20 
On Residual Phenomena . 
January, 
II. ON RESIDUAL PHENOMENA. 
C* 
T is a well-known — indeed almost a trite — faCt that the 
residues of manufacturing operations have proved a 
most fruitful source of novel and interesting bodies. If 
we wish to deteCt an element hitherto unknown we search 
for it among the refuse of metallurgical or chemical pro- 
cesses, in flue-dust, in furnace-soots, in slags, in burnt 
pyrites, in the mud of vitriol chambers, or in mother-liquors 
which have deposited their crop of crystals. If we are in 
quest of some new or valuable organic compound we operate 
upon the residue of the gas-works, in which Liebig prophet- 
ically declared that we might find whatever we wished if we 
would only seek intelligently ; upon wood-tar, or upon natural 
products which have most probably undergone a process of 
destructive distillation in the recesses of the earth. In this 
manner we have obtained, on the one hand, bromine, iodine, 
selenium, caesium, thallium, &c. ; and on the other, phenol, 
rosanilin, artificial alizarin, and other the like marvels of 
modern chemistry. Nay, we sometimes elicit important 
products even from the residues of a residue. The “tailings” 
left from the manufacture of magenta are themselves a source 
of other colouring matters. 
But we are not about to enlarge on the utilisation of waste 
products. That fecundity in novelties which seems to cha- 
racterise refuse and residues is an apt type or illustration of 
the importance of “ residual phenomena ” as a source of un- 
suspected truths; and it is to such, as a sphere for discovery, 
that we wish to draw the attention of our readers. 
What are “ residual phenomena ?” We will suppose a 
man of science setting to work to “verify” some theory — 
that is, to examine whether and in how far it accords with 
the faCts it is intended to harmonise and to explain. There 
are here three cases possible : — In the first place, the theory 
in question may agree exactly and completely with the faCts, 
leaving merely such minute errors as are plainly due to the 
shortcomings of experiment and observation. We may take, 
as an instance in point, the law of chemical combination in 
definite proportions. If we examine whether this is a cor- 
rect statement of faCts, we find it confirmed the more com- 
pletely the more precise and accurate are our experiments. 
Secondly, the theory may distinctly fail to account for the 
phenomena before us, and may prove utterly contradictory 
