231 
of Edinburgh, Session 1880-81. 
I have lately tried iodide of zinc in place of iodide of potassium. 
The electromotive force is the same, and in other respects it does as 
well, iodine being very soluble in it. By using it, the formation of 
new salts in the cell is avoided. 
The advantages of this cell are that it gives a fairly constant 
electromotive force, and can, if the zinc is removed, be left standing 
unused for any length of time. This is, of course, impossible in the 
case of the Daniell. 
3. Note on Chemical Affinity and Atomicity. 
By William Durham. 
( Abstract .) 
The theory of “Valency” or “Atomicity,” while explaining 
satisfactorily many chemical phenomena, still leaves unexplained 
many facts, such, for instance, as the varying atomicities of several 
elements, the composition of double salts, water of crystallisation, 
&c. This arises from assuming that chemical affinity acts in an 
atomic indivisible manner, which is not warranted by the facts. 
If we take, for instance, nitrogen in the compound, NH 3 and NH 4 Cl, 
it acts in the one case as a triad, while in the other it is said to be 
a pentad. Now, in the case of the NIi 4 Cl in this view, we have the 
chlorine represented as directing all its affinity to the nitrogen, for 
which it usually has such a feeble affinity, while it has no action 
on the hydrogen, for which its affinity is usually so intense. 
iNow, if we get rid of the idea of the atomic action of affinity, we 
may represent the chlorine dividing its action among all the four 
atoms of hydrogen, giving on the average \ to each; and the nitro- 
gen, in the same manner, giving f to each : and thus, the whole 
molecule is bound together. 
2 G 
VOL. XI. 
