Rands. — Action of Phosphorus on Solutions of Copper Sidjihate . 351 



the phosphide plays an important part in the reduction, which is explained 

 by the action between metallic copper and phosphorus when placed in 

 water in a vessel open to the air. In this case the water round the phos- 

 phorus slowly becomes black and opaque, and then dark-reddish, owing 

 to the growth in it of exceedingly delicate feathery crystals of copper. 

 Straub gives the following steps in the reaction : — 



(a.) Phosphorus (oxidized by air) + copper (oxidized by air) = acid 

 copper phosphate. 



(&.) Acid copper phosphate -f- phosphorus -|- water = phosphide + phos- 

 phoric acid. 



(c.) Phosphide -f- oxygen + water = copper -I- phosphoric acid. 



He concludes that in the well-known action of phosphorus upon a solu- 

 tion of copper sulj^hate the same series of changes takes place, except that 

 oxidation by the air is replaced by more rapid oxidation by the copper 

 sulphate. The present paper is a summary of a series of experiments show- 

 ing the inaccuracy of some of Straub's conclusions, and also extending the 

 investigation to other metallic salts. 



Phosphorus on Copper Sulphate. 



By sealing up phosphorus and copper sulphate solution with the com- 

 plete exclusion of air it can be shown that atmospheric oxygen is unneces- 

 sary for the progress of the reaction. 



If the sulphate solution is very dilute, the phosphide formed is not at 

 first attached to the phosphorus, but remains suspended as a black cloud 

 in the solution. After a time, however, some of the phosphide may form a 

 film on the phosphorus, and metallic copper will then soon appear. Thus, 

 while the phosphorus and the solution are directly in contac , phosphide 

 alone is formed. Further, the copper phosphide cloud and the sulphate 

 solution may remain indefinitely in contact without change, showing that 

 the bodies do not react in the manner stated by Straub. 



If the phosphorus is suspended in the sulphate solution by means of a 

 copper wire, metallic copper is deposited directly upon the wire as well as 

 upon the phosphorus. This deposition of copper, which may take place 

 several inches away from the phosphorus, is evidently not due to the inter- 

 mediate formation of phosphide, and is not accounted for in Straub's expla- 

 nation Under suitable co idi ions, long strands of bright metallic crystals 

 of copper grow from the phosphorus down into the solution, clearing it of 

 its blue colour as they develop. Each crystal of copper acts as a nucleus 

 for the deposition of more metal, and beautiful fern-like growths several 

 inches in length may be obtained. Here again we have direct deposition 

 of copper independent of the phosphide. It can be shown to be due to the 

 presence of reducing acid in the solution. Thus, after the copper strands 

 have grown to some length, the decolorized liquid surrounding them will 

 readily reduce potassium permanganate, bromine water, mercuric chloride, 

 and gold chloride ; warmed with zinc and sulphuric acid, phosphine is 

 formed (by the nascent hydrogen), which turns a crystal of silver nitrate 

 yellow (forming PAggSAgNOa); with silver nitrate it gives a white pre- 

 cipitate which gradually turns brown, but which if quickly washed and 

 dissolved in dilute sulphuric acid decolorizes potassium, permanganate 

 solution. These facts prove that the liquid contains a lower acid of phos- 

 phorus. Although the available methods of analysis did not enable a 

 definite distinction to be made between phosphorous and hypophosphorous 



