326 Scientific Intelligence. 



4. Hap id Preparation of Uydriodic Acid. — A convenient 

 and rapid method for preparing this acid is described by Bodroux. 

 He divides a certain weight of iodine into two equal parts. To the 

 first barium peroxide is added in the presence of water : 



Ba0 2 + I 2 = BaI 2 + 2 . 



The remainder of the iodine is then dissolved in the filtered solu- 

 tion, and sulphur dioxide is passed in until decolorization takes 

 place : 



Bal 2 + 1 2 + S0 2 + H 2 = BaS0 4 + 4HT. 



The acid is then concentrated by distillation, for the reaction 

 with sulphur dioxide does not take place normally in extremely 

 concentrated solutions, so that it is recommended to use about 

 180 s of water for 100 g of iodine. — Comptes Pendus, cxlii, 279. 



h. l. w. 



5. The Padio-activity of Polonium. — Mme. Cttrie, who has 

 obtained and described polonium as a radio-active element accom- 

 panying bismuth in pitchblende, finds that the material may be 

 enriched by fractionally precipitating the oxychloride by means 

 of water, when polonium is concentrated in the first precipitates. 

 Having thus obtained poloniferous oxide of bismuth with an 

 activity 250 times that of uranium, she measured its rate of decay 

 and found that it loses one-half of its activity in 140 days. This 

 corresponds very closely to the rate of decay of Marckwald's 



" radio-tellurium," so that it may be regarded as certain that the 

 two substances are identical. — Comptes Rendns, clxii, 273. 



H. L. W. 



6. The Electrochemical Equivalent of Silver. — The importance 

 of this constant is such that investigators still prosecute investi- 

 gations to determine it with all possible accuracy. G. van Dijk, 

 p. 286, in a very full paper, reviews the results of previous investi- 

 gators and gives his own. The following table gives the values 

 (corrected) obtained by various physicists : 



Kalile 0-011181 



Patterson and Guthe 0-01118 



Pellat and Leduc 0-011189 



Van Dijk and Knnst 0-011180 



Mascart 0-011155 



F. and W. Kohlrausch 0-011182 



Eayleigh and Sidgwick 0-011176 



Pellat and Potier 0-011191 



Van Dijk devotes considerable space to a discussion of the cor- 

 rections employed by Richards which led the latter to adopt the 

 value 0*011175, and believes that his own result, a = 0*011180 

 is the true electrochemical equivalent of silver. — Ann. der Physik, 

 No. 2, 1906, pp. 249-288. J. T. 



7. The Electrolytic Coherer. — Under the title of asymmetrical 

 action of an alternating current on a polarizable electrode, Dr. 

 Gundrt discusses the reasons for the action of what is at present 

 probably the most sensitive receiver employed in wireless teleg- 

 raphy. This receiver consists of a very fine platinum point 

 which forms the anode, in an electrolytic solution, of an E.M.F. of 

 several volts. The current through this electrolytic cell is 



