82 
of Iron Ores,” giving full descriptions and results of the 
mode of testing such ores, as practiced in the Assay Labora- 
tory of the School of Mines of Columbia College. The ores 
employed were mainly magnetite, hematite, and limonite; 
also siderite, ilmenite, and franklinite. 'The furnace had a 
cross section of 18 inches square, and a depth to the grate 
bars of 21 inches. The fuel employed was anthracite. 
Specimens of the crucibles used, (Hessian) were first shown, 
and the mode of preparing them described. They are filled 
with a brasque composed of pulverized charcoal, 4 parts, and 
molasses, 1 part, carefully kneaded and packed. A conical 
hollow is then cut out, and its interior well polished, to ren- 
der the button obtained smooth. With such a lining, the 
slag neither adheres, nor takes up any foreign matter; and 
hence it may be weighed in verification of the assay. 
Into this smooth cavity the ore and fluxes are charged, 
after thorough mixing: a thin charcoal cover is then laid on, 
and the whole luted up. The charge of ore is ten grammes. 
As the object is to learn not the absolute percentage of metal 
so much as the probable yield on a large scale, the usual 
blast furnace fluxes are used. These of course vary much 
with the ore. If the composition of the latter is known, it is 
easy to compute the flux needful, to give a slag of the ordin- 
ary blast furnace type,— 
R20;,Si0s, +2(3RO,Si03) 
according to Percy; where the sesquioxide is alumina, and 
the protoxides mainly lime and magnesia. 
If the composition of the ore is not known, three trial- 
fluxes are prepared,—an acid one, a neutral, and a basic,— 
one of which usually gives a good result. 
Eight crucibles are introduced at once, resting upon fire- 
bricks in the midst of the glowing coal. The furnace is filled 
with fuel above the tops of the crucibles ; and the fire is kept 
up in force from 21 to 8} hours, according to the ore. With 
two furnaces, therefore, one man can make, in a single day, 
16 assays in duplicate: these should not differ by more than 
if; of one per cent; and with proper care they will show very 
nearly the real percentage of metal in the ore. But if the 
