55$ PRINCIPLES OF CHEMISTRY 



Metallic potassium was obtained like sodium ; first by the action of 

 a galvanic current, then by reduction of the hydroxide by means of 

 metallic iron, and lastly, by the action of charcoal on the carbonate at 

 a high temperature. The behaviour of metallic potassium differs, how- 

 ever, from that of sodium, because it easily combines with carbonic- 

 oxide, forming ah explosive and inflammable mass. 17 



Potassium is quite as volatile as sodium, if not more so. At the 

 ordinary temperature potassium is even softer than sodium ; its -freshly- 

 cut surfaces present a whiter colour than sodium, but, like the latter, 

 and with even greater ease, it oxidises in moist air. It is brittle at low 

 temperatures, but is quite soft at 25, and melts at 58 At a low red 

 heat (667, Perkin) it distils without change, forming a green vapour, 

 whose density, 18 according to A. Scott (1887), is equal to 19 (if that of 



will decrease. Under these circumstances the weight of the residue will be less for 

 example, 4KaC0 8 + 4S = KjELC^ + 8K 3 8 + 4CO a . Besides which, carbonic oxide has been 

 found in the gases, and potassium bisulphide, KjSg, in the residue of gunpowder. The 

 amount of potassium sulphide, K 2 S, increases with the completeness of the combustion, 

 and is formed in the residue .at the expense of the potassium sulphite. In recent times 

 the knowledge of the action of gunpowder and other explosives has made much progress, 

 and has developed into a vast province of artillery science, which, guided by the 

 discoveries of chemistry, has worked out a ' smokeless powder which burns without! 

 leaving a residue, and does not therefore give any ' powder smoke ' (to hinder the rapidity 

 of firing and aiming), and at the same time disengages a greater volume of gas and con- 

 sequently gives (under proper conditions oJ combustion) the possibility of communl* 

 eating to the charge a greater initial velocity, and therefore greater, distance, force, 

 and accuracy of aim. Such ' smokeless powder' is prepared either from the varieties of 

 nitre-cellulose (Chapter VL, Note 87) or from a mixture of them with nitro-glycerino 

 (ibid). In burning they give, besides steam and nitrogen, generally a large amount of 

 oxide of carbon (this is a very serious drawback in all the present forms of smokeless 

 powder, because carbonic oxide is poisonous), and also COg, EL,, &o. 



17 The substances obtained in this case are mentioned in Chapter IX., Note 81. 

 16 A. Scott (1887) determined the vapour densities of many of the alkali elements and 

 their compounds In a platinum vessel heated hi a furnace and previously filled with nitro- 

 gen. But these, the first data concerning a subject of great importance, have not yet 

 been sufficiently fully described, nor have they received as much attention as could bo 

 desired. Taking the density of hydrogen as unity, Scott- found the vapour densities of 

 <the following substances to be 



Na 12-76 (11-6) El 02(84). 



K 19 (19-5). EbCl 70(60). 



CsCl 89-5 (84-2). Csl 188(180). 



FeClj 68 AgCl 60(71-7). 



In brackets are given the densities corresponding with the formula, according to 

 Avogadro-Gerhardt's law. This figure is not given for FeClj, because in all probability 

 tinder these conditions (the' temperature at which it was determined) a portion of the 

 3FeCl 3 was decomposed. If it was not decomposed, then a density 81 would Correspond 

 with the formula FeCl s , and if the decomposition were Fe8Cl<=2FeCl 2 -J-Cl, then the 

 density should be 64. With regard to the silver chloride, there is reason to think that 

 4he platinum decomposed this salt. The majority of Scott's results BO closely correspond 

 with the formulae that a better concord cannot be expected in each determinations. 

 V. Meyer (1887) gives S3 as the density of KL 



