1901 — 2.] Dr Marshall on Modifications of Sign of Equality . 85 
Suggested Modifications of the Sign of Equality for Use 
in Chemical Notation. By Hugh Marshall, D.Sc. 
(Read January 6, 1902.) 
During recent years the great attention which has been paid to 
the study of reversible chemical actions has led to a desire for 
some method of specially indicating in the equations the reversi- 
bility of these actions. This is generally done by replacing the 
sign of equality by two parallel and oppositely-directed arrows; 
the use of this symbol in such cases does not only imply the 
reversibility of the action, it has the same value as the sign of 
equality in an ordinary equation. Unfortunately, there are several 
drawbacks to the use of this symbol : as generally printed, it is 
rather clumsy in appearance ; the arrows, being widely separated, 
do not suggest the sign of equality which they replace ; and further, 
in conjunction with formulse, arrows are frequently employed, 
especially in organic chemistry, to indicate merely the stages and 
methods by which a substance can be produced from some other 
substance as starting-point. In such cases, as no attention is paid 
to the bye products, there is nothing of the nature of an equation 
involved. Numerous examples are to be seen in Richter’s 
Organische Chemie , and amongst them cases in which oppositely- 
directed arrows, resembling the symbol employed for the equations 
for reversible actions, are used to indicate that each of the two 
substances concerned may serve as starting point for the prepara- 
tion of the other, without involving equality on the two sides of the 
symbols. Such a double use of a symbol is highly objectionable. 
These drawbacks might be avoided by employing a modified 
sign of equality composed of a pair of split or singly barbed arrows, 
the barbs being only on the outer sides of the symbol. This 
symbol can be made neat and comparatively small ; it suggests 
the ordinary sign of equality, and also the idea of direction given 
by ordinary arrows. It is also possible to modify the symbol in 
such a way as to indicate clearly the different varieties of chemical 
