4|^ Pi-oportions ofCurlin in Mineral CoaL 



comatft wlili tlif nitre. Hciice in the experiments of Mr. Hiclm on the quantittes of char- 

 coal of different woods requilite to alkalize 100 parts of nitre, we find thef« quantities to 

 bear for the moil part fome analogy to their fpecitic gravitie?, being generally fuialler when 

 the fpecific gravity of the charcoal is lighter; thus *: 



Grains requifite to alkalize 1 00 grains of nitre. 



Specific gravity. Firft experiment. Second ditto, 



35 , 30 



22 22 



2p. 20 



3J *S- 



19. 



Another circtimtlance of great importance towards procuring juft and uniform refults Is,. 

 that the proje£lions of coal (hould (uccecd each other without delay as foon as the flame 

 •eafes ; for, as ignited nitre gives out pure air fpontaneoudy, and fo much the more as it i) 

 more heated, the acid will be deoonipofed, and the i)itre alkalized, by a quantity of coal fo 

 much the fmaller as the intervals of projeclion are longer. From inattention, perhaps, to 

 this and the laft-mentioned particular, as well as from various conditions of common char- 

 coal, which feldom contains Icfs than -^'j, and often y of its weight of moifture and ab- 

 forbed air, proceeded the various refults of diffeient chemifts, with refpeft to the proportion 

 of it necelTary to alkalize nitre. 



It is almoll fuperfluous to add, that the charcoal Ihould be proje£led in very fmall por- 

 tions. I feldom projefted more than one or two grains at a time : each operation lafted 

 from 20 to 25 minutes nearly. 



There is alvirays fome portion of nitre undecompofed, being protefled by the funrounding 

 alkali. This error is unavoidable, but very fmall. Even the pofition of the crucible in the 

 furnace is not indifferent ; for, if it be near the flue, naore coal muft be employed, which I 

 attribute to the torrent of air, which, in that cafe, affe£\s and carries away more than when 

 tlie crucible is nearer to the anterior part of tlie furnace. 



It may, perhaps, be fufpedled that this and fome other incidental errors may be avoided 

 by previoufly mixing the nitre and coal, and proje£ting the mixture in fmall portions into 

 a red-hot crucible ; but not to mention that this method fuppofes the due proportion of 

 thefe two fubftances to be known, which cannot be till after the experiment, and that alfo 

 •very atom of thefe fubftances is in perfect conta£t with the other fubftance, clfe they can- 

 not a£l on each other— independently, I fay, of thefe unfounded fuppofitions, this mode 

 of experimenting is ftill more fallacious than the former, as during thefe proje£lions a con- 

 siderable proportion of the nitre is fcattered and difperfed, and may be feeruadhering to the 

 fides of the crucible. This lofs being repeated at every projeclion, becomes at laft intolerable. 



I now proceed to relate the experiments themfelves, conduced in the manner I have 



mentioned. The different fpecies of coal and bitumen, whofe compofition I have thus 



examined, were Kilkenny coal. Maltha, Afphalt, Lancaftiire cannel. Slaty, Scotch canncl, 



Whitehaven, Wigaii, Swanfey, anjl Leltrim; fele£ling of each fort the pufcft l^etrimens, 



free from pyrites and vifiblc ftony matter. 



• Schwcd. AbhiuiJ!. 1781, iSS. 



5 Kilhttwy 



