204 E. DIVEE8 AND M. OGAWA : PKODUCTS OF HEATING 



it cannot be prepared by Plessy's excellent process for the po- 

 tassium salt (Ann. Ch. Phys., 1844, iii, ii, 182), or by its 

 slight modification by Hertlein (Z. phys. Ch., 1896, IQ, 287). 

 We therefore made the pure potassium salt by Plessy's method, 

 precipitated the potassium from it by hydrofluosilicic acid, neu- 

 tralised quickly with ammonia, and precipitated the ammonium 

 trithionate by absolute alcohol and dried it in the desiccator. 

 This very deliquescent and changeable salt cannot be kept long 

 in good condition, but it was used by us when freshly prepared 

 and while still almost free from sulphate. 



Effects of heating the salts. 



The process. — The salts were heated in an oil-bath, in a 

 subliming vessel consisting of a test-tube, 15 cm. long and about 

 15 mm. in internal diameter. The tube was closed by a caout- 

 chouc stopper, and a very slow current of dried nitrogen through 

 the tube was maintained during the heating and cooling. The 

 salt, usually about 4 grm., was contained in an open slender 

 bottle, about 6 cm. long, having a platinum wire attached to it 

 for lowering it into and lifting it out of the subliming tube. The 

 tube was immersed in the oil to the level of the mouth of the 

 bottle inside, so as to cause all dry sublimates to collect in the 

 tube above this level. When, as in the case of the hydrated 

 normal sulphite, the heating was divided into stages, the bottle 

 was transferred between these to a second subliming-tube. The 

 heating of the oil was conducted very slowly, so that the tem- 

 peratures mentioned which were those of the oil, may be accept- 

 ed as being very nearly those of the salts at the time. 



In describing the effects of heating them, the salts are taken 



