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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 nature ? 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 Royal 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 

 steam-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 Kirchhoff 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 csesium 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 Bally dehobb mine, co. 

 Cork. The amount of the metal present in every case was extremely 

 minute. 



