170 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



disadvantages, there has been a tendency toward use of the sintered-giass 

 Gooch crucible. In this case, however, there is the need for thorough 

 decontamination of the crucible before reuse, and it is not practical to 

 hold a large number of samples until the results have been studied. 



A typical commercially available filter assembly is shown in Fig. 5-4. 

 The filter paper is placed over the top of the lower section, and when 

 pressed together the barrel of the assembly makes a tight fit, holding the 



Filter 

 paper 



Slip 

 ring 



Sample material 

 I l\ 



I 



Filter J[ 



paper 



mount 



Bose> 



Mounting ring 

 and base 



Fig. 5-4. Filter assembly for collection of precipitates on filter paper. 



filter paper in place. After filtration the paper with precipitate is trans- 

 ferred to a mounting block. 



Settling and Centr if ligation. Many of the difficulties encountered in 

 the use of filtration technique have been eliminated by the development 

 of settling and centrifugation methods. Greenberg (33), working with 

 C^*, has found it very satisfactory to evaporate acetone suspensions of 

 protein onto aluminum disks. He used a simple device consisting of an 

 inverted mayonnaise jar from which the bottom had been removed, with 

 the aluminum disk held in place by the screw cap of the jar. 



A simple device that has been used in this laboratory for the large-scale 

 routine collection of calcium oxalate precipitates is illustrated in Fig. 5-5. 

 The apparatus consists of a tapered-end plastic pipe with a nickel-steel, 

 or preferably stainless-steel, cup forming the bottom. The cups and 



