on the Nature of certain Bodies. 121 



Ijecnnie more copious ; they continue for some time to be 

 emiltcfJ, but at last cease altogether. 



If ihe gas is examined at this time, its volume is found 

 to be a little increased, by the addition of a small quantity 

 of hydrogen. 



No new fumes are prodiR-ed by a second application of a 

 low heat; but when the teiTiperature is raised nearly to the 

 point of sublimation of potassium, the metal rises through ■ 

 the cru^t, becomes first of a copper colour and then of a 

 blueish black., and soon afcer inflames and burns with a most 

 brilliant red iiaht. 



After this combustion, either the whole or a part of the 

 fluoric acid, according as the quantity of potassium is great 

 or small, is found to be desiroyed or abs.'irbcd. A mass of 

 a chocolate colour remains in the bottonj of the retort ; and 

 a sublimate, in some parts chocolate, and in others yellow, 

 is found round the siiles, and at the top of the retort. 



When the re«idual r;as afforded bv ihis operation is 'washed 

 with water, aiui exposed to the action of an electrical spark 

 mixed with oxygen gas, it detonates, and affords a diminu- 

 tion such as might be expected from hvdrogen gas. 



The proportional quantity of this elastic fluid difiTers a 

 little in different operations. When the fluoric acid has not 

 been artificially dried, it amounts to one-sixth or one-seventh 

 of the volume of the acid gas used; but when the fluoric 

 acid has been long exposed to calcined sulphate of soda, it 

 seldom amounts to one-tenth. 



I have endeavoured to collect large quanti;ies of the cho- 

 colate coloured substar.ce for minute examination ; but some 

 difficulties occurred. 



When I used from eighteen to twenty grains of potassium, 

 in a rctori containing from twenty to tluriy cubical inches of^ 

 fluoric acid gas, the intensitv of the heat was such, as to 

 fuse the bottcnj of the retort, and destroy the results. 



In a very thick plate ola^s retort, containing about nine- 

 teen cubical inches of gas, I once succectled in nuiking a 

 decisive experinient on tei\ grains and a half of potassium, 

 .'ifKl I found that about hmrteen cubical inches of fluoric acid 

 disappeared, and alK)ut two and a quarter of hydrogen gas 

 were evolved. The barometer stood at :-J0'3, and the thcr- 

 njometer at Q\° Fahrenheit; the gas had not been artificially 

 dried. In this experiment there was very little sublinlale; 

 but the whole of the bottom of ilic retort was covered with 

 a brown crust, and near the point of contact with the Ijot- 

 loin the substance was darker coloured, and approaching 

 \\\ its tint to black. 



Whci) 



