fitFEOTa ^F. -KEATr 195 



wax and marble. Their cofours are varloufly though fllghlly 

 tinged with yellow and blue; ill particular No. 3, which though 

 produced from common white chalk, refembles a yellow mar^ 

 ble. Nos. 3, 5 and 6 have taken a tolerable polifii. No. 7 

 contains a (hell introduced along with the pounded chalk, and 

 now clofely incorporated with it. 



Nos. 8, 9, 10, H, all formed from pieces of chalk ex- 

 pofed unbroken to heat and prelfure. No. 8 is remarkable for 

 a fliining grain and fern i-t ran fparency. Nos. 9 and 10 (hew 

 parallel planes like internal flratification which has often ap- 

 peared in chalk, in confequence of the a6lion of heat, though 

 nothing of the kind could be ken in the native maf^. No. 11, 

 very com padl, and of a yellow colour. 



By various trials, to be given in detail hereafter, it appears Great lacreafe of 

 that the carbonate in all thefe experiments has undergone a ^.fg'y^gf*" 

 * great diminution of bulk, amounting in forae cafes to more 

 than y of the original mafs; and that its denfity has been pro- 

 portionably increafed. At the fame time the porofity of the 

 iiibftance has diminifhed in a ftill higher degree. Thus it is 

 found that chalk in its natural flate abfojfbs and retains from 20 

 toi*5 per cent, of water; but after being expofed to heal un- 

 der Gorapreffion, that it does not abforb quite 0.2 per cent, or 

 tiie 500 part of its weight. . . 



Nos. 12, 13. Examples of vtrelding, in which the pounded Other fpecimens 

 chalk has been -incorporated with a lump of chalk, upon wi)ich pofe^ roheat 

 it had been rammed, fo that their joining is hardly vifible in under ftrong 

 the fraaure. ' P"^'^"'^' 



- - Nos. 14, 15, 16. Shewing the fuiion of the carbonate well 

 advanced, with a confiderable a6iion on the porcelain tube, in 

 No; 15, the rod of chalk is half melted, and a yellow fub- 

 ilance produced by a mixture of the carbonate with the porce- 

 lain. No. 16 is a lump of chalk, in a ftate indicating foftnefs ; 

 a piece of porcelain, which lay in conta(5l with it, having fuok 



' a little into the fubftance of the carbonate. 



KTos. 17 and 18, being delicate, are inclofed in tubes of 

 ^lafs. No. 17, formed from pounded chalk, (hews in one 

 part the moft complete formation of fpar with its rhomboidal 



- fradure I have ever obtained. The carbonate having loft fomc 

 of its carbonic acid, had crumbled to much in its elTential parts 

 by the aftion of the air, that the cryltallization was no longer 

 vifible, and I had given up the fpecimen for loft till within 



thefe 



