Chemistry and Physics. 465 



influence of the silent discharge. — J. Ghem. Soc, lxxiii, 246-254, 

 April, 1 898. g. f. b. 



4. On the Action of Hydrogen on Sulphuric Acid. — It has 

 been observed by Berthelot that on passing a slow current of 

 hydrogen through concentrated sulphuric acid for an hour at the 

 ordinary temperature, there is no sulphurous oxide formed. If 

 however the contact between the hydrogen and the acid be much 

 prolonged, the gas is finally absorbed and a reduction of the acid 

 takes place. Dilute sulphuric acid is not reduced by hydrogen. 

 At the temperature of 250°, when the acid is concentrated, the 

 reduction takes place somewhat rapidly, particularly in presence 

 of a considerable excess of acid. When mixtures of oxygen and 

 hydrogen are left in contact with sulphuric acid either at the 

 ordinary temperature or at 250° both gases are absorbed. The 

 rate of absorption of hydrogen however is the same as in the 

 absence of oxygen, while the oxygen is absorbed in consequence 

 of its combination with the sulphurous oxide formed by the 

 reduction. If the hydrogen and the sulphurous oxide be dry, 

 they do not act on each other either at 100° or at 280°. The 

 reduction of concentrated sulphuric acid by hydrogen is an exo- 

 thermic reaction, developing +15*1 Cal., this value being 

 increased to +30*1 Cal. when the sulphuric acid is in large excess, 

 owing to the heat of hydration. In the case of dilute sulphuric 

 acid however the reaction would be endothermic. — C. i?., cxxv, 

 743-746, November, 1897. g. p. b. 



5. On the Preparation of dry Hydrogen cyanide and Carbon 

 monoxide. — While it is evident that both hydrogen cyanide and 

 carbon monoxide may be formed by the action of sulphuric acid 

 or potassium cyanide, yet Wade and Panting have now shown 

 for the first time that a practically quantitative yield of either 

 product can be obtained at will by varying suitably the concen- 

 tration of the acid. When the cyanide is distilled with the 

 dilute acid, dilute hydrogen cyanide passes over; but when 

 equal volumes of sulphuric acid and water are used, the distillate 

 contains only small quantities of aqueous vapor ; and this can be 

 removed by passing it over warm calcium chloride. As the sul- 

 phuric acid becomes stronger a certain amount of carbon mon- 

 oxide is formed, the quantity of the gas increasing with the con- 

 centration, while the hydrogen cyanide decreases. So that at 

 last when sulphuric acid of the ordinary commercial strength acts 

 on the cyanide nearly pure carbon monoxide is evolved in almost 

 theoretical quantity. Thus when a mixture of equal volumes 

 sulphuric acid and water (100 cc of each) is allowed to drop on 

 100 grams 98 per cent cyanide in a capacious flask, provided with 

 U-tubes filled with calcium chloride and with condensing tubes 

 cooled to —10°, about 40 grams (58 cc ) of practically pure hydro- 

 gen cyanide is obtained ; which on rectification from phosphorus 

 pentoxide boils at 26 , 2°-26 , 3°; the average yield being 38'5 grams, 

 theory requiring 40*8 grams. On the other hand, when 50 grams 

 of cyanide are treated with cold concentrated sulphuric acid, 14 



