Sealing-in sintered glass discs

A glass tube drawn out at one extremity, and with a glass stopcock sealed on this end, is used to contain the cellulose. Either a perforated porcelain disc is placed on this constriction or a sintered glass disc is sealed in at this point, thus providing a support on which to build up the cellulose column. Temperature control is useful and if a constant temperature room is not available the column may be fitted with a jacket through which water is pumped from a constant-temperature bath (73). 

The sintered disc of the filter stick should be of porosity 3 or larger in order to avoid blockage. A convenient alternative to a filter stick is to use an ordinary glass rod with filter paper wrapped round the end (Fig. 11.4b). Wrap some Teflon tape round the end of the tube, then carefully fold filter paper over the end and secure it with wire. The Teflon tape will give a better seal because the wire will sink into it. Another alternative, for smaller scale work, is to use a long syringe needle (Fig. 11.4c). Again, the end of the... 

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