726 PLUCKER ON THE DETERMINATION OF THE 



tion of a fatty mixture containing 2 parts by weight of iron to 

 100 of lard. 



With this mixture, in the second series of experiments, differ- 

 ent peroxides of iron were first compared ; the first (I.) was 

 prepared in a chemical laboratory; the second (II.) in the che- 

 mical manufactory in this town, which is specially devoted to 

 this purpose ; the third was fibrous red haematite (reniform) ; 

 the fourth a beautiful crystal of micaceous iron ore from Elba : 

 next three hydrated peroxides of iron ; first, that from which 

 the oxide I. was procured, and which, by a direct determination, 

 contained 24*24 per cent, of water ; secondly, brown haematite ; 

 and thirdly, artificial blood- stone, which, according to a subse- 

 quent determination, contained 11*55 per cent, of water; more- 

 over, a beautiful crystal of pyrites ; lastly, protoxide of nickel 

 and its hydrate, the latter containing 24*75 per cent, of water, 

 according to an approximative determination. All these sub- 

 stances were finely powdered ; and when compressed as uniformly 

 as possible, were placed in the watch-glass and their weight de- 

 termined. Both the peroxides of iron, the red ironstone and 

 the protoxide of nickel, after having been powdered, were dried 

 at a temperature of 212° F. immediately before use. 



18. The results obtained are collected in the following table. 

 The first column (A) contains the directly determined weight of 

 the various substances examined ; the second (B) the quantity of 

 metal they contain. These quantities were determined in the 

 case of the five solutions by chemical analysis, but were calcu- 

 lated for other metallic compounds. The third column (C) con- 

 tains the total attraction of the substances examined. Here in 

 each case 0*41 grm., i. e. that weight by which the empty watch- 

 glass was withdrawn, was deducted from the weight which caused 

 the filled watch-glass to separate. The fourth column (D) gives 

 the quotients which are obtained by dividing the total attraction 

 by the weight of the substance ; hence the relative proportion of 

 the magnetism of the substance for the same weight. The fifth 

 column (E) gives the relative proportion of the magnetism of the 

 iron or nickel in the various chemical compounds. This is im- 

 mediately obtained for the solid matters by dividing the total 

 attraction by the weight of the metal they contain. With regard 

 to the solutions, however, bearing in mind the diamagnetism of 

 the water they contain, a slight correction must be made in the 

 total attraction C. But instead of calculating, as in the eighth 



