MACNfcSiAN EARTH. j 279 



penfe; and it Teemed to me that nature, in placing at one fide 

 an inexhauftible mine of fulphur, and at the other inexhautf- 

 ible mafles of the proper earth of ?n extremely rare purity, 

 and between them an abundant fupply of fuel, of the fort 

 moil proper for this kind of work, had done its utmpft in fa- 

 vour of the eftablifliment I intended. 



There only remained to make fome experiments with a view Experiments 

 to afcertain the moll profitable way of proceeding ; and to preparatory. 

 examine principally if the iron which is united to the fulpbur 

 in the pyrites, would not be injurious to the fulphate of alu- - 

 men obtained, » 



With this defign I began by examining the action of the earth 

 of Baudiflero on the fulphate of iron, and the quantity of the 

 earth neceflary for the decompofi tion of a given weight of ful- 

 phur. 



In the different experiments the fulphate of iron diflblved The earth of 



in water, and boiled with this earth indifferent proportions ^^^fX 



became evidently decompofed after boiling for lefs than a quar- phate of iron in 



ter of an hour ; the iron was precipitated of a blackifli grey, the numid way. 



,..,*,. \'%r * -i , • 'A little potafh 



while the lolution was colourlels, and ammonia dropped into was added and 



it formed only a very white precipitate, which did not an- t * iel W uor . fet 



nounce much iron ; I filtered the liquor, of which one part 



was mixed with a little potato* and placed fo as to cryftalize ; 



and to afcertain whether there was any potafh in the earth of 



JJaudiflero, I f e t another part to cryftalize without any alkali. 



I ohferved that the liquors cryftallized immediately after be- j t ga Ve fulphate 

 coming cold; but in the place of octahedrons, I found the °* 'magnefia and 

 mod perfect, the mod beautiful, and pureft cryfials of fulphate" a um * 

 of magnefia. 



*JThe liquor which remained produced, on a new evapora- All the cryftals 



tion, the fame pure cryftals of fulphate of magnefia; and ™. er< : of ^ 

 i- j . r re- • . n i- kind,- and hence 



did the lame on (uccefiive evaporations and cry (taiizat ions to magnefia is an 



the laft drop of the liquor, Jn this manner was a natural alu- e * cel3ent porep* 

 men transformed entirely into magnefia, and at the fame in- 

 ttant magnefia became at once an excellent porcelain earth. 

 \f examples of this kind fhould multiply, the necefiity of che- 

 mical analyu^s for the knowledge qf fpffils will become more 

 ^nd more manifeft, and lefs reliance will be learned to be 

 placed on their external and phyfical characters, w|)ich at p?$» 

 ipnt feem§ to me to be too much abufed. J 



