826 



different modifications are, it is true, not inconsiderable, but they 

 maj' be partially compensated in consequence of the simultaneous 

 presence of different forms. In order to detect the remaining volume 

 changes, very accurate determinations of the density must be made. 

 We shall see below that special precautions must also be taken 

 with lead. Evidently it is to be ascribed to such compensations that 

 these phenomena have escaped the attention of earlier authors. 



J7. We used toluene as a liquid in the pycnometer. 



Its density was found to be : 



25° 

 d — ^ 0.86013 by means of the pycnometer C. 



0.86013 „ „ „ „ „ D. 



The quantity of lead used for each determination was 40-60 

 grams. The thermometers (divided into 0.05 degrees) had been checked 

 against a standard of the Phys. Techn. Reichsanslalt at Charlotten- 

 burg-Berlin. The weighings were carried out on a BuNGE-balance 

 with telescope. The weights had been checked by the method 

 described by Th. W. Richards ^). 



18. In the first place we determined (at 25°. 0) the density ot 

 the lead immediately after its preparation for the experiments. 

 It was melted, cliilled in Avater and filed to powder. It was then 

 treated with a magnet in order to remove traces of iron from the 

 file. We washed the powder with dilute nitric acid, water, alcohol 

 and ether, and dried it in vacuo over sulphuric acid. Its density 

 was now : 



25° 

 d-^ 11.325s (Pycnometer C). 



The metal was then washed and dried again in the same wa}' ; 



,25° 

 d—-' 11.322i (P^'cnometer D). After treating again in this way we 



25° 

 found d ^^ 11.324, (Pycnometer D). 



19. We brought the metal into the solution of the acetate (temp. 



15°). After standing for 3 weeks the material was washed and 



25° 

 dried. Its density was now d — ^ 11.340^ (Pycnometer C) 



11.342, (Pycnometer D). 



Zeitschr. f. physik. Chemie 33, 605 (1900). 



