bf fc'ueral Mines of France. 2^9 



larly to thofe which it experiences till the moment when 

 it pafles into the hands of the confumer: hut thev were ob- 

 liged to confine their rxptrimtnts to each of thofe kinds of 

 coal placed at their difpofal iiy the coLincil, and which were 

 tranfniitted to t!icm direttly by the workers of the mines of 

 Creuflbtj St. Eticnne, Latcuipe, LL.barthe, Lacomballe, and 

 Decife. 



The mfethod by which they were able to afcertain the fpe- 

 cific gravity was as follows : 



After bringing the different kinds of coal ibove mentioned 

 to the uniform fize of peafe or beans, by lifting them, and 

 having carefully picked out all the eart'^v or fchiftous parti- 

 cles, the commiffioners filled a decalitre with each of them, 

 taking care to choofe thofe in the higheft ftate of drynefs, 

 and to pour them in without any fliock, as merchants do 

 who meafine them on the ground or in their barges. The 

 weight of each decalitre being afcertained, the dry coal con- 

 tained in the veflel was then watered in fucceffion without 

 Ihakingor difplacing it; and this was continued till the water 

 floated over the furface. The coals thus moiflened were again 

 weighed, and the difference of weight indicated the fpecific 

 gravity required, fince this article is impermeable to water, 

 which only fills up the vacuities left between the grains of 

 the bruifed coal by their uniting under a greater orlefs ob- 

 tufe angle. 



In regard to the increafe of weight arlfing from hume6ta- 

 !ion, ii will be fufficient to decant the fupernatant liquor ; 

 and the difference of the two, weighed as above, exprelTed 

 this fecond refult. 



They then moiflened fuccefHively, and ia different propor- 

 tions, each kind of coal ; fulfered the fuperf^uous water to 

 drain off for a quarter of an hour; and, comparing the vo- 

 Jume of the drv matter with that which it occupied at dif- 

 ferent degrees of humcftation, were able to difcover the pro- 

 greffive increafe or diminution bv employing for this purpofe 

 a wire placed exaftly level with the furface of the vedel. 



The table annexed exhibits the ferics of the comparative 

 experiments: indicating for each hectolitre of the kinds of 

 coal before mentioned the weight of that article in its flate 

 of drvnefs; that of the water introduced, which may be 

 confidered as folid ; the increafe of weight in the moiffencd 

 roals; the augmentation of its volume arifing from greater 

 or lefs humedtation ; the number of jjarts of folid coal in a 

 hundred parts of dry coal, and the f[)ccific gravity of ihc latter. 



It follows, from the labour of C. Duliamel and Blavicr, 



if^, That the increafe of weight is always in the dirett ratio 



•I the quantity of water added, which itidf increafes accord- 



K % iiig 



