320 Progress of Foreign Science. 



state which decomposes the chromic acid ; once gaseous, it 

 has no longer this power. The mixture of nitre and sal-am- 

 moniac acts as nitrate of ammonia, because a double decom- 

 position is effected, in virtue of the facility with which the 

 nitrate of ammonia is converted into gas. This double de- 

 composition always happens when we heat, along with sal- 

 ammoniac, the nitrate of a metal susceptible of forming a fixed 

 chloride. In order to obtain the protoxide of azote, we may 

 therefore use, instead of nitrate of ammonia, a mixture of nitre 

 and sal-ammoniac, in the proportion of 3 of the former to 1 of 

 the latter, leaving an excess of nitre, to prevent sublimation of 

 the sal-ammoniac. By Dr. Wollaston's scale, 3 of nitre are 

 equivalent to 1.58 of sal-ammoniac; so that M. Grouvelle's 

 excess seems superfluously great ; 2 of nitre to 1 of sal-ammo- 

 niac would be good proportions, and, to secure intimate mix- 

 ture, they should be dissolved together in hot-water. 



M. Grouvelle, in a short section on the chromites, offers no- 

 thing very definite or satisfactory. In treating of chromate of 

 lead, he says, we may obtain a reddish chromate, by employing 

 an alcaline chromate of potash ; or, if we make use of a sub- 

 acetate of lead, and a neutral chromate, boiling both together, 

 a yellow precipitate is formed, which passes in a few seconds 

 into a very brilliant orange-red. We may procure a still deeper 

 tint, by boiling a little alcali with the red, or even with the 

 yellow chromate of lead. He has analyzed, comparatively, 

 the yellow chromate, the red, and the red ore of Siberia, All 

 give exactly the same ratio between the acid and the oxide. 

 They are neutral chromates, only the red chromate contains a 

 small quantity of alcali, which appears to him about 1 or 1 J per 

 cent. A red chromate may be obtained, by boiling together 

 chromate of potash and litharge. From some experiments he 

 infers, that the alcali is combined with the oxide of lead, and 

 that this combination, united to the chromate of lead, gives rise 

 to the red chromate, which thus contains a little more oxide 

 than the neutral chromate. A few drops of dilute nitric acid 

 deprive it immediately of its red colour, by dissolving the alcali 

 and a little oxide of lead. He has found in the Siberian ore a 

 little lime, but he is not sure whether it may not have been ac- 

 cidental. The above circumstances explain the fact known to 

 painters, that the yellow chromate of lead mixed up with whit- 

 ing, for painting walls, produces as great a body of colour as 

 the same weight of the deep orange chromate. 



M. Grouvelle precipitated magnesia, by caustic soda puri- 

 fied with alcohol, washed the precipitate till the water no lon- 

 ger reddened turmeric paper, treated it with nitric acid, cal- 

 cined strongly and repeatedly the compound, then washed the 

 magnesia, and obtained, finally, a nitrite which, with sulphuric 

 acid, gave well-pronounced crystals of sulphate of soda. With 



