t 



222 



MANURE S. 



Sect. X. 7. 2. 



pofed to frofl In its molft (late, which by expand 



h it contains, by 



fuppofed 



th 



part 



f 



ay further from 



h oth 



Th 



IS 



h 



owever 



feems in general to be a nniftaken idea, fince if the ad of freezing 



o 



he not very fuddenly performed, a contrary effedl fee 



as 



d by Mr. Ki 



ho obfe 



that clay in its ufual ftat 



of drynefs can abforb two and a half times its weight of water with 

 out fuffering any to drop out, and retains it in the open air more per 

 tinacioufly than other earths ; but that in a freezing cold clay con' 



a6ls more than oth 



ths fqueezing out its water, and thus part 



ing with more of it than other earths." Mineralogy, Vol. I. p. 9. 

 This curious circumflance, that water, as it cryftallizes, detrud 

 the clay, which is diffufed in it, correfponds with other fads of coi 

 o-elation. Thus when wine, or vinesar, or common fait and 



£3 



folution of blue vitriol 



w 



expofed to frofty air ; th 



cohol, the acetous acid, the marine fait, and the calx of copp 



arb 



of them detruded from the aqueous cryftals, and retreat to the 



central part o 



f th 



e 



fluid 



that laft frozen, or into 



merous 



^ 



furrounded with partitions of ice, as I have frequently obferved 



■ 



whence it appears, that wet clay is in general rendered more 



folid 



and tenacious by being frozen 

 moifture e: 



well as wh 



• 



It 



dried, and its 



haled by too warm 'a fun ; and by both thofe 



m 



cumftances becomes lefs adapted to the purpofes of 

 2. In moft clays a kind of effervefcence occur 



ft 



they 



turned over, and thrown on heaps, and thus acquire air into their in 

 teftines, which renders them much fitter for the purpofes of vitrifica 



tion 



and thusforwards the procefles of the brick-kiln and pottery. 

 This greater facility to vitrify is probably efFeded by the union of 



; contain ; as oxydes of lead 



oxygen with the iron, which moft clays contain 

 and manofanefe are ufed in the more perfed vitrifi 



The calclform ores, or oxydes, of 



manganefe. and 



o 



frequently found near the furface of the earth, where they have been 



I 



u 



lited 



