375 On the relative Proportions of Coals and 
In the application of iron-ftone ‘in the blaft-furnace, the 
following particulars ought rigoroufly to be attended to :— 
1. Their mixtures, whether clay, lime, or filex: their 
relative proportions to each other, judging according to the 
rules formerly laid down; which of them may admit of a di- 
minution of fuel ; which of them will afford the quality of 
iron at the time requifite; and which of them will be moft 
likely, by a judicious arrangement, to give the greateft pro- 
duce of metal, united with value and ceconomy. Iron-ftones, 
united with large portions of filex, have already been ftated 
to require a greater proportion of fuel to carbonate their metal 
than the other genera. When ballaft or forge-pigs are 
wanted, it ftands to reafon that filiceous iron-ftones ought 
to be ufed; not that they contain a greater quantity of iron, 
but becaufe they form a fubftitute for the other kinds, which 
may be more advantageoufly fmelted for the produétion of 
more valuable qualities. 
2. Thequantity of metal which each individual iron-fionemay 
contain, is another object of confideration. Befides the pro- 
portion of mixtures, which chiefly contribute to the fufibility 
of iron-ftones, a fecond degree of fufibility is dependent upon 
the richnefs of the ore in iron: this is fo obvious in the ufe 
of the Cumberland and Lancathire ores, that the ‘confe- 
quences of their introduction will be perceived, by the change 
of the fcoria and metal, in half the time that change would 
be effected by ordinary iron-ftones. It has been frequently 
noticed, that crude iron contained pure carbon in proportion 
to its fufibility ; then the more fufible, or fupercarbonated 
qualities, muft take up, comparatively, a confiderable portion 
of the carbonaceous principle from the fuel. From this refults 
a ftriking confequence, that the quantity of fuel fhould, over 
and above its relation to the mixtures, bear a juft proportion 
to the quantity of iron in the ftone: for example, let the 
weight per charge of fuel at a blaft-furnace be 400lb., and 
let this be fuppofed fufficiently to fufe and carbonate the iron 
contained in 360 |b. of iron-ftone; let the quantity of metal 
be fuppofed 35 per cent. then the produce will be 126 lb. 
Should a change take place, and iron-ftone richer in iron be 
applied, though the fame by weight, and fhould this iron- 
ftone 
