AN INEXPENSIVE APPARATUS FOR THE SYSTEMATIC 

 SEPARATION OF SEDIMENTS BY MEANS OF HEA\'Y 



SOLUTIONS. 



Hv CHARLES R. MAPP. F.R.M.S. 



Figure 1. 



Heavy solutions, such as those of Klein, Sonstadt, 

 Rohrbach, or Braun, offer a read\- and fairly satis- 

 factory means of separating sediments, sands, and 



comminuted rocks into 

 groups varying in specific 

 gravity, and thus materially 

 assist the laboratory ex- 

 amination of such material 

 for the identification and 

 estimation of the com- 

 ponent minerals either 

 qualitati\el\- or quantita- 

 tivelv. In using them, 

 however, numerous small 

 difficulties present them- 

 selves, and the process 

 becomes both lengthy and 

 tedious unless carried out 

 in definite steps, which, hv 

 repeated use, become ciuite 

 mechanical. 



Having recenth" had 

 occasion to so examine 

 numerous specimens of 

 Liassic and Keuper rocks, a simple piece of apparatus 

 which could be made easil}- and at small cost 

 became desirable. Unforeseen defects occurred 

 frequenth'. which rendered modifications necessary, 

 but the apparatus described below will be found to 

 work satisfactorih- for ordinary purposes. It is 

 a modified form of one described by Dr. J. W. 

 Evans (see Geol. Mag. 1891, page 67). 



It can be made readily with a gla 

 spring clip 



tubing. Figure 1 represents a section of the complete 

 apparatus. The funnel is cut off about half an 

 inch below the shoulder, and to the cut end is 

 attached a piece of rubber tubing about one inch 

 long. A spring clip like those employed with 

 burettes, either of Mohr's or Hofmann's pattern, 

 is fixed on this indiarubber tubing. The remaining 

 portion consists of a piece of glass tubing, having 

 the same, or nearly the same, bore as the stem of the 

 funnel, with a short length of rubber tubing at each 

 end. The construction is better seen in Figures 

 2 and 3. The lower end is provided w ith indiarubber 

 tubing of such a size that it forms a fairly tight fit 

 when pressed down into the funnel stem, while it is 



funne 



a thistle funnel, and glass and rubber 



of smaller bore than the glass tubing. Since it has 

 to be stretched to fit on to the glass tube, the portion 

 which projects over the glass, and which should be 

 about half an inch long will form a truncated cone, 

 which will securely close the entrance to the stem 

 of the funnel when pressed down with a rotating 

 motion. At the upper extremity there are two 

 separate pieces of glass, which are used at different 

 stages in the manipulation. In the diagram 

 X is a piece of glass rod, or of glass tub- 

 which can readily be inserted 

 mto the short length of rubber tubing to render 

 that end air-tight. In Figure 3, Y is the head of 

 a thistle funnel, which can be similarly inserted. 

 Now as to the method employed in fractionating 



(Figure 2) 

 ing closed at each end, 

 length 



the 

 rins 



ediments. The funnel can be fixed on the 

 ^ of a retort stand or other convenient 

 support. The heavy solution of the particular 

 specific gra\it\ to be used is now poured in 

 carefully, to within a reasonable distance of the 

 top of the funnel. It will be found to be a good 

 plan to place the bottle under the funnel, and after 

 cautiously opening the clip slightly, to let a small 

 quantity of the liquid flow out, both to remove any 

 air bubbles and to ensure that the whole surface of 

 the rubber tubing is wetted. 



The sediment or grains of matter to be separated, 

 which should previously have been washed and 

 dried, or treated in any way chemically, are now 

 poured on to the surface of 

 the liquid. The stopper 

 with the part X in the 

 upper end, may next be 

 used to stir the sediment 

 thoroughly into the liquid. 

 The object in having the 

 upper end closed by X 

 is to keep the stopper full 

 of air, and so prevent any 

 of the liquid entering it by 

 capillary attraction, in 

 which case grains are in- 



the 

 the 



variably taken up by 

 liquid, interfering with 

 success of the separation 

 at a later stage. The stopper 

 and the liquid is allowed to 

 hours. If tht_> hea\'\- liquid used 



I-'IGLRK 



■ ICL'RE 



is now laid aside, 

 settle for several 

 is hygroscopic, the 



217 



