Chemistry and Physics. 145 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Condensation of Water Vapor in the Presence of Radium 

 Emanation. — Madame Curie has found that when a gas under 

 atmospheric pressure contains radium emanation, the " induced 

 radio-activity" in suspension in the gas acts like a heavy body, 

 as it tends to fall downward. She has shown that this falling is 

 diminished or even prevented if the gas is perfectly dry, and has 

 come to the conclusion that the presence of water vapor favors 

 the formation of agglomerations having as nuclei the particles of 

 the "induced radio-activity," and capable of at taining a size 

 sufficient for acquiring an appreciable velocity in falling. Fol- 

 lowing up this conclusion, she has found that it is possible to 

 observe a fog in moist air containing radium emanation when it 

 is illuminated by the light of an electric arc. The phenomenon 

 was found to take place when the air contained much less moist- 

 ure than was sufficient for its saturation, and dry air containing 

 vapor of petroleum ether gave a similar cloud. When two plati- 

 num electrodes in an experimental vessel were subjected to a 

 difference of potential of several hundred volts, the mist was 

 rapidly dispersed by the electric field and disappeared entirely. 

 Upon disconnecting the electric field the mist gradually formed 

 again, being distinctly visible after 5 minutes, and fully reformed 

 after 15 minutes. This behavior corresponds to that of radium 

 A, the first product of "induced radio-activity." — Comptes Ren- 

 dus, cxlv, 1145. h. l. w. 



2. Gaseous Nitrogen Trioxide. — The compound N 2 3 has been 

 prepared in a pure state as a green liquid, but upon allowing this 

 liquid to evaporate, almost complete dissociation took place into 

 nitrogen peroxide and nitric oxide. Since it had been shown by 

 one of them that traces of moisture were necessary for the disso- 

 ciation of the vapors of ammonium chloride, mercurous chloride, 

 and other substances, H. B. Baker and M. Baker have investigated 

 the behavior of nitrous anhydride in this respect, and find that 

 when it is perfectly dried by means of P 2 B it is capable of existing 

 as a gas at ordinary temperatures, but as the density determinations 

 gave variable results, usually considerably higher than the calcu- 

 lated density, it appears that the gas contains a polymer of 

 N 2 3 . The slightest trace of moisture causes practically com- 

 plete decomposition of the substance when it evaporates. The 

 authors determined the molecular weight of the liquid N 2 3 by 

 the freezing point method, using perfectly dry benzene, and 

 found no evidence of polymerization in the liquid at 4°. This 

 liquid has a specific gravity of about 1-11 ; its color is green at 

 ordinary temperature, but when cooled to — 2°, or below, it 



