PREPARATION OF POTASSIUM. <I43 



temperature ; the potassium then falls from the tube, drop by 

 drop, into the receiver, and does not remain long in contact with 

 carbonic oxide, which is known to combine readily with that 

 metal. One or two other points should also be attended to. 

 The connexion between the tube b and the receiver is not made 

 till the iron bottle has been heated to redness, to allow of the 

 escape of a little water, and of a trace of mercury, which had re- 

 mained in the bottle in the state of vapour, and which come off 

 first. The joining of the tube b is not air-tight at first, and 

 allows a little potassium vapour to escape,, but this burns and 

 forms potash, which immediately closes the openings. This 

 tube being always incandescent, and the refrigeration properly 

 made, the reduction sometimes proceeds without interruption. 

 But the tube is sometimes obstructed, as appears by the gases 

 ceasing to escape by x. Haste must then be made to open 

 the tube , and to clear it by means of a flattened iron rod /, 

 slightly hooked at its anterior extremity. Care has been taken 

 to mark on this rod, with the scratch of a file, how far it has to 

 penetrate into the apparatus to reach the mouth of the bottle, 

 and it must not be introduced farther. The current of air 

 through the furnace is regulated by a register valve in the 

 chimney, and the fire stirred frequently so as to prevent the 

 formation of cavities; the operator being guided in the ma- 

 nagement of the fire by the rapidity of the current of gas which 

 escapes by the tube x. To terminate the operation, the grate 

 bars may be thrown down, by which the fuel will fall into the 

 ash-pit. The quantity of crude tartar mentioned yields about 

 4 ounces of potassium, which is about 4 per cent of its weight. 

 The potassium thus obtained, containing a little carbon che- 

 mically combined with it, is submitted, together with the black 

 mass found in the receiver, to a second distillation. For this 

 purpose a smaller iron bottle with a bent tube may be employed, 

 the end of which is covered by rectified petroleum in a capaci- 

 ous flask, used as a receiver.* 



Properties. Potassium is solid at the usual temperature, 

 but so soft as to yield like wax to the pressure of the fingers. 

 A fresh surface has a white colour, with a shade of blue, like 

 steel, but is almost instantly covered by a dull film of oxide, 

 when exposed to air. The metal is brittle at 32, and has 

 been observed crystallized in cubes : it is semi-fluid at 70, 

 * Mitscherlich, Elemens de Chiinie, t. 3, p. 8. 



