Gf>6 



POTASH. 



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 mathematics, a problem which it is self-evident can 

 be solved ; as, for example, to draw a line about a 

 point, so that every part of the line shall be at an 

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POTASH, OB POTASSA, derives its name from 

 ashes, and the pots (called potash kettles) in which 

 the lixivium from which it is obtained is boiled 

 down. Some of its old names were, vegetable alkali, 

 in allusion to its being derived from the incineration 

 of vegetables ; salt of tartar, from the fact that 

 cream of tartar is another source of potash, and 

 alkali of nitre, from its having been known to form 

 the basis of that salt. The process employed in 

 the arts for obtaining potash is the following : The 

 ley of vegetable ashes is mixed with quick lime and 

 boiled down in iron pots, and the residuum ignited; 

 the substance remaining after ignition is common 

 potash. The purest potash .is obtained from the 

 mutual action in a red-hot iron pot, of nitre and 

 tartar, in the ratio of one of the former to two of 

 the latter ; the basis of each of these salts is potash, 

 and the acids combined with them are destroyed by 

 their action on each other. Those ashes which are 

 derived from plants growing remote from salt water 

 yield this alkali in greatest purity. Herbaceous 

 vegetables yield more than trees ; in trees, the 

 branches yield more than the body, the small 

 branches more than the large, and the leaves most 

 f all. One thousand pounds of the following 

 vegetables yielded saline matter in the following 

 order : 



Wormwood, . 



Stalks of sun-flower. 



Stalks of Turkey wheat, 



Vine branches, 



Fern, 



Box, 



Fumitory, 



Beech, . . 



Elm, 



Fir, 



Oak, . 



Heath, 



Aspcii. 



748 

 349 

 198 

 162 

 116 



78 

 369 

 219 

 106 

 132 

 111 

 115 



01 



The alkali arises from various salts rxisaug in the 

 vegetable juices, and which have been decomposed 

 by the action of fire. To prepare the potash, in a 

 state of perfect purity, from the impure article bear- 

 ing this i in i in- in commerce, we boil the common 

 potash with twice its weight of quick-lime for a few 

 hours, in abundance of water, separate the preci- 

 pitate, and boil the liquid down to the consistence 

 of a sirup ; after which we add an equal bulk of 

 strong alcohol, and let the mixture stand some time 

 in a closed vessel. Some solid matter will collect 

 at the bottom of the vessel, above which will appear 

 a stratum of watery liquor containing several salts 

 in solution ; while the alcohol occupies the top, and 

 is coloured of a dark-red colour. This last is se- 

 parated from the fluid below by decantation, and is 

 evaporated to dryness in a silver basin. The dry 

 substance is a hydrate of potash. It is solid, white, 

 and extremely caustic. In minute quantities, it 

 changes the purple of violets and cabbage to a green, 

 reddened litmus to purple, and yellow turmeric to 

 a reddish-brown. It rapidly attracts humidity from 

 the air. and becomes semi fluid. It is fusible at a 

 heat of 300, and is volatilized at low ignition. It 

 is used in surgery, under the name of lapis infcrna- 

 lis, or lapis causticus. In chemistry, it is very ex- 

 tensively employed, both in manufactures and as an 

 agent in analysis. It is the basis of the common 

 soft soaps, for which purpose, however, it is not used 

 in its pure state. 



Decomposition of potash. If a thin piece of solid 

 hydrate of potash be placed between two discs of 

 platina, connected with the extremities of a voltaic 

 apparatus of 200 double plates, four inches square, 

 it will soon undergo fusion, oxygen will separate 

 at the positive surface, and small metallic globules 

 will appear at the negative surface, which are the 

 basis of potash, and are called by Sir H. Davy, who 

 discovered the fact in 1807, potassium. Other and 

 more convenient methods have been devised for ob- 

 taining this extraordinary substance. That invented 

 by Messieurs Gay-Lussac and Thenard consisted in 

 heating potash to whiteness in a gun-barrel, in con- 

 tact with turnings of iron, the air being excluded - f 

 the potassium is liberated and collected in the cold 

 extremity of the tube. M. Bronner, by acting on 

 calcined tartar in a bottle of wrought iron, has suc- 

 ceeded in obtaining potassium at a comparatively 

 low heat. The bottle is spheroidal, about half an 

 inch in thickness, and capable of holding about a 

 pint of water ; a bent gun-barrel, ten or twelve 

 inches in length, screws into the mouth of the bottle. 

 The bottle, well luted over with fire clay, is set in a 

 strong air-furnace, so that the tube may dip down 

 externally, beneath the surface of the naphtha con- 

 tained in a cylindric copper vessel, standing in a 

 tub containing snow or ice and water. The top of the 

 naphtha vessel has a cover fixed on it, pierced with 

 a hole to receive the end of the gun-barrel ; and 

 from the side of the upper part of the vessel, a small 

 tube goes oft' at right angles, to let the air and va- 

 pours escape. It is advantageous to mix a little 

 ground charcoal with the tartar, previously calcined 

 in a covered vessel, in the same iron bottle, for ex- 

 ample. Nearly 300 grains of potassium have been 

 procured by this apparatus from twenty-four ounces 

 of crude tartar. Potassium is possessed of the fol- 

 lowing properties : It is lighter than water, its 

 specific gravity being only 0.86. At common tem- 

 peratures, it is solid, soft, and easily moulded by 

 the fingers. At 150 it fuses ; and in a heat a little 

 below redness, it rises ii. vapour. It is opaque. 

 When freshly cut, its colour is a bright silver-white; 

 but it suffers a tarnish on a moment's exposure to 

 the air. To preserve it unchanged, it must be kept 





