669 



POTASSIUM. 



POTASSIUM. 



670 



CO, + 2Aq.). It has an acrid, soapy taste, is strongly alkaline to test- 

 paper, is soluble in rather more than its own weight of old water, and 

 in rather less than half its weight of hot water. The strength of its 

 solution may be ascertained by its specific gravity according to Tunner- 

 man's table : 



Specific gravity. 

 1-4812 

 1-4750 

 1-4626 

 1-4504 

 1-4384 

 1-4265 

 1-4147 

 1-4030 

 1-3915 

 1-3803 

 1-3692 

 1-3585 

 1-3480 

 1-3378 

 1-3277 

 1-3177 

 1-3078 

 I-MM 

 l-283li 

 1-2694 

 1-2554 

 1-2417 



Per cent. 

 40-504 

 40-139 

 38-160 

 38-181 

 37-202 

 36-223 

 35-244 

 34-265 

 33-286 

 32-307 

 31-328 

 30-349 

 29-360 

 28-391 

 27-412 

 26-432 

 25-454 

 24-475 

 23-496 

 22-517 

 21-538 

 20-539 



Specific gravity. 

 1-2282 

 1-2150 

 1-2020 

 1-1892 

 1-1766 

 1-1642 

 1-1520 

 1-1400 

 1-1282 

 1-1166 

 l-ltftj 

 1-0940 

 1-0829 

 1-0719 

 1-0611 

 1-0505 

 1-0401 

 1-0299 

 1-0108 

 1-0098 

 1-0048 



Per cent. 



19-580 



18-601 



17-622 



16-643 



15-664 



14-685 



13-706 



12-727 



11-748 



10-769 



9-790 



8-811 



7-832 



6-853 



5-874 



4-895 



3-916 



2-9S4 



1-958 



0-979 



0-489 



Carbonate of potash is insoluble in alcohol. It fuses at a red heat, 

 and slowly volatilises at a still higher temperature. 



Carbonate of potash is largely used in the manufacture of soap and 

 of glass, and is a convenient salt for the preparation of other potash 

 compounds. 



Bicarbonate of potash. (KO,HO,2C0 2 ) is formed when moist car 

 bonate of potash is exposed to the influence of a current of carbonic 

 acid. It forms permanent right-rhombic prisms. Its solution is 

 neutral to test-paper, and by long exposure to air or a boiling tempe- 

 rature is gradually reduced to the state of solution of senjuicarbonate. 



Earatet of potath. There are several of these. The biborate 

 crystallises in six-sided prisms, and resembles borax. [BORACIC ACID.] 



Phosphate* of potash. The different varieties of phosphoric aoid 

 [PHOSPHORUS] form salts with potash, but the resulting compounds 

 have no particular interest. 



Sulphite of ptjtath (KO, SO,) and bisulphite of potash. (KO, HO, 2S0 2 ) 

 may readily be obtained, but the corresponding soda-salts [SODIUM] 

 are nearly always used in their place. 



Sulphate of potash (KO, S0 3 ). Sal polychrest. Bisulphate of potash 

 is neutralised with carbonate, and evaporated ; the resulting sulphate 

 of potaah much resembles quartz in appearance. It requires 16 parts 

 of cold water for solution, but is much more soluble in hot water. It 

 is very hard, and forms double salts with many other protosulphates 

 and with those sesquisulphates that are isomorphous with sesquisul- 

 phate of alumina. [ALUMS.] 



Bitulphate of potash (KO, HO, 2SO 3 ). Sal cnixum. A bye-product 

 in the distillation of hydrochloric or nitric acids. It is much more 

 soluble in water than the neutral sulphate, and crystallises in prisms or 

 plates. 



A tetqwmlphate of potash (2(KO, SO a ) -I- HO, SO,) also exists. 



ffypochlorite of potash, chlnride of potash, or chlorinated solution of 

 potath. (KO, CIO + K, Cl for 2(KO, Cl) = KC1 + KO, CIO). Obtained on 

 passing chlorine into solution of potash. It is a disinfectant ; but the 

 corresponding soda-salt is more generally used. 



Chlorate of potash. (KO, C10 5 ), oxymuriate of potash, is formed on 

 filming chlorine gas into a mixture of 69 parts of carbonate of potash 

 with the slaked fime that is obtained from 168 yarta of quick lime 

 The resulting mass is lixiviated with water, and evaporated till the 

 chlorate crystallises out. The decomposition is thus expressed : 



KO, CO, + S(CaO, HO) + Cl, = KO, C1O 4 + SCaCl + 4HO + CO, 



Hydrate Chlorine. Chlorate Chloride Water. Carbonic 

 of lime. of potash, of calcium. acid. 



Chlorate of potash is soluble in 16 parts of cold water, but in less 

 than twice its weight of boiling water. It has a cooling saline taste 

 When heated, it parts with the whole of its oxygen. [OXYGEN.] It is 

 a powerful oxidising agent, and is used in certain operations connected 

 with calico-printing and in the manufacture of lucifer matches. 



Perchlorate of potash (KO,C1O,) is obtained, as already describee 

 [CHLORINE, Perchloric Acid], in small crystals derived from the octo- 

 hedron. 



