474 Intellig€7ice and Miscellaneous Articles. 



DELVAUXENE — A NEW PHOSPHATE OF IRON. 



This mineral was first found in 1793, at Berneau, near Vise; it 

 occurs in brittle reniform masses, its texture is compact, and its frac- 

 ture perfect conchoidal. It is opake or only slightly translucent 

 on the edges of thin fragments ; its lustre is sometimes resinous ; 

 sometimes it is dull ; colour blackish or reddish brown, but some- 

 times yellowish brown ; the powder is of a yellowish brown, and the 

 finer the brighter. Its hardness is intermediate as to that of calca- 

 reous spar and sulphate of lime : specific gravity r85. When heated 

 in a flask it yields much water, and loses 42 per cent, of water when 

 heated to redness. Before the blow-pipe it decrepitates and fuses 

 into a grej"^ verj^ magnetic globule of iron. 



With borax on a platina wire, in the reducing flame, a bottle- 

 green globule is obtained, and in the oxidating flame a globule, 

 which is brownish while hot, and becomes green on cooling. In 

 water it falls to pieces, effervesces and gelatinizes in hydrochloric 

 acid, forming a brownish orange solution ; the nitric solution gives 

 a white precipitate with nitrate of lead, and a blue one with ferro- 

 cvanide of potassium. This mineral was first found in a lead mine, 

 but it has since occurred in a stone-quarry near the same place. M. 

 Dumont analyzed both varieties — 1st, reddish brown, 2nd, brownish 

 black — the results were 



No. 1 . No. 2. 



Phosphoric acid 13-60 14-30 



Peroxide of iron 29-00 31-60 



Water 42-20 40-40 



Carbonate of lime ll'OO 9-20 



Silica 3-60 4-40 



99-40 99-90 



Neglecting the carbonate of lime and silica, this mineral is a di- 

 phosphate of peroxide of iron + 6 eqs. of water ; the phosphate of 

 iron of the Isle of France, analysed by Laugier, differs from the 

 above in containing only half the quantity of water. 



The name of Delvauxene was given to this mineral by M. Dumont 

 from that of its discoverer M. Delvaux. — L'Institut, No. 276. 



ON THE USE OF AMMONIA IN FIXING PHOTOGRAPHS. BY J. C. 



CONSTABLE, ESQ. 



To the Editors of the Philosophical Magazine. 



Gentlemen, 



Mr. Fox Talbot, in his paper on photogenic drawing, states, that 



he did not succeed in preserving the drawings by means of ammonia ; 



some experiments which I have made lead to a different result. I 



find that the drawing.*, after being soaked for some minutes in a 



moderately strong solution of ammonia and then washed in clean 



water, withstand the action of the hght perfectly, and indeed are 



improved by it : for the first action of the ammonia is to make the 



dark parts of a reddish hue, which, on exposure to the light, become 



again of a dark colour, the light parts being unaffected. This mode 



