PARTS OF TREES FIRST IMPAIRED BY AGE. £75 



only a pure oxldnle, similar to that obtained from the oxi- 

 dation of iron by water, the decomposition of which is as- 

 sisted by heat, and consistin»5 of 0»76 iron to 0*24 of oxigen ; 

 and the latter being a compound of red oxide and black oxi- 

 dulo of iron, in which the proportions of these two substances 

 are variable. 



The powders of oxidulated iron, and of oxidule of iroa 

 obtained by heat and water, appear to be identical. We 

 have analysed several specimens of ore from the isknd 

 of Elba, and found in every one very variable proportions of 

 the two oxides. Of the two varieties mentioned in the pre- 

 redino^ ol)servations, one contained 33, the other 40 of oxigen 

 to 100 of iron. Some others, that we analysed both in the 

 tnoist and dry way, contained 35, 36, and 38 of oxigen to 

 100 of iron. One alone yielded us only 30, like the ore of 

 the valley of Aost: but we had reduced and analysed sepa- 

 rately two fragments taken from different parts of the same 

 specimen. '. 



Among the fine crystals of the isle of Elba a great deal of 

 red oxide of iron is found; and it is principally in this *state, 

 that the ore is extracted for the smelting houses. In the 

 mines of the valley of Aost, on the contrary, the oxide is 

 much more rare, and the ore is pretty commonly extracted 

 for the works in the state of oxidule. 



This addition 1 give only as a sketch, that may assist the These roerelv 

 mineralogist in his researches, and facilitate the discovery ^'^"^ ^o mine- 

 of the causes of the differences presented by these two gpe- ^^ ^^^^^^' 

 cies of iron ore, whicii the learned Haiiy had already di- 

 •tined with that sagacity, which he employs in all his laboura. 



On the Parts of Trees primarly impaired hy Age. In a 

 Letter from T. A. Knight, Esq, F. R, S. to the Rt. Hon. 

 Sir Joseph Banks, Bart. K, B. P. R. S* 



MY DEAR SIR, 



N the first communication I had the honour to addr^s Ciafts last but 

 to you, (it was in the year 1795,) I stated the result of many f >r al>n)u«4 

 » Phil Trans, for 1810, p, 178. 



'i' 2 fxperimentf 



