228 On tl>e Arjcmatcs of Copper and of Iron. 



the liquor becomes red, but ftill gives a blackifli green pre-* 

 cipitate ; but, if it is boiled with nitric acid, it then is con- 

 verted into a red liquor, which yields a red precipitate, by &\\ 

 the alkalis and earths capa!)ie of caufing a precipitation. From 

 thefe obiervations, upon the difl'eient combinations of iron 

 with oxvgen, and of oxide of iron with muriatic acid, fome 

 conclufions njav he drawn inlerefting to mineralocry as well 

 as to chemiflrv. The variety of colour in many ftoncs in 

 which iron has been found, is a fact which, although we 

 cannot deny our alfent to direct experiments, has never been 

 accounted for in a fatisfaclory maimer. In white, green, 

 vellow, black, red; in a word, in follils of every colour, iron, 

 with fometimes the help of manganefc, and lately of chro- 

 mium, has been regarded as the colouring matter of every 

 fiiade ; but it fcems almoft paradoxical, that the fame fub- 

 ftance (lionkl airume and communicate fo many lints. In 

 mica, kaolin, amianthus, afljcftos, rock cryftal, and, all 

 white fiones, I believe it to exift as the white oxide; and 

 that Rate is its fi;li: dcoree of combination with oxygen. 

 In them, this metal is not very abundant; for, if it were, I 

 have fome reafon (as fliall be proved innnediatelv) to think 

 that they would obey the loadftonc ftrongly. In lapis oUaris, 

 ferpentines, and manv green ftonts, we have the green ox- 

 ide; and mod of ihefe are magnetic; nav, as Mr. Humboldt 

 has oljferved, ferpentines enjoy the properly of polarity. And 

 thence I conclude, that the rarity of this metal, in the firft 

 clafs, prevents them from participating that quality. This 

 I believe to be its fecond ftagc of combination with oxygen. 

 In the ftate of black oxide it is frequently found, and is toa 

 well known to nted iuilhcr comment. I believe this to be 

 its third (lage of oxidation. But there is a red liquid muriate, 

 which gives a vcrv dark greenifh precipitate, approaching la 

 dark brown. What the (tale of that precipitate is, I havr. 

 not vet determined ; but I imagine it to be a mixture of black 

 and red. Brown and vellow oxides, I am confident, are mix- 

 tures of fimple oxides, and neither of ihem is an oxide y'wi 

 geiicris. The red oxide is the extreme of oxidation, and af- 

 fords many beautiful colours in nature and in art. 



It is nmch to be dcfired, for the advancement of analytic 

 chemidry, that experiments upon the proportions of oxysfcn 

 with which metals are capal)k- of uniting;, under different cir- 

 cumdances, and upon the coml)ination of thofe oxides with 

 all the known acids, together with many others of their pro- 

 perties, would attraiiV the notice, and ensage the labours, of 

 accurate manipulators. Experiments of this kind have been 

 defpifed, from an idea of their refenibling a mere mechanical 



employment ; 



