1815.] On Vyrophoriis, and llie making of Potassium. 349 



cases the event was the same. It is rather surprising that this 

 ulkaUne pyrophorus should not have been discovered before, as I 

 have lucre than once, since I first noticed it, on preparing the 

 Prussian alkali, seen the lower part of it take fire soon after its 

 having been turned out of the crucible and bruised, even when the 

 matter had not been covered with sand." 



If these experiments of Mr. Bevvly be correct, they evidently 

 show tliat the inflammability of Homberg's pyrophorus depends (at 

 least partly) on tlie mixture of potassium (and perhaps also 

 alumina) with fine powder of charcoal, and that the common 

 theory, according to which the inflammability of pyrophorus 

 depends on the sulphurct of potash, imbibing moisture from the 

 atmosphere, and by that means setting at liberty heat enough to 

 inflame the charcoal mixed with it, is insufficient. It appears that 

 Mr. Bewly followed nearly the same method in order to make his 

 pyrophorus, as Bucholz, Tromsdorf, and Curaudau, did with a 

 view to obtain potassium ; and if Mr. Bewly had happened to 

 introduce into the vessel containing the heated mixture a cold 

 metallic body (as Curaudau did in order to collect the potassium 

 wliich is formed during the process, and driven off in vapours), he 

 would have seen more than 30 years ago one of those bodies by the 

 discovery of which Sir Humphry Davy's name is now immortalized. 

 As Mr. Bewly's experiment was inconsistent with the then prevailing 

 theory, there was hardly any attention paid to it, thcugli it was 

 published as long ago as the year 177^^; at least I do not recollect 

 that it was repeated. I found that an alloy of potassium with iron 

 is a j)yropliorus also. When 1 prepared potassium the first time, in 

 the way which Gay-Lussac and Thenard describe, I did not know 

 the property of this alloy; and having cut off that part of the 

 barrel containing the potassium, I began to scrape it out, holding 

 the barrel over a glas"^ bason containing petroleum. I had poured 

 out my whole stock of petroleum, perhaps two pounds, into this 

 bason, that 1 might be able to immerse into it the whole piece of 

 the barrel, in order not to lose any potassium. After I had scraped 

 out that portion occupying the centre of the barrel, which is the 

 purest, I came to that in immediate contact with the inner surface 

 of the barrel itself, which is generally alloyed with iron ; and a 

 small pitcc of this alloy, being just scraped off, and having there- 

 fore its surface quite free from oxide, in falling down took fire, by 

 coming in contact with the air, and lighted the petroleum con- 

 tained in the gla«s bason, which cracked, and, the burning fluid 

 flowing over my clothes, placed me rather in a dangerous situation. 

 I afterwards have seen the same effect frequently. I think this 

 uyrcipho.us of potassiunj and iron leaves no doubt that there may 

 be one consisting of |)Otassium and charcoal merely; and this will 

 throw liL'ht on the nature of Homberg's pyrophorus. 



in order to obtain a ])otassium free fiom iron, I several times 

 followed a method which is very simple, and on tliat account de» 



