3$ Analysis effren 6ft. 



that it is right to be on our guard against a circumstance 

 which may impose npen us : frequently, after a certain 

 number of precipitations and filtrations, the re-agents indi- 

 cate the presence of lime, in a small quantity to be sure, in 

 the acid liquors which formerly appeared to contain none at 

 all. This lime generally proceeds from a little chalk which 

 some filtering papers contain, as is proved by the efferves- 

 cence which takes place when these liquors are filtered. 



(E) The properties here explained of the unknown sub* 

 stance appear to me to characterize sufficiently one of the 

 earths to direct my attention to that quarter. Magnesia was- 

 the earth which seemed to have the greatest resemblance to 

 the above substance ; in fact, both were equally well dis- 

 solved by sulphuric acid ; with the latter a bitter salt 

 was formed as well as with the former. It is not precipi- 

 tated from its solutions in the acids (when the latter are 

 properly diluted with water) by means of the carbonates of 

 soda and ammonia ; with caustic alkalis it yields a precipi- 

 tate insoluble in an excess of alkali, but very soluble in the 

 carbonate of ammonia. One property alone, that of retain- 

 ing carbonic acid, even after a very strong calcination, seems- 

 to exclude all parallel of this substance with magnesia ; be- 

 cause, according to the generality of chemists, nothing is 

 easier than to deprive the carbonate of magnesia of its acid 

 bv means of calcination. But I had often occasion to ex- 

 perience that this result is not so easy to obtain as is gene- 

 rally imagined; the identity of the above substance with 

 magnesia, then, appears to me sufficiently established not to 

 regard it as a new earth. 



(F) In order to complete this analysis, it still remained to 

 know whether the three minerals of spathic iron contained 

 water and carbonic acids. For this purpose, I calcined five, 

 grammes of each in a crucible of platina. No. I. lost by 

 this operation '*70 grammes, No. II. lost 1*85, No. III. 

 lost 1*83: these numbers, it is true, could not represent 

 the amount of water and carbonic acid : the loss in weight, 

 occasioned bv their disengagemet, was diminished by the 

 hvper-oxygenation of the iron. In fact, the nitrous gas, 

 produced by these minerals when they are dissolved in the 



3 nitric 



