602 



POTASSIUM 



opening the cock momentarily, and thrusting in a hot wire, this tube may be readily 

 kept free, without permitting any considerable waste of potassium. The heat should 

 be slowly applied at first, but eventually urged to whiteness, and continued as long as 

 potassuretted hydrogen continues to be disengaged. The retort and the part of the 

 nozzle-tube exposed to the fire should be covered with a good refractory lute, as 

 described under the article PHOSPHOUUS. The joints must be perfectly air-tight ; 

 and the vessel freed from every trace of mercury, by ignition, before it is charged 

 with the tartar-ash. 



Tartar skilfully treated in this way will afford 3 per cent, of potassium ; and when 

 it is observed to send forth green fumes, it has commenced the production of the 

 metal. Instead of the construction above described, the following form of apparatus 

 may bo employed : 



A, fy. 1641, represents the iron bottle, charged with the incinerated tartar; and B 

 is a fire-brick support. A piece of fire-tile should also be placed between the bottom of 

 the bottle and the back wall of the furnace, to keep the apparatus steady during the 

 operation. Whenever the moisture is expelled, and the mass faintly ignited, the tube 

 c should be screwed into the mouth of the bottle, through a small hole left for this 

 purpose in the side of the furnace. That tube should be no longer, and the front 

 wall of the furnace no thicker, than what is absolutely necessary. As soon as the 

 reduction is indicated by the emission of green vapours, the receiver d, a, D, E, must be 

 adapted; this is shown in a large scale infff. 1642. 



1641 



This is a condenser, in two pieces, made of thin sheet copper : n, the upper part, is 

 a rectangular box, open at bottom, about 10 inches high, by 6 or 6 long and 2 wide ; 

 near to the side a, it is divided inside into two equal compartments, lip to two-thirds 

 of its height; by a partition, b, b, in order to make the vapours that issue from c pursue 

 a downward and circuitous path. In each of its narrow sides, near the top, a short 

 tube is soldered, at d and a ; the former being fitted air-tight into the end of the nozzle 

 of the retort, while the Litter is closed with a cork traversed by n stiff iron probe, e, 

 which passes through a small hole in the partition b, b, under c, and is employed to 

 keep the tube c clear by its drill-shaped steel point. In one of the broad sides of 

 the box D, near the top, a bit of pipe is soldered on at c, for receiving the end of a 

 bent glass tube of safety, which clips its other and lower end into a glass containing 

 naphtha. E, is the bottom copper box, with naphtha, which receives pretty closely the 

 upper case, D, and is to be immersed in a cistern of cold water, containing lumps of ice. 



In this process, carbonate of potash is obtained by calcination of the tartar, and this 

 carbonate is then decomposed by the carbon, with formation of carbonic oxide gas and 

 elimination of metallic potassium. For details of the process, and for precautions to 

 be observed, see Watts's ' Dictionary of Chemistry.' 



Pure potassium, thus procured, or by Davy's original method, by acting upon 

 fused potash under a film of naphtha, with the negative wire of a powerful voltaic 

 battery, is a soft metal, which c;m be cut, like wax, with a knife, and its newly-cut 

 surface possesses great brilliancy. It is fluid at 120 F. At 50 it is malleable, and 

 has the lustre of polished silver ; at 32 it is brittle, with a crystalline fracture ; and 





