Biographical Memoir of the late Dr Henry. 9 



suits were thus obtained, which may be pronounced fair ap- 

 proximations to truth, especially when estimated \vith reference 

 to the still imperfect resources of pneumatic chemistry. The 

 apparatus cannot, however, be now recommended when extreme 

 precision is desirable. In this year (1808) he was elected a 

 Fellow of the Royal Society, and in the following year received, 

 by the award of the President and Council, the medal on Sir 

 Godfrey Copley's donation, as a mark of their approbation of 

 his various papers communicated to the society, and printed in 

 the Philosophical Transactions. 



The same analytical method by which the decomposition of 

 muriatic acid gas had been effected, was in 1809 employed by Dr 

 Henry to resolve ammonia into its constituent gases. These 

 experiments may even now be commended as models of ex- 

 treme accuracy. Ammoniacal gas previously dried with great 

 care, was found to expand to double its primitive volume after 

 a sufficient number of electrical discharges. The average of 

 eight experiments (in five of which the volume was exactly 

 doubled) gave the relation of 100: 198.78 between the volumes 

 of gas before and after decomposition, — a conformity between 

 theory and experiment, which modern refinement cannot sur- 

 pass. In this memoir Dr Henry also made known a remarka- 

 bly elegant and expeditious method of analyzing ammonia, by 

 firing it in a volta tube with a deficient quantity of oxygen. 

 In this process all the ammonia is decomposed, though a part 

 only of the hydrogen thus liberated meets with its equivalent 

 of oxygen. More oxygen is then added to burn the residuary 

 hydrogen : — for Dr Henry had observed, that if the whole 

 quantity of oxygen was added at once, the results were disturbed 

 by the production of nitrate of ammonia. In estimating the 

 proportion of hydrogen and nitrogen constituting ammonia, he 

 obtained somewhat less hydrogen than the theoretical quantity, 

 a deficiency which he rightly ascribed to the cooling agency of 

 so large a volume of azote causing a part of the hydrogen to 

 escape unburned. He afterwards, by employing nitrous oxide 

 instead of oxygen, obtained and published in the memoirs of 

 this society, results that estabhsh precise multiple relations. 



The gaseous substances, issuing from the destructive distil- 

 lation of coal and oil, had very early engaged Dr Henry's at- 



