328 F. B. GUTHRIE. 



metrical molecules overloaded in one portion with negative 

 or positive electricity. This agrees with the conclusion 

 of Chapman 1 as to the existence of only two allotropes of 

 phosphorus, and excludes the existence of the so-called 

 44 metallic phosphorus," produced by dissolving phosphorus 

 in lead as an independent allotropic form. It is probable 

 that "metallic" phosphorus and red phosphorus are 

 identical, only the former is better crystallised. 



Schenck's phosphorus, or scarlet phosphorus 2 is also 

 excluded. This substance is obtained by heating phosphorus 

 in PBr 3 , and has not been prepared in a pure state. It 

 appears most likely that it consists of a mixture of a solid 

 hydride of phosphorus and ordinary phosphorus. 



Selenium. 

 According to Saunders, 3 the following well defined 

 modifications of this element exist : — 



1. Amorphous, vitreous, and soluble or colloidal. These 

 are all soluble in carbon bisulphide. They differ in appear- 

 ance, but may be regarded as belonging to the same 

 allotropic form, and are classed by Saunders under the 

 name of "liquid selenium." 



2. Red crystalline selenium. This occurs in two closely 

 allied but distinct crytalline forms, soluble in carbon 

 bisulphide. 



3. Crystalline grey or " metallic selenium." This is the 

 stable form, and is insoluble in carbon bisulphide. 



There thus exist, as in the case of sulphur, four definite 

 forms, for though the red crystalline forms both belong to 

 the monoclinic system, measurements of the crystals made 

 by Mitscherlich and later by Muthmann (both quoted by 



1 Chapman, Journ. Chem. Soc. Trans. 1899, Vol. 75, p. 734. 



2 Journ. Soc. Chem. Ind., 1903, Vol. 22, p. 1226. 



3 Saunders, Journal Physical Chemistry, 1900, 4, 423. 





