FLUORIDE OF CALCIUM IN WATER. ' 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 prociu-ed 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 pai-t at least, have 

 been owing to fluoride of calcium being present in solution. In the 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 hoUow crystals, it will be acknowledged that water, if not the true, 

 would at least be a sufiicient 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 roimd 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 akeady known to occur in 

 many minerals besides fluor-spar. It has been found in hornblende, as weU as 

 in mica, in apatite, waveUite, wagnerite, urinite, phosphorite, &c., along with 

 phosphate of lime. Berzelius and Rose* found it in sulphate of barj^ta ; so did 

 MiDDLETON. I have found it there also ; I have likewise obtained it in one case 

 from gypsum. It has been found in other sulphates, and Middleton 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. Middleton's 

 detection of fluoride of calcium in the shells of marine moUusca, and Silliman'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 cany 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 Rose's Quantitative Chemistry, p. 348. 

 VOL. XVI. PART II. 2 E 



