Determining the Specific Gravity of Solids. 



461 



the beginning of the graduation. By means of the stopcock it 

 is allowed to rise slowly again, till it reaches the level at which 

 it stood before the solid was introduced. In this way the 

 total bulk of water displaced is measured in the tube a, 

 which being of small diameter admits of the volume being 

 measured with great accuracy. The tube may be graduated to 

 grains or grammes ; and the specific gravity is then found 

 directly by dividing the weight of the substance in air by the 

 number of grains or grammes indicated. 



The Messrs Gray, of the Physical Laboratory of this 

 University, suggested to us that by attaching to the tube b 

 a small tube in the form of a loop, so placed as to have its 

 limbs nearly at right angles to b, we should be able to bring 

 back the water in b to its original level with much greater 

 accuracy than by reading direct!}' on the wide tube, even 

 with the aid of a float, since a small alteration in the level of 

 the water gives a large horizontal displacement in the loop- 

 tube. 



The following table will exhibit the degree of accuracy 

 which can be attained by the method we have described. 

 Obviously, to obtain good results with bodies of high specific 

 gravity, as large a piece of substance as possible should be 

 used. 





Specific gravity. 

 By ordinary method. 



Specific gravity. 

 Ey new method. 



Difference. 



Lead 



11-333 

 8-090 

 8-480 

 7-160 

 2-456 

 3232 

 4762 

 2 704 

 2-649 

 3953 

 2-629 

 0-988 

 0*202 

 1-404 

 1-777 



11-310 

 8-090 

 8-440 

 7-150 

 2-452 

 3-240 

 4-756 

 2-723 

 2-620 

 3-940 

 2-611 

 0-997 

 0-201 

 1-404 

 1-780 



0-023- 

 6-040- 



o-oio- 



0-004- 

 0-008+ 

 0-006- 

 0-019 + 

 0029- 

 0-013- 

 0-018- 

 0-009+ 

 0-001- 



6-6o3+ 



Copper 



Steel 



Zinc 



Glass 



Iron Ore 



Copper Pyrites . . . 

 Dolomite 



Quartz 



Malachite 



Granite 



Wax 



Cork 



Sugar 



Alum 





The advantages of the method are twofold : — 



(1) Its rapidity. Several determinations can be made by- 

 it in the time required for a single determination by the 

 ordinary method. 



(2) It is applicable to all solids. In the case of bodies 

 lighter than water or soluble in water, the tube has only to 

 be filled with the liquid appropriate to the substance. In 



Phil Mag. S. 5. Vol. 17. No. 108. June 1884. 2 I 



