Pottok—A New Thermo-Chemical Notation. 501 
any other equation similarly stated to eliminate common terms of 
the equations, and evolve the value of any unknown term; thus in 
dilute solution, we have 
E[Zn + 2HOCl=Zn0l, + 2H] = 342K°, 
and 
E[ZnO + 2HCl = ZnCl, + H,0] = 17-8K°. 
Expand these in true thermal equations by lifting the brackets, 
affixing the energy sign to every quantity within them, placing a 
_ negative sign before each substance in its initial condition, a posi- 
tive sign before each in its final condition, and removing the sign 
of equality within the brackets, and we have 
—~€Zm —- &HOCl+ ZnCl, + €H, = 34:2K°, 
— ZnO — €2HCl + EZnCl, + €H.0 = 17°8K°. 
Subtracting, transposing, and omitting zero quantities, we have 
at once 
EZnO = 34:2 —-17°8 + €H.0, 
= 34°2 — 17-8 + 69, 
= 85°4K°. 
Possibly in a simple case like the above there is no necessity to 
go through this form of demonstration, or even use the energy 
signs, but the process of reasoning would be precisely that actually 
expressed above, and, if we take a complicated case, we find that 
the clearness of expression is a very real help in calculation, and 
avoids risk of confusion. If elements are capable of existing in 
allotropic forms, the best known, or most defined, is taken as the 
Standard of reference and termed the a state, and all others 
indicated by Greek letters added at the right-hand upper corner 
of the symbol S¢, Sy, S°. 
We have now a full and clear expression of every quantity 
likely to occur in thermal equations, and for use, all that is 
necessary is to tabulate the heat of formation of all ordinary 
compounds in their normal condition at 15° C., from their elements 
in their normal condition at a like temperature, and also the mole- 
cular specific heats in the solid, liquid, and gaseous states, the 
SCIENT. PROC. R.D.S., VOL. IX., PART Iv. 20 
