2o 4 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
phosphorus determination in the residue obtained by evaporating off the ether and 
acetone from the mother liquor. But the lecithin thrown out by the first precipitation 
as shown by a phosphorus determination is impure, and must be purified by re»-solu- 
tion in a small volume of ether and reprecipitation by acetone, the loss of lecithin in 
the process of reprecipitation is negligible, and determination of the phosphorus in 
the reprecipitated lecithin shows that it is pure enough to allow of determination of 
the lecithin by direct weighing as such. 
The method of isolation accordingly gives a higher yield than former methods, 
on account of the more complete extraction and of very small loss in the subsequent 
precipitation, and the amount of labour involved is much decreased. 
Experiment i. The yolks of six eggs were separated and weighed; weight 108-82 
grammes. The yolks were well mixed with 300 c.c. of absolute alcohol, allowed to stand 
tor some hours, the solution decanted, and the rest of the alcohol pressed off as 
completely as possible through linen cloth. The treatment was repeated, with a 
second and a third quantity of 300 c.c. of alcohol. The three alcoholic extracts were 
united and the alcohol distilled off under diminished pressure, until a thick syrupy 
mass was obtained. This was twice dissolved in as little ether as possible, precipitated 
with acetone, then separated and dried from ether and acetone, in a steam bath to a 
constant weight of 10-38 grammes, percentage of lecithin, 9-5 of the total weight of 
fresh egg yolk. 
Experiment 2. Carried out similarly. Weight of egg yolk = 1 20- 1 8 grammes ; 
yield of lecithin, 11 -02; percentage of lecithin, 9*1. 
In order to determine whether the lecithin is completely precipitated by the 
acetone from ethereal solution, the mixture of ether and acetone separated at each 
precipitation was evaporated down. The residue was extracted with alcohol in the 
cold, thus leaving behind most of the cholestearin. The process of extraction with 
alcohol was several Times repeated, the extracts mixed and evaporated down. A very 
small amount of a brown oily fluid was obtained, which was treated by baryta water 
and filtered. The filtrate was treated with dilute sulphuric acid and the barium 
sulphate filtered off. The free glycero-phosphoric acid was, after evaporation to dry- 
ness, ignited with fusion mixture, and phosphoric acid estimated as magnesium pyro- 
phosphate. The weight of Mg 2 P 2 0 7 obtained was only 0*0184 gramme, showing that 
practically none of the lecithin had escaped precipitation by the acetone. The barium 
soaps were also investigated by breaking up with dilute sulphuric acid, formation of 
lead soaps, separation of lead soaps, and determination of amounts of fatty acids, and 
only inappreciable traces were found. .: 
The purity of the yield of lecithin obtained was investigated by making- 
determinations of the phosphorus, by a procedure which, when we first used it, we 
thought to be novel, but afterwards we discovered that it was similar to that described 
by Neumann 1 for determination of phosphorus in nucleo-proteid, and later by 
I. Archie, f. [Attar, w.] Physiologic (1900), S. 159. 
