38 
IOWA ACADEMY OP SCIENCES. 
passing a dry current of air or of carbonic anhydride through 
it. The escaping gas was then tested (in flask C) by suitable 
reagents, to be described, for sulphuric and sulphurous anhy- 
drides respectively. Flask A contained concentrated sulphuric 
acid of the ordinary temperature (25°C) to dry the gas, which 
was usually passed at the rate of about eighty bubbles per min- 
ute. The importance of securing absence of dust from the 
acid being recognized, the interior of the whole apparatus was 
washed with boiling concentrated sulphuric acid and dried in 
dustless air. 
Experiment I . — Flasks A and B were charged with concen- 
trated sulphuric acid and C with a solution of barium chloride. 
Air was drawn through the whole in a slow current for fifteen 
minutes. The solution in C remained clear. B was now very 
slowly heated while the current of air v/as maintained. 
Before the bath reached 70°C there appeared in C a faint tur- 
bidity of barium sulphate, which at the temperature named 
became distinct. At 60°C the solution 'remained unchanged, 
even after passing the air for a long time. Hence sulphuric 
acid of the given concentration begins to give up sulphuric 
anhydrides, that is, it begins to dissociate at a temperature 
lying between 60° and 70°C. 
Experiment II . — The apparatus charged as before, with the 
addition of pure bright copper wire in B, and with highly dilute 
iodide of starch instead of barium chloride in C. After passing 
air for several hours at the ordinary temperature, much of the 
copper had gone into solution and anhydrous copper sulphate 
had begun to crystallize out, but the iodide of starch, made 
originally very pale blue, retained its color. 
This shows that in the presence of air, sulphuric acid is 
attacked by copper at ordinary temperatures, but without 
reduction of the acid. The reaction must take place in accord- 
ance with the equation: 
2Cu+0, 2H,SO,=2Cu SO,+2Hp. 
Experiment III . — This was like the last, except that the appa- 
ratus was filled with carbonic anhydride, and a current of this 
gas was substituted for air. 
The copper was not attacked, and the starch iodide was not 
decolorized. The temperature of B was now slowly raised, and 
when it reached 90° the solution in C was bleached. In a sim- 
ilar experiment a solution of dilute sulphuric acid, colored pale 
straw with potassium bichromate, was used as an indicator for 
