152 
IOWA ACADEMY OF SCIENCES. 
poses into chlorine and perchloric acid, water and oxygen, 
when heated above 40°, it was deemed necessary to test the 
stability of the 2.5 N. acid at higher temperatures, and this 
was done in the following way: A volume of 30 c.c. of 
the acid of 2.5 N. strength was placed in a tube so arranged 
that pure air from a gas cylinder could be passed through 
the acid and then by suitable exit tube into a flask con- 
taining potassium iodide. The tube was placed in a beaker 
of water which could be heated. While a slow current of 
air was passed through the acid the temperature was slowly 
raised to the boiling point of the water in the beaker, and 
the boiling was maintained for half an hour. At about 95° 
the solution of potassium iodide began to show a trace of 
color, due to separated iodine. At the end of the experiment 
the free iodine was titrated with N / 10 thiosulphate and 
required 0. 2 c.c., which corresponds to 0. 6 mg. of chlorine. 
The strength of the acid then remaining in the tube was 
found to be 2. 65 N. and on testing with silver it gave 
apparently only the usual slight opalescence. It seems 
clear, therefore, that one may heat even the strongest, pure 
chloric acid that is likely to be found in the market to 
temperatures near the boiling point of water without fear 
of essential decomposition. It seems probable that the 
statement that chloric acid decomposes when heated above 
40° might be due to the fact that the author used impure 
acid, containing possibly hydrochloric acid which might 
decompose the chloric acid, or -that the statement refers to 
an acid of about the maximum concentration. 
The methods of experiment were in general very simple. 
In some cases where no hydrogen was evolved, the flask 
or tube containing the weighed metal and measured acid 
was allowed to stand at room temperature. In cases 
where the solution was slow, the vessel was placed in 
water which was heated to 40 or 50 degrees. The condi- 
tions are mentioned under the metals to which they apply. 
Save in two or three cases no attempt was made to 
exclude the air for the two reasons, that at best the acid 
would contain some air which could not with safety be 
expelled by heating, and that in two or three cases where 
