8 Biographical Memoir of the late Dr Henry. 



the hydrogen was eliminated from the muriatic gas, and not 

 from aqueous vapour. He also ascertained, that the muriatic 

 acid gas, when completely insulated in a closed glass vessel, 

 sustained no change of volume from a succession of electrical 

 discharges. This permanence of bulk was made more appa- 

 rent by repeating the experiment in a vessel with a neck only 

 one-fifth of an inch in diameter. After admitting water to ab- 

 sorb the undecomposed muriatic acid, there remained one hun- 

 dred measures of chlorine, and one hundred and forty of hy- 

 drogen. In conformity with the law of Gay Lussac, the quan- 

 tities should have been equal, but the deficiency of chlorine 

 was justly referred to its large absorbability by water. The 

 perfect accordance of muriatic acid gas with the law of volumes 

 was further shewn by the observation that the contraction of 

 volumes in muriatic acid gas electrized over mercury ; — a di- 

 minution due to the combination of the liberated chlorine with 

 mercury, — is precisely equal to the quantity of hydrogen gas 

 obtained. 



In 1803 Dr Henry made known to the Royal Society his 

 elaborate experiments on the quantity of gases absorbed by 

 water at different temperatures, and under different pressures. 

 The absorbabilities of the different gases, under a constant 

 pressure, by water of 55° Fahrenheit, were first accurately 

 measured. Elevation of temperature was found to lessen the 

 amount of absorption, the diminution for each increment of 10° 

 above the standard temperature being equivalent to about ^^th 

 of the entire bulk absorbable at 55° Fahr. In investigating 

 the absorption of the same gas under varying pressures, Dr 

 Henry arrived at the simple law, " that water takes up of gas 

 condensed by one, two or more additional atmospheres, a quan- 

 tity which, ordinarily compressed, would be equal to twice, 

 thrice, &c. the volume absorbed under the common pressure of 

 the atmosphere." This exact proportionaUty of the quantities 

 absorbed to the pressures, makes strongly in favour of the the- 

 ory^proposed by Dr Dalton, that the absorption of the gases 

 by water is due entirely to mechanical agencies. 



Dr Henry described in the Philosophical Transactions for 

 1808, a form of apparatus, adapted to the combustion of larger 

 quantities of gas than could be fired in eudiometric tubes. Re- 



