Shak ae aes “ 


( 483.) 
XXXII-—On two New Processes for the detection of Fluorine when accompanied by 
Silica ; and on the presence of Fluorine in Granite, Trap, and other Igneous 
Rocks, and in the Ashes of Recent and Fossil Plants. By Georce Wi1son, M.D. 
(Read April 19, 1852.) 
In several communications made to this Society and to the British Associa- 
tion, I have announced the results of a series of observations on the distribution 
of Fluorine throughout the mineral, vegetable, and animal kingdoms. To myself, 
the least satisfactory part of these investigations has been the inquiry into the 
presence of fluorine in plants, for I have been more frequently foiled than suc- 
cessful in my attempts to detect it in them. Others have not, apparently, been 
more successful. DAvBENY was as unable as SPRENGEL at an earlier period had 
been, to obtain evidence that the element under notice is present in vegetable 
structures; and Wit of Giessen, the discoverer of fluorine in plants, speaks only 
of “ traces” of it having been detected in barley. Later observers have not spoken 
more confidently concerning its abundance in vegetables; and in the many ana- 
lyses of the ashes of plants which have recently been published, it seldom, if ever, 
finds a place. 
That one cause of this apparent rarity of fluorine in vegetables, is the small 
extent to which it occurs in them is certain ; but I have never doubted that the 
chief reason why it appeared to be so scanty a constituent of plants, was its 
occurrence along with silica, which makes its recognition very difficult. I had 
given up, accordingly, all hopes of satisfactorily demonstrating its wide distribu- 
tion, till better processes than are at present in use, were devised for its de- 
tection when accompanied by silica. 
For the same reason I have thought it hitherto useless to endeavour to trace 
back fluorine from the plants, animals, natural waters, and more accessible strata 
which are the main seats of life at the present day, to those earlier rocks and 
geological formations which have furnished our soils, and have contributed the 
chief soluble matters which are found in the lakes, rivers, and seas of the globe. 
The more ancient rocks abound in silica, and, with our present processes, the 
prospect of discovering fluorine in trap and similar siliceous masses, was not 
encouraging. A representation, however, from Professor JAMESON, as to the im- 
portance attaching to the detection of fluorine in the most ancient rocks, led me to 
reconsider the geological and mineralogical interest which the inquiry possessed ; 
and within the last six weeks I have put in practice two methods of investigation, 
which | shall now explain. 
VOL. XX. PART III. 60 
