We know that the sulphides, or minerals with a metallic lustre, can be floated either with or without oil and that the carbonates, silicates, etc., cannot be floated so readily. Why do certain oils have the power of selecting certain minerals? Why do certain oils produce froth? Why do certain oils give a watery froth? Why do some give an ephemeral froth and others a tough one? Of the thousands of oils known, only a few classes have found successful application in this new process...This leads us to the question, what property or combination of properties make oils valuable as flotation agents?--Introduction, page 5-6
