196 
ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
It is usually of a light fawn colour, or of various shades of yellowish or bluish light 
grey. 
The following are typical analyses of those slags : — 
A. 
B. 
c. 
Silica 
. t 38-00 
40-93 
44-80 
Alumina 
. . 10-00 
9-49 
11-21 
Lime 
. . 42-00 
42-01 
36-05 
Magnesia 
. . 1-65 
0-68 
1-24 
Manganese protoxide . 
trace 
1-83 
2*12 
Iron protoxide . . . 
. . 2-08 
0-64 
0-84 
Potash 
. . 1-60 
0-591 
1-56 
Soda 
. . 2-03 
0-57) 
Sulphide calcium 
. . 2-45 
2-72 
2-35 
Phosphoric acid . . . 
• * 55 
0-01 
55 
All these analyses show an excess from oxidation of the iron and manganese in the 
process. 
The limestone used as flux contains about 97 per cent, carbonate of lime, with about 
2 per cent, of silica, alumina, magnesia, and protoxide of iron, so that the greater pro- 
portion of these last found in the slag were contained in the hcematite ores. 
146. If we compare these analyses with the following of basalts &c., it will be seen 
that these slags in composition approach them closely : — 
Basalts. 
A. 
B. 
c. 
Silica 
.... 36-68 
48-47 
55-16 
Alumina 
.... 14-341 
30-16 
7-42 
Iron oxide . 
.... 22-30) 
10-12 
Magnesia . 
.... 9-18 
6-89 
12-68 
Lime . . 
. . . . 15-59 
11-87 
13-60 
Soda . . . 
.... 3-93 
1-96 
0-66 
Potash . . 
.... 0-77 
0-65 
0-36 
A and C are the extremes of 11 analyses of various basalts, and B is the normal 
basalt of Bunsen, from a mean of many analyses (Blum’s Handbucli der Lithologie &c. 
I860, pp. 180-192). 
147. The difficulties in the way of obtaining any reliable measure of total contraction 
of fused rocks are undoubtedly great. Consideration as to their nature, and some pre- 
liminary experiments, caused the writer to conclude that the only method for approach 
to exactness was to operate upon very large volumes so as to extinguish many errors of 
experiment, and in such a manner that the volume of the fused rock could be directly 
measured , as well as its volume after solidification. 
148. Three very large and thick hollow cast-iron cones, open at both ends (used at 
