560 Kenneth A. Mickle: 



being repeatedly sunk. If the water is boiled free from air 

 the metals will not float when the first bubbles attaching them- 

 selves are removed. A piece of copper foil, which was immersed 

 in air-free water, and which would not .float when the pressure 

 was reduced, floated on the surface when brought in contact 

 with the vapour above the surface of the water. Crystalline 

 pieces of the following minerals under water under reduced 

 pressure were all coated with bubbles : — Galena, zinc blende, 

 garnet tourmaline, pyrite, gypsum, ardalusite, calcite, cerussite, 

 and quartz. These minerals were then placed in water, boiled 

 free from air, and again became coated with bubbles on re- 

 ducing the pressure, thus showing that some gas is carried down 

 with each mineral as it sinks. The metals had also bubbles 

 attached to them, but in freeing these with a glass rod only a 

 few very minute ones formed again. After the bubbles have 

 formed on these minerals, if atmospheric pressure is restored, 

 the bubbles become almost invisible, but form again in the 

 same position on again lowering the pressure. Tarnished 

 minerals form as many bubbles on their surfaces as the clean 

 faced ones. 



Behaviour of Minerals and IVIetals in Dilute Acid 



Solution. 



On the surface. 



Cold. — 'Similar to water even with strong H^SO.^. 



Hot. — None of the minerals would float when sprinkled on 

 the surface of a hot H,,SO^ solution even when very dilute 

 (1 per cent.) becoming at once Avetted and sinking. Copper 

 foil will float on a hot 3 per cent. H^,SO.j solution. The sample 

 of zinc concentrates forms a film the thickness of one particle 

 only, the remainder falling through the surface, but coming up 

 again in the form of agglomerated masses. 



Heated in acid solutions. — Most of the sulphides will float 

 if heated in a weak H^SO^ solution. Some samples of pure 

 galena and zinc blende would not float, but on the addition of 

 calcite and generation of CO., floated. Haematite, biotite, 

 quartz, wolfram, cassiterite, rhodonite, calcite, siderite, musco- 



