Magnestan earth. 281 



The hardnefs of this earth is variable, fometimes it is foft, Soft* or hard ft 

 irt which ftale I (hall call it the earthy fort, and forne pieces of ^ra^ftecl. 

 it have a confiderable hardnefs; as in all my experiments I % 

 tried them comparatively, I (hall name this laft variety the 

 ftomj kind, to diftinguifh it from the preceding. 



T! -e ftony variety is fcratched by ft eel, fometimes, on the 

 contrary, it is hard enough to fcratch fteel. It can be eafily Pulverable, tha* 

 reduced 10 powder; but with much difficulty to very fine pow- ranenTia the^ 

 der, and this only takes place after long trituration in a mortar air. 

 of porphyry. Its hardnefs neither increafes nor diminilhes by 

 the action of the air; in this refpecl it differs from the magne- 

 fia of Moravia, which is very friable, and from that of Sali- 

 nelie, which is foft in its bed, and only grows hard on exfic- 

 cation in the air. 



The fracture of this variety is conchoidal and unequal. Fraaure con- 



Its furface is dull ; fometimes, but Very rarely, fhining fpots p°j, a o * ke 

 appear. It is conftanily perfectly opaque, and moderately moderately 

 heavy; its fpecific gravity is variable. heavy. 



It is a little unctuous to the touch in the friable and earthy Slightly und*tu- 

 fort, and but very little fo in the (tony variety. « us a » d *dhe- 



It fenfibly adheres to the tongue, though not much; it ac- 

 quires this property in a considerable degree when it is mo- 

 derately warmed at the fire. 



Plunged in water, the ftony variety does not abforb it at all ; The foftfped- 



the friable fort abforbs it greedily, and with an 'biffing, but the mensabf ? rb . 



& ' ' ° water and nux 



mixture does not grow hot. like clay. 



The friable fpecies mixes with water to a confiderable de- 

 gree, in the fame manner as clay ; the fine particles of this 

 earth, like thofe of clay, continue a long lime fufpended in 

 water, with this difference from thofe of clay, that they do • ' 

 not unite together. Urged by the blow-pipe, on a cianiteAre notfufible 

 cryftal, it is infufible. by the blow. 



Treated in a mafs, on the fire in a crucible, efpecially in a P 

 red hot crucible, it foon decrepitates, and divides into thick 

 fcaly pieces, which leap out of the crucible; this does not 

 happen if it is heated by degrees and moderately. 



If it is reduced to a fine powder, and then traited on the But apparently 

 fire, as foon as the bottom of the crucible begins to grow red fo in a crucible. 

 hot, this earth boils for a fhort time, and feems to unite toge- 

 ihiT, as if moderately moiftened, 



A* 



