216 Peters — Estimation of Calciwn, Strontium and 



Art. XXY. — The Estimation of Calcium, Strontium, and 

 Barium, as the Oxalates ; by Charles A. Peters. 



[Contributions from the Kent Chemical Laboratory of Yale University — CL] 



A former article from this laboratory* describes the condi- 

 tions under which oxalic acid may be titrated by potassium 

 permanganate in the presence of hydrochloric acid, and states 

 that the extra consumption of permanganate which ordinarily 

 takes place when oxalic acid is titrated by permanganate in 

 the presence of hydrochloric acid, may be prevented by the 

 addition of a manganous salt. This fact led to the idea of 

 effecting the solution of the alkaline earth oxalates in hydro- 

 chloric acid and titrating the free oxalic acid with perman- 

 ganate in the presence of a manganous salt, and so to the study 

 of the conditions under which precipitates of strontium and 

 barium oxalates could be obtained sufficiently insoluble for 

 quantitative purposes, the conditions under which calcium 

 oxalate is insoluble being already known. 



The permanganate solution was standardized against freshly 

 recrystallized ammonium oxalate, and on oxalic acid, the 

 standards agreeing. 



Calcium Oxalate. 



It is well known that calcium may be estimated by treating 

 the precipitated oxalate with sulphuric acid and titrating by 

 permanganate the oxalic acid set free.f In the work described 

 in the present article, the precipitate of calcium oxalate has 

 been dissolved in hydrochloric acid and the oxalic acid titrated 

 by permanganate in the presence of a manganous salt. The 

 process was as follows : The boiling hot solution of calcium 

 chloride was precipitated with ammonium oxalate, allowed to 

 stand 12 hours, and the supernatant liquid decanted on asbes- 

 tos. The precipitate was washed two or three times by decan- 

 tation with 50-100 cm3 of cold water and brought on the felt. 

 The crucible containing the precipitate was returned to the 

 beaker, 100-200 cra3 of water were added, together with 5-10 cm3 

 of strong hydrochloric acid and 0'5-l*0 gm. of manganous 

 chloride, and the oxalic acid was titrated at a temperature of 

 35°-i5°. The results given in Table I are obviously excel- 

 lent, and show that calcium, taken as the oxalate, may be esti- 

 mated by potassium permanganate in the presence of hydro- 

 chloric acid and a manganous salt. 



Extended washing with hot water, however, is to be avoided 

 after the precipitant, ammonium oxalate, has been removed. 



* Gooch and Peters, this Journal, vii, 466. 

 f Mohr, Titrirmethode, 6 te Aufl., s. 227. 



