204 Proceedings of the Royal Society 
treated with tin or zinc and hydrochloric acid, might be used as a 
test for the substance, care being previously taken to separate any 
sulphide which might exist. 
Action of Nitrous Acid on Cystine. 
Cystine was placed in water and a stream of nitrous acid gas 
passed through it. No action took place until the water was 
heated ; it then commenced and proceeded briskly, with abundant 
effervescence, until the whole of the substance was dissolved. 
The clear solution contained a large quantity of sulphuric acid, 
but not a trace of oxalic acid. When boiled with an ammoniacal 
solution of nitrate of silver, considerable reduction took place, a 
beautiful mirror of silver being deposited on the glass. The fluid 
was again subjected to the action of nitrous acid ; still no oxalic 
acid could be found, and the reduction of an ammoniacal solution 
of oxide of silver continued. A portion of the fluid was treated 
with carbonate of barium and heated; the clear filtrate had an 
alkaline reaction, and was abundantly precipitated by nitrate of 
silver and acetate of lead. The remainder of the fluid, after the 
treatment with BaC0 3 , was treated with solution of nitrate of silver. 
An abundant canary-yellow precipitate was formed. This was 
suspended in water and decomposed with H 2 S ; the filtrate was 
evaporated to dryness, and presented the appearance of a sticky 
solid. It was soluble in water. The aqueous solution was evapo- 
rated and treated with absolute ether, which dissolved the greater 
part. The ethereal solution left on evaporation an acid fluid. 
This was dissolved in water, neutralised with ammonia, and pre- 
cipitated with solution of nitrate of silver. The yellow precipitate 
obtained was amorphous ; it was dried in vacuo. Two specimens of 
the silver salt prepared at different times were analysed by us. 
The following are the results of two analyses 
Silver, 
56-9 
57-5 
Carbon, . 
19-43 
21-32 
Hydrogen, 
5-29 
4-64 
In considering the discrepancies of these analyses, it must be 
borne in mind that we were operating in excessively small quan- 
tities of a substance prepared at different times by complicated 
processes. 
