VOL. LXXIX.] PHILOSOPHICAL TKANSACTI0N8. 607 



tention of philosophical chemists. The history of the experiments alluded to is 

 as follows. 



2. As soon as he had heard of the production of inflammable air by the trans- 

 mission of steam through red-hot iron tubes, he had the curiosity to try whether 

 some other substances in the form of air or vapour might not, by a similar pro- 

 cess, undergo material alterations. In particular, the nitrous acid seemed well to 

 deserve a trial, both on account of the obscurity and difficulties attending the 

 theory of its production, and also of its important and extensive usefulness in 

 chemistry. 



3. I began with boiling a little strong nitrous acid in a small retort, the neck 

 of which was closely luted to one end of a gun-barrel. The other end of it was 

 immersed sometimes in water, and sometimes in quicksilver, and J 8 or 20 inches 

 of the middle part was surrounded with burning charcoal in a proper furnace. 

 In this manner the vapour and fumes of the boiling acid were transmitted 

 through the red-hot tube, and the produce received at the end in the usual 

 manner. When the acid was made to boil violently, there passed over a consi- 

 derable quantity of undecomposed red nitrous vapour, together with a mixture 

 of nitrous and phlogisticated airs. When the process was conducted more mo- 

 derately, there was less nitrous vapour; and in the mixture of airs which was 

 received in the glass vessels, there was a nmch greater proportion of phlogisti- 

 cated air. 



4. In order to increase the surface of the red-hot iron, and effect a more com- 

 plete decomposition of the nitrous vapour, the gun-barrel was crammed full of 

 iron filings. The experiments were repeated with great caution, and almost the 

 whole of the produce was found to be phlogisticated air. It is however proper to 

 mention, that notwithstanding every possible care, still there will generally be in 

 some degree an admixture of nitrous air, and frequently of dephlogisticated ni- 

 trous air. But he is satisfied that if the iron tube were sufficiently long, so that 

 a very large portion of it might be heated red-hot, all the air received in this 

 manner from any quantity of nitrous acid slowly boiled, would be found of that 

 species called phlogisticated air. 



5. These experiments seem altogether analogous to those of Dr. Priestley, in 

 which nitrous air, by exposure to iron, is converted first into dephlogisticated 

 nitrous air, and afterwards into phlogisticated air. The only difference seems to 

 be, that in these experiments the effect is brought about suddenly ; whereas in 

 the method of exposition to iron much time is required. And further, in this 

 method of operating, it is very difficult to conduct the process so as to insure 

 the production of that singular species of air called dephlogisticated nitrous ai r 

 If the acid boil very quick, the product is nearly all nitrous vapour and nitrous 

 air. If it boil very slow, and a sufficient quantity of the iron tube be well 



