242 PROCEEDINGS OF THE AMERICAN ACADEMY 



conducted, the filter may be completely incinerated with great ease, and 

 without loss of molybdic oxide from volatilization. A weighed quan- 

 tity of fused and pulverized neutral sodic tungstate is then to be added, 

 when the crucible may be heated to redness, and the mercurous and 

 mercuric oxides completely expelled. A second heating and weigh- 

 mg are always advisable. In this manner the sum of the weights of 

 molybdic and vanadic oxides is obtained. To determine the quantity 

 of vanadic oxide alone, the same process is to be repeated ; only after 

 burning off the filter the mass is to be carefully heated with a free sup- 

 ply of air to act mechanically until the whole of the molybdic oxide is 

 volatilized and vanadic oxide remains as an orange-brown liquid, and, 

 after cooling, as a crystalline mass. The complete expulsion of the 

 molybdic oxide requires long heating, at a full red heat. The vanadic 

 oxide is not volatile, but it has the inconvenient habit of creeping up 

 the sides and over the edge of the crucible, — a habit for which there 

 appears to be no remedy. The weight of the molybdic oxide may 

 then be determined by difference. This method gives good results, 

 and in some cases may be used with advantage. 



Another method is the following, which applies directly to the vana- 

 dio-molybdates of the alkaline metals, and to those of the alkaline 

 earths, after the separation of the base. Ammonia is to be added in 

 excess to the solution, which is then to be boiled for a few minutes, 

 so as to convert the salt into a mixture of an alkaline vanadate and 

 molybdate. A saturated solution of ammonic chloride is then added 

 in very large excess, after which the liquid must be concentrated 

 by continued boiling until reduced to a relatively small volume. The 

 solution must then be allowed to stand for twenty-four hours, when a 

 greater or less deposit of ammonic meta-vanadate will have formed in 

 colorless crystals.* These crystals are to be brought upon an asbestos 

 filter, and washed with a cold saturated and pure solution of ammonic 

 chloride. The vanadic pentoxide may then be found by carefully 

 igniting the salt with free access of air. It is, however, better to dis- 

 solve the salt upon the filter with boiling water, reduce the solution by 

 means of a current of sulphydric acid gas after adding a little sulphuric 

 acid, filter, and titrate with potassic hypermanganate. The clear blue 

 solution contains vanadic dioxide only. The end reaction is tolerably 

 sharp in dilute solutions — say 0.25 gramme — of VO^ in 250 c. c. of 



* The best commercial chloride of ammonium always contains iron not pre- 

 cipitablc by ammonia. If bromine water be added first to the boiling solution, 

 ammonia in small quantity separates the iron completely. 



