Chemistry and Physics. 299 



point. Potassium permanganate acted similarly. This salt 

 decomposes at 218° in air; but in hydrogen it begins to evolve 

 oxygen at 155° and gives it off freely at 182°. Barium peroxide 

 does not give off oxygen during reduction. — Ber. Berl.Chem. Ges., 

 xxx, 2515-2519, November 1897. g. f. b. 



4. On Chromium Tetroxide and Perchromates.—lt has been 

 observed by Wiede that on cautiously treating with ammonia the 

 blue solution obtained by extracting a mixture of hydrogen per- 

 oxide and chromium trioxide with ether, the color gradually dis- 

 appears, and on sufficient cooling the underlying aqueous layer 

 takes a deep brown color and deposits a greenish-brown precipi- 

 tate on standing. On dissolving this in warm 10 per cent 

 solution of ammonia, and allowing it to cool, pale brown needles 

 separate having the composition (NH 3 ) 3 Cr0 4 . The new compound 

 dissolves in water, suffering partial decomposition, evolves oxygen 

 when treated with strong acids and explodes .when heated. If 

 treated with alkalies or if the ethereal solution itself is treated 

 with a concentrated solution of potassium or sodium hydrate 

 instead of ammonia only alkali chromates are formed. On using 

 substituted ammonias, corresponding perch romates are formed. 

 When for example the ethereal solution is treated with pyridine 

 and the ether is evaporated in a rapid current of air, blue scales are 

 produced. And if one of these be placed in the ethereal solution 

 after the pyridine has been added, long dark blue glistening 

 prisms gradually form having the composition H. C fi NH 5 Cr0 6 . 

 These crystals are so unstable that they explode violently even 

 at the summer temperature. But if dry, they can be kept for 

 weeks in the cold ; though when moist they decompose rapidly. 

 It is soluble in most of the neutral organic solvents, and is acted 

 upon only gradually by potassium permanganate in acid solution. 

 Aniline, when added to the ethereal solution of perchromic acid, 

 gives, on diluting the solution with an equal volume of light 

 petroleum naphtha, dark red crystals, H . NH 2 Ph . Cr0 5 resembling 

 potassium permanganate. It is even more explosive than the 

 pyridine compound. — Ber. Berl. Chem. Ges., xxx, 21*78-2189, 

 October 1897. g. f. b. 



5. On Potassium Percarbon ate. — It has been shown by Con- 

 stant and von Hansen that in very concentrated solutions, the 



+ - 



alkali carbonates will dissociate into the ions M and MC0 3 the 

 latter uniting, on being set free by electrolysis at the anode, to 

 form percarbonates M 2 C 2 6 . If a solution of potassium carbonate 

 be electrolyzed the evolution of oxygen decreases as the tempera- 

 ture falls, becoming almost nil at —10°. At the same time in 

 place of the hydrogen-potassium carbonate which at first forms at 

 the anode, there is produced a bluish amorphous powder consist- 

 ing of potassium percarbonate. Von Hansen has further studied 

 this reaction and finds that if the density of the solution of potas- 

 sium carbonate surrounding the anode is not allowed to fall below 

 1*52, small temperature variations do not markedly affect the 

 yield, even when it rises to 0°. When the concentration falls, 



