376 Peters and Moody — Determination of Per sulphates. 



an iodide added and the amount necessary to oxidize the arsen- 

 ite remaining after boiling the solution, are all in quite close 

 agreement and are all higher than those obtained by the pro- 

 cesses of Namias or Mondolfo. 



It is readily seen that the results of the experiments obtained 

 by the process of LeBlanc and Eckardt are nearer the average 

 of the results of all the methods than those of Namias or the 

 similar process of Mondolfo, and this fact would show that the 

 statements of JSTamias regarding the inaccuracy of the method 

 of estimating persulphates by the reduction with a ferrous salt 

 is without foundation. 



The process of LeBlanc and Eckardt is simple, rapid and 

 convenient. The method of Griitzner is advantageous in 

 that the ordinary arsenite solution is the standard for the pro- 

 cess, but requires the application of a correction. The method 

 of Mondolfo is simple and fairly rapid, but tends to give low 

 results. The method of Namias is slow because the experi- 

 ments must stand 10 to 12 hours, and the results of these ex- 

 periments, like those obtained by the method of Mondolfo, are 

 lower than the results obtained by the other methods. The 

 arseniate-iodide method introduced as a control, is accurate 

 but less simple than the other methods. 



We wish to thank Professor F. A. Gooch for help given 

 during the progress of this investigation. 



