156 
Analyses of Books. 
should be found at the surface of the globe, but probable that they might exist in 
the interior; and allowing this hypothesis, it became easy to account for volcanic 
fires by exposure of the metals of earths and alkalis to air and water, and to ex- 
plain, not only the formation of lavas, but likewise that of basalts and many other 
crystalline rocks, from the slow cooling of the products of combustion or oxydatioa 
of the newly discovered substances.” 
This opinion was given by Sir H. Davy in 1808, and he has since 1812 en- 
deavoured to collect such evidence as might throw light on it. Vesuvius is the moun- 
tain which he has principally examined, and the present paper contains the par- 
culars he has collected. 
“ One of the most important points to be ascertained was, whether any combus- 
tion was going on at the moment the lava issued from the mountain.” To determine 
this point some of the fused lava was put into a glass bottle furnished with a ground 
stopper to exclude the external air ; and on examining the air within the bottle, some- 
time after, no diminution was found to have taken place. 
He threw upon the surface of the lava nitre in mass and in powder ; no appear- 
ance occurred similar to what takes place when nitre is thrown on combustible 
matter raised to a high temperature. Some fused lava was thrown into 
water, and the disengaged gas collected. It was in very minute quantity, and 
when analysed proved to be common air almost pure. “ A wire of copper nt, of an 
inch in diameter and a wire of silver of ^ inch introduced into the lava near its source 
were instantly fused. An iron rod of | of an inch, and a piece of iron wire of 
about s ' 0 , were kept for 5 minutes in the eddy in the stream of lava, but were not 
melted. They did not produce any smell of sulphuretted hydrogen when acted 
on by muriatic acid.” 
“ A tin plate funnel filled with cold water, was held in the fumes disengaged 
with so much violence from the aperture through which the lava issued : fluid 
was immediately condem ed upon it, which was of an acid and subastringent. taste. It 
did not precipitate muriate of baryta, but copiously precipitated nitrate of silver and 
rendered the triple prussiate of potassa a bright blue. When the same funnel was 
held in the white fumes above the lava where it entered the bridge, no fluid was 
precipitated upon it, but it became coated with a white powder which had the taste 
and chemical qualities of common salt, and proved to be this substance absolutely 
pure.” 
“ A bottle of water holding about -J pint, with a long narrow neck, was emptied imtne- 
ditely in the aperture from which the vapours pressing out the lava issued, and the 
neck was immediately closed. This air examined on my return was found to give 
no absorption with solution of potassa, so that it contained no notable proportion of 
carbonic acid, and it consisted of 9 parts of oxygen and 91 of azote. There was 
not the least smell of sulphurous acid in the vapour from the aperture, nor were 
the fumes of muriatic acid so strong as to be unpleasant ; but during the last quar- 
ter of an hour that I was engaged in these experiments the wind changed and blew 
the smoke from the crater upon the spot where I was standing : the sulphur ms acid 
gas in the fumes was highly irritatiug to the organs of respiration, and I suffered so 
much from the exposure to them that I was obliged to descend.” 
In another visit Sir Humphry Davy made similar observations, with similar 
results. Neither pure silver nor platinum were at all changed in colour when ex- 
posed to the fused lava. The sublimations were collected from various parts of 
the cooled lava ; they were of a white yellow and reddish colour, and consisted chiefly 
of common salt, chloride of iron, and sulphate of soda. There was also in small 
quantity sulphate and muriate of potassa, oxyde of copper, and muriate of cobalt. 
The same observations nearly arc repeated in the details of other visits, with the 
addition of particulars relating to other phenomena, such as the subterraneous noises, 
the showers of stones, &e. which we regret we have not room to dilate on, and we 
must hasten at once to his conclusions. 
“ I shall now offer some observations on the theory of these phenomena. I* 
appears almost demonstrable that none of the chemical causes anciently assigned for 
volcanic fires can be true. Amongst these the combustion of mineral coal is one 
of the most current, but it seems wholly inadequate to account for the phenomena. 
However large a stratum of pit coal, its combustion under the surface could never 
produce violent and excessive, heat ; for the production of carbonic acid gas, when 
there was no free eirculation of air, must tend constantly to impede the process; and 
it is scarcely possible that carbonaceous matter, if such a cause existed should not 
he found in the lava, and be disengaged with the saline or aqueous products from 
the bocca or craters. There are many instances in England of strata of mineral 
