﻿of Phosphorus j Sulphury and Aldehyde. 



511 



in which the mercury was replaced by bromnaphthalene. 

 This allowed of a more accurate reading of the pressure, and 

 the vapour of the bromnaphthalene did not appear to inter- 

 fere in any way with the course of the reaction. The phos- 

 phorus was purified by melting it under a dilute solution 

 of potassium bichromate and sulphuric acid, and carefully 

 washing it. 



Fig. 1. 



A piece of this phosphorus was brought into the apparatus 

 through E, melted at P, distributed in as thin a layer as 

 possible over the upper surface of the bulb, and allowed to 

 solidify in that position. This was generally done in an 

 atmosphere of carbon dioxide, sometimes in vacuo. By this 

 means as large a surface of the phosphorus as possible is 

 exposed to the cooling action of the water in the bath in 

 which the apparatus is plunged. The product of the oxida- 

 tion also tends to fall and not to collect on the surface of the 

 phosphorus. A little water was placed in the apparatus at A, 

 and E sealed up before the blowpipe. 



After placing the apparatus in position in the water-bath, 

 it was evacuated as completely as possible and oxygen allowed 

 to enter. This operation was repeated several times. A. 

 precaution which is of importance is to keep the phosphorus 

 cold ; otherwise, on allowing the oxygen to flow into the 

 vacuous apparatus, it is very apt to take fire. This is 

 especially the case when the oxygen is dry and the pressure 

 is very low ; with oxygen which had been dried by passing 

 over phosphorous pentoxide I have even seen the spontaneous 

 inflammation occur at 0° C. The pressure was probably less 

 than that due to 1 millim. of mercury. 



