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 was 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: 



2Cii+0, 2H,SO,=2Cu S0,+2H,0. 



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 



