

 which resume their original volumes and elastic force. 



