OF AKTS AND SCIENCES. 213 



supposed oxide yields to analysis chromic acid and chromic oxide by 

 imagining that the original oxide is decomposed by contact with water 

 into chromic acid and chromic oxide, as hyposulphurous acid is decom- 

 posed by water into sulphurous acid and sulphur, or as nitrous acid is 

 resolved by water above 0° into nitric oxide and a solution of nitric 

 acid ( 3 NO3 + Aq = 2 NO2 + NO5 + Aq). This might perhaps be a 

 possible supposition, if the brown substance in question were prepared 

 by methods in which water had no part ; but when we see it preci^iitated 

 from dilute solutions of monochi'omate of potash and a neutral chrome 

 salt, or subsiding in the course of days from a very dilute solution of 

 bichromate of potash, we are forced to the conclusion, that the substance 

 is from the first composed of the chromic acid and chromic oxide which 

 analysis shows it to contain. In short, we have all the evidence, analyt- 

 ical and synthetical, that this brown precipitate is a chromate of chromic 

 oxide, which we have of the real constitution of sulphate of potash. 



The compound is well worthy the attention of those chemists who 

 deny that formulas ever express the actual constitution of bodies ; it 

 seems questionable whether any formula for the chromate of chromium 

 can readily be written on the unitary theory which will express its 

 properties and reactions as well as the dualistic formula. When, at 

 this distance we look back at the feebleness of the theoretical argu- 

 ments which Berzelius opposed to the facts of Maus, Thomson, Dobe- 

 reiner, and others, we marvel at the weight of a name whose authority 

 outweighed the accumulated evidence of several trustworthy observers, 

 and prevented the truth from prevailing thirty-four years ago. Ber- 

 zelius himself became much less confident in after years of the truth of 

 his earlier views ; in his Traite de Chimie * he calls the precipitate 

 formed by mixing a neutral chrome salt with chromate of potash, chro- 

 mate of chromic oxide, and in a subsequent paragraph merely says that 

 it is very possible that this compound is the oxide of chromium, CrOa. 



An observation made by Rammelsbergf added something to our 

 knowledge of the precipitate formed by mixing a solution of chrome 

 alum with a solution of chromate of potash. He made a determination 

 of the water contained in the washed precipitate, and weighed the 

 chromic oxide obtained by igniting it ; the oxygen which was expelled 

 by ignition was determined by loss. The analysis led to the formula 

 (Cr203)3 (Cr03)2 -|- 9 HO, showing -that the washing of the precipitate 



* II. 307 (Paris, 1846). t Pogg. Ann., LXVIII. 274 (1846). 



