Identification of Potassium and Sodium. 267 



chlorate, and in such case precautions must be taken to have 

 sufficient of the acid present. Upon treating with 97 per 

 cent alcohol the presence of potassium is revealed by an insol- 

 uble residue. This is removed by a dry filter and the filtrate 

 saturated with gaseous hydrochloric acid, whereupon sodium, if 

 originally present in amount greater than 0'0005 grms. of the 

 oxide, will be precipitated in granular condition. 



The fact that minute traces of sodium and potassium are 

 found in the blank tests is to be expected from the delicacy of 

 the method as proved by Tables I and II, when it is remem- 

 bered that but very few of the so-called chemically pure 

 reagents are absolutely free of sodium and that even distilled 

 water kept in glass vessels contains a trace of the alkaline 

 elements. However, the indication for sodium in the blank 

 tests appeared only as a cloudiness and after complete satura- 

 tion, while when the quantity of sodium oxide present is not 

 less than 0*0005 the precipitate appears in granular form and 

 before the alcohol is completely saturated, which leaves the 

 method all that could be desired for qualitative determinations. 



Prej>aration of the Perchloric Acid. — The perchloric acid 

 prepared according to the method previously published by one 

 of us,^ by converting sodium chlorate into the perchlorate by 

 heat, destroying the residual chlorate by treating with the 

 strongest hydrochloric acid, from which the sodium chloride was 

 separated by filtering through a Gooch filter and the excess of 

 hydrochloric acid removed by evaporation — while answering 

 perfectly well for the detection of potassium, is inapplicable to 

 the test for sodium, because of the small amount of this ele- 

 ment which the acid always contains, due to the partial solu- 

 bility of sodium chloride in hydrochloric acid. As distillation 

 seems the only method for the removal of this residual sodium, 

 our attention was given to a study of the best conditions for 

 the distillation. Yarious experiments led to the adoption of 

 the following treatment, which we found in every case perfectly 

 safe and fairly rapid. To prevent loss by decomposition the 

 distillation must be carried on under diminished pressure, and 

 unless the acid has been previously concentrated by evaporat- 

 ing until the white fumes appear, if there is any considerable 

 amount of the acid in the distilling flask, even with porcelain 

 chips to check it, it bumps with such violence as to throw the 

 liquid to all parts of the flask and possibly into the condenser. 

 It appeared to be essential, therefore, to start with only a small 

 amount of the concentrated acid in an apparatus which would 

 permit of the gradual addition of the acid without relieving 

 the vacuum. Rubber stoppers or connectors are not advisably 

 used where the acid may condense upon them and flow back 

 into the flask. Invariably oxidizable matter is carried back, 



* Kreider, this Journal, vol. xlix, 443. 



