VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 633 



composed by the electric spark, Dr. A. was induced to try it on the heavy in- 

 flammable air, as soon as he suspected that it contained the lighter air as a con- 

 stituent part. This experiment immediately detected the light inflammable air ; 

 for such an expansion took place as could not arise from any other known sub- 

 stance. Thus the heavy inflammable air was sometimes expanded to twice its 

 original volume ; and yet not a 6th part of the whole was found to have under- 

 gone a decomposition : for instance, when 2^ measures were expanded to 6, it 

 appeared by experiment, that nearly 24- measures remained in their original state. 

 After the inflammable air has been expanded to about double its original bulk, 

 he does not find that it increases further by continuing the shocks. 



From this partial decomposition of the heavy inflammable air we obtain a 

 mixture of the 2 inflammable airs with phlogisticated air ; that is, of the heavy 

 inflammable air not decomposed, of the light inflammable air disengaged by the 

 spark, and of phlogisticated air. How much of this phlogisticated air pre- 

 existed in the heavy inflammable air, and how much was disengaged during the 

 operation, it is not easy to determine. Neither are we acquainted with any 

 substance which will separate the 2 kinds of inflammable air by combining with 

 the one and leaving the other ; but we know that dephlogisticated air will com- 

 bine, in certain proportions, with each of them, either mixed or separate ; that 

 with one of them it forms fixed air, with the other water. Therefore, by in- 

 flaming dephlogisticated air with a mixture of these 2 airs, and observing the 

 quantity of dephlogisticated air consumed, and the quantity of fixed air pro- 

 duced, we discover the excess of dephlogisticated air consumed, above what is 

 sufficient for the production of the fixed air ; and may conclude, that this excess 

 of dephlogisticated air has combined with light inflammable air. This conclu- 

 sion is further confirmed by attending carefully to the contraction which takes 

 place on inflaming these airs, which is much greater in proportion to the quan- 

 tity of fixed air produced, when a mixture of the 2 inflammable airs is inflamed, 

 than when the heavy inflammable air is burnt alone. It is well known, that in 

 all experiments of this kind, what remains after the combustion of the airs 

 mixed together in due proportion, and after the separation of the fixed air, is 

 chiefly phlogisticated air. From a considerable number of experiments con- 

 ducted with great care and attention to all these circumstances, the Dr. endea- 

 voured to approximate to the quantities of the phlogisticated and light inflam- 

 mable airs disengaged, when a given quantity of the heavy inflammable air was 

 decomposed. But all that could be attained to, was only an approximation 

 to truth. The quantity of air decomposed by this method was so small, and 

 the separation of the difi^erent parts into which it was resolved was attended with 

 such difficulties, that an accurate analysis of the heavy inflammable air can 

 never be obtained in this manner, 



VOL. XVI. 4 M 



