130 



BOTANICAL GAZETTE 



[august 



of the quality usually employed in the serum industry* the clear 

 solution was slowly poured in a fine stream or spray into 10 

 times its volume of neutral acetone. The agar was precipitated 

 in the form of fine shreds. It was subsequently extracted with 

 hot absolute acetone, absolute alcohol, and absolute ether. The 

 final product was ground to a granular powder in a porcelain ball- 

 mill with porcelain balls. The resulting preparation contains 

 only a trace of nitrogen and a trace of ash. 4 



Samples of this agar made up as a 2 . 5 per cent solution with 

 distilled water had a light brown tinge, dissolving completely 

 within an hour at about ioo° C. It was found that the material 

 made up as a o. 75 per cent solution, when poured into a test-tube, 

 formed a " slant " which kept in place when the tube was set in an 

 upright position at 15 C. for 2 weeks. Layers 1 cm. deep in small 

 flasks retained their form when the flasks were inverted in some 

 instances. Some water was separated, gathering on the upper part 

 of the tube or flask, and the appearance of same on the surface of 

 the agar suggested syneresis. Tests of this agar by the colorimetric 

 process of Duggar gave it a hydrogen ion concentration denoted 



byP 



H 



6.5- 



The mucilage of Opuntia, cherry gum, mesquite gum, Acacia, 

 and tragacanth gum was extracted or dissolved in water (nearly 

 always showing a solid residue), precipitated with alcohol, filtered, 

 and dried in a desiccator. These substances go into solution at 

 lower temperatures than agar, and differ from it in many important 

 features, as may be seen in the table of swelling reactions. 



Special preparations were also made of salt-free water-soluble 

 albumins from oats, wheat, the common bean, soy bean, and 

 castor bean, as well as of lipins and amino compounds, by methods 

 commonly used and need not be described here. The gelatine 

 used was the " bacto-gelatine " now available in quantity. 



The measurement of the swelling of these colloids must take 

 into account the structural features resulting from dehydration. 

 Sections or plates of agar, for example, tend to return to the form 

 and dimensions of the layer of watery gel from which they were 

 produced. This is not true of gelatine, as will be described later, 



4 The description of this process was furnished by Dr. Isaac Harris. 





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