IOWA ACADEMY OP SCIENCES. 
89 
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 r&o 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 fiask. 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.. 
