130 Prof. Berzeliuson the Orange Gas Produced, fyc. 



method is at present the only one which gives chromic acid 

 perfectly pure. 



If the gas is received in a platina vessel of some depth, 

 whose sides have been slightly wetted, and into the bottom of 

 which the gas has been made to descend, the water begins to 

 absorb the gas, but, by and bye, crystals of a fine red colour 

 are seen to form themselves round the opening of the metal- 

 lic tube which conveys the gas, and, in a short time, the ves- 

 sel is filled with a red snow, consisting of crystals of chromic 

 acid. The fluoric acid dissipates itself in vapour, and ab- 

 sorbs entirely the water added at the beginning of the ex- 

 periment. These crystals have this curious property, that, when 

 they are heated to redness in a platina dish, they begin at 

 first to melt, and afterwards, by a slight explosion, accompa- 

 nied with a flash of light, they decompose themselves into 

 oxygen gas, and the green protoxide of chrome. The chro- 

 mic acid which has been dissolved in the water does not pre- 

 sent this phenomenon. It fuses during its decomposition^ 

 but it does not give a flash of light. This difference does not 

 arise from its containing water, for it is perfectly free from 

 it when it is heated to a little above 100° centigrade. 



M. Unverdorben had already observed, that crystals of 

 chromic acid, introduced into ammoniacal gas, are decomposed 

 with a flash of light. The ammonia is destroyed, and the acid 

 leaves the protoxide as a residue. It is necessary to make 

 these experiments quickly, as the crystallized acid is deli- 

 quescent. 



In distilling chromate of lead with chloride of sodium, we 

 obtain a gas similar to the preceding, and which contains 

 chrome combined with chlorine, in such proportions, that the 

 water, by its decomposition, gives rise to the formation of the 

 hydrochloric and chromic acids. The gas is red, and may 

 be collected over mercury, but it is very much charged with 

 chlorine, when it it is prepared by means of the common con- 

 centrated sulphuric acid, whose water of combination destroys 

 a certain quantity of the gas. 



