334 F. B. GUTHRIE. 



If the two crystalline forms obtained on subliming arsenic 

 are identical or form only one allotrope, then arsenic falls 

 definitely into line with phosphorus, and the two stable 

 allotropic forms (crystalline and amorphous), may be assumed 

 to have the same molecular structures as are assigned 

 above to yellow and red phosphorus. 



Oarbon, Silicon, Boron. 



Speculation on the foregoing lines is not justified in the 

 case of these elements, whose molecular weights have not 

 yet been ascertained with certainty. In the case of carbon 

 it appears probable that the molecule consists of twelve 

 atoms or some multiple of twelve. A representation of a 

 twelve-atom molecule, the atoms of which are tetravalent 

 obliges us to recognize more than three stable symmetrical 

 forms if freedom of direction is assumed for the corpuscles 

 exchanged between the atoms. 



Conclusions. 



It would appear that the corpuscular theory of valency, 

 involving valency direction, may afford a possible explana- 

 tion of certain cases of allotropism among the elements. 

 It is suggested that the relative directions of the discharged 

 electron or " valectron" may be due to the condition under 

 which the molecule is produced. Variation in the direction 

 of these corpuscles gives rise to molecular figures which 

 differ from each other in the manner in which the electric 

 charge is distributed amongst the atoms. Those molecules 

 in which the electric charge is neutralized or symmetrically 

 distributed, may be regarded as being more or less stable 

 molecules and as representing the various allotropic forms 

 of the elements. It is not suggested that this is the sole 

 cause of allotropy nor that it supplies an explanation in all 

 cases. The case of oxygen and ozone would appear to be 

 sufficiently explained by molecular condensation. 



