288 ELEMENTARY CHEMICAL MICROSCOPY 



ing, cigar-shaped plug. It should be rolled dry and rolled long 

 enough to make it fine and even. If the paper is cut, not torn, 

 there will be a seam in it, and it cannot be so readily made tight. 

 The plug thus formed is inserted in the small end of the tube 

 from the outside and worked in by rotating the tube until from 4 

 to 8 millimeters of the paper are within. The rest of the paper is 

 then cut off a millimeter or two from the end of the tube." 



The filter is first moistened with distilled water and then in- 

 serted in the drop to be filtered, suction is applied to the larger 

 end and the clear liquid drawn up through the filter into the tube, 

 from which it is removed by a capillary pipette or by carefully 

 removing the filter paper with a pair of fine forceps and expelling 

 the liquid in exactly the same manner as in the Behrens method. 



A tightly rolled cigar-shaped plug of filter paper or fibrous 

 asbestos may be inserted in a straight Behrens tube in a similar 

 manner to that described above, and will be found to yield even 

 more satisfactory results than the fragile drawn-out tube of 

 Savage. 



The author has found in certain instances that alundum filters 

 have proved of great value. Such filters are made by grinding 

 tiny conical plugs from pieces of broken alundum crucibles and 

 fusing these plugs into the ends of glass tubes 2 to 2.5 millimeters 

 in diameter and 50 to 60 millimeters long. After fusing, excep- 

 tional care must be taken in cooling and annealing. In like man- 

 ner porous porcelain plugs may be used, but in such an event 

 a powerful suction pump is required, suction by means of the 

 mouth being insufficient to cause the passage of the liquid. 



Sublimation. — This operation, though of somewhat limited 

 application and comparatively seldom employed in inorganic 

 qualitative analysis, is so very important, and of such inestimable 

 value in the examination of organic compounds, that every worker 

 should become thoroughly familiar with it, particularly with the 

 method of performing fractional sublimations. 



The usual method is that of sublimation from one slide to 

 another. The material to be tested is placed at the corner of a 

 thin slide. If it is a solid it is wise to moisten it with water and 

 then dry it thoroughly; this will generally effectually prevent 



