a5o On the Specific Gravity i>f the Coals 



ing to the degree of the trituration of the coal, and in the 

 inverfe ratio of the fpeciJic gravity of the article. 2d, That 

 the latter alfo is in the inverfe ratio of the weight of the liquid 

 which the dry coal retains after decantation. 3d, That the 

 increafe of volume is the move fenfible as a greater quantity 

 of humeftation has been produced j and that there exifls a 

 term at which the addition of water occafions no change, 

 and beyond which the volume decreafes in determinate pro- 

 portions. 4th, In the laft place, that all thefe rcfults vary 

 not only in regard to the different kinds of coal, but even in 

 the fame kind of coal, according to its nature, its mixture 

 with parts more or lefs earthy, and particularly its fize or 

 degree of trituration. 



The mod natural conclufion to be deduced from thefe ex- 

 periments is, that in the fale of coals there may be introduced 

 abufes, which it will be of more importance to reform, as in 

 100 parts of dry coal there are fcarcely 70 parts of folid coal ; 

 and befides, it is proved, that from humeftation carried to a 

 certain degree, there may refult an augmentation or diminu- 

 tion of volume to the lofs of the confumer or even of the 

 merchant himfelf. 



In confeqxxence of thefe confidcrations, C. Duhamel and 

 C. Blavier, in a report dated Pluviofe 8, year 10, have con- 

 cluded that the fale of coals by weight is atlei;ded with the 

 fame inconveniences as thofe which take place in a deter- 

 minate meafure of capacity. They perfift in believing that 

 the combinations of the two methods could not be employed 

 but on the fuppofition of coal entirely dry, and yet by ex- 

 preffing a wiili that an accurate table of the fpecific gravities 

 of all the coals in France, coinparing them with each other 

 in different degrees of fize and humeftation, might be drawn 

 out. The refult would at leaft be approximative data, by 

 help of which ;i^ would be poffible to expofe the (hameful 

 traffic of fome coal-merchants, who alter the nature of their 

 commodity by mixtures more or lets earthy. This labour 

 would be particularly important were it accompanied with 

 experiments proper for determining t]\e real value of coal in 

 regard to the ulc for which it is bed fitted. It is thus, for 

 example, that C. Blavier has already found, by repeated 

 trials, that the fcra of Decife muft be felefted to heat rever- 

 berating and evaporating furnaces in preference to the fmall 

 coal of St.Elienne; while the latter, which is fold in general 

 for at leaft a fourth more, may be employed with advantage 

 in forges and in all circumftances where a fi.rong concen- 

 trated heat is required. The mixture of thefe two kinds of 

 coal, in the proportion of four to three, gave him an article 

 of fuel the more valuable, ,as, by fuiuifhing a more ardent 



and 



