Chemistry and Physics. 315 



SCIENTIFIC INTELLIGENCE. 



I. Chemistey and Physics. 



1. The Separation of Hydrochloric and Hydrocyanic Acids. — 

 In order to determine small quantities of chlorides in alkaline 

 cyanides, Richards and Singer dissolve about l*25 s of the sub- 

 stance in 400 cc of water, add 5 CC of sulphuric acid to the solu- 

 tion, and boil for two hours in a retort, the neck of which slants 

 upward, with replacement of the water lost by evaporation so 

 that the volume does not become less than 300 cc . In this way all 

 the hydrocyanic acid escapes with the steam, while there is no 

 loss of hydrochloric acid, even after boiling for more than eleven 

 hours. The residual hydrochloric acid is readily determined by 

 the usual method of precipitation with silver nitrate. The 

 authors explain the difference in behavior of the hydrocyanic 

 and hydrochloric acids on the ground that the former is but 

 slightly ionized in solution while the latter is very thoroughly 

 ionized in dilute solutions. Ions have little or no tendency to 

 leave an aqueous solution with steam, while the unionized hydro- 

 cyanic acid displays its usual volatility when its solution is 

 boiled. ' The time of boiling which has been mentioned, two 

 hours, while sufficient to remove the hydrocyanic acid from a 

 small quantity of hydrochloric acid, is insufficient when larger 

 quantities of the latter, for instance amounts corresponding to 

 about one-tenth of a gram of potassium chloride, are present. 

 In this case boiling for eight or nine hours appears to be neces- 

 sary. From this interesting result the conclusion is drawn that 

 the chloride ion must tend to form a complex with hydrocyanic 

 acid, and that this complex seems to be entirely broken up by 

 prolonged boiling without the loss of hydrochloric acid. — Amer. 

 Chem. Jour., xxvii, 205. h. l. w. 



2. Volumetric Determination of Copper, Antimony, Iron, etc., 

 by Means of Stannous Chloride. — In 1878 Weil described a 

 method for determining these substances. The titration, accord- 

 ing to the original plan, is carried out in a flask in the presence 

 of very strong hydrochloric acid. During the operation the 

 liquid is kept boiling so that air cannot enter the flask and cause 

 an error by its oxidizing action. The end of the reaction in the 

 cases of copper and iron is distinctly marked in strong acid solu- 

 tion by the disappearance of color. When antimonic acid is 

 present with copper it is reduced with the latter by stannous 

 chloride, but after the resulting liquid has been exposed to the 

 air for a few hours the cuprous chloride is oxidized to cupric 

 chloride while the antimonious chloride remains unchanged, so 

 that the former can be determined by a repetition of the opera- 

 tion, and the amount of antimony present can be calculated. 

 When ferric salts are present with copper they are also reduced 

 by stannic chloride, but the copper can be removed by means of 



