METHOD OF PREPARING CHROMIC ACID, ETC. 20 
large crystals. In volume there may have been used the 
same or 1| time the amount of sulphuric acid, but the solu- 
tion contains far more chromic acid than with Warington' s 
process. The produce in chromic acid for the same quan- 
tity of sulphuric acid is consequently far greater, almost in 
proportion to the increase of solubility of the potash salt at 
the ordinary temperature and boiling-point; 1 part by weight 
of the salt requires at boiling-point nearly 1 part by weight 
of water, and the solution boils at 2iS c ; at 64° it requires 
ten times the amount of water. 
If, in this method, sulphuric acid is saved, the chromate 
of potash, on the contrary, is not wholly turned to account 
as in the other method ; this does not render it less prefera- 
ble in a pecuniary point of view, for all the residues, both 
the solid sulphate of potash which is mixed with chromic 
acid, as well as the acid liquid drained from the chromic 
acid, may be advantageously employed for the preparation 
of oxygen. It is only necessary to evaporate the acid some- 
what previously, because when very dilute it does not de- 
compose the chromic acid when heated with it. Bottger 
states that the residuary sulphuric acid may be used for 
purifying phosphorus from oxide of phosporus, an applica- 
tion however which is of far less frequent occurrence than 
the preparation of oxygen. 
All the methods above described for preparing chromic 
acid from its potash salt, readily lead us to believe that the 
chromic acid is insoluble in monohydrated sulphuric acid, 
because it is precipitated by it from its aqueous solution ; 
such however is not the case. Sulphuric acid (SO 3 , HO) 
dissolves considerable quantities of chromic acid at the or- 
dinary temperature, becoming yellow, and finally quite 
dark brown and opake. I soon cleared up this apparent 
contradiction, by adding a few drops of water to the solu- 
tion of the chromic acid in the sulphuric acid ; the chromic 
acid immediately separated. Since this proves that the 
chromic acid is precipitated from its aqueous solution by 
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