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LI. Note on an Easy and Rapid Method of Determining the 

 Specific Gravity of Solids. By James J. Dobbie, M.A., 

 D.Sc>, and John B. Hutcheson, Assistants to the Pro- 

 fessor of Chemistry, University of Glasgow* \ 



THE specific gravity of a substance is the weight of a 

 volume of that substance compared with that of an 

 equal volume of some other substance selected as standard 

 and measured under the same conditions of temperature and 

 pressure. Water is the standard universally employed for 

 solids and liquids. Hence, in taking the specific gravity of a 

 solid, the data which have to be determined experimentally 

 are the weight of a volume of the solid and the weight of 

 an equal volume of water. The weight of water is usually 

 determined by making use of the well-known principle that 

 a solid when weighed in a liquid weighs less than in air by 

 the weight of the volume of liquid which it displaces. By 

 subtracting therefore the weight of the solid in water from 

 its weight in air, the weight of w r ater displaced, i. e. the 

 weight of a volume of water equal to that of the solid, is 

 found. For accuracy this method leaves nothing to be 

 desired; but the operation of weighing a solid in water is one 

 which always involves some trouble, and frequently requires 

 some delicacy of manipulation. And in the case of solids 

 which are soluble in water, the weighing must be performed 

 in some other liquid, and, the gravity having been found 

 relatively to that liquid, must be reduced subsequently to the 

 standard of water. In the case, too, of a solid which is 

 lighter than water, the weighing must either be performed in 

 a liquid of less specific gravity, or else a heavy body must be 

 attached to sink it in water. Whichever method be em- 

 ployed, additional weighings are required and subsequent 

 calculation is involved. 



The method which we now propose briefly to describe, and 

 which we have employed for some time in this laboratory, is 

 applicable in all cases, and gives results which agree as closely 

 with those obtained by the ordinary method as two different 

 determinations by the ordinary method usually agree with 

 one another. 



Instead of finding the weight of water in the usual manner, 

 we find the exact volume of water displaced by the solid. 



The accompanying figure shows the apparatus which we 

 employ, which may be termed a specific-gravity burette. It 

 consists of a U-tube, one limb of which (a) is of small diameter 



* Communicated by the Authors. 



