1920] 



MACDOUGAL 6* SPOEIIR—AGAR 



269 



In table II are given the results of some earlier experiments 

 made with plates prepared from the "bacto-agar" of the Digestive 

 Ferments Company. The swellings in the solutions of the corre- 



TABLE I 



Swelling of agar plates o.ii mm. in thickness at i5°C. 

 in 0.01 normal solutions of amino acids, calculated 

 on basis of swelling in water taken as ioo; solu- 

 tions renewed every 24 hours; swelling of agar 

 plates in water 2000 per cent 



Water 



Glycocoll 



Alanin 



Phenylalanin 



IOO 



165 



151 



l6l 



V 



Jfc Vi^ * 



sponding organic acids are also given for comparison. Thus it 

 can be seen that in acetic acid agar exhibits a much lower swelling 

 than in the a-amino compound, glycocoll. The same relation is 

 maintained with the other acids. 



TABLE II 



Swelling of agar plates 0.10-0.23 mm. in thickness at i6-i7°C. in solutions 

 of amino acids and corresponding organic acids, calculated on basis of 

 swelling in water taken as ioo j dried plates swelled 25 70 per cent in 

 water; duration of swelling 20~6o hours, during which time solutions 

 were not renewed 



Normal 

 concentration 



O.OI. . . 



. 002 . . 

 . 0004 . 

 . 00008 



Water 



100 



IOO 

 IOO 

 IOO 



Glycocoll 



"5 

 123 



103 



Acetic 

 acid 



Alanin 



Propionic 

 acid 



61 



59 



76 



102 



94 

 108 



51 



70 



Aspara 

 gine 



91 



94 

 106 



126 



Aspartic 

 acid 



49 

 58 

 69 

 81 



Succinic 

 acid 



49 

 62 



68 



98 





It is worthy of note that agar behaves quite differently from 

 gelatine in relation to acids and bases, and that this also applies to 

 the amino acids, as shown in table HI. Agar is a carbohydrate, 

 and as such exhibits some of the properties of an exceedingly weak 

 acid. Dr. McGee of this laboratory determined by means of the 

 indicator method 2 that in 0.75 per cent solution the purified agar 

 shows a hydrogen ion concentration expressed by P H = 6. 5. 



2 Duggar, B. M., The use of the colorin ter in the indicator method of H ion 

 determination with biological fluids. Ann. Mo. Bot. Gard. 6:61-70. 19 18. 



, The micro-colorimeter in the indicator method of hydrogen ion determi- 

 nation. I bid. j 6:179-181. 1919. 



