92 Dr Rees on Fluoric Acid in Animal Matter. 



pitate of phosphate of silver was thrown down. A further 

 examination shewed the presence of sulphuric acid, and traces 

 of hydrochloric acid. I was much sui*prised to find phosphoric 

 acid in this result of aqueous distillation, as the heat had not 

 been m'ged during the process ; for I had considei'ed that acid 

 was of too fixed a nature to volatilize with water at so low a 

 temperature. It appeared to me now, that the presence of 

 phosphoric acid, in this distilled liquor, might be a source of 

 fallacy in the above experiment for establishing the presence 

 of fluoric acid as a constituent of human bone ; for it is a well 

 known fact, that phosphoric acid, if heated on glass of inferior 

 quality till it volatiUze, will act upon it with considerable 

 energy,* and all the animal substances in which fluorine has 

 been said to exist, are particularly rich in phosphoric acid; — 

 thus the ashes of ivory, of human bone, and the enamel of 

 teeth, as also the precipitate obtained from urine by means of 

 lime-water, are all of them composed, in very great part, of 

 phosphate of lime. 



Mr Richard Phillips has mentioned (in the Ai^nals of Philo- 

 sophy, Vol. v.), that when the water contained in uranite is 

 driven off from the powdered mineral, a portion of the phos- 

 phoric acid is volatilized with it ; the heat used being that of 

 a common spirit-lamp. This is the only fact with which I am 

 acquainted (with the exception of my own observation), to 

 shew that phosphoric acid will volatilize with water. The 

 heat used in Mr Phillips's experiment was, most probably, con- 

 siderably higher than any which I applied. There seems no 

 doubt that phosphoric acid is much more volatile than it has 

 heretofore been supposed. Having failed in detecting fluoric 

 acid in human bones, I determined on testing for its presence 

 in the enamel of teeth, in recent ivory, and in the precipi- 

 tate obtained from urine by the addition of lime-water. Two 

 different specimens of ivory (tusks of the elephant) gave no 

 evidence of the presence of fluoric acid, when carefully tested, 



* It must be borne iu mind, tliat the fluoric acid acts with facility on every 

 kind of crown or flint glass, however good their quality may be. The sup- 

 position that bad glass was used in the experiment, is the only means I 

 liavc of explaining away that which 1 feel sure is an error on the pai't of 

 several continental chemists. 



