216 
Proceedings of the Royal Society of Edinburgh. [Sess. 
For tartrelic acid, formed by loss of water from tartaric acid, Couper 
gives the following formula : — 
Tartrelic Acid. 
a 
0 
1 
o 
C "" 
••• o- -OH 
C "" 
OH 
— o 2 
-o 
( O 2 
!\ 
>0 2 
C 
H 
C\ 
H 
.O 2 
0 
/ / 
Ik 
c/ 
H 
C--' 
H 
) 02 
C- 
— O 2 
... 0 
( 0— OH 
• 0 OH” 
C-. 
OH 
All these compounds belong, according to Couper, to the type ?iCM 4 . 
At the close of his paper in the Philosophical Magazine , Couper expresses 
his intention to discuss, in a later paper, the second type (nCM 4 — mM 2 ) and 
to apply his principles to the cyanogen compounds. His paper in the 
Annales de chimie et de physique closes with formulae for hydrocyanic 
acid, cyanic acid, and cyanuric acid : — 
H ) 
Hydrocyanic acid > Az 
c I 
HO— 0 ) HO J 
Cyanic acid > Az or, with O = 16, >Az 
C I C 
H— 0—0— Az— 0— Az— 0— OH 
Cyanuric acid 
C— A: 
( c 
or, with 0 = 16, 
I 0— OH 
HO— Az— C— Az— OH 
I I 
C— Az— C 
OH 
Thus in cyanuric acid Couper assumed that the three carbon atoms and 
the three nitrogen atoms are combined alternately in ring form. 
By his method of writing formulae Couper took an important step 
forward. His formulae, in fact, enabled him, in a simple and clear way, to 
express his views as to the mutual combination of the atoms in the 
