196 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



melting point of ordinary white phosphorus. The two new forms 

 have perfectly distinct characteristics; in this they are different from 

 the questionable modifications of red phosphorus often announced. 

 The first of these modifications is a new form of white phosphorus, 

 which changes into the ordinary white modification reversibly under 

 the proper conditions. The second is a form obtained irreversibly 

 from white at high pressures and moderate temperatures, which is 

 15 per cent more dense than Hittorff's " metallic " red phosphorus. 



WHITE PHOSPHORUS II. 



The new modification of white phosphorus was first produced by 

 increasing pressure on ordinary white phosphorus to about 11,000 

 kg./eni. 2 at 60°. The existence of the new form was shown by a dis- 

 continuous change in the volume at this pressure. A number of 

 points on the transition curve of these two modifications were then 

 obtained at temperatures down to 0°, and the corresponding changes 

 of volume, when one modification passes to the other, were measured. 



The appearance of this new form in bulk is much like that of ordi- 

 nary white phosphorus. It may possibly be a trifle yellower, and 

 there are likely to be cracks formed because of the volume contraction 

 of about 2 per cent when the transition occurs. 



An attempt to obtain the crystalline form was partially successful. 

 A solution of white phosphorus in carbon disulphide was allowed to 

 crystallize at the temperature of a mixture of carbon dioxide snow and 

 gasoline. The phosphorus separates out as a slush composed of fine 

 crystals. Microscopic examination showed that the usual crystalline 

 habit is in needles, about five times as long as broad, with pointed ends 

 of about 60°. It was not possible to specify further the shape of the 

 needles. Scattered among the needles, however, there were occa- 

 sional plate-like forms of unmistakable hexagonal shape; several 

 nearly perfect hexagons were found. The great probability is, 

 therefore, that this new modification belongs to the hexagonal system. 

 The crystalline form of the usual modification is regular. 



BLACK PHOSPHORUS. 



Black phosphorus was discovered during an attempt to force ordi- 

 nary white phosphorus to change into red phosphorus by the applica- 

 tion of high hydrostatic pressure, at a temperature below that at 

 which the transformation runs with appreciable velocity at atmo- 

 spheric pressure. Pressure up to about 6,000 kilograms per square 

 centimeter was applied at room temperature to the phosphorus 

 through the medium of the kerosene; the cylinder was raised to 200° 

 in an oil bath controlled by a thermostat, and the pressure was then 



