GENERAL APPARATUS AND MANIPULATION 



177 



ternal diameter, 6 mm. external diameter) the end of which is 

 tapered and contains a fused-in 4 mm. section of sintered glass at 

 the tip. Kirk ( 1935) discussed the preparation of sintered-glass 

 filters for those who cannot obtain them commercially. A layer of 

 fine asbestos 1 mm. thick is sucked onto the tip of the filter to form 

 a pad; after pressing this pad down with the fingernail, a layer of 

 asbestos is deposited on the pad to form a cone about 2 mm. deep 

 The filter is used as shown in Figure 61. Only the tip of the cone ia 

 allowed to be in contact with the liquid in order that tlie precipitate 

 may be collected entirely on this part of the asbestos. The precipitate 

 can be transferred quantitatively by disengaging the pad at its base. 

 These filters are available from Microchemical Specialties Co. 



Fig. 61. Filtration detail. A represents 



an asbestos filtering cone; B, an asbestos 



base pad; and C, a sintered-glass plug. 



From Cunningham, Kirk, and 



Brooks (1941b) 



Fig. 62. Ultrafilter for small 



volumes of liquids. 

 From Johnson and Kirk (19IiO) 



Bott ( 1943) employed a capillary tube filter with paper pulp (Fig. 

 76) in the determination of sodium. A description of the preparation 

 of filter and its use is given on pages 204-207. 



Ultrafilters. Various devices have been employed for the ultra- 

 filtration of small volumes of liquids, and only that of Johnson and 

 Kirk (1940), designed for about 0.1 ml., will be described, since 

 it is one of the simpler and more efficient types. The ultrafilter shown 

 in Figure 62 consists of two brass tubes, A and B, drilled to fit snugly 

 the glass capillary tubes having a bore of 2 mm. or less and an out- 

 side diameter of 7-8 mm. Kronig cement ( 1 part white wax and 4 



