608 PHILOSOPHICAL TRANSACTIONS. [aNNO l7Sg, 



heated, then the decomposition is almost complete, and little is received but 

 phlogisticated air. In both cases, the progress of the conversion of nitrous acid 

 to the state of phlogisticated air seems to be the same. First, nitrous air is 

 formed, then dephlogisticatcd nitrous air, and lastly phlogisticated air. This 

 seems to be the natural order of the conversion. From what has been said, the 

 most common process will probably appear to be, that a particle of the acid in 

 the form of vapour first generates nitrous air; that the parts of this are applied 

 to fresh surfaces of hot iron, and suddenly changed into dephlogisticatcd nitrous 

 air; which, lastly, is applied to still fresh surfaces of the tube or fragments of 

 iron, and so converted into phlogisticated air. When these successive contacts 

 with fresh surfaces of hot iron are not sufficiently numerous or exact, it is not 

 unnatural to conclude, that some portion of air may escape not perfectly de- 

 composed. 



(5. These considerations induced Mr. M. to alter the process a little. Instead 

 of boiling the acid in the retort, he put some thin pieces of copper into a phial, 

 poured nitrous acid on them, and forced the nitrous air, as it was generated, to 

 pass through the red-hot tube. The event answered his expectation ; the decom- 

 position was effected in this way easier than in the former. But before making 

 this experiment, he examined what would be the effect of mere heat on nitrous 

 air, as he had already learned from the experiments of others, that nitrous acid, 

 forced in the form of steam through red-hot tubes of clay or glass, underwent 

 the most important alterations. What might be the effect of long continued 

 exposure to a red heat he could not say ; but he was soon convinced, that nitrous 

 air might be forced through a red-hot glass tube, without suffering any material 

 change. 



7. Lastly, he determined to try the effect of the gun-barrel on dephlogisti- 

 catcd nitrous air. For this purpose, he diluted a saturated solution of copper in 

 the nitrous acid, and put pieces of iron wire into it, and as the neck of the retort 

 which contained the solution was luted to one end of the gun-barrel, the dephlo- 

 gisticatcd nitrous air was exposed in its passage to the action of the red-hot tube, 

 and also to the surfaces of the red-hot iron turnings which it contained. In this 

 case, when the process is conducted with proper care, all the air which is received 

 at the other end of the tube will be found phlogisticated. 



8. When the air received at the end of the gun-barrel was in the last men- 

 tioned state, viz. perfectly phlogisticated, Mr. M. frequently observed a white 

 fume issuing along with the air, and sometimes ascending through the water or 

 mercury into the glass receivers. On examining this white fume, he soon per- 

 ceived by the smell that it contained volatile alkali. 



9. Most of the experiments hitherto related were made in the summer of 

 3786; in general they agree with those of Dr. Priestley; the changes and pro- 



