Rands. — Action of Phosphorus on Solutions of Copper Sulphate. 353 



the copper salts, and long strands of beautiful white shining silver are de- 

 veloped in a few hours. The solution also becomes golden yellow in colour, 

 owing to the formation of colloidal silver. This colour is destroyed by the 

 addition of potassium nitrate, by warming, or by mere shaking. It is known 

 that these differently coloured solutions of Carey Lea's allotropic silver are 

 obtained by the action of weak reducing agents on silver salts, and hypo- 

 phosphorous acid has been used by different investigators fo ■ this purpose. 



With silver acetate, sulphate, and phosphate similar phenomena are 

 observed. With a very dilute solution of gold chloride, ruby-red particles 

 stream out from the phosphorus until the whole liquid is of this colour ; 

 with a stronger solution a deposit of brown metallic gold is formed on the 

 phosphorus. 



As with other reducing agents, ease of reduction of salts by phosphorus 

 increases with rise of atomic weight in the group copper, silver, and gold. 



General Conclusions. 



The general conclusions arrived at from the whole series of experiments, 

 of which the above is a brief summary, are as follows : — ■ 



1. Moot, if not all, of the metallic copper is produced by means of the 

 reducmg action of a lower acid of phosphorus. 



2. The phosphide is not a secondary but an intermediate compound, its 

 formation probably being expressed by 



2P4 + 3CuS0, + 12H,,0 = CU3P2 + 6H3PO2 + 3H2SO4. 

 This equation theoretically involves two simpler ones — 

 (a) 2 [P4 + 6H2O = 3H3PO2 + PHg]; 

 (6) 2PH3 + SCuSO^ = CU3P2 + 3H2SO4. 

 With (a) compare 



P4 + 3K0H + 3H2O = 3KH2PO2 + PH3, 

 which is a very well-known reaction. 



Thus in the presence of metallic salts a reaction can take place between 

 phosphorus and water similar to that between phosphorus and the alkalis. 

 Cross and Higgins* concluded that some such action as this was possible 

 between amorphous phosphorus and water at high temperatures. 



If phosphide and reducing acid continued to be produced in equivalent 

 quantities this explanation would suffice, but the amount of phosphide 

 formed is always much less than this. 



The action is apparently catalytic, and Straub's statement that the 

 phosphide acts as an oxygen-carrier was meant to solve this difficulty. 



If atmospheric oxygen were available and necessary, the following steps 

 would be possible, and would explain all the phenomena observed : — 



1. Phosphorus -I- sulphate -f- water = phosphide -f- reducing acid -|- sul- 

 phuric acid. 



2. Phosphide + oxygen (atmospheric) + water = acid phosphate (soluble). 



3. Phosphate -I- phosphorus -f- water = phosphide -f- reducing acid -I- 

 phosphoric a-T'id. 



The exact manner in which the catalytic production of reducing acid 

 takes place after the formation of the film of phosphide must for the present 

 be left an open question. It will probably not be solved until more reliable 

 data are available dealing with the metallic oxysalts of phosphorus, and 

 especially with the properties of the metallic phosphides. 



* Journ. Chem. Soc, 1879, vol, 35, 253. 

 12-Trans. 



