Amilyfis of the Chromnte df Iron. 2^5 



the flFght refldue left by the potafli was treated with the nitric acid, It fwellcd ap like a ve- 

 getable extract, which is one of the mofl: prominent characters of the chromic acid. 



A. It being therefore afcertained that the chromic acid is the predominating ingredient in 

 this compound, 5O0 centigrammes of this metallic fait were taken, reduced into impalpable 

 powder^ and cxpofed to heat in a crucible of platina, with eight times the weight of potafli. 

 The mixture entered into pcrfe(5l fufion, and was kept red-hot for half an hour, after which 

 the crucible was taken from the fire,- and left to coot. THe mafs, when cold, had a iine yel- 

 fow colour, much inclining to green. This was diflblved in water, to which it communi- 

 cated a very fine lemon-yellow colour, a brown powder fubfiding to the bottom, which was 

 collefled on the filter. After well walhing and drying, its weight amounted to 300 centi- 

 grammes. 



B. This powder was boiled in- muriatic acid. Much oxygenated rriiiriatic acid was dif- 

 engaged. ^The liquor aflumed a fine emeraldcolour. It w^ then diluted with water, and 

 filtered, to feparate a brown powder, which had not been attacked by the acid. 



This powder was of the fame nature as the natural metallic fait, and after three fucceffivc 

 operations with potafli and the acid alternately, it was totally decompofed. It appears. How- 

 ever, that this alternation is neceflary, becaufe the chromate of iron, with excefs of the oxide, 

 is not decompofable by potafli, however great the quantity may bej fo that it becomes ne- 

 ceflary to remove the excefs of oxide by an acid, before the potafli can take up another por- 

 tion of the chromic acid. If the nitric acid be ufed, inftead of the mirriatic, to remove the 

 excefs of oxide, which is fet at liberty by the alkali, the matter is feen to fwell up like a 

 vegetable extra£t, a property which immediately manifefts the prefence of chrome. 



C. After the whole of the mafs was converted into chromate of potafli and metallic muriate, 

 the latter folution was decompofed by potafli, and afforded a precipitate of a dark brown co- 

 lour. This laft, after wafliing and drying, weighed 185 centigrammes, and conflfted, for the 

 mofl: part, of oxide of iron. The fluid feparated from this precipitate, had a fine lemoa- 

 yellow colour, and was, therefore, added to the chYomate of potafli. 



D. As it was fcifpefted that the oxide of iron contained a portion -of chr6mic acid, or per- 

 haps oxide of chrome, it was boiled with nitric acid, and afterwards with cauftic potafli, and' 

 afforded a fmall portion of chromate of potafh, which was feparated from the oxide. The 

 latter, after being well calcined, weighed 186 centigrammes ; it was then difliblved in mu» 

 riatic acid ; the folution was a fine yellow colour, and afforded a black precipitate by the ad- 

 dition of gallic acid. With the prufliates it afforded blue, fo that it cannot be doubted bu^ 

 that it was the oxide of iron. 



E. All the Solutions of chromate of potafli being then put together, they were Saturated 

 with nitric acid, taking care to add a flight excefs ; after which> the whole was diluted with' 

 a fufficient quantity of water, and a folution of the nitrate of lead was added. A very abun- 

 dant precipitate of a fuperb yellow colour fell down. It weighed 883 centigrammes, which» 

 according to the proportions of component parts in the chromate of lead, gives 318 centi- 

 grammes. , , 



It 



