220 
IOWA ACADEMY OF SCIENCE 
even if present, but if constant, would have mattered little, since 
in the series of titrations hydrochloric acid, sodium hydroxide, 
benzoic acid, for example, the influence of the carbonate would 
have been eliminated. For the same reason no correction was 
made for the error due to the fact that phenoltalein, which was 
used as the indicator, shows the pink color only after the hy- 
droxyl ions are slightly in excess. 
All titrations were made in air free from carbon dioxide. A 
small Erlenmeyer flask was fitted with a thin section cut from 
a two-hole rubber stopper. One hole received the long delivery 
tube of the weight buret, and through the other was a tube 
reaching to the bottom of the flask, and connected with an ap- 
paratus to purify the air. The compressed air was contained in 
a large steel cylinder and passed from it to a large storage 
bottle with a layer a few centimeters deep of strong caustic 
potash. It then passed through three gas-washing bottles con- 
taining potash, through a similar bottle with water and Anally 
to the titration flask. 
In titrating the acid against the alkali both were weighed in 
weight burets, and the alkali was run into the hydrochloric acid. 
The air was allowed to run through the flask a short time before 
the addition of alkali was begun. This stream of air also served 
to agitate the liquid, and so obviated any need of shaking or 
stirring. Five closely agreeing titrations gave the ratio in grams 
of alkali to acid as 1 to 1.10991. A second solution of sodium 
hydroxide was prepared in the same way and its ratio to the acid 
was 1 to 1.1859 grams. Which value applies in any series of 
titrations will be indicated. 
Standardizing with Benzoic Acid. The benzoic acid used by 
Morey^ in his investigation as to its reliability as a volumetric 
standard was fractionally sublimed in vacuo, which demands an 
amount of time and labor that might seem excessive in ordinary 
volumetric work. It seemed desirable, therefore, to make ti- 
tration of the best acid on the market after purifying by crys- 
tallization only. A quantity of such acid was recrystallized from 
dilute alcohol and from water. The air-dried acid was fused in 
an oven heated at 130°. After fusion the platinum dish was 
placed in cold water which caused the cake of acid to crack 
loose. In weighing the acid for titration a platinum crucible 
was used since platinum is far less hydroscopic than glass. The 
^Bureau of Standards, Bulletin 8, p. 643. 
