66 WHY GASES CONTRACT AND EXPAND 



phosphorus, sulphur, and various other bodies, 

 they are deprived of their elastic force, and in 

 many cases without any disengagement of 

 caloric. 



The following observations will shew at once 

 how chemical affinity modifies the specific gra- 

 vity and elastic force of gases. It has been seen 

 that the specific gravity of chlorine is 36 times 

 that of hydrogen. Its elastic force is also small, 

 as it may be condensed by a pressure equal to 4 

 atmospheres, or even by cold without pressure. 

 But when 100 cubic inches of chlorine unite che- 

 mically with 100 cubic inches of hydrogen, (the 

 elastic force of which is immense), they form 200 

 cubic inches of hydrochloric acid gas, the elastic 

 force of which is equal to the pressure of 40 

 atmospheres, at the temperature of 50. During 

 this combination, the larger atoms of chlorine 

 take from those of hydrogen a definite ratio of 

 caloric, by which the elasticity of the hydrogen 

 is diminished, and that of the chlorine increased. 

 At the same time, the atoms of chlorine are re- 

 moved farther from each other, causing an altera- 

 tion of specific gravity in the resulting compound. 

 In like manner, when one volume of iodine va- 

 pour, the specific gravity of which is 8*75, unites 

 chemically with an equal volume of hydrogen, 

 the specific gravity of the resulting compound is 

 diminished to 4*385 and so of the rest, together 

 with many other like combinations not set down 

 in the Table. 



