ACID POTASSIUM AND ACID SODIUM PHTHALATES 221 
<?rucible was never handled with the bare hands. The weighed 
portions were dissolved in the titration flask in about 20 cc. 
•of pure alcohol, whose neutrality had been tested, about an equal 
volume of water was added, and the titration was carried out 
as described under standardization of the sodium hydroxide. 
The following are the results, using the alkali having the rela- 
tion to the acid 1 to 1.10991. 
Weight of NaOH. 
Weighed benzoic acid. 
Calculated HCl in 
1 gram of solution 
1. 
91.829 
1.2470 
of HCl. 
.0036559 
2. 
82.139 
1.1148 
.0036547 
3. 
89.695 
1.2169 
.0036525 
4. 
79.778 
1.0838 
.0036574 
Average of all titrations 
.. .00-36551 
As under silver chloride reducing the weight of the HCl solu- 
tion in air to volume, the HCl in 1 cc. is .0036511. 
Another series of titrations was made using the special sub- 
limed benzoic acid prepared by the Bureau of Standards for 
calorimetric and volumetric work. It was fused, weighed and 
titrated in the same way as the benzoic acid prepared by myself, 
but the more concentrated alkali having the ratio to the hydro- 
chloric acid 1 to 1.1859 was used. 
Calculated HCl in 
Weight of NaOH. Weighed benzoic acid. 1 gram of solution 
of HCl. 
1. 34.903 .5062 .0036544 
2. 54.767 .7941 .0036536 
3. 96.481 1.3990 .0036536 
4. 139.791 2.0264 .0036526 
5. 133.900 1.9410 .0036525 
Average of all determinations 0036533 
Reducing the weight of the HCl solution to volume as ex- 
plained under the silver chloride method, these results give the 
value of HCl to 1 cc., .0036494. 
Acid Potassium Phthalate. This salt is anhydrous. It is 
moderately soluble in cold water, very soluble in hot water, and 
may be easily purified by repeated crystallization. Its molecular 
weight is high, 204.14, so that the amounts that may be weighed 
for titration are large, thus reducing! the influence of the un- 
avoidable errors in weighing. 
Acid potassium phthalate was prepared by dissolving in hot 
water pure sublimed phthalic anhydride and a little more than 
the calculated weight of pure potassium carbonate necessary to 
form the acid phthalate. The salt was recrystallized five times 
