Optical Properties of Phosphorus. 33 



From these indices may be calculated — 



Length of spectrum .... =0*1537 

 Dispersive power =0'1613 



The angular measurements from which these various indices 

 were calculated were made only to minutes, as the fluctuations 

 due to temperature rendered any greater nicety of no value. 

 Another and more serious obstacle arose from a certain indi- 

 stinctness of the spectrum as seen through phosphorus, which 

 caused the recognition of the fixed lines to be very difficult. 

 It is not easy to assign a reason for this : it is not due to 

 the great refraction or dispersion ; and though the extreme 

 degree of sensitiveness may be a partial cause, it certainly will 

 not account for the whole phsenomenon. It is independent of 

 the more or less crystalline condition of solid phosphorus, and 

 of the presence of unmelted matter in the same substance when 

 liquified ; for it is equally observable in a solution of the element 

 in bisulphide of carbon, which of course may be obtained per- 

 fectly clear. It is curious to observe how, on the addition of 

 successive portions of phosphorus to bisulphide of cai-bon, the 

 lines of the spectrum, which were originally sharp, become more 

 and more cloudy. We are rather disposed to attribute this in- 

 distinctness to a slight opalescence, caused by the beam of light 

 converting a little of the phosphoi'us into that allotropic condi- 

 tion which does not melt at so low a temperature, and which is 

 insoluble in bisulphide of carbon, and therefore assumes the 

 solid form even while the observer is looking at the rays. 



The phosphorus experimented on was colourless, having been 

 heated under water with bichi'omate of potash and sulphuric 

 acid. The ordinary yellowish phosphorus, unlike most yellow 

 substances, absorbs the extreme red rays, and transmits the 

 blue, no doubt much weakened in intensity. This appears the 

 more worthy of notice when we reiiiember that another form of 

 the same element reflects the red and absorbs the other rays. 



Phosphoi-us flame. — A strong solution of phosphorus in bisul- 

 phide of carbon was burnt in a lamp. The intense white flame 

 which resulted was found to exhibit a spectrum extending from 

 about the fixed line a of the solar spectrum to the extreme violet, 

 but perfectly free from any indication of dark lines or bands. 



Phil. May. S. -i. Vol. 18. No. 117. July 1859. 



