I 



COMBINATIONS OF OXIMURIATfC GAS AND OXIOEN. 217; 



reduced silex from the glass, I shall not at present attempt - 

 to decide. 



Potassium I find heated in a similar manner with fused 

 potash, in a tube of platina, gives, after having been ignited, 

 a dark mass that effervesces with water ; but even in this : 

 ease, it may be said, that the al'oy of platina and potassium 

 interferes, and that the substance i» not a protoxide, but 

 merely dry alkali mixed with this alloy. 



As the pure alkalis were unknown, till the discovery of 

 potassium and sodium*, and as their properties have never 

 been described, it will perhaps be proper in this place to 

 notice them briefly. 



When potassium and sodium are burnt in oxigen gas upon Description 



platina, and heated to redness to decompose the peroxide of ^"^ properties 

 , . ^ . 1 , mt of the pure al- 



potassiiira, the alkalis are of a grayish green colour. They kalis. 



are harder than common potash or soda, and, as well as 1 

 could determine by an imperfect trial, of greater specific 

 gravity. They require a strong red heat for their perfect 

 fluidity, and evaporate slowly, by a still farther increase of 

 temperature. When small quantities of water are added 

 to them, they heat violently, become white, and are con- 

 verted into hydrats, and then are easily fusible and volatile. 

 When potassium or sodium is burnt on glass, freed from 

 metallic oxides, and strongly heated, or when potash or soda 

 is formed from the metals by the action of a minute quan« 

 tity of water, their colour approaches to white; but in other 

 sensible properties they resemble the alkalis formed upon 

 metallic substances; and are distinguished in a marked 



* Stahl approached nearly to Ihe discovery of the pure alkalis He Stahl nearly 

 cemented solid caustic potash with iron filings in a long continued heat, discovered Ihe 

 and states, that in this way an alkali **valde causticum" is produced. ^""^ ^ *^* 

 Specim, Beck, part ii, p. 255. He procured caustic alkali also, by decom- 

 posing nitre by the metals. Id. p. 253. 



1 find, that, when nitre isdecomposed in acrucibleof platina by a strong Affinity of 

 red heat, a yellow substance remains, which consists of potash and oxide potash for 

 of platina, apparently in chemical combination, The undecompounded J^^'^^^ip <^* 

 potash, which comes over in the process for procuring potassium by the 

 gunbarrel, is of an olive colour, and affords oxide of iron during its solution 

 in water. Pure potash will probably be found to hate an ?iffinity (or 

 pjany metallic oxides, 



manner 



