822 



Chemistry. — ''Tlie allotropy of Lead.'' I. By Prof. Ernst Cohen 

 and W. D. Helderman. 



(Communicated in the meeting of Oct. 31, 1914.) 



1. Indications concerning tiie existence of allotropic forms of 

 lead are found not only in the earlier chemical literature. Fourteen 

 years ago Ernst Cohen ^) pointed out in his studies on tin a clause 

 in Plutarch's (50 — 120 A.D.) Symposiaca (VI, 8) in which allusion 

 is made ^) to the fact that lead is sometimes disintegrated spontaneously 

 at low temperatures. 



This clause runs as follows: "No, the craving for food is not caused by the 

 cold, but in the body something takes place similar to that which happens with 

 metals in a very strong winter. There it is seen that cooling not only causes 

 congealing, but also melting, for in strong winters ctxovai [loU^öov (pieces of 

 lead) occasionally melt away, consequently something similar may be supposed to 

 take place in the intestinal process, etc. . . .'" 



Moreover Theophrast (390 — 283 B.C.) mentions such phenomena in his book 

 rrfoi ctvoó^: ^'^y.arrir^Qov yiio (paol y.ai [lóXiiSöov V^ér^ TayS]V(a iv rto 

 nóvTCi rtdyov y.ai yfj/icuro»^ orrog vsaviyov, x^(?.y.ov öè Qctyr^vai. 

 (It is told that tin and lead melled sometimes in the Pontos when it was very 

 cold in a strong winter, and that copper was disintegrated. 



2. Sainte-Claire Deville 'j stated that the density of lead is a 

 function of its previous thermal history. He gives the following 

 figures (water at 4° — 1 ; Temp. ?) 



After quick cooling of molten lead 11.363. 

 slow „ „ „ „ 11.254. 

 In a second experiment he found : 



Density of lead electrolytically deposited 11.542. 

 After melting and rapid cooling 11.225. 

 About the value 11.542 he says: 



"Mais telle est la rapidité avec laquelle se carbonate a Fair ce plomb extrême- 

 ment divisé, qu'il a fallu le transformer en sulfate pour en deduire ensuite le 

 poids de la matière employee. Cette complication introduit- elle quelque incertitude 

 sur le premier nombre, ou ne doit on pas plulot I'admettre comme représentant 

 la densité de ce plomb parfaitement cristaUisé?" 



3. These values as well as others given in earlier literature have 

 to be accepted with reserve as generally no data are given about 



1) Proceedings of the meeting of Jan. 26, 1901, p. 469. Zeitschr. f. physik. 

 Chemie 36, 513 (1901). 



2) PLUTARcm Chaeronensis varia scripta quae moralia vulgo vocantur. Lipsiae, 

 ex officina Gar. Tauchnitii 1820. Tomus IV, 389. 



3) C. R. 40, 769 (1855). 



