212 I'HILOSOPHICAL TRANSACTIONS. [aNNO 17Q2. 



not been sufficiently careful to let the lute fix before we commenced the experi- 

 ment, and it soon failed. On taking off the pressure of the mercury entirely, 

 and repairing the lute as well as we could, we had every reason to believe that the 

 air soon ceased. The air received in the mercury contained 4-th of carbonic acid. 

 The remainder exploded. The plumbago lost 4 grs. Mr. Pelletier, if I remem- 

 ber right, found that native plumbago, exposed to a fierce and long continued 

 heat, lost 10 grs. in 200. In the present experiment its appearance was unaltered. 

 Probably the loss was owing to moisture imbibed by the particles of coak, and to 

 a small combustion by the air in the retort. 



It will, I think, be admitted, that these experiments abundantly confirm the in- 

 ferences I had fonnerly drawn from appearances by their nature less decisive. The 

 real extrication of air, varying in its nature at various periods of the process, 

 seems to be placed beyond doubt. The experiments in glazed and glass vessels, 

 were made with a view to exclude the possibility of the supposition of the air 

 entering through the pores. I think that Dr. Priestley, if he should repeat these 

 experiments, and find that they have been accurately made, will, with his ac- 

 customed openness to conviction, abandon an opinion he has for some time 

 entertained, and no longer consider water as essential to the constitution of elastic 

 fluids. Several observations might be made on this point, and those which I have 

 just noticed above; but they will readily occur to persons conversant in chemistry, 

 and it is not the object of the publications of the r. s. to teach the elements of 

 science. I shall therefore confine myself to the unexpected and anomalous ap- 

 pearances, and then attempt to draw a few useful inferences. 



1. I was surprized at the extrication of infliammable air in such low degrees of 

 heat. We have seen that cast iron, highly charged with charcoal, the phlogisto 

 onustum of Bergman, yields air at the temperature of melting lead. For un- 

 doubtedly the blisters of lead, which lay on the iron, are to be considered as air- 

 bubbles caught in a solid film of lead. Perhaps white cast iron would not yield 

 air so readily ; possibly iron holds its charcoal with more force as it contains less. 



2. I am at some loss how to explain the occasional discharge and cessation of 

 air, in one experiment in which a crown glass retort was used, and in another 

 with an unglazed earthen tube. There was no flaw in the lute, nor in the vessels, 

 for it was discharged for the space of several hours under a small pressure. Either 

 then it was forced through the softened glass in the first, and the dilated pores of 

 the tube in the 2d case ; or it was absorbed by the substance of the vessels ; or 

 it was not extricated from the iron. Of these suppositions the 3d seems the most 

 probable. It is not likely that a hole should be made through the melted glass, 

 under the pressure of the half, and closed under that of perhaps the 8th of an 

 inch ; or that pores in the tube should open and shut in conformity to such a 

 variation of circumstances : and, with regard to the tube, there can be no ques- 



