ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
201 
Table II. — Results of Experiments on Slag Contraction, Barrow Iron-Works. 
1. 
2. 
3*. 
4. 
5. 
6. 
7. 
No. of 
experiment. 
Dimensions of cones 
at 51° Fahrenheit. 
Dimensions of cones 
at 450° Fahrenheit. 
Cubic 
contents 
of moulds 
when cold. 
Temp. 
=51° F. 
Cubic 
contents 
of moulds 
at a 
temperature 
of 450° F. 
Volumes 
of cones 
of slag 
as measured 
at 53° F. 
Total 
contraction 
= difference 
of volumes of 
columns 
5 and 6. 
Dia- 
meter 
at top. 
Dia- 
meter at 
bottom. 
Height. 
Dia- 
meter 
at top. 
Dia- 
meter at 
bottom. 
Height. 
Cone No. 1 . . 
Cone No. 2 . . 
Cone No. 3 . . 
inches. 
14-25 
14-40 
14-30 
inches. 
16-00 
15-75 
15-80 
inches. 
46-00 
45-44 
45-45 
inches. 
14-28 
14-44 
14-34 
inches. 
16-04 
15-79 
15-84 
inches. 
46-12 
45-56 
45-57 
cubic inches. 
8274-1550 
8115-5705 
8091-9931 
cubic inches. 
8334-2310 
8175-0005 
8156-5373 
cubic inches. 
7646-2269 
7796-3884 
7658-0758 
cubic inches. 
688-0041 
378-6121 
498-4615 
Mean values.. 
— 
8160-5722 
8255-2896 
7700-2303 
521-6926 
Mean coefficient of total contraction, original volumc=1000, from 3680° to 53°, as 1000 : 932-76. 
Mean coefficient of contraction from fluidity to solidification, or (By estimation) from 3680° to 3000°, as 
1000 : 983. 
Or if volume at 53°= 1000, at or near above the fusing-point it will be 1072 nearly. 
Or if volume at 53°= 1000, at the temperature of solidification it will be 1017'3 nearly. 
161. On inspecting Table II. we arrive at the following results : — 
The coefficient of cubic contraction for the slag between the temperature of its issue 
from the furnace and that of its incipient consolidation, or between 3680° and 
3000°= x ^o, or the original is to the contracted volume as 
1000 : 983 ; 
and the coefficient of total cubic contraction, or that between 3680° and 53°, is nearly 
or the original is to the contracted volume as 
1000 : 933, 
which is scarcely 6 per cent, in place of 20 to 25 per cent,, as given by Bischoff. 
162. We thus at once see that the difference in specific gravity, less than that between 
ice and water, between red-hot but solidified or even cold slag (or analogous fused 
rocks) and the same in liquid fusion is so slight that, coupled with the viscous or 
pasty condition which intervenes between the two states, it would readily admit of 
a thin or a thick terrestrial solidified crust being supported by and upon the surface 
of the liquid globe beneath, and lends no support to the view of terrestrial consolida- 
tion at the centre first, by continual subsidence of such crusts, as imagined by Poisson, 
nor to the notions as to the nature of volcanic action which Sir W. Thomson has based 
on that assumption (Thomson and Tate, Nat. Phil. p. 726 &c.). 
163. A few experiments were made by the writer on the rate of cubic expansion of 
fragments (of a few pounds weight) at ranges between 55° and 600° Fahr., by heating 
them immersed in mercury in a glass vessel with a graduated stem, eliminating by cal- 
culation the expansion of the glass and the mercury, whose coefficients are well known. 
These seemed to indicate that within these low ranges the expansion of the slag does 
* The columns 3 are deduced from the coefficient of dilatation of cast iron, taken = 0-00000618 for l°Ealir. 
