518 PHILOSOPHICAL TRANSACTIONS. [aNNO I789. 



//. Objections to the Experiments and Observations relating to the Principle of 

 j4cidityj the Composition of Water , and Phlogiston, considered ; with further 

 Experiments and Observations on the same Subject. By the Rev. J. Priestley, 

 LL.D,, F.R.S. p. 7. 



Having never failed, says Dr. P., when the experiments were conducted with 

 due attention, to procure some acid whenever I decomposed dephlogisticated and 

 inflammabk-air in close vessels, I concluded that an acid was the necessary 

 result of the union of those 2 kinds of air, and not water only ; which is an 

 hypothesis that has been maintained by Mr. Lavoisier and others, and which 

 has been made the basis of an entirely new system of chemistry, to which a 

 new system of terms and characters has been adapted. The facts that I alleged 

 were not disputed ; but to my conclusion it was objected, that the acid I pro- 

 cured might come from the phlogisticated air, which in one of my processes 

 could not be excluded ; and that it was reasonable to conclude that this was the 

 case, because Mr. Cavendish had procured the same acid, viz. the nitrous, by 

 decomposing dephlogisticated and phlogisticated air with the electric spark. In 

 other cases it has been said, that the fixed air I procured came from the plumbago 

 in the iron from which my inflammable air had been extracted. 



With respect to the former of these objections 1 would observe, that my 

 process is very different from that of Mr. Cavendish ; his decomposition being a 

 very slow one by electricity, and mine a very rapid one by simple ignition, a 

 process by which phlogisticated air, as I found by actual trial, was not at all 

 affected ; the dephlogisticated and inflammable airs uniting, and leaving the 

 phlogisticated air (as they probably would any other kind of air with which they 

 might have been mixed) just as it was. I would also observe, that there is no 

 contradiction whatever between Mr. Cavendish's experiment and mine, since 

 phlogisticated air may contain phlogiston, and by means of electricity this prin- 

 ciple may be evolved, and unite with the dephlogisticated air, or with the acid 

 principle contained in it, as in the process of simple ignition the same principle 

 is evolved from inflammable air, in order to form the same union ; in conse- 

 quence of which, the water, which was a necessary ingredient in the composi- 

 tion of both the kinds of air, is precipitated. That in other circumstances than 

 those in which I made the experiments, the acid wholly escaped, and nothing 

 but water was found, may be easily accounted for, from the small quantity of 

 the acid principle in proportion to the water, and the extreme volatility of it, 

 owing, I presume, to its high phlogistication when formed in this manner. 



In order to ascertain the effect of the presence of phlogisticated air in this 

 process, I now not only repeated the experiment of mixing a given quantity of 

 phlogisticated air with the 2 other kinds of air, and found, as before, that it 

 was not affected by the operation ; but I made the experiment with atmospheric 

 air, instead of dephlogisticated. Since the air of the atmosphere contains a 



