of Edinburgh, Session 1871-72. 645 
been observed tending towards the synthesis of this interesting 
substance. 
The most important fact ascertained with regard to the chemical 
relation of cystine in memoir referred to was the production of 
pyruvic acid, when it was treated with nitrous acid. In this re- 
action the amido residue was not alone eliminated, the sulphur also 
separating as sulphuric acid, however carefully the experiment was 
performed. The fear of allowing the action to proceed too far, on 
the necessarily small quantity of substance operated upon, pre- 
vented us from purifying the product thoroughly, and, consequently, 
the analysis differed slightly from that of pure pyruvic acid. We 
had no hesitation in saying, however, the acid agreed better with 
the chemical characters of the syrupy modification of pyruvic acid 
than with that of Wischelhaus’s carbacet oxylic acid, that we had 
anticipated would be produced, and that in all probability cystine 
would be found to be an amido-sulpho pyruvic. 
If cystine is directly related to pyruvic acid, it must contain five 
instead of seven hydrogen atoms (and this supposition agrees well 
with the published analysis). The formula of the compound will 
then be, C 3 H 5 N0 2 S. On this supposition, we may derive from 
pyruvic acid at least five isomers, that will all have the general 
characters of cystine, although there are many other possible con- 
stitutional formulas. 
Pyruvic Acid. 
1. 
2. 
oh 3 
ch 2 nh 2 
ch 2 nh ; 
CO 
CO 
CO 
CO. OH 
CO.SH 
CSOH 
3. 
4. 
5. 
CH 2 (NH 2 ) 
CH 
CHS 
cs 
CO 
C N ^ 
CO. OH 
CO. OH 
CO. OH 
Of the five possible cystines formulated, it is impossible to select 
that of the natural substance, because of our ignorance of the inter- 
mediate sulpho-acid. All attempts to replace the amido group 
alone by the action of nitrous acid having failed, I have tried several 
experiments, with the object of replacing the sulphur alone, with 
the small quantity of cystine at my disposal. 
If cystine is one of the above five substances, the replacement 
VOL. vii. 4 a 
