POTASSIUM 601 



from the part v, strikes on the pot or retort only -when the pipes w, w , w", V'', are 

 sufficiently heated. 



Infy. 1639 are represented the junction-tubes, which connect the four pipes -with 

 their gas-burners, z, z, and the cocks mm', r, r, Jig. 1640, are covers, closing the pipes, 

 and having holes formed in them ; these holes are shut by the stoppers e. 



Whether the pipes are placed in the vertical or horizontal position, it is always 

 proper to be able to change the direction of the current of gas ; this is easily done by 

 closing, during one hour (if the operation is to last two hours), the cocks u, m! (fig. 

 1639), and opening those, u', m ; then the gas passes through &', into the branch K, and 

 entering V", passes through v into "w', through g into w*, and through 2nd g into w, 

 and finally escapes by the burner z. During the following or other hour, the cocks 

 M', m, must be closed ; the cocks , m', being opened, the current then goes from u, 

 into K, TV, TV', \v", V, and escapes by the burner z', where it may be ignited. 



The changing of the direction of the current dispenses, to a certain degree, with the 

 labour required for stirring with a spatula the matters contained in the pipes ; never- 

 theless, it is necessary, from time to time, to pass an iron rod or poker amongst the 

 substances contained in the pipes. It is for this purpose that apertures are formed, so 

 as to be easily opened and closed. 



The patentee remarks, that although this operation is only described with reference 

 to potash, for obtaining prussiate of potash, it is evident that the same process is 

 applicable to soda ; and when the above-mentioned ingredients are employed, soda 

 being substituted for potash, the result will be prussiate of soda. 



The process employed in the manufacture of ferrocyanide of potassium, by Hoffmayr 

 and Priikner, is as follows : The potash must be free from sulphate, for each atom of 

 sulphur destroys an atom of the cyanide of potassium. A very strong heat is advan- 

 tageous. The addition of from 1 to 3 per cent, of saltpetre is useful, when the mass 

 is too long in fusing. A reverberatory furnace is recommended ; but the flame must 

 not beat too much upon the materials for fear of oxidising them. When the smoky 

 red flame ceases, it is useful to throw in from time to time small portions of uncar- 

 bonised animal-matter, particularly where the flame first beats upon the mass, whereby 

 the resulting gases prevent oxidation by the air. The animal-matters should not bo 

 too much carbonised, but left somewhat brown-coloured, provided they be readily 

 pulverised. Of uncarbonised animal-matters, the proportions may be 100 parts dried 

 blood, to from 28 to 30 of potash (carbonate), and from 2 to 4 of hammerslag 

 (smithy scales), or iron filings. 2nd. 100 parts of horns or hoofs ; from 33 to 35 

 potash; 2 to 4 iron. 3rd. 100 leather; 45 to 48 potash; and 2 to 4 iron. From 

 blood, 8 to 9 per cent, of the prussiate are obtained ; from horns, 9 to 10 ; and from 

 leather, 5 to 6. The potash should be mixed in coarse particles, like peas, with the 

 carbonised animal-matter, which may be best done in a revolving pot, containing 

 cannon-balls. Of the animal-charcoal and potash equal parts may be taken, except with 

 that from leather, wffich requires a few more parts of potash per cent. On the average, 

 blood and horn-charcoal should afford never less than 20 per cent, of prussiato, nor the 

 leather than 6 ; but by good treatment they may be made to yield, the first 25, and 

 the last from 10 to 11. 



POTASH, RED PRUSSIATE OP, or Ferricyanide of potassium, is prepared 

 by passing chlorine gas through a solution of the ferrocyanide of potassium until it 

 ceases to give a precipitate of Prussian blue, with a persalt of iron, and no longer. 

 Its formula is KWCy 8 (X 3 FeCy a ). 



POTASSIUM (Eng. and Fr. ; Kalium, Ger.) Symb. K ; At. wt. 39. This is a 

 metal deeply interesting, not only from its own properties, but from its having been the 

 first link in the chain of discovery which conducted Sir H. Davy through many of the 

 formerly mysterious and untrodden labyrinths of chemistry. It is the metallic base of 

 potash. 



The easiest mode of obtaining this elementary substance is that contrived by 

 Briinner. Into the orifice of one of the iron bottles, as A, Jig. 1641, in which mercury 

 is imported, adapt, by screwing, a piece of gun-barrel tube, 9 inches long ; having 

 brazed into its side, about three inches from its outer end, a similar piece of iron tube. 

 .Fill this retort two-thirds with a mixture of ten parts of cream of tartar, previously 

 calcined in a covered crucible, and 1 of charcoal, both in powder ; and lay it hori- 

 zontally in an air furnace, so that while the screw orifice is at the inside wall, the 

 'extremity of the straight or nozzle-tube may project a few inches beyond the brick- 

 work, and the tube brazed into it at right angles may descend pretty close to the 

 outside wall, so as to dip its lower end a quarter of an inch beneath the surface of 

 some rectified naphtha contained in a copper bottle surrounded by ice-cold water. By 

 bringing the condenser vessel so near the furnace, the tubes along which the potassium- 

 vapour requires to pass run less risk of getting obstructed. The horizontal straight 

 end of the nozzle-tuba should be shxit by screwing a stopcock air-tight into it By 



