Modification of Phosphorus. 369 



length. Some of them could be seen on end, and the lengths 

 of these axes appeared to be in about the ratio 1 : 2. The 

 crystals from the modification of phosphorus with the definite 

 melting-point, on examination in the same way, were observed 

 to consist of masses of octahedral crystals. In size they were 

 scarcely as large as those of the preceding modification, but 

 there was no difficulty in identifying them. It is thus con- 

 cluded that it is the variety of phosphorus with the definite 

 melting-point and crystallizing in octahedra which has pre- 

 viously been examined and described ; while the variety with 

 the undefined melting-point, crystallizing in rhombic prisms, 

 is the modification not previously described. 



As the different crystalline modifications of sulphur exhibit 

 a marked difference in their 'specific gravities, that of octa- 

 hedral sulphur being 2*02, and that of prismatic sulphur 1*97, 

 a similar difference might be expected to obtain for phos- 

 phorus. The specific gravity was determined by first weighing 

 about 20 grams of the phosphorus, cut in oblong lumps and 

 well dried, in a small stoppered weighing-bottle, then filling 

 up the bottle with distilled water and weighing again, and 

 lastly weighing the bottle full of water only. All determina- 

 tions were made at 13° C, and were compared with water at 

 the same temperature. Two different specimens of the octa- 

 hedral modification were found to have the specific gravities 

 1*8177 and 1*8184; while for two different specimens of the 

 prismatic modification the values 1*8272 and 1*8254 were 

 obtained. The discrepancy between these two last values is 

 probably due to the fact of one specimen containing some of 

 the other variety of phosphorus in it, so the extreme value, 

 1*8272, is probably the more correct. A sample of phosphorus 

 known to contain both varieties had a specific gravity 1*8237. 

 The difference between the specific gravities of the two modi- 

 fications is about half a per cent. This is not nearly so great 

 as that of the two varieties of sulphur, which is about two and 

 a half per cent., but it is large enough to be easily appreciable. 

 The phosphorus used in these determinations was generally 

 only purified by shaking it with a hot solution of sulphuric 

 acid and potassium bichromate. Some of it was also distilled, 

 but no difference in specific gravity or other properties was 

 obseiwable, so the oxidizing agent alone is probably enough 

 to remove any impurities existing in it. 



As the curves for the rate of rise of temperature show a 

 considerable difference in the latent heat of fusion of the two 

 varieties of phosphorus, a corresponding difference ought to 

 be exhibited in the amounts of heat given out on solidification. 

 Curve (3) shows the rate of cooling of octahedral or definite- 



Phil. Mag. S. 5. Vol. 32. No. 197. Oct. 1891. 2 G 



