reduced by Hydr iodic Acid. 451 



aeteristic color is evident ; the treatment of the solution with a 

 measured amount of standard arsenite in known excess ; the 

 neutralization of free acid by potassium bicarbonate, first 

 taking pains to introduce, after the destruction of the per- 

 manganate by the arsenite, tartaric acid to prevent precipita- 

 tion of the molbydenum compound ; and the titration of the 

 excess of arsenite by iodine. 



The operation requires the use of a standard solution of 

 arsenite, easily made with accuracy, a solution of iodine in 

 potassium iodide standardized directly against the arsenite in 

 the usual manner, and a solution of potassium permanganate 

 the value of which in terms of the arsenite is found by 



bleaching a measured portion of it with an excess of arsenite 

 and titrating back with iodine the arsenite remaining. The 

 preparation and adjustment of the standard solutions is there- 

 fore simple. ' The theory of the operation is plain, the value 

 (in terms of molybdic acid) of the permanganate used, dimin- 

 ished by that of the arsenite and increased by that of the 

 iodine, giving the amount of molybdic acid present. 



In carrying out our tests of the method proposed we used 

 a preparation of ammonium molybdate made by recrystalizing 

 the presumably pure salt. The constitution of this salt was 

 determined by careful ignition, both by itself and with sodium 

 tungstate free from carbonate. It held 81*83 per cent, of Mo0 3 . 



From 0*3 grm, to 0*5 grm. of the molybdate, at least 20 cm3 

 of hydrochloric acid of sp. gr. 1*20, with from 0*2 grm. to 

 0*6 grm. of potassium iodide, according to the amount of 

 molybdate used, were put into a 150 cm3 flask, trapped loosely 

 by means of a short bulbed tube hung in the neck, as shown in 

 figure 1. The solution was boiled until the original volume of 

 40 to 60 cm3 had been reduced to exactly 25 cm3 as determined 

 by a mark upon the flask, the base of which was of a size 

 permitting close reading of the volume of the liquid. The 

 residue was diluted immediately to a volume of 125 cm3 and 

 thus cooled, transferred to a Drexel wash-bottle, shown in 

 figure 2, fitted with a ground glass stopper carrying the usual 

 inlet and outlet tubes. To the inlet tube had been sealed a 



