408 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. A New -Method for the Determination of Iodides and Free 

 Iodine. — Bugarsky and Hovrath have devised a method for the 

 determination of iodine which appears to be particularly well 

 adapted to mineral waters and similar solutions containing small 

 quantities of this element. It is based upon the fact that free 

 iodine is slowly converted into iodic acid by the action of bro- 

 mine, particularly at about 100°, according to the equation 



I 2 + 5Br 2 + 8lI 2 = 2HIO 3 + 10HBr. 



The liquid to be analyzed is placed in a narrow necked flask of 

 100 cc capacity. Not more than 10 or 12 mg. of iodine should be 

 present. The liquid, if alkaline, is acidified w T ith sulphuric acid 

 to such an extent that it is finally less than -j-j-^- normal in terms 

 of free acid. Then about 50 cc of saturated bromine water are 

 added, and the flask is filled to the lower part of the neck with 

 distilled water. The flask is then suspended in a beaker of 

 water and this water is boiled for one hour. After this opera- 

 tion the contents of the flask are transferred to a capacious Erlen- 

 meyer flask of at least 250 cc capacity, a little powdered pumice 

 stone is added, and the contents of the flask are boiled very vigor- 

 ously for four or five minutes to remove the bromine. The liquid is 

 then cooled, 1 or 2 grams of potassium iodide, and sulphuric acid 

 corresponding to about 10 cc of the normal solution are added, and 

 after waiting two or three minutes the iodine set free is titrated 

 with t 1-q normal thiosulphate, using starch solution as an indicator. 

 One-sixth of the iodine found corresponds to the amount origi- 

 nally present. Since commercial bromine usually contains a little 

 iodine, this reagent should be analyzed once for all by the same 

 method before use. 



The authors have obtained extremely good results in carrying- 

 out this method with known amounts of iodine. They have 

 found that even large amounts of ehlorides and bromides do not 

 interfere with the method, and also that such impurities as may 

 be present in natural waters and certain medicines — nitrites, 

 nitrates, ammonium salts and glucose — do not affect it. Even 

 compounds of iron and manganese do not interfere if the final 

 titration is stopped when the blue color first disappears for a 

 moment. — Zeitschr. anorgan. O/iem., lxiii, 184. h. l. w. 



2. Chemical Action of the Penetrating Bays of Radium -upon 

 Water. — It has been shown by M. Kernbaum that the radium 



rays which pass through glass act upon distilled water with the 

 formation of hydrogen peroxide and the liberation of hydrogen, 

 according to the equation 2H 2 = H 2 2 + H 2 . In one experi- 

 ment where about 0*1 g. of nearly pure radium chloride in a 





