556 Kenneth A. MicJde: 



Cold n-ater. — Minerals and other substances differ in their 

 inclination or otherwise to become wetted by water or by other 

 liquids. Many minerals when dropped carefully on to the sur- 

 face of water remain on it and do not sink. Some at once sink 

 to the bottom. Particles of considerable size may be floated 

 in this manner, and sometimes considerable force is required 

 to make them sink. Some minerals, when ground so as to pass 

 a 30 mesh sieve, form a film on the surface of the water, and 

 this film will support a considerable weight. A certain sample 

 of zinc blende concentrates could be heaped up in this manner 

 to a depth of \ inch on the surface of water in a 50 c.c. cylin- 

 drical beaker. The weight of material was 15 gms., and the 

 top portion was quite dry. The following is a list of the 

 minerals tried that would float on the surface of water : — 

 Galena, zinc blende, sulphur, azurite, malachite, rhodonite, 

 garnet, calcite, mica, telluride of gold, pyrite, pyrrhotite, 

 wolfram, cassiterite, serpentine. And besides this all the metals 

 in the form of foil would easily float. Some samples of quartz 

 will float and others will not. Particles of glass and turquoise 

 would not float. 



The weight of each particle on the surface causes a distinct 

 depression or sag round itself, and the apparent attraction of 

 one particle for another is probal^ly due to the depressed surface 

 caused by this sagging. If some liquids (such as alcohol in the 

 form of a drop on a glass rod) are brought near the particles 

 floating on the surface, the particles are repelled from the rod. 

 If alcohol is added to the water the particles become wetted 

 and sink. Caustic soda acts similarly. This is apparently a 

 surface tension phenomenon. In the case of alcohol on the 

 glass rod, the vapour of the alcohol mixing with the water de- 

 creases the surface tension and increases the adhesion of the 

 water for the mineral. The water wets the particle at a higher 

 level on the side nearest the glass rod ; an inclined plane is 

 formed on the side furthest from the rod, and the particle is 

 apparently repelled. Water has the greatest surface tension of 

 any liquid xmder ordinary atmospheric conditions except mercury, 

 and thus, if another liquid is added to it, the surface tension is 

 decreased. If the minerals in the above list have been pre- 

 viously wetted they will not float on the surface until they are 



