of the Argillaceous Irori'Ore. 279 



carbonate of soda than would be necessary to precipitate the 

 whole of its earthy contents ; immediately afterwards digest it 

 with a considerable excess of caustic potash or soda. The al- 

 kali will dissolve the alumina ; but the lime and the magnesia, 

 in the state of carbonates, and the iron and manganese, in that 

 of oxides, will remain unacted upon. This mixture may be 

 examined according to the rules which have been already laid 

 down. 



If the presence of any of those obnoxious ingredients, sul- 

 phur and phosphorus, be suspected in the ore, it will require 

 a separate analysis to ascertain their respective quantities. 

 Fortunately, however, the phosphorus, which is the most in- 

 jurious constituent, is of rare occurrence ; but it is otherwise 

 'with sulphur. This substance, whenever it is present in the 

 ores, appears to exist in them in combination with iron, con- 

 stituting iron pyrites. Its amount may be ascertained in the 

 following manner. Into a small glass retort put 100 grains 

 of the pulverized ore, and pour over it, in small quantities 

 at a time, half an ounce measure of concentrated nitric acid. 

 A receiver containing a small quantity of water should be at- 

 tached to the beak of the retort, for the purpose of condensing 

 any sulphuric acid which may be carried over with the evolv- 

 ed gases. A very violent effervescence will be produced by 

 the first addition of acid, and there will be given off abun- 

 dance both of carbonic acid gas and nitrous gas. When the 

 whole acid has been gradually poured on, set the mixture 

 aside for five or six hours, and agitate it occasionally : then 

 add half an ounce measure of water, and 10 grains of nitre, 

 in order to prevent any sulphuric acid from being volatilized, 

 and digest this upon a sand-bath for a few hours. Through- 

 out the whole process, the receiver, containing a little water, 

 ought to be kept attached to the beak of the retort. The 

 whole of the sulphur will now have beccwne oxidized, and con- 

 verted into sulphuric acid. Return the liquid contained by 

 the receiver into the retort, then filter the clear solution from 

 the insoluble portion, and by a very gradual addition of caus- 

 tic ammonia, neutralize the excess of acid, as far as can be 

 done without causing precipitation. A solution of nitrate of 

 barytes, now poured into it will throw down the sulphuric 



