558 Kenneth A. Mickle: 



Uuihr tJie surface of water. 



When the minerals are sul)njerged in water and the water is 

 heated, many of them will tloat either wholly or partially. 

 Sulphur, crystalline azurite and malachite, some galenas, some 

 blendes, some chalcopyrites and stibnites, and some of the 

 metals, copper being- the most persistent, will float in water on 

 heating. A sample of zinc concentrates from the Potter pro- 

 fess (floated with HoSO^) floated when heated in water, and 

 when boiled the " scum ' continued indefinitely. If boiled 

 violently and continuously, the concentrates will sink, but if 

 allowed to cool will again float on heating. Ttis was repeated 

 twelve times, a.nd would apparently continue indefinitely, if after 

 ■each time the water was allowed to cool for some time. Air 

 will get into boiling water either being dissolved or being car- 

 ried down mechanically as bubbles, as the following will show. 

 A large beaker of distilled water was boiled continuously for 

 two hours. An inverted funnel was then placed in the beaker 

 and an inverted burette filled with the boiled water was placed 

 with the wide end fitting over the stem of the funnel. Air was 

 then slowly collected in the burette by the bubbles coming under 

 the funnel and displacing some of the water in the burette. The 

 funnel was arranged so that it did not rest on the bottom of 

 the beaker, but allowed the water to circulate under it. In some 

 cases the minerals appear to evolve a gas, and usualh- the water 

 begins to boil and water vapour forms first on the minerals, or 

 substances introduced into it, the latter giving a starting point 

 apparently preferable to the sides of the containing beaker. 



A sample of zinc concentrates under water was heated in a 

 10 c.c. graduated pipette and the expansion observed. These 

 concentrates were from a Potter (acid) float, washed and dried, 

 and then introduced into the pipette, which was immersed in a 

 large beaker of water, and this water was then heated to boil- 

 ing. The volume of concentrates as measured in the pipette 

 was 2 CO., and the surface of the water above them was 5.9 c.c. 

 The greatest expansion noted by taking the difference in the 

 reading of the level of the top of the water was 1.3 c.c. The 

 expansion noted by the dift'erence in the levels of the top of the 

 concentrates before and after heating was 0.8 c.c. The volume 



