186 
THE GEOLOGIST. 
What we call carbonate of lime in nature — take even the purest marble 
— is not pure. At one time the lecturer was anxious to investigate this 
point, and he went to a sculptor and obtained numerous varieties of marble, 
but in not one of them did he fail to detect alumina. Chalk is an impure 
body, and the presence of foreign matter might altogether modify the re- 
sults of experiments made with it. There is, for example, a well-known 
variety of fire-brick, which consists almost entirely of silica. Upon taking 
hold of it, you will find that it is a hard, solid, enduring brick. You may 
ask, " How could you get this silica to unite so as to form a hard brick ?" 
For a long time it was kept secret : it was done by the intermingling of a 
very small proportion of lime, which caused the formation of one solid 
brick ; and it is very possible that foreign matters might be present, and 
modify the result of experiments made on the crystallization of carbonate 
of lime. We ought to appeal to chemical analysis to inform us what we 
are doing. It is vain to rely upon experiments where chemical analysis is 
not brought into use, or we may be led into serious error. 
The next question we shall have to consider is, the derivation of lime in 
nature. What ready source of carbonate of lime is there in natui'e ? Ac- 
cording to Bischoff, in his valuable and compendious book on chemical 
geology, it exists in the so-called Plutonic rocks in combination with 
silica, forming silicate of lime ; and this compound is decomposed by water 
containing carbonic acid, even when in mechanical suspension in the water. 
Dublin Eotal Society. — January 18. — Mr. E. J. Reynolds read a 
paper "On Spectrum Analysis." In the latter part of his discourse, the ap- 
plication of the method of spectrum-analysis to the examination of minerals 
was treated of. In examining refractory minerals in order to obtain the 
characteristic spectra of the metals contained in them, the author employs 
a peculiar form of gas-jet, which is essentially a Herapath's blowpipe-jet 
urged by a current of steam rendered acid by hydrochloric acid. The 
«team-jet should never be so powerful as to blow the test specimen off the 
platinum wires. By this means the decomposition of many minerals is 
effected without having recourse to the previous action of ordinary che- 
mical agents upon them, as has been hitherto necessary in preparing them 
for examination in the spectrum apparatus. The discussion of the real aid 
to be derived from the application of the spectrum analytical method to 
mineral analysis was then entered upon, and Mr. Reynolds expressed his 
belief, on experimental grounds, that the various spectra materially inter- 
fered with each other, notwithstanding the statements of MM. Bunsen 
and Kirchhofii* and others to the contrary ; and he showed that the presence 
of a considerable proportion of sodium and barium compounds, in a mix- 
ture of salts of different acids and bases, serves to completely mask or in- 
tercept the spectra of lithium, potassium, strontium, and calcium when 
present in comparatively small quantities. After discussing this portion 
of the subject at some length, the author expressed his belief that the me- 
thod of spectrum-analysis, as it now stands, beautiful and delicate though 
its indications are, must be looked upon rather as a useful aid to the or- 
dinary analytical process than as a method of analysis perfect in itself 
under all conditions. Mr. Reynolds concluded by observing that he has 
hitherto been unable to find any traces of rubidium or caesium in any Irish 
minerals ; but thallium was found in three specimens of copper-pyrites 
from different portions of the Knockmahon mines, Bonmahon, co. Water- 
ford, and in one specimen of the same mineral from Ballydehobb mine, co. 
Cork. The amount of the metal present in every case was extremely 
minute. 
