A Specific Gravity Balance for Large Rock Specimens

Abstract

THE specific gravity balance represented in the accompanying illustration was devised by me some ten years ago for the determination of the specific gravity of hand specimens of rocks in the laboratory of the Geological Survey of India, Calcutta. In the ordinary form of Walker's balance the weight used on the short arm must be considerable in order to balance even a very small fragment of rock on the longer arm, and in consequence the specific gravity of an ordinary hand specimen has to be inferred from that of a small chip, which, unless the rock is of very homogeneous composition and texture, may give a very misleading result; and it is evident that if this form of balance were capable of accommodating a fairly large specimen, the whole instrument would have to be immoderately large. It occurred to me that if the specimen could be substituted for the heavy weight of Walker's balance, not only would it be possible to construct a balance of moderate size by which the determination of large specimens could be made directly, but the manipulation of the specimen and of the vessel containing the water might be greatly facilitated.