18 



Hydration and Growth. 



of material for measurement of swelling under the influence of various 

 reagents or agencies would therefore require that the shrinkage of the 

 material as it dries should be controlled. This may be done in many 

 cases in the manner described. Thus in the case of biocolloids con- 



FiG. 4. — Diying-frame with plate of colloid, ready to be put into the desiccator. The molding- 

 bars A have been removed and the free portions of the filter-paper have been carried down 

 over the side of the frame and fastened securely in place with paste. 



Fio. 6. — Sectional views of desiccator for drying plates of colloids, a, frame with drying- pi ate 

 lying on a sheet of stretched filter-paper, which in turn is placed on a shelf of slats; b, metal 

 pan containing water to maintain relatively high humidity ; c, electric fan arranged to keep 

 current of air moving over the smface of the water, the plate of colloid, and in circulation in 

 the chamber; d and e, hinged lids which may be raised to control ventilation and the rela- 

 tive humidity of the chamber. A wooden chamber about a meter in height, over a meter in 

 length, and 80 cm. in width. 



sisting of 9 parts agar and 1 part bean albumen a plate cast in this 

 manner came down so perfectly that a strip 30 mm. in length placed in 

 distilled water swelled over 2,000 per cent in thickness, but did not 

 increase any measurable fraction of a millimeter in length. A strip 



