224 Intelligence and Miscellaneous Articles. 



A paper was read, entitled " Experiments on Candle-wicks, and 

 on the Effects of Chlorine upon the combustible properties of the 

 Wax of the Candle-berry Myrtle." By Mr. Reed. 



A paper ". On the Exotic Plants which have been introduced into 

 South Africa, with remarks on their Cultivation and Uses." By Mr. 

 Bowie. 



" A Description of two supposed undescribed species of Fishes." 

 By Mr. Webster. 



" A Description of the Birds inhabiting the South of Africa, &c." 

 By Dr. Smith. 



XXXVII. Intelligence and Miscellaneous Articles. 



ALTERATION OF COLOUR IN WOOD BY OXYGEN. 



MARCET has observed that the wood of certain trees, and espe- 

 • cially the elm, becomes of a more or less intense red colour when 

 exposed to the air. He has found, by a great number of experiments, 

 that the alteration does not occur, if at the moment in which the 

 branch is transversely cut it be placed in a perfect vacuum, or in a 

 gas which contains no oxygen ; and, on the contrary, that the colour 

 is more intense in oxygen gas than in atmospheric air. If the wood 

 after being cut is immersed in water, it always becomes red, even 

 when it is immediately afterwards introduced into a vacuum, or into 

 a gas which contains no oxygen. Elm-wood which had acquired a 

 yellow colour, yielded it gradually to water ; and this water being 

 evaporated to dryness, the residuum, when examined, exhibited all the 

 characters of pure tannin. As the result of his experiments, M. 

 Marcet attributes the colouring of elm-wood to a kind of oxygenation 

 which the tannin suffers at the moment of exposure to atmospheric 

 air. 



It is to be remarked, that in the experiments here described., the 

 branches of the elm were always cut transversely ; for if the bark be 

 simply detached, the alteration of colour is much less distinct. — Bib. 

 Univ. Feb. 1830. 



DURABILITY OF STONES. 



When the felspar of the granite rocks contains little alkali, or cal- 

 careous earth, it is a very permanent stone ; but when in granite, por- 

 phyry, or syenite, either the felspar contains much alkaline matter, or 

 the mica, schorl, or hornblende, much protoxide of iron ; the action of 

 water, containing oxygen and carbonic acid, on the ferruginous ele- 

 ments tends to produce the disintegration of the stone. The red granite, 

 black syenite, and red porphyry of Egypt, which are seen at Rome in 

 obelisks, columns, and sarcophagi, are amongst the most durable com- 

 pound stones 3 but the gray granites of Corsica and Elba are extremely 

 liable to undergo alteration : the felspar contains much alkaline 

 matter, and the mica and schorl much protoxide of iron. A remark- 

 able instance of the decay of granite maybe seen in the hanging 

 tower of Pisa : whilst the marble pillars in the basement remain 



scarcely 



