Fundamental Features of Phytocolloids. 



17 



of the shallow cell are removed and the filter-paper is peeled from the 

 margins and the free flaps are fastened by paste to the edges and sur- 

 faces of the wooden frame so as to be perfectly taut and so firmly that 

 when the colloid dries it may not shrink in width or length. Addi- 

 tional care should be taken to see that the material does not tear loose 

 from the paper at this time, and if it does it should be secured by using 

 some fresh material as a paste to fix it to the paper. The margin dries 

 most rapidly, and if securely attached to the paper holds the plate in 

 place throughout (see fig. 4). 



FIG. 3. 



Drying-frame with sheet 

 of hard filter-paper 

 fitted in place ready to 

 receive liquid colloidal 

 mixture which is to be 

 poured on the,'paperto 

 ajfdepth of about 

 8 to 10 mm. 



The drying-frame is now placed on a rack in a desiccator which 

 consists of an inclosed chamber in which is placed an electrically driven 

 fan and a large, shallow pan of water. The best results are secured by 

 a rate of drying which results from having air with high humidity 

 driven over the plates constantly without dehydrating the surface 

 layers too rapidly (fig. 5) . Drying will occupy about 40 hours, during 

 part of which time it may be advisable to stop the fan. As soon as 

 the sheet appears to be dried to a flexible, leathery consistency the 

 paper may be freed from the frame and then stripped from the plate 

 of material, which should remain plane, with but little curling or buck- 

 ling. The rough and uneven margin should be cut away with scis- 

 sors, the data as to composition, etc., written on one end with common 

 ink, and then placed in a closed dish for preservation until used. 



The precautions described are necessary in any effort toward accuracy 

 in the measurement of the swelling of a colloid, as the increase will, 

 among other factors in its experience, reflect most strongly the method 

 in which it was laid down, deposited, or dehydrated. A dried section 

 of a colloid of the kind used in these experiments tends to return to the 

 dimensions which it had when the gel set or cooled. Standardization 



