504 



IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



On the other hand the loss on heating was determined by weigh- 

 ing the dish as soon as taken from the desiccator. 



To throw more light upon this low hygroscopic value about 

 seven grams of the finely divided salt which had been dried in 

 the above series of experiments was exposed in a desiccator over 

 sulfuric acid of such concentration as to give a humidity of the 

 enclosed air equal to 70 per cent, which is not likely to be ex- 

 ceeded in the ordinary laboratory. It was left over the acid 

 forty-seven days and about every four days a weighing was 

 made. There were small variations as always, due to changes 

 of temperature and the like, the largest being two milligrams. 

 Summing up the minus and plus differences they show a net 

 loss of one-tenth milligram in the forty-seven days. These two 

 sets of experiments seem to justify the conclusion that the hygro- 

 seopicity of the acid potassium phthalate is practically nil, and 

 in using it and weighing it attention need be directed only to 

 the containing vessel. By use of an open platinum crucible this 

 source of error may be almost completely avoided. 



It seemed desirable to know the solubility of acid potassium 

 phthalate in water, and this was determined at three different 

 temperatures. At 25" and 35° the method used was that recently 

 described by the Avriter in these Proceeding's." For the solu- 

 bility at the boiling point the method of Panvlewski was used.^ 

 The following are the results : 



Department of Chemistry, 

 Grinnell College. 



«Proc. Iowa Acad. Sci., Vol. XXII, pp. 217-224, 1915. 

 »Berichte d. Deutsch. Chem. Gesel., VoL 32, p. 1040. 



