104 PROF. F. CRACE-CALVERT ON THE 



on Ben Lawers by Dr. Stirton, but was for some years 

 confounded with Hypnum commutatum, to which species it 

 bears much resemblance. The Rev. J. Fergusson, how- 

 ever, satisfied of its distinctness, distributed it in 1870 

 as Hypnum rigidulum, Ferg., sp. nov. ; and a few months 

 since Juratzka identified it with Thuidium decipiens, De 

 Notaris, Briologia Italiana, 1869. It occurs in springs, 

 and is found in Britain on Ben Lawers and Glas Mheal, 

 Perthshire — at Auchinblae, Kincardineshire, first observed 

 by Mr. John Sim — and abundantly in various places in 

 Clova and Braemar, first observed by the Rev. J. Fer- 

 gusson. From every form of Hypnum commutatum it is at 

 once separated by its papillose leaves with much dilated 

 auriculate bases, by its larger alar cells, by the ovoid 

 cells of the upper portion of the leaf (those of H. com- 

 mutatum being linear), by its monoicous inflorescence, 

 and by the time of the fruit (which is at maturity in 

 autumn). Fruit has been found only in Italy and in 

 South Prussia. 



XII. Experiments on the Oxidation of Iron. 

 By Professor F. Crace-Calvert, Ph.D., F.R.S. 



Read January 24th, 1871. 



Some two years since Sir Charles Fox inquired of me if I 

 could give him the exact composition of iron-rust, viz. the 

 oxidation found on the surface of metallic iron. I replied 

 that it was admitted by chemists to be the hydrate of the 

 sesquioxide of iron, containing a trace of ammonia ; to this 

 he answered that he had read several books on the subject, 



