Philosophical Transactions. 135 



Dr. Henry then says, that" the process by which carburetted 

 hydrogen gas is evolved in natural operations is no doubt the 

 decomposition of water, and admits of being explained on the 

 atomic theory of Mr. Dalton, by supposing two atoms of char- 

 coal to act at once on two atoms of water," Sfc. Now we con- 

 fess that we have great doubts as to the above origin of car- 

 buretted hydrogen gas, and rather suspect that the decomposi- 

 tion of vegetable and animal matter, is its principal, if not 

 exclusive, source in nature ; arising perhaps in coal-mines, from 

 the action of whin dikes upon the coal, as suggested by Dr. 

 Hutton ; and derived in stagnant pools from the decomposition 

 of the organic relics contained in the mud. As to the absence 

 of carbonic oxide in the products of stagnant water, we would, 

 in the first place, ask, has its absence been satisfactorily ascer- 

 tained? and, secondly, admitting that it does not exist, why 

 should we expect the presence of a compound which neither 

 fermentation, putrefaction, nor respiration produce, and which 

 is only sparingly and equivocally generated during the action 

 of heat on pit-coal ? 



The next portion of Dr. Henry's paper relates to the action 

 of chlorine on carburetted hydrogen; a subject, putting the 

 purity of the carburetted hydrogen out of the question, so full 

 of difficulties, so mixed up with the joint agency of light, heat, 

 and water, upon the mixed gases, that we cannot presume here 

 to review it in all its bearings, and shall therefore rest con- 

 tent with thanking Dr. Henry for the new facts which he has 

 stated in relation to it. 



In his " Experiments on the gas from oil" Dr. Henry has 

 shewn that the gas obtained at different times from oil of the 

 same quality is by no means uniform in composition. The 

 readers of this Journal will probably require an apology for this 

 mere mention of the " oil question ;" but the following remark, 

 coming from a person of Dr. Henry's experience and accuracy, 

 we think weighty in relation to it. " So far," he says, " as my 

 experience goes, no temperature short of ignition is sufficient 

 for the decomposition of oil into permanent combustible gases ; 

 but the lower the heat that is employed, provided it be adequate 

 to the effiict, the heavier and more combustible is the gas, and 

 the better suited to artificial illumination." This paragraph is 

 also important to the manufacturer of oil gas for domestic use, 

 but least he should be led into error, we would observe that 

 although Dr. Henry is perfectly correct, it still does not answer 

 to the manufacturer to obtain the gas in Messrs. Taylors' stoves, 

 at the lowest possible temperature, that is, a dull red heat, for 

 at that temperature, much empyreumatic condensible vapour 

 is produced, and the bulk of the gas proportionably diminished : 

 and though it be perfectly true that the increased bulk of the 

 gas obtained at higher temperatures is partly referable to the 



