644 Proceedings of the Royal Society 
The circumstance that these minerals are thus able to arrest and 
retain organic substances, was so suggestive in relation to the origin 
and physical characters of coal, that I was led to make this property 
of coal a special object of study, and as the course the investigation 
took rendered it very desirable to test the solubility of coal, this 
subject was also carefully examined by me, and as the results of 
these investigations appeared to have some degree of interest, I 
submitted them to the attention of Dr Hector, and with his advice 
and assistance, I now endeavour to state them in a concise form. 
In communicating a detailed account of the various experiments 
employed in these investigations, the results arrived at, and the 
inferences they appear to justify, I have divided the whole subject 
into three parts, the first of which is — 
[ I. On Absorption as a Property of Lignite^ Coal, and Graphite, 
in common with Charcoal. 
a. Absorption of Acids. 
h. Absorption of Basic Substances. 
c. Absorption of certain neutral Organic Substances. 
d. Absorption of certain decomposed Organic Substances. 
e. Combining quantities of bodies probably observed in their 
absorption. 
/. Substitution effected in certain cases. 
Summary. 
Sufficient has been adduced by the experiments conducted by me 
to prove the existence of an absorptive power in lignite, coal, or 
graphite for many organic and inorganic substances. There is no 
doubt the list of such might have been almost indefinitely extended 
if it had been necessary ; but I desired rather to establish the general 
fact of absorption, and to ascertain the principles which regulate it. 
So far as these results enable us to judge, it would appear that 
generally when any substance has but a feeble solubility in water, 
or when it has its affinities for this liquid lowered or overpowered 
by other agents, such substance will be withdrawn from solution 
by contact with any of the foregoing bodies, lignite, coal, graphite, 
or charcoal. Those substances which possess basic or acid pro- 
perties especially, are subject to absorption, providing such pro- 
