202 Mr. H. Medlock on the Reciprocal Action of Metals 
rock would very frequently open alternately upwards and down- 
wards*, 
Time will not allow of my dwelling now upon other points 
explanatory of geological problems, which are afforded by the 
theory of an expansive subterranean crystalline mass preserved 
by external pressure in a more or less solid condition beneath 
the crust of the globe, but always ready to expand and perhaps 
to intumesce upwards on any relaxation occurring in the over- 
lying pressure. But I suggest it now, as I did thirty years 
since, as the solution most reconcileable with the known facts of 
the structure and relative position of the great elevated rock- 
formations of the globe, and as a theory founded, not upon mere 
guess-work, but on careful and extended observation of the phe- 
nomena of both active and extinct volcanoes, and the disposition 
of volcanic products of all ages. 
XXIV. On the Reciprocal Action of Metals and the Constituents 
of Well- and River-waters. By Henry Meptiock, Esq. 
I. The Action of Lead. 
fi pee solvent action of water on lead is a subject of special 
importance, and one that has attracted the attention of 
many of the most able chemists of the day. 
To determine by analysis whether or not a particular water 
will become impregnated with lead when placed in contact with 
that metal, is a question of high scientific interest, and one affect- 
ing the health of every civilized community. This question has 
occupied my attention for several years, and with the view of 
elucidating it still further I have undertaken a series of experi- 
ments, the result of which will be communicated in the following 
ages. 
3 On referring to the opinions of the distinguished chemists 
who have investigated this subject, many discrepancies are ob- 
served. Some consider the action of water on lead to be due to 
the softness of the water, and absence of any considerable quan- 
tity of earthy salts; some attribute it to free carbonic acid ; 
others to oxygen dissolved in the water ; whilst some conjecture 
it to be due to the presence of nitric acid, which is one of the 
products resulting from the oxidation of organic matter contain- 
ing nitrogen. 
Dr. Smith {, in his able paper on the waters of the Dee and 
* See the diagram at p. 205 of ‘ Volcanoes.’ 
+ Communicated by the Author. 
+t Quart. Joum. Chem. Soe. vol. iv. p. 123. 
