FLUORIDE OF CALCIUM IN WATER. 159 
mined in the present state of our knowledge. But fluorine may be expected 
to occur in the fluids of all the higher plants. On this subject Wit. observes, 
“fluorine occurs in the teeth and bones of animals, having been derived by them 
from vegetable food; it will doubtless, therefore, exist still more abundantly in 
the ashes of plants.”* This expectation was probably founded on the supposed 
insolubility of fluoride of calcium in water, and is not likely to be fulfilled. 
Animals which may derive fluorine both from their solid food, whether animal or 
vegetable, and likewise from the water they drink, are likely to excel plants in 
the proportion of fluorine they contain. 
6. Of the presence of Fluorine in Animals. 
As there exists, then, a twofold source of fluorine for animals, we may antici- 
pate its occurrence in various parts of their structures. Passing by for the 
moment, as a disputed point, the occurrence of fluoride of calcium in recent 
bones, and excluding the consideration of its presence in shells and corals, it may 
be noticed that the urine of man is the only animal product in which fluorine has 
been quite certainly ascertained to occur. Gay Lussac appears to have been the 
first who suggested the probability of fluorine being found in the secretion of the 
kidneys,+ but he did not make any experiments on the subject. With the pre- 
cipitate obtained by adding lime water to human urine, Berzeius etched glass 
distinctly ; and from the period of his experiments, fluorine has been ranked among 
the normal, or at least the occasional, ingredients of the fluid in question. The 
fact, however, has always been referred to with a kind of hesitation, and had it 
rested on the authority of any less distinguished chemist than the great Swedish 
one, it would have dropped, I fear, out of notice altogether. t 
REEs repeated BERZELIUS’ experiment, but quite unsuccessfully, and, as in 
the case of bones, affirms that fluorine cannot be found in urine. I made but 
one trial on the subject, but it was so decisively confirmatory of BERZELIUS’ 
original result, that it seemed unnecessary to repeat it. About 50 ounces of 
urine (wrina potus), were precipitated by nitrate of baryta, which, for reasons 
already fully detailed, is preferable to lime, as forming a less soluble salt with 
fluorine. The precipitate, consisting chiefly of sulphates and phosphates, was 
collected on a filter, and dried without washing. Warmed with Nordhausen 
acid, it corroded glass deeply, the lines being filled with white silica, exactly 
as if fluor-spar had been used. In none of my experiments, except with the 
dissolved fluor, and with sea-water, has the etching been so distinct as it was 
in this case. I recommend those who wish to succeed in this experiment to 
employ what the older physiologists distinguished as wna potus. In districts 
where fluorine is not abundant in the soil or waters, it may not so frequently 
* Chemical Society’s Memoirs, vol. ii. p. 182. + Ann. de Ch., t. lv. 
{ Smon’s Animal Chemistry, vol. ii. 
