FLUORIDE OF CALCIUM IN WATER. s 157 
which penetrated most readily between the planes of cleavage.” The contents of 
the different crystals were not alike, and, unfortunately, Mr Fox, doubtless from 
the belief that fluor-spar is insoluble in water, made no search for that substance 
in the liquid procured by breaking the hollow octohedrons. In several cases, 
however, it precipitated nitrate of baryta and oxalate of ammonia, an action re- 
ferred to the presence of sulphate of lime, but which may, in part at least, have 
been owing to fluoride of calcium being present in solution. Inthe matrix of these 
crystals, alternate layers of quartz and fluor-spar were found in lines like fortifica- 
tion-agate. When we connect these facts with the solubility both of fluoride of 
calcium and of silica in water, and with the observed presence of fragments of the 
former in the hollow crystals, it will be acknowledged that water, if not the true, 
would at least be a sufficient cause of the phenomena described by Mr Fox, and 
of the still more familiar one of square impressions on quartz, previously referred 
to. I have tried the experiment of placing powdered fluor-spar on a filter, and 
percolating distilled water through it, and have found that the latter precipitated 
oxalate of ammonia. Whilst, however, I think it cannot be denied that water in 
contact with fluor-spar must round off the edges of its crystals and dissolve it 
away, we have no data from which to determine what effect salts held in solution 
by water may have in increasing or diminishing its solvent power. 
It is necessary to mention here that fluorine is already known to occur in 
many minerals besides fluor-spar. It has been found in hornblende, as well as 
in mica, in apatite, wavellite, wagnerite, urinite, phosphorite, &c., along with 
phosphate of lime. Brrzexius and Rose* found it in sulphate of baryta; so did 
Mipp.LetTon. I have found it there also; I have likewise obtained it in one case 
from gypsum. It has been found in other sulphates, and MippLeTon has fre- 
quently detected it in carbonate of lime. In general, it may be expected to occur 
along with the insoluble salts of baryta, strontia, and lime, and probably also 
with those of lead, especially when these are of aqueous origin. MmppLETON’s 
detection of fluoride of calcium in the shells of marine mollusca, and SrLLIMAN’s 
recent elaborate analysis of corals, which resulted in shewing that in nine different 
species (the only ones in which it was sought for) fluoride of calcium occurred, 
lead directly, as the latter gentleman has indicated, to the conclusion, that shell, 
coral, and metamorphic limestones, may be expected to contain that salt. When 
to these sources of fluorine we add animal remains, especially their bones and 
excretions, but in truth their whole mass, it will be manifest that in all parts of 
our globe, water may meet with fluorine, and carry it into the tissues of plants 
and animals. This remark leads directly to its occurrence in the two latter ; 
and, first, of plants. 
* Griffin’s Rosé’s Quantitative Chemistry, p. 348. 
VOL. XVI. PART II. 2k 
