Intelligence and Miscellaneous Articles. 155 



to ebullition for some time ; the violet colour of the hydrate of cobalt 

 will soon disappear, and it will be replaced by a precipitate of a dirty 

 yellow colour. In this case the hydrate of cobalt decomposes the 

 sulphate of iron, is substituted for the proto- or sesquioxide of iron, 

 which it renders insoluble, and precipitates in the state of hydrated 

 sesquioxide; this hydrate is necessarily mixed with a small quantity 

 of hydrate of cobalt, which should be used in excess, in order to be 

 certain of the complete precipitation of the oxide of iron. Nothing 

 remains to be done but to filter and wash the precipitate. The salt 

 of cobalt thus obtained yields no indication of the presence of iron 

 to the most sensible reagents. It yields, accordingly, no precipitate 

 whatever when, after having added hydrochlorate of ammonia to it, 

 it is supersaturated with great excess of ammonia. 



For the sake of greater simplicity, a solution of carbonate of soda 

 may be employed instead of the hydrate of cobalt, and the mixture 

 digested at a boiling heat for some time ; in both cases the precipi- 

 tate will contain all the iron. [This appears to be identical with the 

 method proposed by Scheerer for separating iron from cobalt, de- 

 scribed in the Phil. Mag. for February 1840. — W. F.] 



To recapitulate : it follows that in order to purify oxide of cobalt 

 it is sufficient to dissolve it in dilute sulphuric acid, to evaporate to 

 dryness, and calcine at a red heat, treating the mass with boiling 

 water, and adding to the solution either hydrate of cobalt or carbo- 

 nate of soda in the manner described. Sulphate of nickel appears 

 to decompose more readily than sulphate of iron, under the circum- 

 stances described ; when zafFre is treated according to M. Liebig's 

 process, it yields oxide of cobalt quite free from nickel, but contains 

 a large quantity of oxide of iron. — L'Institut, Juin 27, 1849. 



ON ALUMINATE OF COBALT. BY M. LOUYET. 



M. Louyet remarks it as well known, that alumina and the salts 

 of cobalt may combine in certain circumstances, and form a fine blue 

 colour. It is by this process that M. Thenard prepared the blue 

 which bears his name, by mixing certain proportions of alumina and 

 phosphate or arseniate of cobalt, and subjecting the mixture to a 

 long- continued calcination. All these substances are employed in 

 the gelatinous or hydrated state. As the precipitate formed by- 

 carbonate of soda in a mixture of alum and a salt of cobalt also yields 

 a blue compound by calcination, it has been inferred that the consti- 

 tuent elements of cobalt-blue were alumina and oxide of cobalt, so 

 combined that the compound may be considered as a salt, or an alu- 

 minate of cobalt. 



The facts which M. Louyet has ascertained are, that the sub- 

 stance obtained by the mixture of gelatinous alumina and phosphate 

 or arseniate of cobalt, also in the gelatinous state, yields a blue when 

 subjected to a red heat. At this temperature the mixtures of gela- 

 tinous alumina and hydrated oxide of cobalt yields only blacks or 

 grays, whatever may be the proportions of the constituents. In order 

 that the alumina and cobalt may produce blue, the mixture must be 

 exposed to a temperature very near that of melting glass. It results 



