144 Penjield and Kr elder — Miner cdog iced Notes. 



Fig. 2. 



Fig. 3. 



water bath. After a separation is completed and the fusion 

 cooled, the test tube is broken and the solid cake divided, 

 when the heavier and lighter portions may be obtained by dis- 

 solving the double salt. There are some disadvantages, how- 

 ever, in working with test tubes, especially as it is always con- 

 venient and frequently quite necessary to secure fractional 

 separations or to draw off the heavy material from the bottom 

 for examination, and with a test tube this cannot be accom- 

 plished without interrupting the whole experiment and clear- 

 ing the material. As the ordinary glass stop-cock separating 

 funnels are not well adapted for use with a 

 fused salt at a temperature of near 100° 0. 

 an apparatus has been devised, which is illus- 

 trated by fig. 2 in one-fourth its natural 

 size. The glass rod is ground into the tube 

 with fine emery and serves as a stop cock. 

 This apparatus slips inside of a test tube, 

 and a rubber band is so adjusted around the 

 top of it that the lower end of the 

 tube comes to within a few millimeters of 

 the bottom of the test tube. The tubes are 

 most conveniently heated in a beaker of hot 

 water and can be held in a vertical position 

 by a simple rack or test-tube stand made of 

 metal. The contents of the tube are con- 

 veniently agitated by means of a plunger 

 made from a glass rod bent at one end as in 

 fig. 3. Before drawing off the heavy mate- 

 rial from the bottom it is best to place a 

 loosely fitting perforated cork in the end of the separating 

 tube, through which the rod passes and is supported so 

 that the rod can be raised straight up and dropped back 

 into place without fear of breaking the tube. Difficulty some- 

 times arises at this point from particles getting caught in the 

 stopper, so that after the heavy portion has been drawn off the 

 rod will no longer close the tube. If the particles are small 

 and not too hard they may be ground out by twisting the rod, 

 or if this cannot be done the fusion must be allowed to run 

 out and the apparatus cleaned. But even in this latter case, 

 there is a decided advantage in saving of time over the use of 

 a test tube, as a separation has been accomplished, and the 

 mineral powder and apparatus can soon be made ready for 

 another treatment with a fresh portion of the fused salt. The 

 stop-cocks need to be carefully ground in order to make them 

 perfectly tight, as they are subjected to a considerable pressure 

 from the column of heavy liquid, but a slight leakage is not 

 especially objectionable as the few drops that leak out are 

 caught in the outer test tube. 



Laboratory of Mineralogy and Petrography, 

 Sheffield Scientific School, New Haven, April, 1894. 



