FURTHER WORK ON ACID POTASSIUM PHTHALATE 

 AS A STANDARD IN VOLUMETRIC ANALYSIS. 



W. S. HENDRIXSON. 



Neary three years ago the writer showed that acid potassium 

 and acid sodium phthalates may be used with advantage a& 

 standards in volumetric analysis.^ They can be easily prepared 

 in a state of great purity, they have large molecular weights, 

 and the acid potassium salt has the distinct advantage of absence 

 of water of crystallization. So little work on these salts has 

 been done and so limited is the knowledge of them that it was 

 thought desirable to make further study of the properties and 

 value as a standard of at any rate the potassium salt. The par- 

 ticular objects in view were : 



1. To determine the practicability of the preparation, and 

 use of the salt as a standard, hy other hands. 



2. To determine the extent of the work of purification of the 

 salt for ordinary use, and the yield on the basis of the phthalic 

 anhydride used. 



3. To study the hygroscopic character of the salt, the neces- 

 sary^ means to dry it, and its stability at higher temperatures. 



The laboratory work represented in this paper was done under 

 the writer's direction iby Mr. Sereno G. Norton, an undergradu- 

 ate in Grinnell College, and to his skill and industry is due very 

 largely whatever merit the paper may have. 



Acid potassium phthalate was prepared by the method de- 

 scribed in the paper already cited. Several preparations were 

 made and titrated as described in the former paper. There is 

 one chance of error which should be mentioned, since the error 

 might easily be made by comparatively inexperienced hands. 

 Phthalic anhydride is very sparingly soluble in water, even in 

 hot water. If not quite enough potassium carbonate is used in 

 neutralizing the anhydride a portion of the latter will be left 

 undissolved, and may be easily overlooked since the sparingly 

 soluble acid salt is likely to form a layer of crystals over the 

 surface of the hot solution. Since the neutral potassium phtha- 

 late is extremely soluble even in cold water there is no danger 

 of its contaminating, the acid salt. Therefore a slight excess of 

 potassium carbonate should be used, and of course the hot solu- 

 tion should be filtered in the first instance at any rate. 



'Journal of the American Chemical Society, Vol. XXXVII, p. 2352. 



