142 Phelps and Weed — Acids and Acid Anhydrides. 



Phtlialic acid was prepared by boiling in distilled water some 

 commercial phtlialic anhydride. The solution was filtered 

 while still hot ; the crystalline product obtained on cooling 

 was separated by filtration, air-dried, and finally dried to con- 

 stant weight in a desiccator over sulphuric acid. The phtlialic 

 anhydride was prepared in a state of purity by distilling in 

 vacuo the phtlialic anhydride of commerce. The product ob- 

 tained was dried to constant weight in a desiccator containing 

 sulphuric acid. 



In Table IV, experiments II and VIII alone were carried 

 on at ordinary temperatures. In the other experiments in this 

 table the titrations were all performed after heating the solu- 

 tion until the phtlialic acid or the phtlialic anhydride used had 

 entirely dissolved. 



It is evident from the results recorded in the four tables 

 that succinic acid, succinic anhydride, malonic acid, benzoic 

 acid, phtlialic acid and phtlialic anhydride may be used with 

 great exactness as standards for decinormal solutions of 

 sodium hydroxide and of barium hydroxide. As a standard 

 for a solution of barium hydroxide, these organic acids and 

 acid anhydrides are even more accurate in our experience than 

 the determination of the barium hydroxide solution gravi- 

 metrically as the barium sulphate. In the various tables are 

 given results which show the accuracy with which barium 

 hydroxide may be standardized by the different organic sub- 

 stances when compared with the standard of decinormal hydro- 

 chloric acid established as the silver chloride. This same solu- 

 tion of the barium hydroxide which gave a value of 0*006896 

 grm. per cubic centimeter in terms of hydrochloric acid when 

 standardized against the organic acids and acid anhydrides, gave 

 a value of 0'006I:30 grm. per cubic centimeter in terms of 

 hydrochloric acid when standardized by precipitating and 

 weighing as the barium sulphate, by the usual procedure for 

 the determination of barium. 



As standards in alkalimetry and acidimetry, these organic 

 acids and acid anhydrides, in pure state, are equally as accurate 

 as the best previous standard — hydrochloric acid determined 

 gravimetrically as the silver chloride. The most serviceable of 

 these organic substances tested are those most readily soluble 

 in water — succinic and malonic acids — although they are no 

 more accurate than the other organic acids and acid anhydrides, 

 as is shown by the results given in the tables. Since these 

 substances can be readily prepared in a known state of great 

 purity, their serviceability as most accurate standards is 

 evident. 



