456 On a Ccmpcund of Sesquioxide of Iron and Lime. 



The existence of a little protoxide of iron is accounted for by 

 the presence of silica, which at a high temperature, even in an 

 oxidizing atmosphere, reduces sesquioxide of iron to protoxide, 

 with the formation of silicate of this oxide- — though, when this 

 silicate is heated in an oxidizing atmosphere at a lower tempera- 

 ture, its protoxide of iron is converted into sesquioxide, the pro- 

 duct after such treatment being merely a mechanical mixture of 

 silica and sesquioxide of iron, as has been demonstrated by ex- 

 periment. 



Assuming the existence of a compound represented by the 

 formula CaO, Fe 2 O 3 , the calculated percentage composition is 



Sesquioxide of iron . . 74*07 

 Lime 25-93 



100-00 



A comparatively large quantity of this beautiful substance 

 has recently been prepared by heating a mixture of 1600 grains 

 of haematite and 1000 grains of chalk ( = 560 grains of lime) in 

 a platinum vessel in a muffle, precisely as iii the last experi- 

 ment, except that at first the temperature was carefully mode- 

 rated until the carbonic acid had been expelled from the chalk 

 and the mixture had become soft. The mixture was kept at a 

 white heat during about three hours, and left to cool gradually in 

 the furnace during the night as the fire died out. The product 

 weighed 2148 grains; but supposing no loss to have occurred 

 and the materials to have been pure, it should have weighed 

 2160 grains. It had the same characters as that previously de- 

 scribed ; and some of the crystals on the surface were 2 inches 

 long. 



On a future occasion I hope to be able to communicate in- 

 formation concerning the crystalline system of this compound on 

 the authority of a trustworthy crystallographer, and to report 

 the results of analogous experiments with other oxides of the lime 

 and sesquioxide of iron types respectively. I have much pleasure 

 in stating that the foregoing recent experiments have been con- 

 ducted, in the metallurgical laboratory of the Royal School of 

 Mines, by my colleague, Mr. Richard Smith. 



In chemical constitution this compound may be regarded as 

 a lime magnetite, or magnetic oxide of iron in which the prot- 

 oxide of iron is replaced by lime. 



It should be stated that Lampadius more than seventy years 

 ago subjected various mixtures of sesquioxide of iron and lime to 

 high temperatures* ; but as his experiments were made either in 

 clay crucibles, or in similar crucibles lined with carbon, the re- 

 sults are obviously unsatisfactory. 



* Journal des Mines, vol. xviii. p. 168. 



