Hillebrand — Vanadium and Molybdenum in Itocks. 215 



contents is carefully ignited in porcelain and the delicate sul- 

 phuric acid test for molybdenum is applied. 



The filtrate, in bulk from 25 to 100 cc , is boiled in a current 

 of carbon dioxide to expel hydrogen sulphide, and titrated at a 

 temperature of 70-80° C. with a very dilute solution of perman- 

 ganate representing about one milligram of V 2 5 per cubic 

 centimeter as calculated from the iron strength of the perman- 

 ganate, one molecule of V 2 5 being indicated for each one of 

 Fe 2 3 . One or two checks are always to be made by reducing 

 again in a current of sulphur dioxide gas, boiling this out in a 

 current of carbon dioxide again, and repeating the titration. 



As shown in a previous paper" the presence of even thirty 

 times as much Cr 2 3 as Y 2 5 does not prevent a satisfactory 

 determination of the vanadium if the precautions therein given 

 are observed, provided there is present not less than \-\ mg. 

 of Y 2 5 in absolute amount. In absence of chromium less than 

 half a milligram can be readily estimated. The phosphoric 

 acid almost invariably present does not affect the result. 



In case the volume of permanganate used is so small as 

 to make doubtful the presence of vanadium, it is necessary to 

 apply a qualitative test which is best made as follows : The 

 solution is evaporated and heated to expel excess of sulphuric 

 acid, the residue is taken up with two or three cubic centi- 

 meters of water and a drop or two of dilute nitric acid, and a 

 couple of drops of hydrogen peroxide are added. A character- 

 istic brownish tint indicates vanadium. Unless the greater 

 part of the free sulphuric acid has been removed the appear- 

 ance of this color is sometimes not immediate and pronounced, 

 hence the above precaution. 



The above is a surer test to apply than the following: 

 Reduce the bulk to about ten cubic centimeters, add ammonia 

 in excess and introduce hydrogen sulphide to saturation. The 

 beautiful cherry-red color of vanadium in ammonium sulphide 

 solution is much more intense than that caused by hydrogen 

 peroxide in acid solution, but the action of ammonia is to pre- 

 cipitate part or all of the vanadium with the chromium or 

 aluminum that may be present or with the manganese used in 

 titrating, and ammonium sulphide is unable- to extract the 

 vanadium wholly from these combinations. Usually, however, 

 the solution will show some coloration, and addition of an acid 

 precipitates brown vanadium sulphide, which can be collected, 

 ignited and further tested if desired. 



*Jour. Am. Chem. Soc, xx, 464, 1898. 



