86 Chronicles of Science. [Jan., 



Professor Schimper considers the plant more nearly allied to Selagi- 

 nella than to Lycopoclium. A specimen of Lepidodendron fruit was 

 purchased aboiit fifteen years ago by a physician of Lower Alsace, 

 from an antiquary in Paris, who did not know the locality whence it 

 had been taken. The upper half of the specimen belonged to Robert 

 Brown (Botanicorum facile princeps), who bought it for about 700 francs, 

 whilst the lower half came into the possession of Professor Schimper. 

 Another equally good specimen has been recently found in a valley of 

 the Pyrenees, near to Bareges. 



IV. CHEMISTEY. 



(Including the Proceedings of the Chemical Society.) 



First among the additions which have been made to our knowledge 

 of Chemistry since the date of our last ' Chronicle,' we must notice 

 Mr. Graham's continuation of his experiments with Silicic acid and 

 other colloid substances.* 



It is impossible to condense into a short space this highly import- 

 ant paper, in which a series of most interesting facts, arrived at by 

 a long course of investigation, are expressed in the fewest possible 

 words. We have no option but to refer the chemical reader to the 

 original, which will be found in the Journals indicated below. 



A good deal has at different times been written about a passive 

 state of metals, or a condition in which they are insensible to chemical 

 agents ; and a day has been looked forward to when iron would never 

 rust, and silver never tarnish. That day now appears more distant 

 than ever, for Dr. Heldt has shown that the facts on which this hope 

 was based admit of a very simple explanation. The author shows 

 that by certain agents the surfaces of metals become coated with an 

 insoluble compound which prevents further action. But other agents 

 remove this covering, and the action again proceeds.'!' 



The preservation of iron ships is a subject to which we have before 

 alluded, when speaking of the patent of Messrs. Johnson and Calvert. | 

 The subject has recently been investigated by M. Becquerel,§ who 

 finds that it is not necessary to cover the iron plates entirely with 

 zinc, but that bands of this metal placed at intervals around the ship 

 suffice to protect the iron from oxidation. 



We may refer, in passing, to the discussion of a question of great 

 industrial importance which has lately engaged the attention of the 

 French Academy of Sciences. || It is the question, By what agency 

 is iron converted into steel ? M. Margueritte contends and quotes ex- 



* ' Proceedings of Eoyal Society,' vol. xiii., with additions in ' Chemical News,' 

 vol. x. pp. 97-109. 



t ' Les Mondes,' t. vi. p. 413. 



% 'Quarterly Journal of Science,' vol. i. p. 119. 



§ ' Comptes Rendus,' Oct. 31, 1864. 



| * Comptes Rendus,' t. lix. pp. 185-376 et seq. 



