PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 489 
inclosed in and under the dome. The lead was melted: in a dark room in a 
Bunsen furnace, which fitted closely round the sides of the pot, so that only 
the faintest glimmer of light escaped from between the surfaces of contact. 
Upon the melting of the lead, the floating iron sank slightly into it, effectually 
inclosing the shale fragments. Very shortly after the lead had liquefied, the 
iron was heard bumping against the sides of the pot; the sound of bursting 
bubbles was likewise audible; and wreaths of a flickering lambent vapour, 
which reflected apparently more light than that which escaped from the 
erevice in the furnace, were seen to ascend for a height of a foot or more from 
around the sides of the floating iron. The form of the iron was clearly 
delineated in black shadow in the midst of these luminous fumes, while the 
surface of the lead emitted no light whatever. Whether these gaseous 
exhalations be phosphorescent or not, the experiment was not arranged to 
determine,—they so appeared. ‘The result sufficed to show that the organic 
matter could be and was driven out of the shale at a heat. below redness. 
A quantity of the shale was next inclosed in a capacious iron retort, along 
with a large quantity of mercury; the retort placed in a furnace, and. the 
orifice of its tube conducted beneath jars filled with water, and standing in the 
pneumatic trough. 
There distilled: over—/jirst, water; second, carbonic. acid, mixed with white 
_ yapours of a hydro-carbon; third, a. combustible faintly-illuminating gas ; 
| fourth, mercury, along with vapours of paraffin, a highly-illuminating gas,.and 
a quantity of one of the paraffin oils ; 7th, mercury abundantly, much heavy 
| oil, and little feebly-illuminating gas; and finally, after anything but. mercury 
| had ceased to distil, the retort was: opened; whem there was: found much 
mercury remaining, with the fragments of shale; unaltered in shape and bulk, 
darker in colour, and somewhat greasy in appearance. 
On being analysed they yielded almost no»volatile ingredients, and about: 5 
per cent. carbon, which is less than when decomposed by a red. heat. 
These shales; therefore, are decomposed,, partially at. a: temperature some- 
what below that at which mercury boils, and. totally, as regards illuminants, 
at that temperature. 
Upon the examination, of the Lydian, stone bombs, it was found that they 
contained 6:9 per cent. of water,,of which 1-01 was hygroscopic ; now this is 
about the normal quantity of water for that mineral: wherever obtained ; the 
heat, therefore, had not reached the point at. which Lydian stone is: dehydrated. 
In operating to. discover the temperature:at which ordinary Lydian stone is 
dehydrated, it. was found to lose; when continuously heated just below visible 
redness, 1 ‘963 per cent.; at a feeble red heat, a total.of 4. 272:per cent.; at a full 
red, 4-503 per cent.; and when heated to whiteness in the furnace, 5 * 889 per 
cent. At the full red heat the powdered mineral slightly agglutinated ; while 
VOL. XXVIII. PART II. 6 L 
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