170 



Oooch <nu I Xorton — Iodometric 



formerly, is actually essential to the reduction of molybdic 

 acid according to the theory of the process. 



Our experiments were made with ammonium molybdate 



twice recrystallized from the presumably pure salt. The con- 

 stitution of the preparation was determined by careful ignition 

 per se and, for greater security, with sodium tungstate free 

 from carbonate. It contained 81*83 per cent of molybdenum 

 trioxide. 



The potassium iodide which we used was prepared by acting 

 with re-sublimed iodine upon iron wire, and precipitating by 

 potassium carbonate — the proportions of iodine and iron hav- 

 ing been adjusted to secure the formation of the hydrous mag- 

 netic oxide of iron. The filtrate from the iron hydroxide gave 

 on evaporation and crystallization potassium iodide which was 

 free from iodate. 



The hydrochloric acid was taken of sp. gr. 1*12, because this 

 is the strength used by Friedheim and Euler. 



The sodium thiosulphate employed was taken in nearly 

 decinormal solution, and was standardized by running it into 

 an approximately decinormal solution of iodine which had been 

 determined by comparison with decinormal arsenious acid 

 made from carefully re-sublimed arsenious oxide. We chose 

 this method of standardizing — the introduction of the thio- 

 sulphate into the iodine — rather than the reverse operation, in 

 order that the conditions of the actual analysis might be fol- 

 lowed in the standardization. 



The distillation apparatus was constructed with sealed or 

 ground joints of glass wherever contact with iodine was a pos- 

 sibility. It was made by sealing together a separating funnel 

 A, a 100 cm3 Yoit flask B, a Drexel wash-bottle C, and a 

 bulbed trap g, as shown in the figure. Upon the side of the 



distillation-flask B was pasted 

 a graduated scale by means of 

 which' the volume of the liq- 

 uid within the flask might be 

 known at any time. Carbon 

 dioxide, generated in a Kipp 

 apparatus by the action of di- 

 lute hydrochloric acid (carry- 

 ing in solution cuprous chlor- 

 ide to take up free oxygen) 

 upon marble previously boiled 

 in water, was passed through 

 the apparatus before and dur- 

 ing the operation, so that it 

 was possible to interrupt the process of boiling at any point of 

 concentration, to remove the receiver by easy manipulation, to 



