524 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
Benzoic Acid. — Kahlbaum’s “C. P.” acid was first fractionally 
resublimed, then fused and preserved in a desiccator until it 
was needed. 
Sodium Hydroxide Solutions . — The solubility was determined 
by titrating weighed portions of the saturated solutions with a 
standard solution of sodium hydroxide, using phenolphthalein 
as indicator. For this purpose two aqueous solutions of sodium 
hydroxide were prepared, approximately .5N and .ION, re- 
spectively. A slight excess of solid barium hydroxide was added 
to each to remove any carbonates present. After being allowed 
to stand for some time they were quickly filtered into ceresin- 
coated stock-bottles.. Each of these stock-bottles was connected 
with the upper end of a certified burette by means of a ceresin- 
coated glass tube, thus forming a single piece of apparatus. 
The burettes.' were filled by suction. Entrance of carbon dioxide 
into the apparatus was prevented by trains of test-tubes con- 
taining the respective standard solutions. 
The alkaline solutions were standardized (Morey’s Method 1 ) 
by titrating against weighed portions of benzoic acid, care being 
taken to insure complete neutrality of the alcohol used. Here 
as elsewhere in the work only hot redistilled water was used. 
The saturation apparatus consisted of a large glass test-tube 
(22x150 mm.) provided with a tight-fitting, one-hole rubber 
stopper. Into this hole was pressed a metal sleeve through 
which passed the axle of the stirrer and to which was attached 
a stout spiral of heavy platinum wire. The only possible open- 
ing into the test-tube was kept effectually sealed by the flange 
of the axle which rotated upon the metal sleeve. The stirrer 
was driven at the rate of 1,200 to 1,600 revolutions per minute 
by means of a small electric motor. The saturation apparatus 
thus arranged was; immersed in the constant temperature bath 
which was electrically heated and electrically controlled at the 
desired temperature to within ±0.02°. 
While preliminary experiments showed that saturation is com- 
plete in two hours, the time allowed for saturation was rarely 
less than four hours. After saturation the stirrer was stopped, 
the crystals allowed to settle and several portions of the clear 
saturated solution were withdrawn by means of certified 5 cc. 
pipettes. To prevent the entrance of fine crystals into the 
^Bureau of Standards, Scientific Paper, No. 183, 1912. 
