Chemistry and Physics. 85 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Titrations with Potassium Iodate. — A new application of 

 iodates in volumetric analysis has been devised by Lathntcelot 

 W. Andrews. This depends upon the fact that in the presence 

 of a great excess of hydrochloric acid the reaction 



HI0 3 + 2HI + 3HC1 = 3IC1 + 3H 2 



takes place, and upon the fact that while iodine itself colors an 

 immiscible solvent, such as chloroform or carbon tetrachloride, 

 the iodine monochloride imparts no color to the solvent, although 

 it gives a bright yellow color to the hydrochloric acid solution. 

 Therefore, the iodine in an iodide may be accurately determined 

 by placing the solution of the iodide in a glass-stoppered bottle, 

 adding about an equal volume of concentrated hydrochloric acid 

 and about 5 CC of chloroform, and then running in a standard 

 solution of potassium iodate until, after shaking, the chloroform 

 becomes colorless. The end-reaction is exceedingly sharp, while 

 ferric and cupric salts, oxalic acid and small quantities of bro- 

 mides do not interfere with the operation. The process may be 

 used also for the determination of free iodine, in which case the 

 following reaction takes place : 



HI0 3 + 41 + 5HC1 = 5IC1 + 3H 2 0. 



It may be used in determining chromates, if a titrated solution 

 of potassium iodide is at hand. In this case an excess of the 

 iodide is added to the chromate solution, and the excess is deter- 

 mined by the addition of iodate solution. Chlorates can be 

 determined in a similar manner, but here an amount of pure fum- 

 ing hydrochloric acid at least one-third greater than the volume 

 of the solution should be added, and the bottle should be allowed 

 to stand for 15 minutes before titrating with potassium iodate. 

 Solutions of arsenious acid or chloride can be titrated in the 

 same way as iodides. Here, however, the amount of actual 

 hydrochloric acid in the liquid must be kept between 15 and 25 

 per cent. The determination of antimony is precisely like that 

 of arsenic. Since copper as a cupric salt does not interfere, it is 

 possible to determine arsenious acid in Paris green without a pre- 

 liminary separation. Ferrous salts can be titrated in exactly the 

 same way as iodides, but here the end reaction appears to lack 

 sharpness, although test analyses with ammoninm-ferrous sulphate 

 gave very satisfactory results. 



The method promises to be an important addition to our volu- 

 metric processes, since nearly all of the analyses usually made by 

 Bunsen's method of distillation can be made by it more easily, 

 and also because it is applicable to some important special cases. 

 — Jour. Amer. Chem. tioc, xxv, 756. h. l. w. 



