120 CONTRACTION AND EXPANSION 



quires a temperature of about 640 F. to maintain 

 it in the gaseous form, when not united with other 

 bodies. But if brought into contact with hydrogen 

 gas, or if sulphur be volatilized in contact with 

 hydrogen, they both undergo remarkable changes. 



1. In the first place, 16 parts by weight of sul- 

 phur combine chemically with 1 of hydrogen, 

 forming hydrosulphuric acid (sulphuretted hy- 

 drogen), the specific gravity of which is 17 times 

 that of hydrogen, and its elastic force compara- 

 tively low. The particles of sulphur, which are 

 16 times larger than those of hydrogen, attract 

 from the latter gas a portion of the aether which 

 encompassed its atoms, by which they are inti- 

 mately united. 



2. During this process, the particles of sulphur 

 acquire a much greater repulsive force, and are 

 removed so much farther from each other, that 

 they occupy 6 times the volume which they did 

 in the form of vapour, before combining with the 

 hydrogen. 



3. The elastic force of the hydrogen is so far 

 diminished by uniting with sulphur, atom to 

 atom, that sulphuretted hydrogen maybe liquefied 

 by a pressure equal to 17 atmospheres at the tem- 

 perature of 50, according to the experiments of 

 Faraday. It was afterwards discovered by Davy 

 that when reduced to the temperature of 3 F., 

 the elastic force of its vapour was equal to the 

 pressure of only 14 atmospheres. 



