M. Beketoff on the Displacement of some Elements by others. 307 



a saturated solution, and in the third a saturated solution along 

 with crystals of the same salt, while in the fourth was some sul- 

 phuric acid, and in the drawn-out end of the tube some zinc. By 

 inclining the tube, zinc was brought into sulphuric acid ; the hy- 

 drogen liberated had to pass first of all through the layer of satu- 

 rated solution of the silver-salt, by which it was purified; it could 

 then act upon the second saturated solution, and finally on the 

 dilute solution. After some days a dark precipitate appeared on 

 the surface of the dilute solution, which increased in the following 

 days, while both saturated solutions remained unchanged. Hence 

 reduction by hydrogen only takes place in dilute solutions. 



A dilute solution of nitrate of copper was not reduced by hy- 

 drogen even under a pressure of forty atmospheres. A mixture 

 of nitrate of copper and silver only gave dubious indications of a 

 separation of copper. Lead solutions could not be reduced by 

 hydrogen. 



The author repeated the experiments with the aid of platinum. 

 In a glass tube he arranged in layers hydrochloric acid, zinc, and a 

 dilute solution of copper, in which dipped a platinum-foil which 

 had been previously ignited. After sealing the tube, the zinc was 

 brought into the hydrochloric acid by shaking. In a few days 

 all the zinc was dissolved, so that the internal pressure must have 

 amounted to about 110 atmospheres. After the lapse of this 

 time a crystalline rose-red deposit could be seen on the platinum. 



The author filled glass tubes one-third full with metallic solu- 

 tions, placed platinum-foils in them so that about half the 

 platinum was out of the solution, and filled the tubes with hy- 

 drogen. The tubes were then sealed. On the following day 

 crystallized silver was deposited on the platinum in the solution 

 of sulphate of silver. After several days there was a precipitate 

 of copper in the dilute solution of nitrate of copper. Lead solu- 

 tions were unchanged. In these experiments the platinum ma- 

 nifestly acts by its condensation of hydrogen on the surface. It 

 follows from this that hydrogen, as a reducing agent, takes a place 

 between lead and copper, mercury, silver, palladium, gold, and 

 platinum. 



In order more accurately to determine the pressure under 

 which the reduction of metals takes place, the author repeated 

 his experiments, in tubes one end of which was drawn out. This 

 end was divided, calibrated, and then bent in a U-shape so as to 

 serve as a manometer. Some mercury was placed in the tube ; 

 then acid, zinc, and metallic solutions were arranged in layers 

 on one another. After the position of the mercury was read 

 off, the manometer and the other open end of the tube were 

 melted. A solution of 1 part of sulphate of silver in 350 parts 

 of water exhibited no decomposition under a pressure of 4| atmo- 



