HIGH PRESSURE BRIDGMAN. 199 



It may pay to pause here to take thought of this conductivity of 

 black phosphorus. Here is a substance which in two modifications 

 possesses no electrical conductivity, but in some way, when the atoms 

 are rearranged more closely together, sets free electrons and becomes 

 a conductor. As we might expect from its electrical conductivity, 

 black phosphorus is also a rather good conductor of heat. 



THE RELATION OF THE SEVERAL MODIFICATIONS. 



The most important problem conected with this new modification 

 is the determination of its relation to the other known modifications 

 of phosphorus. It was hoped that the existence of this new modifi- 

 cation might offer some clue to the vexed question as to the true 

 nature of red phosphorus. Some facts of importance have been 

 found, but the exact nature of the relationship has not yet been 

 discovered. 



In the light of experiments [here omitted] the explanation is sug- 

 gested that red phosphorus is a transformation product from white 

 phosphorus to something else, in which the transformation has not 

 run to completion, but is prevented by friction. 



With regard to the relation between black and red phosphorus 

 we can offer only conjectures. It does seem pretty certain, however, 

 that red and black can not stand in the relation of ordinary mono- 

 tropic solids. If they did bear this relation, the black must be the 

 more stable form, because of its lower vapor pressure, and in this 

 case we can not understand the failure of the red to condense as black 

 out of its vapor. The fact that the black apparently melts to the 

 same liquid as the red is puzzling. It may be that the relations 

 here are the same as in the vapor phase ; that is, liquid black phos- 

 phorus may be unstable, and may transform itself irreversibly to 

 liquid red as rapidly as it is formed. 



In a later paper x Doctor Bridgman gives by the aid of diagrams 

 the evidences of transformations of 30 substances. Some are solid, 

 others liquid in their ordinary forms, but like water and phosphorus 

 they each change into several solid modifications of new properties 

 when placed under different conditions of temperature and immense 

 pressure. In addition to these he has examined about a hundred 

 other substances which do not show such transformations. No 

 doubt all these facts will be made use of in the now rapidly pro- 

 gressing new theory of the internal structure of atoms and mole- 

 cules which has been born out of the discovery of radio-activity. 



Doctor Bridgman's views in regard to the nature of the phenom- 

 enon are expressed as follows : 



A crystal is supposed to be composed of units, atoms, or molecules, as the 

 case may be, which remain the same in different polymorphic forms. Poly- 



1 Proc. Nat. Acad. Sci., Vol. I, p. 518. 



