4a2 [June 12, 



tained all of them neai'ly the same proportion of fluoride of cal- 

 cium, viz. 11 per cent., while in the bones of the Greek the 

 proportion was only a little more than 5 per cent., and in the 

 mummy about 2 per cent. The difference in the two latter is 

 accounted for, it would seem, by the circumstances of deposition, 

 this being sufficiently evident from the appearance of the speci- 

 mens ; since the bone of the Greek has assumed a soft powdery 

 character, tinged with peroxide of iron, the result of exposure to 

 atmospheric and other influences, while that of the Egyptian ex- 

 hibited all the structure of recent bone, having been preserved in 

 a sarcophagus, and scarcely changed from its normal state. 



From these results, and from having ascertained the presence 

 of fluorine in the recent bones both of men and reptiles, I 

 was led to suppose that the presence of fluorine must be due to 

 some general condition, the same in ancient times as at present, 

 for I could not believe that in this matter there could be any 

 alteration in the laws of organic life, implying different propor- 

 tions of the mineral at different periods. I was thus led to suspect 

 that water might be the agent producing this apparent change ; 

 and this seemed to me to offer a ready solution of the whole 

 problem. That there is a great tendency in flvioride of calcium 

 to unite itself to phosphate of lime, is evident from the almost uni- 

 versal association of the two in nature ; and thus, if the moisture 

 constantly present at the earth's surface should contain the mineral 

 in question, the bones might absorb it by simple exposure ; a 

 larger proportion being obtained, according as the bones had been 

 longer exposed to its influence. Bearing this in mind, I was led 

 to institute a series of experiments on aqueous deposits of dif- 

 ferent ages, and I found that, with one exception, — a pure but 

 incompact stalactite of carbonate of lime, — fluorine exists in aU, 

 from the most recent deposit down to the old red sandstone, and 

 that it is present in the older in larger proportion than in the 

 newer beds. I think it is therefore beyond a doubt that it is pre- 

 sent in water, though perhaps in very minute quantity ; what its 

 solvent may be I know not, but that it is so held in solution my 

 own experiments have demonstrated ; and if they had not, the 

 simple fact that the blood conveys it to the bones, would, I appre- 

 hend, sufficiently refute any scepticism on the subject.* 



It now remains for me to show, that the relative geological age 

 of rocks may be estimated by the proportion of fluoride of cal- 

 cium which they contain ; and for this purpose I append the 

 following results of my analyses in the cases of recent bone, the 

 bone of a Greek already alluded to, a fossil bone from the Sewalik 



* Note hy the President. " I am informed by Professor Graham, that he is well 

 acquainted with these researches of Mr. Middleton ; that, previous to his return 

 to India, Mr. Middleton ascertained the presence of fluoride of calcium in the 

 deposit obtained by boiling the ordinary pipe-water supplied' to the houses in 

 London ; and that there is reason to believe, from this and other observations, 

 that the fluoride of calcium is held in solution by the carbonic acid usually 

 present in water." — L. H,, April 7. 1845. 



