VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 6l 1 



15. As manganese is known to produce a very extraordinary change on spirit 

 of salt in a moderate heat, it seemed not improbable, that a still greater change 

 might take place by working in this method. Accordingly Mr. M. forced the 

 vapour of boiling spirit of salt to pass through red-hot manganese. This ex- 

 periment did not answer expectation ; the product was a mixture of fixed and 

 inflammable air. But it deserves to be noticed, that even in this case, after the 

 effect of the spirit of salt had been tried for a long time, a production of nitrous 

 air on the application of volatile alkali to the same manganese soon took place. 



16. As there are many other substances besides the calx of manganese, which 

 are known, per se, to afford dephlogisticated air, or a mixture of this with fixed 

 air, it was natural to conclude from analogy, that such substances on the appli- 

 cation of volatile alkali would not fail to afford nitrous air. It is best however in 

 these matters to trust as little as possible to conjectures, and to bring every 

 opinion to the test of experiment. Manganese is so singular a substance, that 

 it is perhaps hardly safe, from what happens in making trials with it, to infer in 

 any instance of another calx of a metal a similarity of effect. Red lead how- 

 ever, is known to agree in such a variety of chemical effects with manganese, 

 that it was difficult to believe that the volatile alkali properly applied to it would 

 not yield nitrous acid or nitrous air; yet he hitherto in vain attempted to bring 

 this about. The red lead indeed melts during the process, flows into the cooler 

 parts of the tube, and often chokes the passage of the air; but in some trials a 

 great deal of air had been collected before that happened, and without any 

 symptom of a nitrous mixture. It seems difficult to explain the reason of the 

 failure; perhaps with a better adapted apparatus, and more perseverance, either 

 the production in question may be obtained, or the cause of the failure dis 

 covered. 



17. With calcined green vitriol Mr, M. had much better success. The salt 

 was calcined to whiteness, and put into a gun-barrel; and, after several trials of 

 forcing the volatile alkali through the hot tube, he procured by the operation 

 some ounces of strong nitrous air. 18. As calcined green vitriol, per se, in a 

 strong heat yields dephlogisticated air, Mr. M. had now no doubt but that any 

 substance which had this property might, by similar treatment, be made to afford 

 nitrous air. But in this supposition he was entirely mistaken. The volatile al- 

 kali was applied to some calcined alum at the moment when it was yielding in a 

 strong heat plenty of dephlogisticated air. The product was an astonishing 

 quantity of inflammable air, mixed with hepatic air and actual sulphur. The 

 residuum of the alum had a strong hepatic smell, and contained particles of 

 perfectly formed sulphur. 



19. It now only remains briefly to propose what occurred as the probable 

 theory and explanation of the facts related. The ingredients which enter into 



4x2 



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