ON THE MANUFACTURE OF IRON. 747 
that of the comparative volatile nature of the earths, or of the comparative 
facility with which they are decomposed and vaporized. In all the analyses 
hitherto made by the writer, the composition of none of these slags corresponds 
with the amount of earthy matter introduced into the furnace ; thus, in the 
three specimens of slag from the Clarence furnaces, the silica, alumina, lime, 
and magnesia bear the following average ratio to each other, as expressed in 
whole numbers :— 
Silica. Alumina. Lime. Magnesia. 
> RE ie ae a eee Sr, ee RE Eo 
After analyzing the Normanby ironstone which was used about that time, 
and adding to its earthy constituents those introduced in the coke and lime- 
stone, the slag, by calculation, should have been, as regards the above-named 
elements, composed of — 
Silica. Alumina. Lime. Magnesia. 
29 + 16 + 46 + 9, -=1, 190 
The analysis in the School of Mines would, it is true, give a somewhat 
different result, but one which, nevertheless, does not correspond with actual 
examination of the slags, even had a similar quality of mineral been in use at 
Clarence. The Eston stone smelted with the same kind of coke and limestone 
should have given slags containing the earths in the following proportions ;— 
Silica. Alumina. Lime. Magnesia. 
28 + 18 + 45 + 9 = 100 
There escapes, as may be easily seen, from the furnaces on the Tees, cc., 
vast volumes of white vapour, which condense, or partly condense, with great 
facility. That there is a difference in the readiness with which it does this 
may be inferred from the fact, that while large quantities of condensed matter 
are intercepted in the pipes for leading the gas to the boilers, a great amount 
travels many yards before it reaches a lofty chimney, from which it escapes 
as a white cloud, and this cloud goes a long distance in the atmosphere before 
it is finally dispersed. Nothing short of entire interception of the vapour will 
enable us to judge whether the discrepancy between calculation and fact can 
be reconciled. The writer is now engaged in arranging a steam-pump which, 
by continued exhaustion through water or otherwise, will effect, no doubt, 
complete condensation of each of the component parts of this fume, when some 
light may be thrown upon the nature of the volatilized portions of the minerals 
used in our blast-furnaces. ; 
This fine dust has been examined at the Clarence Laboratory, and although 
the analysis proves nothing, having been taken at one place only in the con- 
necting pipes, a statement of its composition may not be devoid of interest. 
It gave— 
Silica and sand aa ae 5 we ais 34°82 
Alumina iS ‘tg Fe tes BA ae 16°00 
Lime ... ne wee oie sea so oi 12°15 
Magnesia ots ed Fee oe et oe °57 
Peroxide of iron as = afi = Sea 8*20 
Oxide of zinc ... cc og oa sis a a ha HOO 
Sulphuric acid os “5 es ss ass 8°80 
Potash... Pee oot = ae te Bh *40 
Soda ... ote eee pe ae ot oe 6°85 
Chlorine o> re ag 4 7 oa 1°56 
Water ... a a = He ae aie 5°60 
99°55 
__ From a more recent examination of the fume, taken at different distances 
from its point of exit from the furnace, the varying proportion of lime would 
indicate that this earth maintains the condition of vapour longer than the 
other constituents of the condensed matter :— 
