352 Transactions. 



acids iu these solutions, the behaviour when titrating with perrnanganate 

 in acid sohition indicated the presence of two different reducing agents. 



The Reaction between Phosphorus and Metallic Copper in Water. 



This reaction, which is used by Straub to explain the reducing action 

 of phosphorus on all metallic salts, proceeds in the following manner : A 

 black cloud, consisting of extremely fine particles of copper phosphide, 

 appears round the phosphorus. After a few days some of the phosphide 

 forms a film on the phosphorus, and then metallic copper soon appears. 

 As Straub suggests, the copper and the phosphorus are both oxidized by 

 the air, and by diffusion soluble acid copper phosphate is formed. The 

 case is then exactly analogous to that of phosjjhorus acting on very dilute 

 copper sulphate, and it will be noted that the effects observed are the same. 

 The presence of air is necessary, but the only function of the metallic copper 

 and the atmospheric oxygen is to keep up the supply of copper phosphate. 

 The fact that copper in the presence of water and acids — even very feeble 

 acids like carbonic — readily absorbs oxygen from the air, and forms salts, 

 is well known {vide Mendeleeff's Principles, ii, 42-5). The formation of 

 metallic copper round the phosphorus in this case is seen to be really more 

 complex than in the copper-sulphate case, and Straub is not justified in 

 explaining the one by the other in the manner he does. 



The black phosphide mentioned above Avas separated from the rest of 

 the system, and found to consist of very fine particles, which pass through 

 all ordinary filter papers and even through special baryta papers. 



If left in the liquid and exposed to the air, the phosphide is slowly 

 oxidized to the white phosphate ; readily on boiling. It decolorizes acidi^ 

 fied permanganate, being itself oxidized to phosphate and dissolved. It is 

 slowly soluble in dilute mineral acids, most readily in nitric. With stronger 

 acids it is dissolved readily with evolution of a gas. The phosphide does 

 not react with copper sulphate alone. 



Phosphorus on other Metallic Salts. 



With copper nitrate reduction takes place with the formation of phos- 

 phide and copper, as in the case of the sulphate. On cupric chloride the 

 action is somewhat different, the reduction being chiefly to white cuproua 

 chloride. After several days a very little dark-red copper may appear here 

 and there on the phosphorus. The reason a metallic film is not formed is 

 that if metal is produced it is immediately acted on by the excess of cupric 

 chloride with the formation of the cuprous salt. That the phosphide 

 formed is not merely a secondary product due to combination of the reduced 

 copper and phosphorus is shown by the fact that the black film appears 

 long before any metallic copper, and also before the cuprous chloride. 



In the action of phosphorus on copper acetate, besides the phosphide 

 and metallic copper, a flocculent white precipitate appears round the phos- 

 phorus. This is copper orthophosphate (a mixture of the normal and the 

 acid salts), which after a time decreases in amount, and ultimately dis- 

 appears, its copper being deposited as metal. 



Phosphorus readily reduces acid copper phosphate to phosphide and 

 copper. Straub's explanation would require modification in this case, for 

 we would have copper phosphate oxidizing copper phosphide to phosphate 

 and itself being reduced to copper. 



Phosphorus acts on silver salts with the formation of silver phosphide 

 and metallic silver. The reduction proceeds much more quickly than with 



