Fundamental Features of Phytocolloids. 23 



while being dried. When a layer of powdered gelatine was placed in 

 the bottom of a Stender dish to a depth of 1.5 mm. and covered with a 

 perforated glass triangular plate which would go into the dish readily, 

 a swelling of 270 per cent in water at 18 C. was registered by the auxo- 

 graph. Furthermore, this increase was not the rapid swelling of a 

 mass with subsequent relaxation, but lasted over 5 days; the greater 

 part of the swelling occurred during the first half hour, then continued 

 at a decreasing rate for the period mentioned. 



A similar experiment was made with powdered agar, the particles of 

 which were probably of a much smaller average size. The swelling 

 was of the same kind, but was complete in 4 days, although reaching 

 the higher total of 317 per cent. This higher hydration capacity is 

 characteristic of agar as compared with gelatine. 



It is of course to be expected that when two colloidal substances in a 

 two-phase system are combined and the resulting material is subjected 

 to agencies that will coagulate or neutralize one of them, the section 

 would then show the relations of the one still in the colloidal state. 

 This was demonstrated with some completeness by a mixture of agar 

 and milk albumin. 



Preparations in which 1 part albumin from milk was stirred into 

 9 parts melted agar at 40 C. and under, thus remaining active and 

 suspended, showed swellings in the form of dried plates 0.1 to 0.15 mm. 

 in thickness at 16 C., as shown in table 4. 



TABLE 4. 



p. ct. 



Water 1,792 



Citric acid, 0. 01 N 333 



Sodium hydroxid, 0.01 M 386 



The high swelling in water, the increased imbibition in acid, and the 

 equalization of the acid and alkali effects are characteristic of agar- 

 protein mixtures and are in contrast with the reactions of the following 

 test, in which the albumin was coagulated. As a result it no longer 

 intermeshed with the agar in the gel, but aggregated as small particles, 

 indifferent to the presence or proportion of water. A mixture of agar 

 95 parts and milk albumin 5 parts was prepared, in which the last- 

 named substance dissolved in water was added to the melted agar at 

 a temperature near 100 C., at which coagulation followed. The mix- 

 ture, however, when poured on a glass plate, dried into a film about 

 0.13 mm. in thickness, wilich had a leathery texture and was trans- 

 parent and appeared homogeneous. Sections swelled under the auxo- 

 graph at 16 C. increased 261.5 per cent in distilled water, 346.2 per 

 cent in hundredth-molar sodium hydroxid, and but 191.2 per cent in 

 hundredth-normal citric acid. The proportions are in general accord 

 with those obtained by swelling of agar alone, suggesting that the 

 neutralized or coagulated albumen has no effect on the imbibition 

 capacity of agar, in which it may be incorporated. 



