202 Proceedings of the Royal Society 
substance is left which is precipitable by nitrate of silver, mercuric 
chloride, as well as by acetate of lead. 
The cystine used in our experiments was obtained from two 
portions of calculi, one of which was furnished to us by Professor 
Maclagan, the other by the Eoyal College of Surgeons of Edin- 
burgh. The cystine was obtained by treating the pounded calculi 
with strong liquor ammoniee, which dissolved the greater part, and 
allowing the solution to evaporate at a very gentle heat. The 
cystine which separated was then again dissolved in ammonia and 
recrystallised. 
Preparation of Hydrochlorate of Cystine. 
One gramme of cystine was dissolved in boiling hydrochloric acid; 
on cooling beautiful needle-shaped crystals separated, which were 
very soluble in water. When thoroughly dried in vacuo over quick- 
lime the crystals were found not to be readily soluble in water. 0*05 
grm. of crystalline hydrochlorate of cystine yielded 0*0452 grm. of 
AgCl, corresponding to 22*2 per cent, of HC1 (Calcd. 22*5). 
Action of Nitrate of Silver on Cystine. 
Cystine was dissolved in strong solution of ammonia, and to the 
solution was added a solution of silver nitrate in ammonia. No 
precipitate-occurred, nor did the solution darken in the cold. When 
slightly acidified with nitric acid, a canary-yellow precipitate was 
thrown down, which was collected and dried in vacuo. The fil- 
trate blackened when heated, and on filtering off the black preci- 
pitate a clear colourless solution was obtained, which was not 
further blackened when boiled with ammoniacal solution of oxide 
of silver. 
On analysis the substance precipitated proved to be a compound 
of cystine with nitrate of silver. 
In a subsequent experiment an ammoniacal solution of cystine 
was boiled with an ammoniacal solution of nitrate of silver. A 
black precipitate fell which consisted of sulphide of silver. The 
filtrate from the precipitate of sulphide of silver was subsequently 
treated with solution of chloride of ammonium to separate the 
excess of silver. The solution was found not to be precipitated by 
hydrochloric acid and chloride of barium, nor by sulphate of cal- 
