Modification of Phosphorus. 3(>7 



determine the melting-point. The direction of the lower part 

 of the curve is, however, different from that of the curve from 

 about 4G° upwards ; and if these two parts of the curve be 

 produced in their same directions, the point where they meet 

 will approximately indicate what may be taken as the melting- 

 point of the phosphorus. The melting-point thus found is 

 45°*3, or a degree above that of the other variety. It may be 

 wondered where all the latent heat of fusion of this phosphorus 

 has disappeared to. On producing the upper parts of the 

 curves of both varieties of phosphorus, it will be seen that the 

 amount of heat required to melt them, which is represented 

 by the area of the figures abed, efg, is considerable in each 

 case, though it is greatest for the variety with the definite 

 melting-point. With the variety with the undefined melting- 

 point, however, the latent heat of fusion begins to be absorbed 

 at about 38° or lower, and being spread over such a large 

 temperature-interval its effect is at first sight masked. 



As these two different varieties of phosphorus were both 

 obtained from the same specimen, supposed to contain phos- 

 phorus all in the same state, it is evident that it must be 

 possible to easily convert one variety into the other. After a 

 great many attempts had been made at converting them into 

 one another by heating them to different temperatures, it was 

 at length found that the modification into which the phos- 

 phorus solidified depended only on the manner of its solidifi- 

 cation. If it cooled to below its solidification-point and then 

 solidified, the temperature being thereby raised considerably, 

 the variety with the undefined melting-point was formed ; 

 while if it began to solidify the moment it reached its solidifi- 

 cation-point without cooling below it, the variety with the 

 definite melting-point was formed. In order to cool it below 

 43 0, 8, the temperature of solidification, without solidification 

 taking place, the tube containing the liquid phosphorus covered 

 over with a layer of water or oil is placed in hot water, and 

 the whole left to cool. The phosphorus generally cools to 

 about 30° before solidification, and then the temperature 

 rushes up to about 43°, or higher if the mass of phosphorus 

 be large enough. To produce the other variety, the tube of 

 melted phosphorus is plunged into cold water. The sides of 

 the tube thus become cold enough to solidify some of the 

 phosphorus, which causes the whole mass to solidify when it 

 cools to 43°*8. The same effect may be produced by intro- 

 ducing some solid phosphorus into the liquid at about 44°, or 

 by scraping a glass rod against some fragments of glass pre- 

 viously added to the melted phosphorus. 



A single rapid or slow cooling in this manner is not gene- 

 rally sufficient to wholly convert one variety of phosphorus 



