556 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



and the small remaining portion was still unchanged, at least had suffered no 

 change which might not be attributed to its original want of purity; it was rea- 

 sonable to conclude, that inflammable air must be the pure phlogiston, or the 

 matter which reduced the calces to metals. 



2. The same ingenious philosopher mixed together certain proportions of pure 

 dry dephlogisticated air and of pure dry inflammable air in a strong glass vessel, 

 closely shut, and then set them on fire by means of the electric spark, in the 

 same manner as is done in the inflammable air pistol. " The first effect was the 

 appearance of red heat or inflammation in the airs, which was soon followed by 

 the glass vessel becoming hot. The heat gradually pervaded the glass, and was 

 dissipated in the circumambient air, and as the glass grew cool, a mist or visible 

 vapour appeared in it, which was condensed on the glass in the form of moisture 

 or dew.* When the glass was cooled to the temperature of the atmosphere, if 

 the vessel was opened with its mouth immersed in water or mercury, so much of 

 these liquids entered, as was sufficient to fill the glass within about -y-i-j- part of 

 its whole contents; and this small residuum may safely be concluded to have been 

 occasioned by some impurity in one or both kinds of air. The moisture adher- 

 ing to the glass, after these deflagrations, being wiped off, or sucked up, by a 

 small piece of sponge paper, first carefully weighed, was found to be exactly, or 

 very nearly, equal in weight to the airs employed. In some experiments, but not 

 in all, a small quantity of a sooty-like matter was found adhering to the inside of 

 the glass," the origin of which is not yet investigated; but Dr. Priestley thinks, 

 that it arises from some minute grains of the mercury that was used to fill the 

 glass with the air, which being super-phlogisticated by the inflammable air, as- 

 sumed that appearance: but, from whatever cause it proceeded, the whole quan- 

 tity of sooty-like matter was too small to be an object of consideration, particu- 

 larly as it did not occur in all the experiments. 



I am obliged to Mr. De Luc for the account of the experiments which have 

 been lately made at Paris on this subject, with large quantities of these 2 kinds 

 of air, by which the essential point seems to be clearly proved, that the deflagra- 

 tion or union of dephlogisticated and inflammable air, by means of ignition, 

 produces a quantity of water equal in weight to the airs; and that the water thus 

 produced appeared, by every test, to be pure water. As I am not furnished with 

 any particulars of the manner of making the experiment, I can make no obser- 

 vations on it, only that from the character of the gentlemen who made it, there 

 is no reason to doubt of its being made with all necessary precautions and accu- 

 racy, which was further secured by the large quantities of the 2 airs consumed. 



3. " Let us now consider what obviously happens in the case of the deflagration 

 of the inflammable and dephlogisticated air. These 2 kinds of air unite with 



* I believe that Mr. Cavendish was the first who discovered that the combustion of" dephlogisti- 

 cated and inflammable air produced moisture on the sides of the glass in which they were fired. — Orig. 



