438 BANANA GEL 



Hydrogen ion concentrations were determined by use of indicators 

 and suitable standard solutions. 



The various salts which were used were either purified, or the im- 

 purities determined, since in the work to be described, minute amounts 

 of certain substances were found to produce striking phenomena. 



RestiUs. 



I. Dialysis of Banana Extract against Tap Water and against Distilled 



Water. 



The results obtained in a large number of experiments in the dialy- 

 sis of banana extracts may be summarized briefly in the following 

 paragraphs. Essentially the same results were obtained whether the 

 extracts were prepared with water or with molar sodium chloride 

 solution. As a rule, in the preparations 1 part by weight of liquid 

 was used with 4 parts of banana pulp. 



1. Dialysis of extract against tap water. 



{a) Gel formation began in 24 to 48 hours. With small volumes 

 more rapid changes including formation of gel occurred than with 

 large volumes. 



(b) Volume increased about 100 per cent. Most of the increase 

 occurred before gel formation began. Changing bags during the 

 dialysis had no effect. 



(c) After two or three days dialysis the liquid still had a pH of 

 5.0 to 5.5. 



(d) Gel formation began on the inner walls of the bags. 



(e) Continued dialysis caused the dark colored gel to flake or separate 

 out, leaving the liquid clear and colorless. As the flakes were formed, 

 the pH of the supernatant liquid was 5.0 to 5.5 at first, but after 4 to 

 6 days became that of the tap water (pH 7.0). 



2. Dialysis of extract against distilled water. 



(a) No gel formation at any time. 



(b) Continued increase in volume. In one experiment an increase 

 from 25 cc. to 178 cc. in 4 days was observed. 



(c) After dialysis pH of liquid unchanged (about 5.0). 



(d) Liquid became cloudy and light colored (perhaps because of 

 dilution) . 



