104 
IOWA ACADEMY OF SCIENCES. 
with two freshly filled calcium chloride tubes on one side 
and a calcium chloride tube and aspirator on the other side 
as shown in the figure. Air is drawn through the apparatus 
for about twenty minutes while the fiask d is immersed in 
a beaker of distilled water to cool it. The apparatus is 
carefully wiped with silk and weighed, the loss, of course, 
representing the amount of carbon dioxide. The apparatus 
is gently warmed again, and the air aspirated through as 
before while the flask is in the beaker of distilled water. 
A weight that is practically constant is readily attained. 
The writer has made scores of determinations by this 
method, and has supervised hundreds more that have been 
made by students, especially in Iceland spar, dolomite and 
siderite. There is not much difficulty in securing a result 
that differs not more than one-tenth of a per cent from the 
theoretical. It might seem that there would be a tendency 
to get too high a result, but such is not the case, providing 
the rock substance has been sufficiently pulverized, and 
the calcium chloride in tube e is of good quality and is 
changed sufficiently often to keep it in proper condition. 
Besides, the acid becomes further diluted as soon as it 
begins to act on the powder, and at first the action takes 
place with very little heat. 
Where it is desirable to make a carbon dioxide determina- 
tion in a sulphide like chalcopyrite, it is necessary to pre- 
vent the escape of sulphuretted hydrogen as this would 
give a result too high. This is accomplished by the use of 
dilute sulphuric acid instead of hydrochloric acid. If there 
is itill an odor of sulphuretted hydrogen, a small quantity 
of powdered copper sulphate, ferric sulphate, or potassium 
dichromate is introduced into the bulb wdth the powdered 
rock. The carbon dioxide can be easily determined by 
this means. 
After many years of trial, the writer commends this 
method on account of its simplicity and accuracy. It is a 
method that even the student with but small quantitative 
experience can ‘use with success. His ability to secure 
good results at the outset increases his interest for the 
further prosecution of his quantitative work. 
