304 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Preparation of Pure Helium. — Several years ago 

 Jacquekod and Perrot called attention to the fact that helium 

 diffuses through the walls of tubes or bulbs of fused silica at 

 high tempei'atures. These investigators have now made use of 

 this remarkable phenomenon in purifying the crude gas obtained 

 by heating the mineral cleveite. They found, in the first place, 

 that silica is perfectly impermeable to other gases, with the excep- 

 tion of hydrogen and perhaps carbon monoxide, up to the tem- 

 perature of 1067°. The apparatus used for the operation 

 consisted of a bulb of silica provided with a capillary tube of 

 the same material. The bulb was surrounded by a cylindrical 

 vessel of platinum, from which the quartz capillary passed by a 

 gas-tight joint. The space between the bulb and the walls of the 

 platinum vessel was exhausted, and then crude helium was placed 

 in this space at a pressure a little above that of the atmosphere 

 in order to hasten the diffusion. To this helium was added 5 to 

 10 per cent of oxygen in order that any hydrogen and carbon 

 monoxide present might be changed to water vapor and carbon 

 dioxide. At the same time the quartz bulb was exhausted by 

 means of the mercury pump. The apparatus was heated by 

 means of an electric furnace to about 1100°. Under the condi- 

 tions employed, with a bulb of 42 cc capacity the diffusion was 

 quite slow, amounting to about l cc of helium per hour. On the 

 other hand, when the apparatus had been once set up the method 

 worked very simply, a"nd the purification appeared to be perfect. 

 A spectroscopic examination of the gas showed only the charac- 

 teristic lines of helium, extremely brilliant. The nitrogen bands, 

 which are so easily seen, were entirely absent. Only the red 

 hydrogen line, extremely faint, was observed, and this probably 

 came from traces of hydrogen held by the aluminium electrodes 

 of the Pliicker tube employed. — Comptes Rendus, cxliv, 135. 



H. L. W. 



2. Calcium as an Absorbent of Gases. — By means of a special 

 arrangement with an electric furnace, Soddv has found it possible 

 to heat reagents in vacuo, in sealed soft-glass apparatus, to a far 

 higher temperature than the softening point of glass. Calcium 

 heated in this manner is an absorbent for all the known gases 

 with the exception of those of the argon group. If the initial 

 gas pressure does not exceed a few millimeters, all the common 

 gases are rapidly and completely absorbed by calcium at tem- 

 peratures between 700 and 800°. Barium and strontium behave 

 in a similar way. By admitting known volumes of air and 

 absorbing all but the argon, the interesting observation was 



