Laboratory Manual of Elementary Colloid Chemistry

s syphons. Special arrangements are necessary when the sol to be dialysed has an appreciable osmotic pressure, as is the case, e.g., with albumin sols. In this case water flows into the dialyser, diluting the sol and eventually causing it to overflow. The only way te prevent this is to counterbalance the osmotic pressure hydrostatically; in other words, to keep the level of the sol in the dialyser above the water level outside from the beginning. For small quantities, such as come into question here, the simplest arrangement is that shown in Fig. 6. A dialysing thimble of either parchment or paper impregnated with collodion is fitted with a rubber stopper and tied tightly; a strip of gutta-percha tissue about 15 mm. wide is first wound round the end of the thimble and strong thread tied over this. Through the rubber stopper passes a funnel tube about 30 cm. long, which must have a diameter of at least 8 mm., so that the sol can be poured down one side of it, allowing the air to escape and the thimble and tube to be filled to the top. The thimble is submerged in a beaker through which water flows continuously. With this arrangement Fig. 0. 28 DIALYSERS. the liquid remains at its original concentration and the bulk of it is still contained in the dialysing membrane, as the volume of the funnel tube is comparatively small. Literature. Membranes made from collodion of unusually high concentration and capable of standing considerable pressures are described by...