ELISHA MITCHEI^L SCIE^NTIFIG SOCIETY. 25 



(1.84 sp. gr.) not only at the ordinary temperatures of 

 the air, 20°-30°C., but at zero as well. Andrews^ states 

 that the assertion is incorrect and that it does not occur 

 until the temperature 86°C. has been reached, or a point 

 above the dissociation temperature ot the concentrated 

 sulphuric acid, 67°C. according- to him. Andrews fur- 

 ther says that the author's statements were based "not 

 upon the demonstrations of the formation of sulphurous 

 acid, but solely on the formation of copper sulphate," 

 which, he says, occurs only "in consequence of the pres- 

 ence of the air." It is to be reg-retted that Dr. Andrews 

 did not note carefully the statements of the au.thor in his 

 previous communication, as no reason whatever exists for 

 any such, conclusions, because it was distinctly stated that 

 not only the copper as sulphate, but as sulphide was de- 

 termined, as well as sulphurous acid, and moreover, that 

 the experiments were carried out when the air had been 

 replaced by a meutral gas, either hydrog-en or carbon di- 

 oxide. 



The author, althoug-h confident of the correctness of 

 his former statement, carried out further experiments to 

 correct the error, if committed or to establish, be3^ond 

 question, the fact that concentrated sulphuric acid of 1.84 

 sp. g-r. is reduced by copper below 86°C., the limit posi- 

 tively set by Dr. Andrews. 



The fact that these experiments but confirmed the for- 

 mer statement of the author allows the incorporation of 

 of the results in this paper. 



As far back as 1838 the fact that copper is acted upon 

 by concentrated sulphuric acid at ordinary temperatures, 

 if sufficient time be g-iven, was made known by BarrueP. 

 Calvert and Johnson,^ however, failed to obtain any ac- 

 tion below 130° C, and considered that none took place. 



1 J. Am. Chem. Soc, 18, 253. 

 2/. depharm.,20, 13, 1834. 

 3 /. Chem. Soc, 19, 438, 1866. 



