Answer to Observations on Vegetation. 353 
many times to the same process, after having triturated it, and 
agitated it with the same acid, it first became fluid, afterwards 
divided into globules, and finally appeared purified mercury si-+ 
milar to that produced by the preceding experiments. Hence 
it appears that, by,the action of sulphuric acid aided by the me- 
chanical division effected bv agitation, the adulterated mercury 
of commerce, and even that which contains a greater portion 
of extraneous metals, may be purified in a manner sufficient to 
serve all the common purposes of experimental philosophy and 
chemistry. This method does not require continual attention, 
is not expensive, particularly where the mercury is little altered, 
aud does not expose the operator to any danger. 
LVII. Answer to W. H. G.’s Observations on Mr. Tatum’s 
Experiments on Vegetation. By Mr. J. Tatum. 
To Mr. Tilloch. 
Sir, — Vicon correspondent, W. H. G., in reply to the paper 
I communicated to your Magazine of July, accuses me of * un- 
pardonable ignorance for pretending to enlighten one of the most 
controverted subjects of experimental science, by views and ex- 
periments which have been detailed in half a dozen professed 
treatises, and otherwise promulgated in every possible way.” 
Lucca baths has published someaccount of them: but, as usual with writers on 
baths, his workis more panegyrical and historical than chemical ;—-a much bet- 
ter account may be expected from his relative Dr. Domen. Pieri, professor 
of chemistry in the college of Lucca. A very satisfactory and able analysis 
of the Pisa bath waters may also be expected from the modest and ingenious 
author of the preceding memoir; who pursues the discovery of facts with 
unremitting zeal, and leaves the development of crude theories to those 
self-called chemists. whose pen, ink, and paper are more useful to them 
than acids, retorts, and furnaces. There are still persons who ascribe these 
hot-baths to the influence of volcanoes; but there is not the smallest trace 
of any thing like volcanic matter, or even any combustible substance, to be 
discovered within many miles of them; nothing that, either chemically or 
geologically speaking, could sanction the belief that they owe their warmth 
to exhausted subterraneous volcanoes. Vast ridges of mountains surround 
them, ertirely of carbonat of lime or hard and coarse marble, with occasion- 
ally veins of felspar, rock crystal, and very rarely traces of tourmaline; but 
very considerable intersections of these calcareous masses frequently oceur, 
consisting of various combinations of magnesia and lime, forming all the 
gradations from the hardest to the most friable schist. Gypsum and pyrites, 
particularly the former, are of rare occurrence, and never in such quantities 
as would sanction the conjecture that the caloric developed by the decom- 
position of the latter might contribute to raise the temperature of these 
Springs. It is true that in the valleys adjoining these hot springs inflamma 
ble gas, chiefly carburetted hydrogen, abounds ; but whether connected as 
a cause or an effect is not so easy to determine. 
~ Vol. 50. No. 235, Nov. 1817. Z From 
