1818.] Scientific Intelligence. 311 



a very thin coating upon silica, and the whole is so light that 

 the pieces float upon water. That the metal obtained is not 

 silicon (supposing silicon to be a metal) is obvious from this, 

 that the lustre is neither altered by water, nor nitric acid, nor 

 muriatic acid, nor nitromuriatic, even when in contact with these 

 liquids for 24 hours. Whereas silicon, as we learn from Davy's 

 experiments, cannot be obtained in a separate state, because it 

 decomposes water and every other liquid which he applied to it. 

 I fused a little of the matter sent me with potash, before the 

 blow-pipe, in a platinum forceps. The bead had a greenish 

 shade, and contained a little iron, which was the only metal I 

 could discover in it. But I rather think the metallic lustre is 

 connected with the oil. I have frequently obtained charcoal 

 from animal oil, having a metallic lustre little inferior to that 

 exhibited by the specimens sent me with the preceding commu- 

 nication. The fine silvery colour is probably owing to a very 

 thin coat of this charcoal covering the white silica. — T. 



VIII. Septaria. By Wm. Davis, Esq. 



(To the Editors of the Annals of Philosophy.) 

 GENTLEMEN, 



In the Annals for January, page 39, is an interesting paper on 

 the uses of the Septaria ; after, reading which, I immediately 

 turned to the new edition of Thomson's Chemistry, 1817, for 

 further information, but without success ; for I could not find any 

 one of the names, septaria, ludus helmontii, or loam-stone, in 

 the index to that valuable work. You would confer an obliga- 

 tion, therefore, on some of your readers, if you would refer us 

 to the proper article for information, or give in your Annals such 

 a description as would enable us to determine whether that 

 valuable substance occurs in our own neighbourhood. 



At the same time I beg leave to inquire what is the best means 

 of preventing the oxidizement of steel, or brass wire, when ex- 

 posed to water ? My view in asking this question is the improve- 

 ment of wire " gig-mills," used for dressing, or facing woollen 

 cloth. The wires act on the cloth something like a brush, or 

 comb, and are constantly wetted. I am, Gentlemen, 



Your obliged servant, 



Gloucestershire. "Willi am Davis. 



In answer to the first queiy of our correspondent, we reply 

 that the septaria are balls mostly in the form of an oblate sphe- 

 roid, which, on being broken, appear to be composed ot 

 brownish, or bluish indurated clay, intersected by veins, or 

 partitions {sepia) of calcareous spar. These veins are widest 

 about the centre of the ball, and generally terminate a little 

 short of the surface. Hence, they have probably been produced 

 not by infiltration, but by a spontaneous separation of the 

 original ingredients composing the mass of which the ball was 

 formed. 



