226 Prof. A. B. Macallum. On the Nature of the [Mar. 3, 
water, and this was continued for two weeks or more, the water being 
frequently removed by decantation and as often replaced by fresh fluid. 
Portions of the globulin thus undergoing extraction were from day to day 
dissolved in dilute solutions of ammonium sulphate, free from chlorides, and, 
after the addition of some of the silver reagent, placed in the sunlight for 
days to determine how far the purification had advanced. 
It is important not only in the case of globulins, but also in that of all 
albumins to have them in solution when the reagent is to be added. In the 
precipitate which silver nitrate produces, the latter is intimately mixed 
throughout with the proteid. This is an advantage,for when the reagentis added 
to the undissolved proteid it penetrates very slowly, and, consequently, the 
superficial reaction, if any occurs, may be so slight as to escape observation. 
The egg albumins and the serwm albumins and globulins which had undergone 
the indicated number of precipitations as well as the egg globulins which had been 
extracted for over a fortnight with distilled water, did not yield any reaction 
whatever with the silver nitrate reagent,* even after weeks of exposure to bright 
sunlight, although the original unpurified material in every case gave an intense 
reduction effect. 
The purification of gelatin is more easily attained. For this purpose one 
dissolves the gelatin in water at 45° C. and adding to the solution, while it is 
maintained at that temperature, anhydrous sodium sulphate till the mixture 
is saturated. Stirred with a glass rod, the greater part of the gelatin collects 
on it and it can be thus liftéd out of the solution and transferred to, and 
dissolved in, a fresh quantity of distilled water at 45° C., to which also 
anhydrous sodium sulphate is added till saturation obtains. The precipitated 
gelatin is once more in the same way transferred to a fresh quantity of 
distilled water at 45° C. The process of precipitation and solution was 
repeated many times, but each stage required only a few minutes, and 
consequently as many as twelve precipitations and as many solutions of the 
gelatin were obtained in two and a half hours. The purified product was 
found to set firmly and was in every case very clear and transparent. 
The gelatin of commerce gives an intense reaction with the silver reagent in 
sunlight, but the gelatin of the ninth precipitation gave not the slightest reaction 
with silver nitrate solution after two weeks in sunlight, not even producing a 
precipitate or an opalescence. It mattered not from what crude preparation of 
commerce the purified product was obtained, the result was in every case the same. 
That the compound or compounds in crude gelatin which react with silver 
nitrate in the sunlight are chlorides only, was demonstrated satisfactorily. 
* When a neutral, instead of the acid, solution of nitrate of silver was used the result 
was the same. This is true also of purified gelatin similarly treated. 
