86 
Proceedings of Royal Society of Edinburgh. [sess. 
action which it may be desirable to distinguish, without affecting 
the general character of the symbol. 
I would therefore suggest the adoption of some definite scheme 
similar to that indicated below. 
(1) The use of ordinary arrows should he restricted to the 
indication of chemical actions, when it is desired to follow only 
some of the substances involved in the change, without writing 
complete equations, in the manner referred to above as being 
frequently used in organic chemistry. Thus — 
c 6 h 4 < 
,ch 2 
CHo 
c 6 h 4 < 
•CH, 
'CH- 
>g 6 h 4 ^. 
u / 
CO, 
C 6 H 4 , 
'CO 
>C 6 H 4 
{Richter. ) 
(2) The ordinary sign of equality should be used only in 
equations which are required merely for purposes of calculation, 
etc., to represent equalities in quantities of matter (or of matter and 
energy, as in thermo-chemical equations), irrespective of whether 
the substances represented on one side of the equation change 
directly into those on the other side or not. Thus, the equation — 
KCl + 3H 2 0 = KClOg + 3H 2 
does not represent a chemical change capable of being directly 
carried out, but it might be employed for calculations concerning 
the electrolytic preparation of potassium chlorate. 
Similarly with tliermo-chemical equations — 
2K + 2S + 80 = K 2 S 2 0 8 + 454*5 Cal. 
(3) When it is desired to write a complete chemical equation, 
not only representing the quantities of matter involved, but also 
indicating clearly that chemical change can take place directly in 
accordance with the equation, then the sign of equality should be 
composed of singly barbed arrows as illustrated below, modifications 
being introduced for the principal varieties of chemical action 
which it is desirable to differentiate. 
(a) For irreversible actions, the sign thus : — 
KC10 4 ==^IvC1 + 20 2 ; 
4KN0 3 + 5C == 2K 2 C0 3 + 3C0 2 + 2lS r 2 . 
