Wlien wc talk nbout " coal," i t is not suficicntly rcaliscd that this is n gcncrnl namc for a class of mntcriol rathcr than a substnncc of tlefinitc composition nnd chnrnctcristics. Con1 may rangc from thc almost pure carbon known as antliracitc to tlic scmilignite with no uncombincd cnrbon in its composition, nnd consisting mainly of volatilc hydrocnrbons, nioisturc and inconibustiblc mnttcr or nsli. 33ctn.cen tlic two cstrcmcs mentioned there is mi infinitc vnrintion in tlic composition. \Thilc, on tlic onc hnnd, thc vnrintion in tlie propcrtics of coal prcscnts tlic \diinl)lo fcntiirc that we linrc a sclcction of \ d i n t is virtually n lnrgc variety of conibustiblc nintcrinl, cnch variety of which has certain propertics which makc it of cspccinl valric for spccific purposes, on tlic otlicr hand tlic variability, if ncglcctcd, niag icnd to considcrnblc financial loss through insuff icicnt nttcntion to the pnrticulnr properties rcquircd in the fuel for the spccinl work to which it is to tic applicd.
Only too often is the purclinse of fucl for ninnufncturing works left in the hands of a quite 11011tcclinical Stores Dcpartnicnt which nsks for con1 of some particulm iininc or decides upon purclinsc 011 the basis of sizc and pricc only. Such n nietliod of buying almost invariably lcnds to finnncinl loss, I)ocausc cvcn with coal from tlie snnic scam tint1 pit large variations will occur from tinic to tinic in tlic coinposition of thc fuel supplied, whilst tlic lnbcl on the truck or nanic of coal on tlic invoicc docs not always givc a corrcct description of tlic niiitcrinl supplied by thc agent.
This scrics of articlcs bcing particuliirly conccrncd with mntters rclnting to stcnni raising, \ I C will confine oursclws to tlie discussion of thc tlcsirnblr: propcrtics to bc lookcd for d l c n selecting H suitable fucl for economical steam raising.