071 the non-existence of Fluoric Acid in Animal Matter. 559 



Baron Berzelius has published a paper in the 6l8t volume of the 

 " Annales de Chimie ;" in which he states, fluoric acid may be de- 

 tected in human teeth, bones, and urine ; and may be demonstrated, 

 in the latter case, by operating on the precipitate obtained from the 

 excretion by means of lime-water. Since the publication of this 

 paper by Baron Berzelius, the existence of fluoric acid, as a con- 

 stituent of the animal substances above mentioned, has been ac- 

 knowledged by chemists generally ; and it is mentioned as such in 

 the standard chemical works of the present day. 



Having lately been engaged in the analysis of human bone, with 

 more especial reference to those ingredients which have been stated 

 to exist in small proportion, I was led to search particularly for 

 fluoride of calcium. My experiments were made in the usual man- 

 ner, by trying to obtain the corroding action of fluoric acid on a 

 plate of glass, which was used as a loose cover to a platinum cru- 

 cible, which contained the substance for examination, mixed with 

 strong sulphuric acid. A gentle heat was applied to the bottom of 

 the containing vessel. In this way, several specimens of human 

 bone (both before and after calcination) were subjected to experi- 

 ment ; but in no instance could I obtain any action upon the glass. 



The experiment which the Baron recommends, in order to ob- 

 tain corrosion from bone-earth, is, to distil equal parts of strong sul- 

 phuric acid, and water upon it, until the measure of water is brought 

 over. He states, that the distilled liquor, if evaporated in the glass 

 receiver, will produce a corrosion. — I repeated this experiment using 

 100 grains of bone-ash, and an ounce of the acid mixture ; but could 

 obtain no action on the receiver, by evaporating the distilled liquor; 

 nor was there any corrosion or opacity produced on any part of the 

 apparatus. 



During the evaporation of the last portions of the liquor, dense 

 white fumes appeared ; and there was some diflSculty in vaporizing 

 the whole of it. On neutralizing a portion with ammonia, and 

 testing it with nitrate of silver, a yellow precipitate of phosphate of 

 silver was thrown down. A further examination showed the pre- 

 sence of sulphuric acid, and traces of hydrochloric acid. I was 

 much surprised to find phosphoric acid in this result of aqueous di- 

 stillation, as the heat had not been urged during the process ; for I 

 had considered that acid as 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 pre- 

 sence 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 volatilize, will act upon it with considerable energy * ; 



* It must be borne in mind, that the fluoric acid acts with facility on 

 everj' kind of crown or flint glass, however good their quality may be. 

 The supposition that bad glass was used in the experiment is the only 

 means I have of explaining away that which I feel sure is an error on the 

 part of several continental chemists. 



