Chemistry and Physios. 483 



adding cold solutions of potassium permanganates to ammoniacal 

 solutions of metallic salts. With silver nitrate the compound 

 (NH 3 )„AgMn0 4 is obtained as a dark violet crystalline powder 

 which detonates on warming. Similar salts are given with copper, 

 cadmium, nickel and zinc. The most interesting, however, are 

 the salts of the ammonio-cobalt bases, particularly luteocobalt. 

 Its permanganate is obtained by mixing concentrated solutions of 

 luteocobalt chloride (NH 3 ) 12 Co 2 Cl 6 and potassium permanganate 

 at a temperature not above 60°, in the proportion of one molecule 

 of the former to twelve of the latter. The new salt separates on 

 cooling in little black quadratic octahedrons having a brilliant 

 luster. If powdered and carefully warmed in a test tube these 

 crystals decompose suddenly' with incandescence, but if heated 

 without pulverization, they incandesce with detonation, the tube 

 being shattered into fragments. When struck with a hammer, 

 the crystals detonate violently ; even powdering them in a mor- 

 tar being sometimes accompanied by daugerous crepitations. 

 This salt has the formula (NH 3 ) 12 Co 2 (Mn0 4 ) 6 . Other compounds 

 have been obtained in which hydrogen chloride and hydrogen 

 bromide partially replace the hydrogen permanganate. A beau- 

 tiful salt of this kind has the composition (NH 3 ) 12 Co 2 (Mn0 4 ) 4 Cl 2 . 

 (KC1) 2 . It forms dark violet hexagonal plates bearing often low 

 six-sided pyramids, and sometimes grouped together in the form 

 of six-rayed stars resembling snow flakes in shape. These salts 

 are less explosive than the others. — Ann. Chim. Phys., VI, xii, 

 5-33, September, 1887. G. f. g. 



6. On the Character of Solution. — Mendelejeef- has given a 

 definition of solution and has illustrated his views in the particu- 

 lar case of solutions of ethyl alcohol in water, the data being 

 here very accurate. "Solutions" he says " may be regarded as 

 strictly definite atomic chemical combinations, at temperatures 

 higher than their dissociation temperature." Just as definite 

 chemical substances may be formed or decomposed at tempera- 

 tures higher than those at which dissociation commences, so in 

 solutions; they can be either formed or decomposed at ordinary 

 temperatures. Moreover, the equilibrium between the quantity of 

 the definite compound and of its products of dissociation is 

 defined by the laws of chemical equilibrium, which laws require a 

 relation between equal volumes and their dependence on the mass 

 of the active component parts. If, therefore, the above hypothesis 

 of solution be correct, comparisons must be made of equal vol- 

 umes, and the specific gravities are the weights of equal volumes. 

 Moreover, we must expect the specific gravities of solutions to 

 depend on the extent to which the active substances are pro- 

 duced. Hence the expression for specific gravity s, as a function 

 of the percentage composition p, must be a parabola of the 

 second order: s=N (^»±c<) (100— p^fa) 



This may be represented by the general equation 

 s=C+Ap + Bp 2 



Am. Jour. Sci.— Third Series, Vol. XXXIV, No. 204.— Dec, 1887. 

 32 



