272 LIFE AND DEATH. 



the surface, while the stones are at the bottom. We 

 have here the celebrated experiment of the flask with 

 the three elements, in which are seen the liquids 

 mercury, oil, and water superposed in the order of 

 their density, but in this case demonstrated with 

 solid bodies. 



Influence of Diffusion. — Diffusion, which dissemin- 

 ates liquids throughout each other, may also cause 

 solids to pass through other solids. Of this W. 

 Roberts Austen gave a convincing proof. This in- 

 genious physicist placed a little cylinder of lead upon 

 a disc of gold, and kept the whole at the temperature 

 of boiling water. At this temperature both metals 

 are perfectly solid, for the melting point of gold is 

 1,200° C, and of lead is 330°. Still, after this contact 

 has been prolonged for a month and a half, analysis 

 shows that the gold has become diffused through the 

 top of the cylinder of lead. 



Influence of Electrolysis. — Electrolysis offers another 

 no less remarkable means of transportation. By its 

 means we may force metals, such as sodium or lithium, 

 through glass walls. The experiment may be per- 

 formed as indicated by M. Charles Guillaume. A 

 glass bulb containing mercury is placed in a bath of 

 sodium amalgam, and a current is then made to pass 

 from within outward. After some time it can be 

 shown that the metal has penetrated the wall of the 

 bulb, and has become dissolved within it. 



Influence of Mechanical Pressure. — Mechanical pres- 

 sure is also capable of causing one metal to pass into 

 another. We need not recall the well-known experi- 

 ment of Cailletet, who, by employing considerable 

 pressure, caused mercury to sweat through a block of 

 iron, In a more simple manner W. Spring showed 



