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XV. On the Chemical Comtitution of Childrenite. 

 By Prof. Rammelsberg*. 



A I^IONG the rarest crystallized minerals, and one that in a 

 "^^ chemical point of view may be said to be hardly known at 

 all, may be classed childrenite. This species, which was at first 

 met with in very minute crystals, many years ago, in piercing a 

 timnel near Ta\'istock, has of late years been found in much finer 

 specimens at the George and Charlotte Mine, some of the cry- 

 stals indeed measuring full half an inch in length. Within the 

 last twelvemonth, two specimens of a peculiarly dark colour have 

 occurred at Wheal Crebor. Both these mines are situated near 

 Tavistock. 



On exposure to heat, childrenite gives off a considerable quan- 

 tity of water. Before the blowpipe, it swells, and puts forth in- 

 sulated branches, tinging the flame distinctly of a bluish-green 

 colour, and forms a fissured, rounded mass, black in part, and in 

 part brownish-red on the edges. With fluxes it gives the reaction 

 of manganese and iron. In the form of a fine powder, the mineral 

 is soluble by lengthened digestion in hydi'ochloric acid, leaving 

 generally a slight residue consisting principally of quartz. The 

 solution at length assumes a faint yellow colour ; ammonia pro- 

 duces in it a voluminous dark blackish-green precipitate, which 

 turns brown on exposure to the air, and which consists of phos- 

 phoric acid, alumina and the oxides of iron and manganese. The 

 filtrate contains only phosphoric acid ; there is no alkali in it. A 

 freshly formed solution of the mineral showed a strong reaction 

 of the protoxide of iron j of the peroxide the reaction was far 

 less marked. 



On exposure to a red heat in a covered platina crucible, the 

 powdered childrenite loses its water. In one experiment, where 

 the mineral was not altogether free from copper pyrites, this loss 

 amounted to 16'35 per cent., a small quantity of sulphm'ous acid 

 being given off. On employing the material in as pure a state 

 as possible, the loss was 16'30 per cent. The powder, thus 

 heated, is of a bluish-red, black internally ; when heated with 

 access of air, it is I'ed throughout. 



The loss of weight on exposm-e to heat corresponds to the 

 amount of water in the mineral minus the oxygen, which the 

 protoxide of iron (and of manganese) has taken up in its con- 

 version into the peroxide. 



As the crystals of childrenite are very fiimly implanted on 

 their gangue, which consists of carbonate of iron, quartz and 



* From Poggendorff's Annalen, No. 3, 1852, with a few iiniiupoitant 

 additions as to localities. Communicated bj W. G. Lettsora, Esq. 



