Chemical Constitution of Saline Solutions. 283 



if submitted to the temperature of boiled linseed oil, the red insoluble salt is 

 formed. The red insoluble salt may also be made by adding a great excess of 

 oil of vitriol to either a green or violet solution of chromic sulphate, and boiling 

 till sulphuric acid is evolved ; the red salt is then precipitated. Schrotter ascribes 

 the change of colour when violet salts are heated to a loss of water of crystalliza- 

 tion, his evidence consisting of the changes referred to above, the salt, Cr23(S04), 

 being unaffected througliout. Loewel* supposes the violet solutions of chromium 

 to contain normal, and the green, basic salts. Krugerf states that when a green . 

 solution of chrome alum, obtained by boiling the strong solution with water, is 

 mixed with alcohol, the spirit takes up a portion of the acid, and the liquid then 

 contains KoO'CrjOa; this green compound is converted into the violet by adding 

 sufficient acid to reproduce KoO'CrsOa'JrSOs.J Loewel experimented on solu- 

 tions of chromium in hydrochloric acid. Two different nitrates of chromium 

 exist — one hydrated and crystallizing in octahedra; the other green, uncrystalliz- 

 able, and producible by heat. The violet crystals consist of a normal nitrate, 

 with nine molecules of water. 



Tichborne attributed the change of colour in chromium solutions when heated 

 to a basic condition of the salt, and not to dehydration. § His method of workino- 

 was to heat a dilute solution of a ferric, aluminic, or chromic salt, either to 100°, 

 or, under pressure, to a higher temperature, when the oxides separate out. 



I have heated chromic sulphate, Cr23S04-15H20 to 100° C, when diluted with 

 10,000 times its weight of water, without the slightest turbidity resulting, and 

 yet a saturated solution of the salt turns green at 70° C, and remains perfectly 

 clear. Having weighed all the evidence afforded by our knowledge of chromium 

 compounds, I have obtained new facts leading to a definite conclusion as to the 

 difference in constitution between violet and green salts of chromium. Loewel 

 heated the comjDound obtained by dissolving chromic hydrate in hydrochloric acid 

 to 150° C. The resulting compound, if heated to 300° C, gives partly the violet 

 insoluble chromic chloride, Cr2Cl2, and partly the green oxide, Cr203, hydro- 

 chloric acid being evolved. Therefore, Loewel's conclusion that the constitution 

 of these compounds is that of chromic oxide, combined with hydrochloric acid, is 

 not borne out by facts. That the ultimate change leaves chromium in combi- 

 nation with chlorine is evidence that these two elements were combined directly 

 with each other in the first instance. 



With modern formulas, Loewel's first compound would be Cr2Cl6'3H20, and 

 the second might be written thus, Cr20Cl4'2H20; it is an oxychloride, and its 

 formation may be thus expressed — 



Cr2Cl6-3H20 = Cr20Cl4-2H20 + 2HC1. 



* Journal fiir praktische Cliemie, vol. xssvii., p. 38. f Pogg. Annalen, vol. Ixi., p. 218. 



I See also Siewert, Ann. der Chemie, vol. 127, p. 86. § Chemical News, 1871, p. 82. 



