152 DR WILSON ON THE SOLUBILITY OF 



lain. I endeavoured to substitute for these, silver basins, but found it impossible 

 to prevent them gaining weight from the sulphuretted hydrogen constantly pre- 

 sent in an analytical laboratory. Through the liberality of Dr Gregory I have 

 recently obtained a platina basin of much larger dimensions than the resom-ces of 

 my ovm laboratory afforded, and by means of it I shall be able to announce the 

 proportion of fluor-spar taken up by Avater. Meanwhile, we cannot doubt that 

 the proportion of fluorine has hitherto been estimated too low in most of the 

 substances ascertained to contain it. In some cases the eiTor must have been 

 considerable. 



I had hoped that the barium salt of fluorine would prove suitable for the 

 quantitative esthnation of the latter. It certainly would be much better than the 

 fluoride of calcium, but according to Berzelius it possesses a certain though 

 slight solubility in water. Fluoride of barium must accordingly be rejected also, 

 unless no better compound for estimating fluorine quantitatively can be discovered. 

 I may remark, in passing, that the fact that fluoride of barium is soluble in water 

 might have led to the discovery that the similar salt of calcium was so likewise. 

 The salts of barium, as a class, are much more insoluble than those of calcium. 

 If, therefore, the barium compound of a salt-radical be soluble in water, the 

 calcium salt of the same radical shoiild, a fortiori, be still more so. 



The observation of the previously unsuspected solubility of fluor-spar in 

 water, promised to throw light on some interesting problems connected with 

 geology, mineralogy, and physiology. I was induced, in consequence, to make a 

 series of researches in reference to these points, the results of which I shall now 

 briefly state. 



Many of the investigations were very tedious, and I take this opportunity of 

 expressing my obligations to two of my pupils, Mr Henky C. Briggs and Mr 

 Henry William Stansfeld, for the cordial and untiring assiduity with which 

 they aided me in my researches. To my assistant, Mr David Forbes, I have 

 likemse been greatly indebted for the most active co-operation throughout the 

 inquiry. 



3. 0/ the presence of Fluorine in Well, River, and Sea Water. 

 It was impossible to doubt, after the facts I had observed in the laboratory, 

 that fluorine must be no infrequent constituent of well and river as well as of sea 

 water. Berzelius mentions that fluoride of calcium has been found in the waters 

 of Carlsbad.* Dr Christison has pointed out to me that Hunefeld detected a 

 trace of it in the waters of Gastein in the Tyrol,! and that Planiava found 

 gi-. 0-07 of the fluoride in 10,000 grains of the water of Lukatschowitz in 



* Lehibuch der Chemie, vol. ii., p. 607- 



t Bulletin des Sciences Medicales, vol. xvii., 425. From Jahrbuch der Chemie und Physik, xxii. 458, 



