S82 ON- THE OXIDES OF IRON. 



were made with great care, they presented anomalies, which 

 it was impossible to reconcile with the opinions at present 

 received. I shall describe one of my experiments particu- 

 Oneexpeii- larly. Of the 300 grains of iron introduced, 63*37 grains 

 meut described, ^^g;^, ^^j,j f^yjjj in the state of iron at the end of the ex- 

 periment. The surface indeed had lost its lustre, but the 

 wialleability and other qualities remained. The specific gra- 

 ■vify ®f the black oxide formed was 5-025, which agrees 

 nearly with that of specular iron ore. The hidrogen gas 

 evolved, reduced to the temp, of 60", barometer 30 inches, 

 measured 415"5 cubic, inches. Hence the oxigen, which 

 combined with the 236*63 grains of iron that had been con- 

 verted into black oxide, must have been equivalent to 207'75r 

 cubic inches, or 69 grains nearly. But if 236*63 grains of 

 iron combine with 69 grains of oxigen "to be converted into 

 black oxide, it is obvious, that 100 grains would have com- 

 bined with 29*1 grains of oxigen. This is a greater pro- 

 portion than results from the preceding experiments; but 

 the apparent differences was probably owing to the surface 

 of the wire, which still retained its ductility, being oxi- 

 dized. Were we to suppose 14*3 grains of that portion to be 

 oxidized (and some of it certainly was, as it had all lost its 

 lustre) it would reconcile this experiment with the preceding. , 

 Increase of But if the 236*63 grains of iron had combined with 69 



weight above grains of oxigen, they ou^ht to have weisfhed 305*63 grains. 



that of the oxi- ^ , ..,.,. . 



geii expended. D»t the actual weight was found to be 330*68 grams, or 25 

 grains heavier than they ought to have been from theory. 

 This increase of weight, which was constant in all my trials, 

 cannot be accounted for on the present universally received 



Was this Giving chemical theory ; unless we suppose, that a little water, as 



to water com- ^g]j gg oxigen, has actually combined with the iron — a sup- 

 hineil v/ith the ^ ' "^ ^ 



iron? position which was strenuously maintained by Dr. Priestley. 



I attempted to ascertain exactly how much of the water had 

 disappeared in a similar experiment, but the apparatus used 

 was so bulky, that 1 could not weigh it with sufficient pre- 

 cision, to determine so delicate a point. 



5. From the whole of tlicse experiments it seems to fol- 

 lovv, that black, oxide of iron is composed of 100 parts of 

 metal and about 27*5 of oxigen. . .i 



Thfiiard's III. When iron is dissolved in diluted sulphuric, acid,- if 



white oxide of 



Thcnard 



it be prcciiutated by an alkali, a white powder falls, which 



