Chemistry and Physics. 397 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Formation of Red Phosphorus. — The usual, well 

 known, method of converting colorless phosphorus into the red 

 modification consists in heating the substance in closed vessels 

 for some time at about 250° C, a temperature near its boiling- 

 point. Stock, Schradeu and Stamm have now found that when 

 the vapor of phosphorus is highly superheated and then quickly- 

 condensed, a considerable amount of red phosphorus is found in 

 the product. Experiments were made by heating the vapor in 

 tubes of quartz glass to various temperatures and suddenly cool- 

 ing by plunging the hot tubes into cold water. In this way it 

 was found that after heating to 450° C. the condensed product 

 was slightly colored, and that the amount of red phosphorus 

 formed increased, as the temperature of heating was higher, up 

 to 1175° C. and above. The duration of the heating was found 

 to have little effect, but the rapidity of the cooling was of the 

 greatest importance. For instance, when a tube heated to 700° C. 

 was immediately cooled the product was very red, if the cooling 

 was delayed two seconds after removing the tube from the 

 furnace there was very little red phosphorus produced, after a 

 delay of five seconds there was only a trace, and when the tube 

 was allowed to cool in the air the condensed phosphorus was 

 almost colorless. Under favorable conditions of high heating 

 and very rapid cooling it was found that as much as about one- 

 third of the total phosphorus was obtained in the red modifica- 

 tion. It has been known for a long time that the vapor of 

 phosphorus has a density at 300-400° C. corresponding to the 

 molecular formula P 4 , while at higher temperatures the molecule 

 becomes smaller, being intermediate between P 4 and P 2 at 1700° C. 

 It is the opinion of the authors that the sudden cooling of the 

 superheated vapor causes the molecules that are smaller than P 4 

 to combine either with the latter or with each other to form red 

 phosphorus molecules. They do not believe that the molecule of 

 red phosphorus is smaller than that of the colorless substance, 

 since all the properties of red phosphorus indicate that the oppo- 

 site is true. — Berichte, xlv, 1514. h. l. w. 



2. Devitrification of Silica Glass. — The use of apparatus 

 blown and worked from melted quartz has become very common 

 in chemical laboratories, on account of the resistance of the mate- 

 rial to solvents, its high melting point, and its remarkable endur- 

 ance of sudden changes in temperature. Several years ago it 

 was found that silica glass is permeable to helium and to hydro- 

 gen at a low red heat, and now Sir William Crookes has 

 observed that the material when kept for a long time at a high 

 temperature becomes devitrified and opaque, and then permits 



