1822.] Sixth Edition of his System of Chemistry, 265 



coal. It was the heat and effect on metals to which I alluded 

 under the name chemical effects ; but the phrase, it appears, from 

 the Reviewer mistaking it, was not sufficiently precise. 



5. I never mention chlorate of potash nor red oxide of mer- 

 cury as convenient substances for furnishing oxygen. — (RevieW-, 

 p. 140.) Had this statement been true, I do not think the omis- 

 sion would have been of any consequence. But in vol. ii. p. 232, 

 of my System, I expressly say that 100 parts of chlorate of pot- 

 ash, when heated, give out 38*69 parts of oxygen. 



I never employ these bodies myself for procuring oxygen gas, 

 because I can obtain it equally pure, and at a much smaller 

 expense, from the black oxide of manganese. If the oxygen 

 gas given out about the middle of the process be collected, it 

 will be found very pure. I obtain it every year by this process 

 with less than a half per cent, of azote. 



6. What am I to make of the following quotation from my Systern? 

 " The weight of an atom of oxygen in the subsequent part of this 

 work will be denoted by 1st, a volume of oxygen is equivalent to 

 two atoms, provided we suppose, as I have done, that water is a 

 compound of one atom of oxygen and one atom of hydrogen.'* — ■ 

 (Review, p. 140.) The passage in my System is really as fol- 

 lows : " The weight of an atom of oxygen in the subsequent 

 part of this work will be denoted by 1 . A volume of oxygen is 

 equivalent to two atoms, provided we suppose, as I have done, 

 that water is a compound of one atom of oxygen and one atom of 

 hydrogen."— (System, i. 179.) The Reviewer must have been 

 sadly put to it in his search into mistakes, when he was driven 

 to the necessity of creating them by misquotation, that he might 

 have an opportunity of animadverting upon absurdities which 

 originated with himself. 



7. I quote the following passage from the Review, without 

 pretending to understand it. " The deutoxide of chlorine was 

 discovered about the same time by Sir H. Davy and Count Von 

 Stadion, of Vienna ; but Davy's account was published sooner 

 than that of Count Von Stadion." The account of the former 

 was pubUshed in Thomson's Annals eight months before that of 

 the latter appeared. Surely some qualm of conscience must 

 have smitten our compiler in writing his next page. ** But the 

 properties of the substance described by the Count differ so 

 much from those of the gas examined by Davy, that it is proba- 

 ble they are distinct substances." — (Review, p. 142.) 



Does the Reviewer mean to arraign the accuracy of my state- 

 ment respecting the experiments of Count Von Stadion ? It 

 looks a little hke it. Davy's paper was read to the Royal 

 Society in May, 1815, and pubHshed about the end of July, 

 The Count's paper appeared in Gilbert's Annalenfor Feb. 1816, 

 or about six months later than Davy's, My reason for believing 

 that Von Stadion was unacquainted with Davy's paper was not 

 merely because the Count no where alludes to it, but because 



