68 ON THE DOCTRINE OF PHLOGTSTON. 



decifive than degree of heat decompofe fixed air. For my experiment with 

 that of them- a burning lens, in which it could not be done, is far more un- 

 exceptionable than Mr. Cm ick (hank's with bladders and a 

 gun barrel. His objection to my procefs has no weight. It 

 was made with a few ounce meafures of the air over mercury, 

 with a lens fixteen inches in diameter, and continued feveral 

 hours, generally from ten o'clock to one ; fo that no particle 

 of the air could efcape being expofed to a far greater degree 

 of heat than could be communicated through a gun barrel. 

 His experiment I have frequently made both in England and 

 here, but could never be fatisried with the refult. The fcale 

 upon the iron, I have no doubt, came from moifture in the 

 air, or from the bladders. Indeed, I cannot think that any 

 perfon converfant as I have been with both thefe modes of 

 operating, can hefitate in deciding that the preference muft 

 be given to mine. 

 Charcoal In- # 6. Mr. Cruickfhank feems to think that charcoal cannot 

 oxrctfromMr". 0011 ^ 111 an ? oxi g en 5 but Mr - Tenant's fine experiment deci- 

 Tenant's expe- fively proves that it does. For where are we to look for the 

 riments. oxigen (which we all acknowledge to be a component part of 



fixed air) which is feparated from the marble, but in the char- 

 coal which is produced, and in that it makes part of a folid 

 fubftance, and does not take the form of air. 

 If oxigen exifted 7. Since oxigen and all combuftible fubftances unite, and 

 k o^hTto^ro- ex pl°d e > m a certain degree of heat, the oxigen that is ex- 

 duce the phe- pelled from the finery cinder uniting with carbon from the 



nomena of com- cna rcoal when red hot muft enable it to burn; and therefore 



buftion in char- .'','-'"".''„ i i i * r 



coa j # in thele circumftances there ought to be an exploiion, or at 



leaft a gradual combuftion of them in the courfe of the pro- 

 cefs, as there is when oxigen is put to the fame fubftance, 

 and heated with it afterwards. 

 Invitation to It is now near twenty years fince this new theory was ad- 



Mr. Cruick- vanced, and from that time to the prefent I have not ceafed 

 intoafuHdif- to exprefs my opinion of its fallacy, and to give .my reafons 

 cuffion of the for that opinion ; but I have not till very lately been able to 

 new theory. <j raW any degree of attention to the fubjecl. Now, however, 

 I am happy to have fucceeded in this ; and as I find that the 

 chemifts in France, the great patrons of the fyftem, look to 

 Mr. Cruickfhank as the ableft defender of it, I earneftly wifh 

 that he would undertake the difcuffion of every article of my 

 objections to it. What he has animadverted upon is only one 

 2 out 



