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Proceedings of the Royal Institution of Great Britain. 



FRIDAY EVENING MEETINGS, 1831. 



Jan. 2Sth. On the determination of the ages of rocks, of supposed 

 igneous origin, by Mr. Ainsworth. Mr. Ainsworth's object was, 

 by a mineralogical and physical examination of those rocks known 

 to be of igneous origin, together with the circumstances of associa- 

 tion in which they are found, and those in which they differ from 

 neighbouring rocks, to form such associations of indications as 

 would lead to a comparative estimate of the ages of these rocks, 

 and in many cases, by consequence, throw light on the rocks with 

 which they were grouped. His discussions were purely geological, 

 and he drew for his data from his personal observations of Plutonic 

 rocks, both at home and abroad, and from the descriptions of others 

 who have studied this part of science. 



Amongst the things on the library tables were a small collection 

 of minerals from South America, presented by Mr. Bolleart, formerly 

 chemical assistant in the laboratory. Samples of improved porce- 

 lain ware, for chemical uses, recently manufactured by Messrs. 

 Wedgwood, and two large cakes of British silver, from the lead 

 mines of the Duke of Devonshire, covered upon their upper sur- 

 faces with those tortuous and tubular configurations which result 

 from the evolution of oxygen from the metal at the moment of its 

 solidification. See page 627, ' Miscellaneous Intelligence.' 



Feb. 4th. Mr. Brandeora^e relation of the vegetable, alkalies to 

 the common alkalies, and to certain proximate principles of vegetables. 

 Alter adverting to the generic characters of the alkalies and to 

 their importance as chemical agents, Mr. Brande proceeded to 

 remark that, before the discovery of the composition of the fixed 

 alkalies, various speculations, hypotheses and theories had been 

 adopted respecting their probable constitution, the most prevalent 

 being that they contained nitrogen, a notion derived from the exist- 

 ence of that element in ammonia. Experiments had, however, 

 actually been made to shew that they were (as was afterwards, 

 proved) metallic oxides ; and this view of their nature was founded 

 upon the well-known fact that by far the greater number of the 

 salifiuble bases, that is, of bodies neutralizing and forming definite 

 saline compounds with the acids, included a metal and oxygen. 

 Hence, therefore, analogy had led to a right conclusion, but experi- 

 ment long failed in its verification ; and had it not been for the 

 invention and application of a new power, as it were, in chemistry, 

 we might still have remained ignorant of their real nature. The 

 knowledge of the nature of the fixed alkalies led, by more successful 



