28^ EARTHS AND ALKALIES.-^ 



horaxata p6tass(R et sodcB. Borax 2lb., potassae supertartras olb., 

 dissolve in water q. s., evaporate to dryness : is soluble in an equal 

 weight of water. 



Chromate of potash. Heat cbromate of iron with an equal 

 weight of saltpetre in a strong blast fire, wash out the salt, filter 

 the leys, evaporate, crystallize, redissolve and recrystalHze two or 

 three times, then dissolve the crystals in five times their weight of 

 water. Used as a test liquor for metals, particularly lead. 



Triple prussiate of potash, Ferruretted liydrocyanate of 

 potash. Digest Prussian blue lib. in oil of vitriol lib., previously 

 mixed with five pints of water : boil, filter, and wash the sediment 

 well ; then put it into a sufficient quantity of pure potash-water 

 to turn the blue to a yellowish brown, filter, evaporate, crystallize, 

 and redissolve the crystals. Used as a test liquor for metals. 



Cyanuret or potassium and Hydrocyanate of potash. Ob- 

 tained by exposing ferruginous prussiate of potash for some time 

 to a well-sustained heat in a stone crucible, taking care to stop the 

 mouth of it during the period of its cooling. By this means the 

 cyanuret of iron is completely decomposed, and that of potash 

 remains unaltered. The residue of this calcination is a blackish 

 lamellar mass, which is the cyanuret of potassium rendered dark 

 by the iron and carbon belonging to the cyanuret of iron. This 

 mass is to be washed in water ; it deposits iron and carbon, whilst 

 the cyanuret of potassium dissolves, and is transformed into 

 hydrocyanate of potash. The solution should be perfectly colour- 

 less ; when well prepared cyanuret of potassium is white and 

 transparent. The action of cyanuret of potassium and of hydro- 

 cyanate of potash resembles that of Prussic acid. By dissolving 

 cyanuret of potassium in eight times its weight of distilled water, 

 we obtain what may be called medicinal hydrocyanate of potash. 

 This solution should always be extemporaneous. It may be given 

 in the same dose as medicinal Prussic acid, and under the same 

 circumstances. 



Hydrosulphate of potash, Hijdrosulphuret of potash. Pre- 

 pared as hydrosulphate of ammonia, putting pure potash-water 

 into the second bottle. Used as a test liquor for metals. 



Iodate of potash. Dissolve iodine in pure potash-water, 

 evaporate to dryness, separate the hydriodate by spirit of wine ; 

 then dissolve the iodate in water, and crystallize. Used in bron- 

 chocele. 



Hydriodate of potash. Obtained from the mixed mass 

 in the preceding process ; by washing with spirit of wine, filter- 

 ing, and distilling off the spirit. Used in bronchocele and in 

 chronic rheumatism, commencing with two grains and a half three 

 times a day in solution, gradually increased to ten grains. 



