ROTARY PROPERTIES OF SOME PROTEIDS. 125 



were more or less colored. On account of their opacity, only 

 dilute solutions containing about one or two per cent of 

 proteid matter could be used, so that the angles measured had 

 to be multiplied by a large reduction factor to find the rotation 

 for the standard length and density. The errors of observation 

 were thus multiplied many times. For this reason the results 

 were not sufficiently exact, nor were the variations sufficiently 

 great, to determine the manner in which the rotary power 

 varied either with the temperature or the concentration of the 

 solutions. The maximum range in concentration was from 

 0.50 per cent of proteid to about 2.50 per cent, and in tem- 

 perature from 20 C. (below which precipitation was likely 

 to occur) to 70 C., above which coagulation soon took place. 

 The specific rotation, as will be seen later, appeared to decrease 

 with the percentage of proteid in solution. The variation 

 with the temperature was apparently slight, and it seemed 

 useless to try to determine it exactly. In fact, the variation 

 of the specific rotation with the solvent was the only factor 

 that could be determined with any exactness. 



Preparation of Solutions. 



Salt Solutions. The salt solutions used as solvents were 

 all prepared hi the same manner. A given quantity of the 

 chemically pure salt, dried in a desiccator, was weighed out, 

 dissolved in distilled water, and made up with distilled water 

 to the required volume. The solution was then filtered. The 

 residue of salt, when dried at 110 C., was next carefully 

 determined, several portions of the solution of 20 or 30 cubic 

 centimeters each being dried to constant weight at 110 C., 

 and the results, which never differed by more than 2 or 3 

 milligrams, averaged. None of the vegetable globulins ex- 

 perimented upon being completely soluble in these solutions, 

 as concentrated a solution of globulin as possible was made 

 and then filtered clear of the undissolved proteid. The per- 

 centage of proteid matter in solution was afterward determined 

 by drying down 20 cubic centimeters or so to constant weight 

 at 110 C., and subtracting from the residue the weight of the 



