I 



FLUORIDE OF CALCIUM IN WATER. I59 



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 Will observes, 

 " fluorine occm-s in the teeth and hones 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 

 insolubiUty 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 Fluor me in Animals. 



As there exists, then, a twofold som-ce 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 occun-ence 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, f but he did not make any experiments on the subject. With the pre- 

 cipitate obtained by adding lime water to human urine, Beezelius 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 Beezelius' experiment, but quite unsuccessfully, and, as in 

 the case of bones, afl&rms that fluorine cannot be found in urine. I made but 

 one trial on the subject, but it was so decisively confirmatory of Beezelius' 

 original result, that it seemed unnecessary to repeat it. About 50 ounces of 

 urine (urina potiis), 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 urina 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. t Ann. de Ch., t. It. 



% Simon's Animal Chemistry, vol, ii. 



