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LIIL— ON A MODIFICATION OF SPEENGEL'S APPAEATUS 

 FOE DETEEMINING THE SPECIFIC GEAVITY OF 

 SOLIDS. By PEOF. SOLLAS, LL.D. (Plate XIII., 

 Figs. 2-7.) 



[Eead, February 16, 1887.] 



The simple and elegant specific gravity tube of Sprengel is not so 

 well known among mineralogists as to render its description as 

 a preliminary to indicating a slight modification of it unnecessary. 

 It consists (fig. 2) of a small U-tube, drawn out at eacli end into a 

 capillary. The capillary tubes are bent outwards, at right-angles 

 to the limbs of the U-tube, and one of them grows wider (fig. 2, e) , 

 and the other narrower (fig. 2, a), as it recedes from the limb of 

 the tube, with which it is continuous. A mark (m) for reference 

 is etched at any point chosen on that capillary which expands 

 outwards. This apparatus affords us a means of obtaining a 

 definite volume of any fluid with an ease and accuracy which is 

 not approached by any other direct method. The method of 

 working is as follows: — The distally converging capillary (a) is 

 immersed in the fluid with which it is desired to fill the apparatus, 

 and by sucking at the end of the other capillary, the fluid naturally 

 flows in. When it is filled beyond the mark on the expanding 

 capillary, excess of fluid is drawn off by applying a piece of blotting- 

 paper to the end of the converging capillary, the meniscus in the 

 expanding capillary then slowly travels inwards, and when it 

 reaches the fixed mark the volume of the fluid is defined. 



So far this apparatus has only been used in the case of fluid 

 bodies ; and even were it not possible to extend its application to 

 solids, it might fairly be regarded as almost indispensable to the 

 mineralogist for determining the densities of the heavy fluids used 

 in the separation of the mineral constituents of rocks ; but by a 

 very simple modification it can be adapted to determine the 

 densities of these minerals themselves when in a state of powder, 

 as they necessarily always are when obtained separate by the use 

 of heavy fluids. This modification consists in directing the distally 

 expanding capillary vertically upwards, and enlarging it at its 



