

1905.| Silver Reaction in Anamal and Vegetable Tissues. 225 
in a large quantity of distilled water with the consequent separation of 
globulin, from which, on sedimentation, the supernatant solution was 
removed by decantation, and from this the albumins were precipitated on 
the addition of enough ammonium sulphate to saturate the solution. Tested 
with silver nitrate solution,* a precipitate was obtained which gave a deep 
reaction in light in less than 20 minutes. The precipitate obtained with 
the sulphate was dissolved and again precipitated in the same way, the 
precipitate again dissolved and re-precipitated, this process being repeated 
in one case 9 times, in another 14 times, and in a third 11 times before 
the desired degree of purity was attained. It was subsequently found that 
if in each case when the proteid precipitate is re-dissolved the solution be 
allowed to stand for some time, for example, 10 to 12 hours, before the 
subsequent precipitation is brought about, the standard of purity may be 
reached before the eighth precipitation occurs. It would seem asif the chlorides 
are in intimate union with the particles of the colloid, and that when 
precipitation immediately follows solution, salts are largely retained in the 
interior of the colloid molecule groups, but when the latter are acted on for 
hours by water free from chlorides, the latter pass into the water, with the 
result that when precipitation occurs much less of the chlorides is carried 
down. The effect of this may be seen when the filtrates are tested for 
chlorides. When the precipitations followed each other at very short 
intervals the chloride reactions of the filtrates were slight, but when the 
precipitated proteid was dissolved and allowed to remain in solution in each 
case some hours before being again precipitated, the filtrate gave a much deeper 
reaction and of the typically chloride character. When the silver pre- 
cipitate trom the earlier filtrates was allowed to settle, the supernatant fluid 
decanted, the precipitate then washed several times in water free from 
haloids, finally collected in a porcelain crucible, dried at 120° C. for three 
to five hours, weighed, then fused and once more weighed, there was found 
to be practically no loss of weight, this fact showing that organic compounds 
do not enter into the composition of the silver precipitate. 
The albuming and globulins of serum were not separated from each other, 
it having been found easier to carry out one series of precipitations for both 
classes of proteids in order to free them from chlorides. As a rule, it 
required more precipitations to purify the proteids of serum than was the 
case with egg albumins. What the reason for this difference is is not clear. 
The globulins which separated when egg “albumen” was dissolved in 
distilled water were freed from chlorides only by extraction with distilled 
* The solution of silver nitrate used was exactly decinormal, and it contained 25 c.c. of 
nitric acid (60 per cent. strength) to the litre. 
