6 10 PHILOSOPHICAL TRANSACTIONS. [aNNO I789. 



Manganese, per se, gives airs of different kinds, but chiefly fixed and dephlo- 

 gisticated airs, as soon as ever it is subjected to a considerable heat; but nothing 

 nitrous comes from it, either on the first application of heat, or after it has been 

 continued a long time; and he examined this point with great diligence. But 

 soon after the volatile alkali begins to be applied, the jars in which the air is 

 received will frequently turn slightly red, and this redness will increase on admit- 

 ting atmospherical air. 



Here however there exists a cause of deception, against which the operator 

 ought to be on his guard, lest he should conclude that no nitrous air is formed, 

 when in reality there is a considerable quantity. The volatile alkali, notwith- 

 standing every precaution, will frequently pass over in great quantities undecom- 

 posed. If the receivers are filled with water, a great part of this will indeed be 

 presently absorbed; but still some portions of it will mix with the nitrous air 

 formed by the process. On admitting the atmospherical air, the nitrous air is 

 decomposed, and the red nitrous fumes instantly combine with the volatile alkali. 

 The receivers are presently filled with white clouds of nitrous ammoniac; and in 

 this manner a wrong conclusion may easily be drawn, from the want of the 

 orange colour of the nitrous fumes. A considerable quantity of nitrous air may 

 have been formed, and yet no orange colour appear, owing to this circumstance; 

 and therefore it is easy to understand how a small quantity of nitrous air may be 

 most effectually disguised by the same cause. 



12. These observations are made chiefly for the sake of those who may wish 

 to repeat these experiments. The main point to be established, is the actual 

 formation of nitrous air by this method. And this truth he considers as proved 

 beyond all controversy; for by continuing the process patiently, and applying 

 repeatedly fresh portions of strong volatile alkali to the same manganese, kept 

 constantly hot in the gun-barrel, he often collected large jars of air, which was 

 proved to be highly nitrous by mixture with atmospherical or with dephlogisti- 

 cated air. 



13. It is not easy to say whether, in this process, dephlogisticated nitrous air, 

 or even nitrous acid itself, be not sometimes immediately formed by the action 

 of the volatile alkali on the manganese. Traces of the former, in some in- 

 stances, seem to discover themselves. As to the latter, it is very certain, that 

 fumes of the nitrous acid often circulate in the jars that receive the air. But 

 possibly these fumes may arise from the decomposition of nitrous air, by means 

 of the superfluous dephlogisticated air of the manganese. 14. The steam of 

 boiling water was applied to red-hot manganese in a similar way; not the least 

 nitrous appearance; but the fixed and dephlogisticated airs were generated much 

 more plentifully than when the manganese was urged by mere heat. When 

 these airs had been collected in large quantities, the volatile alkali was applied as 

 before to the residuum of the manganese, and nitrous air soon appeared. 



