GENERATION OF ANIMALS, II. ii. 



it by the heat and becomes pneuma. Lead ore," too, 

 when it gets mixed with water and oil, increases its 

 bulk, and whereas it was fluid and black it becomes 

 tliick and coherent and white. The reason is that 

 pjieuma gets mixed in with it, and this produces the 

 increase of bulk and lets the whiteness show through, 

 precisely as it does with foam, and also with snow (be- 

 cause snow too is a foam). Even water itself when it 

 gets mi;xed with oil becomes thick and white, the reason 

 being that some pneuma is left behind in it owing to 

 the friction of mixing, and also that oil itself contains 

 a good deal of pneuma — for of course shininess is a 

 quaUty of pneuma, not of earth or water. And that 

 too is why oil floats on the surface of water ; air is 

 contained in it, as though in a vessel, and this air 

 buoys it up and causes it to float ; thus the air is 

 the cause of its lightness. Further, in time of cold 

 and frost, oil thickens, but does not freeze. Its 

 failure to freeze is due to its heat — because the air 

 is hot and is impervious to frost. But it thickens 

 because the air is coagulated and compressed [as] by 

 the cold. These reasons explain the behaviour of 

 semen as well. It is coherent and white when it comes 

 forth from within, because it contains a good deal of 

 hot pneuma owing to the internal heat of the animal. 



attempt at flotation in modern times was made by the brothers 

 Elmore at the Glasdir gold-mine in Wales (patent 1898), 

 though suggestions for the use of oil had been made by 

 William Haynes of Holywell some years earlier (patent 

 1860). For details see S. J. Truscott, Text-book of Ore- 

 dressing ; T. A. Rickard, Man and Metals, id.. Concentration 

 by Flotation (which includes two essays on the flotation of 

 galena at Broken Hill, N.S.W.). The term crruf>p6s corre- 

 sponds exactly to the "' thick coherent froth " mentioned by 

 Truscott {op. cit. 392, etc.). — For a full account of the mines 

 at Laurium see E, Ardaillon, Les Mines du Laurion (1897). 



G 161 



