The flotation process . we will say, three inches in diameter. It is surroundedby a very thin film of water contaminated or modified by soap. Theamount of water in that film which surrounds the air inside of thebubble is, as we may well imagine, very small. The ordinary soap-bubble bursting upon this piece of paper would hardly leave avisible sign of water. Now, as that bubble exists as a bubble thesurface of that very small amount of water is very large. It is theentire outer surface of that bubble and the entire inner surface,where the film comes in contact with the exterior air and where it
The flotation process . we will say, three inches in diameter. It is surroundedby a very thin film of water contaminated or modified by soap. Theamount of water in that film which surrounds the air inside of thebubble is, as we may well imagine, very small. The ordinary soap-bubble bursting upon this piece of paper would hardly leave avisible sign of water. Now, as that bubble exists as a bubble thesurface of that very small amount of water is very large. It is theentire outer surface of that bubble and the entire inner surface,where the film comes in contact with the exterior air and where itcomes in contact on the inside with the enclosed air. Now, over thatimmense surface, for it is truly immense in consideration of thesmall amount of water, there is this contractile force, as if aroundthe bubble there were stretched a sheet of rubber constantly drawinginward to make that bubble smaller, and the effort of that force ofsurface tension to reduce the area of the water forming the film AIR-FROTH FLOTATION IGl. 162 THE FLOTATION iROCESS of the bubble, simply pulls it in, bursts it, reduces it to a drop,which has the minimum of surface. So I apprehend that the reasonthe bubbles in these froths burst is on account of that shrinkinginward, that tendency of surface tension to gather the water intothe smallest possible compass. The experts who have testified in this case say (and their viewsare in harmony with the literature on the subject) that any substancewhich tends to lower or lessen the surface tension of water tends tomake the bubbles or the froth more persistent or permanent; andin view of what I have said, I think the reason why these modifyingagents w^hich lower the surface tension of water also tend to makethe froth more permanent is clear. In the case of pure water,having a surface tension which I think is—well, it is arbitrarilyrepresented by some numeral—we can say 1. It makes no , that force of surface tension in clear water is strong enoug
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