47<> Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Use of Metallic Silver as a Reducing Agent in the 

 Volumetric Estimation of Iron. — Graham Edgar and A. R. 

 Kemp, of Throop College of Technology, Pasadena, Cal., have 

 devised a new process for the volumetric determination of iron, 

 which appears to be very convenient and rapid, and according 

 to the numerous experimental results of the authors to he exceed- 

 ingly accurate. A solution of ferric sulphate containing 02 g 

 or less of iron and about 3 cc of concentrated sulphuric acid in 

 a volume of about 75 cc is treated with from 3 to 5 g of pre- 

 cipitated metallic silver which has been boiled with dilute sul- 

 phuric acid and well washed. The mixture may next be boiled 

 and then treated with a small excess of ammonium thiocyanate 

 solution, or the latter may be added to the cold mixture at once 

 with shaking for usually 3 to 12 minutes until the liquid is 

 colorless. The cooled or already cold liquid is then filtered 

 and the residue is thoroughly washed with water. To this fil- 

 trate, a little ferric sulphate solution is added to serve as an 

 indicator, an excess of silver nitrate solution is added, which 

 discharges the color, and then, without filtering, the iron is 

 titrated with decinormal potassium permanganate solution. 



Since in this process silver is dissolved only by the ferric 

 sulphate and not by the dilute sulphuric acid, it was found 

 possible to modify the process with just as accurate results by 

 employing a standard solution of ammonium thiocyanate and 

 finally titrating back with standard silver nitrate solution. In 

 this case it is essential to carry out the reduction in the cold. 

 By the use of standard solutions it is possible to titrate with 

 permanganate and then to check the result in the same sample 

 by titrating the excess of silver nitrate with thiocyanate: When 

 both ferrous and ferric sulphates are present in the original 

 solution the thiocyanate titration measures the latter while the 

 permanganate determines both. The process is not interfered 

 with by titanium, but vanadium is reduced to the quadrivalent 

 condition, while molybdenum, chromium and hydrochloric acid 

 cause irregularities. — Jour. Amer. Chem. Soc, 40, 777. 



h. l. w. 



2. The Iodimetric Estimation of Copper and Iron. — H. Ley 

 has devised an interesting volumetric method for determining 

 these two metals when they are present together. Both cupric 

 and ferric salts liberate iodine from potassium iodide in the 

 presence of acetic acid. When it is desired to estimate the cop- 

 per the iron is precipitated as ferric phosphate by the addition 

 of sodium phosphate solution, the liquid is then acidified with 



