260 Mr. Middleton on Fluorine in 



phuric acid at intervals of about a second, the spot b is heated 

 to redness by means of a spirit-lamp. "When this point is at- 

 tained, another strong spirit flame is applied to the mixture 

 progressing from a to/j until all arsenic is expelled (the first 

 flame continues at the same time acting at b): the reduced 

 arsenic precipitates at the spot c forming a mirror, whilst an 

 exceedingly small portion escapes at d and fills the air with 

 the smell of garlic. The second spirit-lamp is at last slowly 

 advanced to the spot 6, so as to drive towards c all the 

 arsenic which has adhered to the walls of the wide tube. After 

 this, both lamps are removed, the tube closed at the point d 

 by fusion, and heat applied progressively from the point d 

 towards c, so as to contract the mirror on this side also, which 

 causes it to exhibit a particularly fine and metallic appear- 

 ance ; the tube is then cut off at the point ^ closed, sealed, and 

 thus becomes a permanent evidence, which may be referred to 

 in any future point of the legal proceedings. The remaining 

 two-thirds of the sulphuret of arsenic (vide supra) are also 

 put into a small glass tube, and this too is then closed and 

 sealed and preserved for reference. 



If sulphuret of zinc or sulphuret of antimony be present, 

 together with the sulphuret of arsenic, the zinc and the anti- 

 mony will be obtained in their metallic state upon dissolving 

 in water the residue found in the reduction-tube (antimony 

 is also found in the solution) ; they must be determined by 

 the ordinary methods now in use. Their weight is calculated 

 upon the whole amount of the residue originally contained in 

 the small porcelain basin (vide D), and the weight of their 

 corresponding sulphates subtracted from the total weight of 

 the residue. The remainder is the amount of sulphuret of 

 arsenic corresponding to the arsenic present. 



XLII. On Fluorine in Recent and Fossil Bo7ies, and the 

 sources from 'whence it is derived. By J. Middleton, Esq.^ 



tTAVING been for some time past engaged in investiga- 

 ■*■-■■ tions, not yet matured, on the absolute and relative 

 quantities of fluorine in fossil bones, I was readily led to in- 

 quire into its presence, or otherwise, in recent bones. The 

 high authority of Berzelius had indeed satisfied me on this 

 subject, and I might not have felt a motive to examination for 

 myself had I not lately heard the fact doubted and disputed 

 before the Chemical Society and elsewhere with an earnest- 

 ness which could only proceed from conviction. The readiness 



* Communicated by the Chemical Society ; having been read May 6, 

 1844 : on the subject of this paper, see the author's previous one, p. 14, 

 and also Dr. Daubeny's, p. 12S of the present volume. 



