Dr Rees on Fluoric Acid in Animal Mailer. 91 



calcium as an ingredient either in recent ivory or the enamel 

 of teeth ; they fonnd it, however, in the fossil ivory of Argen- 

 teuil and Lourqne, though it did not appear to exist in speci- 

 mens from Siberia and Lay. 



Baron Berzelius has published a paper in the 61st volume 

 of the " Annales de Chimie," in vs^hich he states, fluoric acid 

 may be detected in human teeth, bones, urine, and may be 

 demonstrated, in the latter case, by operating on the precipi- 

 tate obtained from the excretion by means of lime-water. 

 Since the publication of this paper by Baron Berzelius, the ex- 

 istence of fluoric acid, as a constituent of the animal substan- 

 ces above mentioned, has been acknowledged by chemists 

 generally ; and it is mentioned as such in the standard chemi- 

 cal woi'ks of the present day. 



Having lately been engaged in the analysis of human bone, 

 with more especial reference to those ingi'edients 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 manner, 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 crucible, Avhich contained the substance 

 for examination, mixed with strong sulphiu'ic 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 experiment ; but in no 

 instance could I obtain any action upon the glass. 



The experiment which the Baron recommends, in order to 

 obtain corrosion from bone earth, is, to distil equal parts of 

 strong sulphuric 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 pi'oduce 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 difficulty in 

 vaporizing the whole of it. On neutralizing a portion with 

 ammonia, and testing it with nitrate of silver, a yellow preci- 



