Sto Effects of Heat modified hj Compression. 



and without any stony character ; when less tlian 2 or 3 per 

 cent., it was considered as good, and possessed the proper- 

 ties of a natural carbonate. In the intermediate cases, when 

 the loss amounted, for instance, to G or 8 per cent., the 

 result was sometimes excellent at first, the substance bear- 

 ing every appearance of soundness, and often possessing a 

 high character of crystallization ; but it was unable to resist 

 the action of the air; and, by attracting carbonic acid or 

 moisture, or both, crumbled to dust more or less rapidly, 

 according to circumstances. This seems to prove, that the 

 carbonate of lime, though not fully saturated with carbonic 

 acid, may possi-ss the properties oF limestone ; and perhaps 

 a diHercnce of this kind may exist among natural carbonates, 

 and give rise to their difterent degrees of durability. 



I have observed, in many cases, that the calcination has 

 reached only to a certain depth into the mass; the internal 

 part remaining in a state of complete carbonate, and, in ge- 

 neral, of a very fine quality. The partial calcination seems 

 thus to take place in two different modes. Bv one, a small 

 proportion of carbonic acid is taken from each particle of 

 carbonate; bv the other, a portion of the carbonate is quite 

 calcined, while the rest is left entire. Perhaps one result is 

 the effect of a feeble calcininti; cause, actinjr durinir a long 

 time, and the other of a strong cause, acting for a short 

 time. 



Some of the results which seemed the most perfect when 

 first produced, have been subject to decay, owing to partial 

 calcination. It happened, in some degree, to the beautiful 

 specimen prod\iced on the 3d of March 1801, though a 

 fresh fracture has restored it. 



A specimen, too, of marble, formed from pounded spar, 

 on 13th May 1801, was so complete as to deceive the work- 

 man employed to polish it, who declared, that, were the 

 substance a little whiter, the quarry from which it was taken 

 would be of great value, if it lay within reach of a market. 

 Yet, in a few weeks after its formation, it fell to dust. 



Numberless specimens, hcnvever, have been obtained which 

 resist the r.ir, and retain their polish as well as any n)arble. 



Some 



