T. M. Chatard on new Analytical Methods. 417 



I tried to determine lead as molybdate, tungstate, and arsenate, 

 but without success, as the presence of an excess of the precipi- 

 tant in such cases seems to exert an injurious effect, the filtrate 

 or washings speedily becoming cloudy. 



It may not be out of place to mention some work upon 

 molybdenum undertaken some time ago, which, though unsuc- 

 cessful, is not without interest. Various methods were devised 

 of weighing the molybdenum as sulphide. 



One way was to precipitate molybdic acid as mercurous 

 molybdate in the usual manner. The suspended molybdate 

 was boiled and sulphydric acid passed into the boihng liquid. 



The mercurous molybdate was decomposed and mercurous 

 sulphide and molybdic sulphide were the results. The sulphides 

 were thrown upon a filter and washed with cold svilphydric 

 acid water, dried and ignited in a current of sulphydric acid, 

 but this process failed to give satisfactory results. 



Again, sodic molybdate was heated with four parts of dry 

 sodic hyposulphite till all the free sulphur was driven off, leav- 

 ing, according to theory, Na^SO^ -f M0S3. The mass was then 

 digested with hot water, filtered and treated as before. When 

 any of the sulphur was left, it was found that some of the 

 molybdenum went into solution as sulphomolybdate of sodium. 

 Even after adopting every precaution, enough was still dissolved 

 to vitiate the analysis. 



§ 2. On the Evaporation to dryness of Gelatinous Precipitates, 



In a former paper* I called attention to the fact that many 

 gelatinous precipitates, when evaporated to dryness, became 

 vey granular and easy to filter. I gave some examples then 

 and have since tested several others. 



. i^tanic Acid.~R\xX\\e was fused with sodic disulphate, the 

 titanic acid precipitated bv ammonic hydrate and evaporated 

 to dryness. It became quite sandy and washed with great 

 fapidity and thoroughness. , . . , 



QliMina. —Pure glucina was dissolved in chlorhydnc acid, 

 precipitated by ammonic hydrate and evaporated to dryness. 

 I^ this case a-s glucina is soluble in ammoniacal salts it was 

 jecessary to ignite the dry mass to expel these. This was 

 done in the platinum dish in which the evaporation was earned 

 "^^ The residual glucina was sandy and washed with great 

 «f e ; zirconic, niohic and tantalic acids when thus treated gave 

 ^nlts which were all that could be desired. 



Cenc, lanthanic and didymic oxalates when treated with sub 

 Pbunc acid, and ammonic hydrate added, gave also perfectly 

 satisfactory results. ^ 



