19S 
ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
By separate experiments it was ascertained that water boiled in all three of the holes 
in the cone in 7 minutes after the commencement of filling, which may be taken as the 
time in which the mass of iron in the cone had reached 212° Fahr. 
It was also found that the firm surrounding solid crust had formed in 22 minutes 
(average), and that consolidation commenced in about 20 minutes from commencement 
of filling. As the difference between the temperature of the iron cone and of the slag 
was very great during the whole of this time, we may admit that the increments of 
heat imparted to the cone were equal for equal intervals of time, and the cone gained 
137° (or from 75° to 212° in these experiments) in 7 minutes. 
152. Hence, as 
7 : 137° : : 22 : a-, 
the temperature of the cone at the period of consolidation of the firm crust may be 
taken at430 c -6 Fahr. But as the interior of the cone was hotter than the outside, and 
so exercised an expanding effect upon the outer portions, we must increase that number 
somewhat, and may estimate it at 450° Fahr. 
153. The coefficient of expansion of cast iron, as given by Lavoisier and Bay (mean 
of both) is 
OOOOOOG18 for 1° Fahr., or 0-00278 for 450°; 
and this is the coefficient of expansion which, applied to the dimensions of the cold 
cones, give those at 450°, as in col. 3, Table II., which are those that fix the volume of 
the slag at the time of its first consolidation. 
154. The temperature of the liquid slag on entering the cone (sensibly the same as in 
the blast-furnace) was considerably above its fusing-point. It has been stated that the 
level of the top of the slag in the cone sunk rapidly, parallel to itself, and then, directly 
after a thin crust had formed, began to become concave. At this moment the mean depth 
of the top of the slag below the brim of the cone was taken by measurement. As the 
altitude of these cones is between four and five times the diameter of the brim, these 
measurements in depth afford very accurate determinations of volume, and it was found 
to average for the three experiments 130 cubic inches ; and as 8160 is the mean capacity 
of the cones as taken cold, corrected for temperature, it follows that, taking the volume 
of the liquid slag as filled into the cones at some temperature above its fusing-point at 
1000, the volume at its inceptive setting-point or fusing temperature is 983. 
155. To approximate to what these temperatures really were, it was necessary to obtain 
that of the blast-furnace itself, which may be admitted as that of the slag issuing from it. 
The difficulties attending the use here of any form of pyrometer, to say nothing of the 
uncertainties of the indications of those instruments, finally determined the writer to 
employ Pouillet’s method, or that of mixtures, by running out directly from the 
furnace a certain quantity of liquid iron into water of known weight contained in a 
large wooden vessel, and weighing afterwards to obtain the weight of the iron which had 
entered. The weight of water and of iron being known, with their specific heats, and 
