68 



Scientific InteUigence, 



[Jan. 



colouring metals, it soon acquires a blue colour, more or less- 



brilliynt, and more or less intense ; aecordiog to the purity and 

 the abundance of the alumina which it contains. " I had 

 never/' says M. Gahn, in a letter to the editor of this journal, 

 <^ extended the application of this experiment to minerals of a 

 very great degree of hardness, such as the sapphire, the spinell, 

 corunduiiij topaze, &c. ; but the ot:her day I was under a kind 

 of necessity of making die trial, and I observed, with pleasure, 

 that all these substance! exhibiied the blue colour as well as 

 others. It is only necessary to pulverize them well, and expose 

 them to the action of the blow-pipe in the manner above de- 

 scribed. Tiiis test labours under one disadvantage, however; 

 for the earth of zircon produces the same blue colour with 

 cobalt as alumina does.^^ 



VIL Extracts from two Letters of Dr. John Redman Coxe, 

 Professor of Chemistry in Philadelphia. 



1, It has long been unknown upon what principle the com- 

 bustion of pyrophyrus depended. Mr. Davy since his discovery 

 of potassium, lias ascribed it to its presence in soj^e way. A 

 few wrecks past I had occasion to lecture on tliis substance 

 (pyrophyrus) ; and finding a portion, w hich I had prepared some 

 time before (but which had failed, except in one or two in- 

 stances), to be useless, I was under the necessity of making 

 some fresh. After the first portion of gas had escaped, and the 

 inflammable gas began to come over, I was, near the period I 

 intended to stop the process, struck with the appearance of the 

 flam^e, Vv^hich possessed, as I thought, the rose-coloured flame of 

 potassium. I immediately stopt the process ; and obtained as 

 fine pyrophyrus as I ever met with. Reasoning upon the subject, 

 I was led to suppose that the frequent failure of the process 

 depended on our carrying it so far, that the potassium formed 

 was entirely consumed. In consequence of this, I poured out 

 all my old pyrophyrus, and found that no combustion ensued. 

 To this mass i added 30 or 40 drops of a pure alkaline solution 

 (potash), and exposed it, as usual, to heat, in a crucible sur- 

 rounded with sand. Inflammable gas began to escape, and at 

 length appeared tinged with a rose-coloured flame; when I stopt 

 the process, and whxcn cool poured the contents into a dry warm 

 vial. This possessed, in a very excellent degree, the properties 

 of perfect pyrophyrus. I apprr^h.-iid, in this compound, the 

 potassium is dill' <sed through the mass in its metallic state, and, 

 seizing on the atmospheric moisture, gives origin to some 

 potasporetted hydrogen, which, inflaming by the contact of 

 lixygen, communicates combustion to the carbonaceous mate- 

 rials suiToundiog ito If it existed in any other form than 

 metallic, ought it to be so long, as we sometimes see it, before 



