122 Dr. Daubeny on the occurrence of 



I am not ambitious to deprive Dr. Draper of any of the 

 fame that he covets, but I hope to be allowed to pursue my 

 investigations, which 1 enjoy from their own exceeding great 

 reward, without disturbance. I shall always feel it my duty 

 to express my opinions on matters which have come under 

 my investigation with that freedom which 1 hope others will 

 use towards me. I remain. Gentlemen, 



Yours faithfully and obediently, 

 Falmouth, July 15, 1844. RoBERT HuNT. 



XVIII. On the occurrence of Fluorine in Recent as well as in 



Fossil Bones. By Charles Daubeny, AI.D., F.R.S."^ 

 XT AVING in the course of the preceding spring paid a visit 

 to the deposit of compact phosphorite which occurs in 

 the province of Estremadura in Spain, 1 was subsequently 

 led to examine into the chemical constitution of the mineral 

 which forms the prevailing ingredient of the vein to which 

 my inquiries had been directed. 



The results of my examination have already been reported 

 in the memoir communicated by my fellow-traveller Captain 

 Widdrington, R.N. and myself to the Geological Society with 

 respect to the rock in question, and read at their meeting on 

 the 17th of January last; from which it will be seen, that the 

 mineral, although, not being crystallized, it is somewhat va- 

 riable in its composition, yet when selected as pure as possible, 

 contains as much as 81 per cent, of phosphate of lime, and 14 

 per cent, of fluoride of calcium, the remainder appearing to 

 consist of silica and peroxide of ironf- 



* Communicated by the Chemical Society; having been read March 

 18, 1844. On the same subject see Mr. Middleton's paper in our last 

 Number, p. 14. 



f The phosphate of lime I have since satisfied myself to possess the same 

 composition as apatite, viz. POg + SCaO ; and this is confirmed by Mr. Mid- 

 dleton and Mr. D, Campbell, in the laboratory of Professor Graham, who 

 were kind enough each to undertake an independent analysis of the mine- 

 ral. They likewise agree with me, and with each other, in their estimation 

 of the amount of fluoride of calcium, determined by the loss occasioned on 

 the addition of sulphuric acid to the pounded specimen, from which loss the 

 proportion of fluorine was calculated. I should however remark that this 

 quantity is double that of the largest amount reported by Rose to be pre- 

 sent in the crystallized apatites which he examined (see Thomson's Mine- 

 ralogy, vol. i. p. 125); and that 1 have never succeeded in obtaining more 

 than 8*8 grains per cent, of fluoride of calcium by the direct method, in 

 which the fluorine was expelled by heat and sulphuric acid from the phos- 

 phorite contained in a platina still, and where, after passing it through a 

 silver vessel kept at 500°, in which any earthy matter carried over with 

 the vapour might be deposited, it was finally received into a glass vessel 

 containing caustic ammonia. As sulphate and fluate of ammonia could 

 alone be formed, I estimated the amount of fluorine by adding chloride of 

 calcium, and separating the resulting sulphate of lime from the fluoride of 



