28 JOURNAIv OF THE 



solely by the copper. The conclusion is that sulphuric 

 acid is reduced by copper when air is present at the ordi- 

 nary temperatures, 20°-30° C. 



Third experiment. — An ordinary Kjeldahl dig-esting- 

 flask was made dust free by the treatment noted above. 

 100 cc. sulphuric acid, 1.84 sp. gr., were placed therein 

 and clean dry strips of copper ribbon were completely 

 submerged' in the acid. Now air-free carbon dioxide was 

 passed throug-h the flask for three hours. The inlet 

 tube was just dipped into the acid. The. flask was then 

 attached to a suction pump, with a sulphuric acid drying 

 flask intervening* to prevent a possible return flow of g-as 

 or air which mig'ht carry moisture or dust into the flask. 

 The flask was exhausted of the carbon dioxide present 

 for three hours at a pressure of 150 mm. It was then 

 sealed with the blast lamp and placed aside in a darken- 

 ed cupboard. Observations were made every few days to , 

 note any reaction taking- place. Within two days it could 

 be easily seen that copper sulphate had been formed and 

 the liquid was somewhat clouded by very finel}^ divided 

 suspended cuprous sulphide. Continued observations ex- 

 tending- over a period of seven weeks showed only an in- 

 crease in the amounts of both of these substances.' The 

 temperature of the cupboard had at no time risen above 

 20° C, and was for most of the time much lower. The 

 flask was then opened as any other sealed tube, and in- 

 stead of an external pressure inward, which had been 

 sufficient to heavily dent the tube in sealing-, there was 

 a strong- internal pressure outward. The g-as evolved 

 was sulphur dioxide, easily detected b}^ its strong- odor 

 and bleaching- effect upon a dilute solution of potassium 

 permang-anate. The sulphuric acid produced by the oxi- 

 dation of the sulphur dioxide by the permang-anate was- 

 precipitated by barium chloride. All solutions and ap- 

 paratus were proven to be free from traces of sulphur di- 

 oxide and sulphuric acid by a blank experiment. 



Conclusioji. — Concentrated sulphuric acid, 1.84 sp. g-r., 



