2 DR JOHN WADDELL ON 



the tungstic acid was separated by solution in ammonia. He found that the 

 reduced metal, when ignited in a current of chlorine, was entirely changed into 

 a volatile chloride. This test proves the absence of silica, which would have 

 formed a residue, but has no bearing whatever upon the question, whether or 

 no molybdenum were present; for molybdenum pentachloride, and tungsten 

 hexachloridc are produced under precisely the same conditions, and are very 

 similar in appearance and characteristics. 



Similar criticisms could be made on all the investigations to which I have 

 referred. It appeared to be too readily assumed that recrystallisation would 

 insure purity, no certainty being afforded either by a trustworthy mode of 

 separation of all possible impurities, or by tests showing the absence of 

 admixture. 



In my work. I kept specially in view the elimination of silicon and molyb- 

 denum, at the same time using all precautions to free from other impurities as 

 well. 



The reason for paying special attention to silicon and molybdenum, was 

 that these are very similar in many respects to tungsten, and are moreover very 

 liable to exist in ores of that metal. The presence of both was proved in some 

 scheelite with which preliminary experiments were made, and their elimination 

 was found to be no very easy matter. 



The material used as starting point in the subsequent investigation was 

 commercial tungsten, a dark grey powder, containing 94-98 per cent, of the metal. 

 The impurity was supposed by the manufacturers to be chiefly lower oxides of 

 tungsten, and in particular molybdenum was said to be absent. The employ- 

 ment of metallic tungsten as starting point is not to be recommended, owing to 

 the great difficulty of oxidation. The most convenient material, doubtless, is 

 sodium tungstate, which can be obtained readily enough. In my work, how- 

 ever, some interesting facts with regard to oxidation were brought into 

 prominence, for I tried several methods, the results of which are here given. 



The first mode of oxidation tested was continued boiling with aqua regia, 

 but at the end of a week a great deal of the metal was still unacted upon, and 

 the method was considered unsatisfactory. 



Another plan tried was mixing the metal with nitre, and throwing the 

 mixture, small portions at a time, into a red hot crucible. Moderately good 

 results were thus obtained; and the process would, I think, work fairly well 

 on the large scale where proper furnaces and crucibles are available. On 

 the small scale, the chief objection is that the crucible itself is attacked. A 

 third method furnished good results, and considerable attention was devoted to 

 the determination of the most favourable conditions. The process consisted in 

 the ignition of a mixture of potassium chlorate, sugar, and metal. After an ex- 

 tended number of trials, the proportions found most satisfactory were 9 : 3 : 5. 



