IOWA ACADEMY OF SCIENCES. 39 



sulphurous acid in C. In this case the change of color did not 

 occur until the temperature had risen to 108°, the indicator 

 being, as might be expected, less sensitive than the other. 



Experiment IV. — Same as III, except that a reagent for both 

 sulphuric and sulphurous acid was used in C. 



This reagent was prepared by slightly acidifying a solution 

 of barium chloride with hydrochloric acid and then adding 

 enough potassium permanganate to render the solution pale 

 rose color. 



This indicator is capable of showing the presence of consid- 

 erably less than do m. g. of sulphurous acid. 



When the temperature of the bath had reached 70 °C 

 the solution in C was distinctly turbid with barium sulphate, 

 but its color was unaltered. At 86° it began rather 

 suddenly to bleach, and at 87° it was colorless. Special 

 care was taken in filling B not to get any sulphuric acid on the 

 neck or sides of the flask. A repetition of this experiment 

 gave identical results, the gas being passed at the rate of two 

 to three bubbles per second. 



The conclusions to be drawn from this investigation are: 



First. — That the dissociation of sulphuric acid of 98.4 per 

 cent, begins to be appreciable at a temperature somewhat 

 below 70°, which may be estimated at about 67°. 



Second. — The reduction of sulphuric acid by copper does not 

 begin below 86°, that is, not until the acid contains free 

 anhydride. 



The assertion made by Baskerville,^ that sulphuric acid is 

 reduced by copper at 0° is, therefore, incorrect. He appears 

 to have based the statement, not on any demonstration of the 

 formation of sulphurous acid, but solely on the formation of 

 copper sulphate, which occurs, as I have shown, ^ in conse- 

 quence of the presence of air. 



A more careful repetition of his experiments under condi- 

 tions securing entire exclusion of air can but lead him to a 

 different conclusion from that he obtained at first. 



The fact adduced by him that under certain conditions 

 cuprous sulphide may be formed by the action of the metal 

 upon sulphuric acid does not allow any conclusions to be drawn 

 respecting the presence of "nascent" hydrogen, since it may 

 be explained perfectly well either by the direct reducing action 



ijournal of the Am. Ohem. Soc, 1895, 908. 



2Traube has shown the same thing for dilute sulphuric acid. Ber: 18, 1888. 