Nitrite of potash (KO, N0 3 ). [NrrRO(, i 



Nitrate of potash (KO, NO 4 ). Nitre. Saltpetre. This important 

 salt occurs native, as already described. Nearly all the nitre used in 

 this country comes from the East Indies. The soil in the neighbour- 

 hood of Tirhut, one of- the most productive districts, contains on the 

 average about 7 parts of nitrate of potash and rather more nitrate ol 

 lime in 1000 parts. The solution of these salts, brought to the surface ol 



jhe ground by capillary action, is rapidly dried by the wind and sun, and 

 ;he salts remain behind as a frost-like efflorescence. The natives scrape 

 up the deposit from time to time, mix it with carbonate of potash in 

 ,he shape of solution of wood-aahes, and evaporate the solution to dry- 

 ness. The use of the carbonate of potash is to decompose the nitrate 

 of lime, carbonate of lime being precipitated and nitrate of potash 

 remaining in solution along with that originally present. After a second 

 solution and crystallisation, it is sent into commerce, though still 

 impure. 



The analysis of crude nitrate of potash, or the estimation of the 

 amount of real salt contained in it, is technically termed the refraction 

 if n itre. Many processes have been devised for the accomplishment of 

 this object, but each requires modification according to the variety and 

 apparent amount of the impurities. They are all more or less based 

 upon the ordinary method adopted in general chemical analysis. 

 Frequently, the only required information is the amount of nitric acid 

 contained in a sample. To this end, about 10 grains are weighed into 

 a porcelain crucible, then fused to drive off water, cooled, a weighed 

 quantity of sulphate of lead added, the whole re-ignited till no more 

 fumes are evolved, and again weighed. The loss sustained during the 

 second heating is due to nitric acid ; for nitrate of potash and indeed 

 other nitrates are decomposed when heated with sulphate of lead, 

 sulphate of potash and oxide of lead remaining, while the whole of the 

 nitric acid is given off as peroxide of nitrogen and oxygen. 



In many parts of the continent of Europe, the nitrogen in every de- 

 scription of refuse animal and vegetable matter is converted into 

 the form of nitric acid, and thence into nitrate of potash, by expos- 

 ing heaps of offal, mixed with old mortar, slaked lime, chalk, 

 and earth, to the free action of the air, but protected from the 

 rain; the whole being occasionally watered with stale urine, stable 

 runnings, &e. Great care and skill is often bestowed upon these 

 saltpetre beds or nitre plantation,*, as they are called, and after two 

 or three years' exposure, the end first formed is lixiviated with 

 water and treated as before described for obtaining nitrate of 

 potash. In the above putrefactive process of nitrification, the nitrogen, 

 as usual, first takes the form of ammonia, and this in the presence 

 of the lime is gradually oxidised by the air to nitric acid : a tempera- 

 ture below 60 Fahr. prevents this action. 



The chief use of nitre is in the manufacture of GUNPOWDER. It is 

 to some extent employed in medicine, and when fused and cast into 

 cakes or bullets is frequently called Sal Prunella. 



Chromatea of potash. The neutral salt (KO, CrO 3 ) is formed on 

 neutralising the bichromate with carbonate of potash. By evaporating 

 the solution it may be obtained in transparent yellow prisms. The 

 bichromate (KO, 2 CrO,) is obtained directly from ground chrome iron 

 ore, by fusion with carbonate of potash and nitre. The resulting mass 

 is digested in water, the liquid saturated with nitric acid and evapo- 

 rated to the crystallising point. Bichromate of potash crystallises in 

 large ruby red four-sided tables. Its chief value depends upon the 

 chromic acid it contains. See CHROMIUM, and LEAD, Chromates of. A 

 terchromate of potash (KO, 3 CrO.) also exists. 

 Acetates of potash. [ACETATE.] 

 Tartrates of potash. [TARTARIC ACID.] 

 Oxalates of potash. [OXALIC ACID.] 



Cyanide of potassium (KCy). Formed by fusing together eight parts 

 of anhydrous ferrocyanide of potassium, three of dried carbonate of 

 potash, and one and a half of charcoal The resulting mass is digested 

 in water, filtered or decanted, and evaporated to dryness. From solu- 

 tion in alcohol it crystallises in colourless cubes. It is used for form- 

 ing and dissolving the cyanides of gold and silver in electro-gilding and 

 plating, and in photography. It is a powerful reducing agent, and is 

 exceedingly poisonous. It forms double salts with other cyanides. 

 [CYANOGEN.] 



Perrocyanide of potassium (K ? Fcy + 2 Aq.) Yellow prussiatc of potash. 

 This salt is prepared by heating together, in a covered iron pot, a 

 mixture of about five parts of horu parings, hide clippings, horse's 

 hoofs or other similar refuse animal matter, with about two parts of 

 pearlash, and a quantity of scrap iron. At the high temperature 

 employed the nitrogen and carbon combine to form cyanogen, and 

 this, with the iron and potassium of the pearlash, forms ferrocyanide of 

 potassium. On digesting the cooled mass in water and evaporating 

 the solution, the salt crystallises out in large yellow crystals derived 

 from the octahedron. 



Ferridcyanide of potassium (K s Fdcy). Red prussiate of potash. This 

 salt is formed on passing chlorine through a dilute solution of the 

 ferrocyanide, till the latter ceases to give a blue precipitate with a 

 persalt of iron. On evaporation and recrystallisation magnificent ruby 

 red prisms are obtained. For the relative composition, probable con- 

 stitution, and uses of ferrocyanide and ferridcyanide of potassium 

 see CYANOGEN; FEHRIDCYANIC ACID; FERROCYANIC ACID; METALS, 

 Iron , ferrocyanogen and ferridcyanogen ; BLUE, prussian blue. 

 Sulphocyanide of potassium. See CYANOGEN. 



/K) \ 

 Potassium-amide [ H | N I is a primary inorganic monamide, formed 



\H ) / 



on gently heating potassium in a current of dry ammomacal gas ; 

 hydrogen is at the same time evolved. It is a fusible, semi-crystalline 

 olive-green compound. Heated to redness it is decomposed, a greenish- 



