Phelps and Weed — Succinic Acid! 143 



Art. XYII. — A Comparison between Succinic Acid, Arsen- 

 ious Oxide, and Silver Chloride as Standards in lodimetry, 

 Acidimetry, and Alkalimetry ; by I. K. Phelps and L. H. 

 Weed. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clxxx.] 



The use of an excess of a mixture of an iodide and an iodate 

 has been suggested by several as a most exact and convenient 

 method for determining quantitatively various acids in alka- 

 limetry and acidimetry. Kjeldahl* suggested the use of these 

 reagents for determining nitrogen as ammonia in organic 

 substances. Later Furryf showed that the conditions of con- 

 centration affected the end-point of this reaction. In very 

 dilute solutions there was an after-coloration which he showed 

 to be due to the incomplete action of the mineral acid rather 

 than to the action of carbonic acid in solution. GrogerJ 

 showed the applicability in alkalimetry and acidimetry of the 

 iodicle-iodate mixture for determining decinormal solutions of 

 acids and of alkaline hydroxides, carbonates, and sulphides. 

 In the case of the acids, he treated directly with an excess of the 

 neutral ioclide-iodate mixture and measured the iodine set free 

 by titration, in presence of starch as an indicator, with sodium 

 thiosulphate, standardized either against a weighed amount of 

 free iodine or against the iodine set free by the action of an 

 excess of hydrochloric acid and of iodate-free potassium iodide 

 upon a weighed amount of pure potassium iodate in solution. 

 In the case of the alkaline hydroxides, carbonates, and sul- 

 phides, the solutions were treated with an excess of standard 

 mineral acid and then this excess was determined in the man- 

 ner described above. The comparison was shown between the 

 results so obtained and those given by direct titration of the 

 solution of the alkalies against decinormal sulphuric acid, in 

 presence of litmus and of phenolphthalein as indicators, and, 

 for the acids, by similar titration with a decinormal potassium 

 hydroxide solution. The agreement was good except in the 

 case of the carbonates where the iodometric results are low, 

 even when the solutions were allowed to stand for thirty 

 minutes before completing the titration. In a later paper§ 

 G-roger suggested pure jjotassiuni iodate as a standard in iodi- 

 metry, acidimetry, and alkalimetry. The results are good 

 but the difficulty in using the process for practical work is not 

 only the necessity of obtaining pure potassium iodate but also 

 the necessity of using potassium iodide free from iodate. 



* Zeitschr. analyt. Chern., xxii, 366. 

 f Amer. Chem. Jour., vi, 341. 

 J Zeitschr. angw. Chem., 1890, 353. 

 £Zeitschr. angw. Chem., 1890, 385. 



