Effects of Heat modified ly Compression. \§9 



parency, and their susceptibility of polish, deserve the name 

 of marble. 



The same trials have been made with all calcareous sub- 

 stances ; with chalk, conuiion limestone, marble, spar, and 

 the shells of fish. All have shown the same general pro- 

 perty, with some varieties as to temperature. Thus 1 found, 

 that, in the same circumstances, chalk was more susceptible 

 of agglutination than spar ; the latter requiring a heat two 

 degrees higher than the former, to bring it to the same pitch 

 of agglutination. 



The chalk used in my first experiments always assumed 

 the character of a yellow marble, owing probably to some 

 slight contamination of iron. When a solid piece of chalk, 

 whose bulk had been previously measured in the gage of 

 Wedgewood's pyrometer, was submitted to heat under com? 

 pression, its contraction was remarkable, proving the apr 

 proach of the particles during their consolidation ; on these 

 occasions, it was found to shrink three times more than the 

 pyrometer-pieces in the same temperature. It lost, too, al- 

 most entirely, its power of imbibing water, and acquired a 

 great additional specific gravity. On several occasions I ob- 

 served, that masses of chalk, which, before the experiment, 

 had shown one uniform character of whiteness, assumed a 

 stratified appearance, indicated by a series of parallel layers 

 of a brown colour. This circumstance may hereafter throw 

 light on the geological history of this extraordinary sub- 

 stance. 



I have said, that, by mechanical constraint, almost the 

 whole of the carbonic acid was retained. An<i, in truth, at 

 this period some loss of weight had been experienced in all 

 the experiments, both with iron and porcelain. But even 

 this circumstance is valuable, by exhibiting the influence 

 of the carbonic acid, as varied by its quantity. 



When the loss exceeded 10 or 1,5 per cent.* of the weight 

 of the carbonate, the result was always of a friable tc:iturc, 



• 1 have found that, in open fire, the eniire loss sustained by t)ie ciirtsonate 

 varies in difTercnt kinds from 4'2 to ■\f>-S per cent. 



N 4 aiul 



