823 



In this way the electrolyte is in constant contact with the metal 

 and the inocnlation which occurs can go on undisturbed. 



The photographic reproductions (natural size) which accompan}- 

 this paper illustrate the development of the phenomenon. Fig. 1 

 sliows a plate of pure lead in its original condition. Fig. 2 represents 

 the plates after having been in contact with the solution for some 

 days ; there are to be seen deep cracks, which show that the material 

 has shrunk locally. In consequence of this an increase of the density 

 was to be expected which was proved by means of the pycnometer 

 (comp. § 'J 9). Fig. 3 shows the plates after three weeks in the same 

 conditions : the metal has been disintegrated. 



Repeating the experiment with 15 or 20 blocks we got in all 

 cases the same results. 



13. We shall prove below that the phenomenon is not a chemical 

 one ; the following experiment may give already an indication in 

 this direction. Ojie of the blocks (=t 40 -grams) was put into a cali- 

 brated tube which had been tilled up with the solution mentioned. 

 This tube stood in a small dish containing the same solution. After 

 three weeks no evolution of gas had occurred, either at room tem- 

 perature or at higher temperatures. 



14. After this the phenomena described above were investigated 

 by means of both the pycnometer and the dilatometer. 



A. Measurements irith the Pi/cnometer. 



15. We exclusively used the instrument (Fig. 4) described by 

 Adams and Johnston'), following the indications given by the authors. 

 Moreover we took the precaution of dipping the pycnometer inlo 



water before weighing (empty) and wiping the 

 water off with a dry cloth. If this is omitted a 

 slight error occurs, as the surface of the pycnomeler 

 is then not in the same condition as at the sub- 

 sequent weighings, after it has stood in a (water) 

 thermostat. 



All determinations were cari-ied out in duplicate 

 with two pycnometers (C and D) which contained 

 ±25 ccm. 



16. Our investigations on bismuth, cadmium etc. 

 had shown that the pycnometer measurements have 

 to be carried out with special care. The volume 

 changes which accompany the transformation of the 



Fie. 4. 



1) Journ. Americ. Ghem. Soc. 34, 5ü3 (1912). 



