92 



which, on being heated with sulphuric acid, gave off hydrofluoric 

 acid. 



The author was, in consequence, inclined to suppose that carbonic 

 acid conferred upon water the power of dissolving fluoride of calcium. 

 But on observing that long after the whole of that gas had been ex- 

 pelled by warming the liquid, the latter remained untroubled, he 

 became satisfied that water alone can dissolve fluoride of calcium, 

 contrary to the universal statement of writers on chemistry. 



On prosecuting the inquiry, he found that water at 212° dissolved 

 more of the fluor than water at 60°, but he has not yet ascertained 

 the proportion taken up by that liquid at either temperature. 



The aqueous solution of fluoride of calcium was found to give, with 

 salts of baryta, a precipitate which required a large addition of hy- 

 drochloric or nitric acid to redissolve it. The author pointed out 

 the difficulty which must in consequence occur, in distinguishing be- 

 tween dissolved fluoride and sulphates, and suggested that fluorides 

 may have been mistaken for sulphates in the analysis of mineral 

 water. 



He referred also to the objection which must now lie against the 

 present method of determining the quantity of fluorine present in 

 bodies, consisting, as it does, in converting that element into fluoride 

 of calcium, which, in the course of the necessary analytical opera- 

 tions, is washed freely, and must be sensibly diminished in quantity ; 

 a fact which has of necessity been hitherto overlooked. Dr Wilson 

 stated that he was not yet able to suggest an unexceptionable quan- 

 titative process ; but that the fluoride of barium, being much less 

 soluble than the fluoride of calcium, might, in the meanwhile, be 

 substituted for it in the estimation of fluorine. 



The author proceeded to state, that in consequence of the obser- 

 vations he had made as to the solubility of fluoride of calcium on 

 water, he had been led to look for that body in natural waters, and 

 had found it in one of the wells of Edinburgh, namely, in that sup- 

 plying the brewery of Mr Campbell in the Cowgate, behind Minto 

 House. At the same time, he stated that preceding observers had 

 already found it in other waters. He believed, however, that he was 

 the first to detect it in sea-water, where, by using the bittern or 

 mother-liquor of the salt-pans in which water from the Frith of Forth 

 is evaporated, he had found it present in most notable quantity. The 

 author referred to the presence of fluorine in sea-water, as adding 

 another link to the chain of observed analogies between that body 

 and chlorine, iodine, and bromine. 



