MR. KOBERT MALLET ON VOLCANIC ENERGY. 
195 
to Dr. Lloyd, of the Park Glass-Works) one of only 212 lineal, on blocks the largest of 
which was but 40 lbs. weight, and not rectangular in form, being lenses in fact. We 
shall see further on what reliability there is in these last. 
141. A few experiments on the expansion of rocks at high temperatures, but far below 
the fusing-points, by 1\. W. Fox, are recorded in the Philosophical Magazine for 1832 
(3rd ser. vol. i. p. 338). Granite increased in bulk at a dull red heat by from - 5 \ to yg-, 
porphyritic felspar (from an “ elvan course ”) the same ; clay-slate augmented in size, in 
the direction of the cleavage, to - 7 - 7 , by redness scarcely visible in the dark, and green- 
stone g-o - The whole of these statements look unreliable, and it is not clear whether he 
means cubic or lineal dilatation. 
142. Bischoff’s final results have been summarized by Mr. Forbes as follows: — 
Volume 
Volume 
Volume when 
when in 
when cooled 
cooled in the 
fusion. 
as glass. 
crystallized state. 
Basalt .... 

963 
896 
Trachyte . 
. 1000 
888 
818 
Granite . . . 
• »••••« 
888 
748 
so that the last is taken to suffer a contraction of about one fourth of its liquid volume ! 
The distinction made between the glassy and the crystalline states is, in this case at 
least, to a great extent arbitrary ; for all mixed silicates which crystallize segregate in 
cooling into crystallized bodies which float in a surrounding glassy magma that never 
crystallizes (unless perhaps when devitrijied by long heating), and it depends upon the 
relative proportions of the two, and upon the rate and other conditions of cooling, whether 
the intermingled crystals shall ever coalesce or the entire mass ever assume a crystalline 
state. 
Beyond the experiments now noticed, the writer is not aware of any others involving 
high temperatures, although we possess some good and reliable data as to the expansion 
of some stony bodies at temperatures not much exceeding the boiling-point of water. 
143. The writer therefore found it necessary to institute experiments himself as to the 
total contraction between liquid fusion or above it and solidification of such bodies as 
might represent tolerably closely in chemical and physical qualities the basic and the 
acid silicates of the natural rocks we are acquainted with. 
The blast-furnace slags of the Barrow Iron-Works seemed to approach pretty nearly 
the former, and British plate-glass the latter. 
144. The writer has to thank Mr. T. F. Smith, the Manager, for enabling him to 
conduct his experiments at the Barrow Works (near Furness Abbey, Cumberland), and 
Mr. Murdock, of the same Works, for aid in carrying them out. 
145. At those Works red haematite only is smelted by coke fuel, with a very pure 
limestone as the sole flux, in blast-furnaces of the very largest class, urged by blast at a 
temperature of 700° to 900° Fahr. The slag formed when the furnaces are making fine 
grey pig iron (for the production of Bessemer steel) was that chosen for experiment. 
mdccclxxiii. 2 D 
