ALKALIES. 247 



combined affinities for the effect ; thus, in the experiment with the 

 gun barrel, iron and hydrogen are concerned." 



It would seem, however, that charcoal alone has succeeded in the 

 hands of Wohler, who employed the cream of tartar, after being 

 heated to redness in a covered crucible. The tartar may be calcined 

 in the same iron bottle in which it is to be decomposed, and it is ad- 

 vantageous to mix a little charcoal with the tartar previous to calcin- 

 ation ; 300 grains have been obtained from 24 oz. of crude tartar. 

 Prof. Berzelius is said to have obtained half a pound at one opera- 

 tion.* 



4. PROPERTIES. 



(a.) At 60 or 70 Fahr. it is imperfectly fluid ; perfectly so at 

 100, and of course at a higher temperature; when melted under 

 naptha, it cannot be distinguished from mercury; at 150, two glo- 

 bules will run into one ; at 50, it is a soft solid, plastic in the hand ; 

 at 32 or lower, it is brittle ; breaks with brilliant lustre ; and when 

 broken, exhibits through a microscope, a crystallization in facets very 

 white and splendid ; at about the heat of ignition, it is volatile, rises 

 in vapor and if air and moisture are excluded, condenses unaltered. 



(b.) It is a perfect conductor of heat and electricity. 



(c.) Sp. gr. about 0.865, (G. L. and Th.) 0.876, Bucholz or from 

 .8 to .9, water being 1 . Davy. That obtained by chemical means, is 

 a little heavier, owing to carbon or iron combined with it, but it is suf- 

 ficiently pure for experiments. 



(d.) In the air or by moisture, it is oxidized and becomes again 

 caustic potash ; it cannot be preserved except under naptha ; if that 

 fluid has been recently distilled, and the vial is full of the fluid, the 

 potassium may be kept under it for years, only it will collect a film 

 of soap around it ; the metal may be examined in the air, if cover- 

 ed with a film of naptha. 



5. OXIDES. 



(a.) The protoxide is formed by the action of water, the air being 

 excluded ; in that case, there is great effervescence, but no flame ; 

 40 grains of potassium decompose 9 grs. of water and evolve 1 gr. of 

 hydrogen gas, while the other 8 grs. combine with the metal ; thence 

 the quantity of oxygen is inferred ; also, from the oxygen absorbed 

 by potassium when it is exposed to dry air ;f if it is in thin slices, 

 the protoxide is formed in this manner also. 



Proportions, potassium, 83.34, oxygen, 16.66 = 100.00, 

 This being nearly in the proportion of 100 potassium to 20 oxygen, 

 it follows, that 20 : 100: : 8 : 40 ; 8 being the representative num- 



* Graham, and Bib. Univ. XXII, 36. 



t According to Thenard, it is the only metal that is acted upon by perfectly dry 

 oxygen gas. 



