of Edinburgh , Session 1877 - 78 . 
541 
in a definite compound, but that there is a fraction of it, so to speak, 
to spare, we should only find Prout’s law to hold good if we could 
analyse only one molecule of any compound, but, as in any analysis 
we can make, there must be many molecules, such atom of the 
molecules having a fraction of its affinity for the other to spare, 
these fractions would unite and hold in combination an extra 
number of the other atoms, not so firmly, perhaps, but still firmly 
enough to make the whole appear a definite compound on analysis, 
and this would affect the calculation for atomic weight. Thus, 
suppose two atoms of Cl = 71 combine with one atom of Ca = 40 
and still have part of affinity to spare, then 200 atoms of Cl 
would take up 101 atoms of Ca, and from this analysis we should 
make the atomic weight of Ca not 40 but 40 ’4. 
4th. If chemical combination and solution are due to the same 
force, then solution will loosen the combination by spreading the 
affinity, and possibly there may be a re-arrangement of the soluble 
and solvent analogous to what is known to take place when two 
salts are mixed having different acids and bases. Hence the power- 
ful effects of solution in promoting chemical reaction and electric 
conductivity. 
5th. A point of practical importance may be noted regarding 
analysis. Many substances are added indefinitely to solution to 
render insoluble some body held in solution, which quantity is to be 
estimated. How, if the way in which one substance renders another 
insoluble is by combination with the solvent, it is quite clear that if 
either too much or too little be added to the solvent, an error may 
be made in the analysis, as the whole of the precipitated body may 
not be thrown down. 
6th. A further investigation of this subject may throw some 
light on the manner in which the solubility of a solid in a liquid is 
related to the chemical composition of the two. 
5. Hote on the Surface of a Body in terms of a 
Volume-Integral. By Professor Tait. 
In § 25 of my paper on Green’s and other Allied Theorems 
(“Trans. R. S. E.” 1869-70) I gave the following relation between a 
VOL. ix. 4 o 
