Progress of Foreign Science. 321 



potash the same result was obtained. We must take care to 

 treat the nitrite by nitric acid, since being very alcaline it would 

 uot fuse on burning coals. 



If we evaporate the washings of magnesia when the water 

 ceases to be alcaline, reduced to about one-quarter it deposits 

 a very notable quantity of magnesia, and then reddens turmeric 

 paper. It is probable that the water decomposes the neutral 

 combination formed, at the moment of precipitation, into a so- 

 luble compound, with excess of alcali, and an insoluble com- 

 pound, with excess of base. The only means, therefore, of 

 estimating exactly the quantity of magnesia which a solution 

 contains, is to precipitate by phosphate of ammonia. 



Magnesia, treated with barytes, presents the same pheno- 

 mena, but they are easier to ascertain. M. G. acted on the 

 compound of magnesia and barytes with a quantity of nitric 

 acid, insufficient to dissolve the whole. The re-agents indi- 

 cated both magnesia and barytes in the part dissolved, as 

 well as in the part undissolved, which proves that there was 

 really a combination, for otherwise the barytes would have 

 been the first united with the acid. About 4 per cent, of ba- 

 rytes is thus associated with the magnesia. In like manner, 

 oxide of copper retains a small portion of the potash, or barytes, 

 employed to throw it down from its acid solutions. 



In treating of the principles of combination at the commence- 

 ment of this article, we promised to return to one of Berzelius's 

 speculations. We shall now bestow a word or two on it. He 

 is investigating the combinations of chromium. " Not having 

 at my disposal," says he, " any metallic chromium, I have 

 endeavoured to deduce the composition of its green oxide from 

 its capacity for the acids. I dissolved the hydrate of chromium 

 in muriatic acid ; I evaporated this solution to dryness, and 

 heated the muriate to a temperature sufficiently high to expel 

 every trace of muriate of ammonia which might be present. The 

 muriate thus heaied appeared under the form of a red, pulve- 

 rulent, and bulky mass ; it dissolved very slowly, but without 

 residuum in water. The solution was precipitated by ammonia, 

 added in so small an excess that the liquid only re-acted 

 feebly ; it was thereafter digested with this excess to remove 

 the muriatic acid precipitated with the oxide, in the form of a 

 submuriate. The oxide thus obtained weighed 3.05 grains. 

 The liquid, neutralized with nitric acid, and precipitated by 

 nitrate of silver, produced 15.61 graies of muriate of silver. 

 The experiment has then given, for 100 parts of muriatic acid 

 102.3 parts of oxide of chromium, which makes 28.5 parts of 

 oxygen in 100 parts of green oxide. If the acid contains the 

 metal combined with twice as mucii oxygen as in the green 

 oxide, this last must contain 29.61) hundredths of its wcitrht 



