828 



At 50°. 8 the decrease of the level was 700 mm. (34 hours). 



„ 74°.4 „ rise „ „ „ „ 275 „ ( 27, „ ). 



Whilst the first preparation (§ 20) had shown at 50^ a decrease 

 of density, we now find an increase. From this result we may 

 conclude that there are more than two allon'opic foims simultane- 

 onsly present. 



24. Special attention may be paid to a phenomenon which we 

 observed with all our preparations and which stands in close con- 

 nexion with the fact that lead as it has been known up to the 

 present, forms a metastable S} stem containing simultaneously several 

 allotropic modifications of this metal. 



It is generally known that when a bar of any metal which is 

 more electro-negative (resp. electro-positive) than lead is suspended 

 in a solution of a lead salt, the lead is thrown out of solution and 

 a lead tree is formed. 



We found that the same phenomenon occurred when our pure 

 lead was placed in the solution mentioned above or in a (neutral) 

 solution of lead nitrate (30 grams of nitrate, 70 grams of wate»-). 

 Both at room temperature or at higher temperatures (50°) a lead 

 tree was formed in a few days. 



25. We are in the case of lead in specially favourable circum- 

 stances for the observation of this phenomenon. The galvanic current 

 which is generated between the stable and metastable modification 

 decomposes the solution. The metal which is electrolytically deposited ^), 

 shows in this case a characteristic form (lead tree) so that the 

 phenomenon is very striking ^). 



26. We hope to report shortly on the different pure modifications 

 of lead and their limits of stability. 



Utrecht, October 1914. van 't Rofy- Laboratory. 



^) That the phenomenon is not to be attributed to the presence of iron (^0.0006 

 per cent) or copper (0.001 per cent) is proveJ by the investigations of Oberbeck 

 [Wied Ann. 31, 337 (1887)] and by tliose of Königsberger and Muller [Physik. 

 Zeitschr. 6, 847 and 84'J (1905)]. 



~i We also carried out an experiment with tin: white and grey tin were put in 

 contact in a sokition of SnCl^ (Temp. 15^). After some time a great many 

 beautiful crystals of white tin were deposited by electrolysis upon the white metal. 

 [Gomp. Ernst Cohen and E. Goldschmidt, Zeitschr. fur physik. Chemie 50, 225 

 (1905)]. 



