Chemistry and Physics. 91 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Volumetric Method for Chlorates. — The best known volu- 

 metric processes for determining chlorates are the iodometric 

 'method and the method depending upon the oxidation of a fer- 

 rous salt. The latter is the more rapid of the two, and it has 

 been extensively employed. To complete this reaction, however, 

 boiling for about ten minutes is necessary. Knecht has recently 

 described a new method for this determination, based upon the 

 use of titanous chloride for the reduction. This reagent acts 

 more rapidly than a ferrous salt, so that no heating is required. 

 The procedure is as follows : 50 cc of standard titanous chloride 

 solution (of which l cc = *0015 g of iron or thereabouts) are run 

 into 5 CC of concentrated hydrochloric acid contained in a conical 

 flask through which a current of carbon dioxide is maintained. 

 Then 10 cc of the chlorate solution (l g in 500 cc ) are added. After 

 a lapse of not less than three minutes, potassium sulphocyanide 

 is added, and the excess of titanous chloride estimated by titra- 

 tion with iron alum solution until a permanent red color is 

 obtained. For the estimation of chlorate in bleaching powder 

 the available chlorine due to hypochlorite is estimated in the 

 usual way by adding potassium iodide and starch and titrating 

 with hydrosulphite in the presence of acetic acid. A second .por- 

 tion of the solution is then titrated with titanous chloride, the 

 result giving total chlorine from hypochlorite and chlorate. — 

 Jour. Soc. Chem. Industry , 1908, 434. h. l. w. 



2. Atomic Weight of Radium. — Mme. Curie's first deter- 

 mination of this atomic weight gave the number 225. Subse- 

 quently she obtained with a larger amount of material (about four 

 decigrams of radium chloride) the higher number 226*2. T. E. 

 Thorpe has now repeated the determination of this interesting- 

 constant, and has obtained three results, 22.68, 225*7, and 227*7, 

 which agree satisfactorily with those of Mme. Curie, although 

 he used a much smaller amount of radium chloride, only 6 or 8 

 centigrams, for the determinations. Both investigators have 

 used the same principle, the comparison of the weight of radium 

 chloride with that of the silver chloride produced from it by 

 precipitation. To avoid losses by transferring, Thorpe made use 

 of small glass-stoppered flasks for all of the operations — weigh- 

 ing the radium chloride, dissolving it, precipitating with silver 

 nitrate, washing the silver chloride by decantation, and drying 

 and weighing in a single flask. Spectroscopic evid-ence is given 

 that the radium chloride was free from all but the minutest 

 traces of barium. It had been very carefully purified by the 

 usual course of fractional crystallization. There are several 

 circumstances which may affect the determination of the atomic 



