ELEMENTARY PHYSIOLOGICAL CHEMISTRY 171 



ment paper. In this they are unlike Crystalloids, such as inorganic 

 salts, which readily diffuse. 



Various forms of dialyser are used, but the simplest consist, either 

 of a bell-shaped glass vessel closed below by a tightly stretched piece 

 of parchment or membrane and open above (Fig. 139), or of a tube of 

 parchment. 



EXPERIMENT III. Place a mixture of diluted egg-white and of a 10 

 per cent, solution of NaCl in a dialyser (the tubular dialyser is 

 the best to use), and place the latter 

 in a large basin or beaker filled with 

 distilled water. Before inserting the 

 dialyser, test a sample of the water 

 for chlorides with argentic nitrate 

 solution, and note that no haze re- 

 sults. Allow the dialysis to proceed for a day, then test a sample 

 of the water again, when a white precipitate of AgCl 2 will result. 



FIG. 140. Crystallised albumin, x 600. 



The NaCl, being a crystalloid, has diffused out, but no proteid has 

 passed out, as can be ascertained by applying the proteid tests (see 

 below). 



II. Crystallisation. Proteids usually exist when dried as amor 



