631 



We used llie elcclrically Iicalud tlieniiostal, iiieiilioiied in our [)jii)(M- 

 on the allo(ro|)\' of cadiMiiiin '). 



Tlie results are given in Tal)le 2. (Zie ]). 630). 



5. This table shows tliat there is a transitionpoiiit at 71°.7 C. 

 From this we conclude that there exist two allotropic(enantiotroj)ic) 

 modifications of coi)i)cr. Tiie phenomena may be described by the 

 equation : 



71°.7 

 Cu{a) ^ C>i{,^) 



6. It may be pointed out that the change in tlie dilatometer has 

 taken j»lacc with great velocity notwithstanding the fact that the 

 copper used in this experiment had not been in contact with a 

 solution of coppersulpliate. On the othei- hand there was a large 

 quantity of finely divided metal present. Here, as in the case of 

 bismuth, tin etc, the presence of this powder suffices to accelerate 

 the transition velocity very strongly. 



7. The following experiment proves that the velocity of the 

 reaction ,?-copper-^ rt-copper decreases enormously when this powder 

 is not present. 



We took 200 grams of electrolytic copper, melted it in an electric 

 furnace and poured the metal into a melting-spoon, where a series 

 of thin rods was formed. These rods were chilled in water and put 

 into a dilatometer which was tilled with paraffinoil. The apparatus 

 was kej)t during 14 days and nights in a thermostat at 25° C. 

 Practically no change occurred. The traiisition velocity of /:?-copper 

 into «-copper is several thousand times smaller than if the finely 

 divided metal is present. 



This phenomenon exj)lains the fact that obj'^cts made of copper 

 disintegrate so slowly in daily life. It is exactly the retardatiou 

 observed in the experiment described above, which makes |)OSsible 

 the use of copper in daily life. We meet here with the same 

 phenomena which have been described already in the case of tin, 

 bismuth, cadmium and zinc. 



8. Our experiments prove that we have to consider copper as a 

 metastahle system ('< -j- ,^ copper), which (below 71°. 7 C.) is continu- 

 ously changing into the stable modification (rt-copper). The very 

 strongly marked retardations have concealed the allotropic change 

 from the physicists and chemists who have studied this metal in 

 different directions. 



9. Dr. Ch. M. van Dfcventi^r has been so kind as to call our 



') Proceedings 16, 485 (1913). 



