134 Analysis of Scientific Books. 



perties of those compound inflammable gaseous bodies of 

 which charcoal and hydrogen are the principal constituents, 

 and which are evolved during the destructive distillation of 

 various vegetable and animal products. Much, however, still 

 remains to be effected ; it remains to be ascertained whether 

 there are two or more definite combinations of carbon and 

 hydrogen, or whether the supposed varieties are merely mix- 

 tures of one definite compound (olefiant gas) with variable 

 proportions of pure hydrogen ; the exact nature, too, of the 

 gases from coal and oil is by no means made out; indeed we 

 do not know whether the anomalies which they present to 

 the analyst, are referable to the presence of some highly in- 

 flammable and volatile oily vapour, or to the existence of some 

 hitherto unexamined compound of hydrogen and carbon ; we 

 are inclined to lean to the former opinion, for the illuminating 

 power of the gas from oil is diminished by violent com- 

 pression ; by subjection to intense cold ; by long exposure to , 

 water ; and by passing it through alcohol ; and in all these 

 cases it loses oily matter, and requires consequently less oxygen 

 for its perfect combustion. Whether there be two definite 

 compounds of carbon and hydrogen, or one only, is a question 

 which should be determined before the other ramifications of 

 this inquiry can be satisfactorily traced ; in the Bakerian 

 lecture for 1820, Mr. Brande has advanced the former opinion ; 

 Dr. Thomson was the first to oppose it in the late edition of 

 his System ; but we have already canvassed and quashed his 

 criticism*. 



Dr. Henry also argues in favour of the existence of light 

 hydrocarbonate ; such part3 of his argument as hinge upon 

 Dr. Thomson's authority we shall not notice ; the others are 

 chiefly the following. The gas obtained from the clayey 

 bottom of a stagnant pool contained ^^^ its volume of carbonic 

 acid, and ^ of nitrogen ; the pure portion required two vo- 

 lumes of oxygen for combustion, and gave one volume of 

 carbonic acid; its specific gravity was about 556. Now as 

 these results agree ivith those obtained by Sir H. Davy in his 

 analysis oi Jire-damp, Dr. Henry says there appears no reason 

 for refusing to consider carburetted hydrogen (light) as a 

 true chemical compound, and were any additional argument 

 necessary to establish its definite nature, he observes that it 

 might be derived from the action of water, which absorbs it 

 in a constant proportion, and again evolves it unaltered when 

 lieated. But with great deference for Dr. Henry's opinion, 

 we suspect that this latter point has not been suflSciently veri- 

 fied, and even if admitted, we doubt whether it would justify 

 the inference which is here drawn from it. 



* Vol. XI., page 145. 



