Chemistry and Physics. 463 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Molecular Weight of Silver Vapor. — Several years ago 

 some vapor density determinations were made by Nernst at tem- 

 peratures in the neighborhood of 2000° C. by the use of an 

 iridium bulb in an electrically heated tube of iridium. The prin- 

 ciple applied was that of Victor Meyer's method, but the process 

 was ingeniously modified, on account of the rarity of iridium, 

 by the use of a very small bulb, a specially devised micro-balance, 

 and the measurement of the displaced air by means of the move- 

 ment of a drop of mercury in a small, horizontal, graduated, glass 

 tube. Nernst obtained interesting and satisfactory results with 

 very minute quantities of several substances, but upon attempting 

 to get the vapor density of silver his private assistant weighed a 

 piece of platinum wire in place of supposed silver wire, so that 

 the apparent result that silver was not volatile at 2000° was 

 obtained. Wartenberg, using Nernst's apparatus and method, 

 with the iridium bulb glazed inside with rare-earth oxides, so 

 that the silver vapor would not attack the iridium, has now made 

 some determinations with silver. The best results showed a 

 molecular weight not far from 107, so that it appears that silver 

 forms a monatomic vapor in the neighborhood of its boiling- 

 point. From experiments made by Nernst it was found that the 

 boiling-point of the metal was about 2050°, and the experiments 

 under consideration were probably made at temperatures but 

 little above this point. — Berichte, xxxix, 381. H. l. w. 



2. Carbon Oxybromide. — Although phosgene, COCl 2 , is well 

 known and readily prepared, no method has been known, up to 

 the present time, for preparing the corresponding bromide in a 

 pure condition and in large quantity. A. von Bartel has 

 studied this problem, and has found that while the oxybromide 

 is formed by the direct union of carbon monoxide and bromine 

 in the presence of aluminium bromide and also by means of the 

 invisible electric discharge, a more satisfactory method of pre- 

 paring the substance in quantity was found in the action of con- 

 centrated sulphuric acid upon carbon tetrabromide. The reac- 

 tions that take place are as follows : 



CBr 9 + H 2 S0 4 = COBr 2 + 2HBr + SO s ; 



then a part of the hydrobromic acid reacts with sulphuric acid : 



2HBr + S0 3 = S0 2 + H 2 + Br 2 . 



To carry out the reaction, the sulphuric acid is allowed to drop 

 slowly into the melted carbon tetrabromide at a temperature of 

 about 150-160°. A strongly fuming, red distillate is produced, 

 from which most of the free bromide is removed by the addition 



