230 Dv George Wilson on the extent to which 



say, all classes of animals. Some difficulty was found at one 

 time, in accounting for the presence of fluorine in the ani- 

 mal tissues and secretions. But when we learn that fluoride 

 of calcium is soluble in water, and is present in many 

 natural waters, and that it, or some other salt of fluorine, 

 exists in the two great formative liquids of the animal 

 organism, milk and blood, we shall cease to wonder at its 

 presence in the animal solids and fluids, and begin to enquire 

 what its functions may be. 



I would suggest, in conclusion, to those who may wish to 

 repeat or extend this enquiry, that — 



1*/. Substances to be tested for fluorine in the way de- 

 scribed, should as much as possible be freed from the salts of 

 volatile acids. Much washing, however, must be avoided, as 

 it may occasion loss of fluorine ; and if complicated processes 

 are followed, care must be taken that the reagents made use 

 of, are free from fluorine.* 



2nd. Substances examined for fluorine, should generally 

 be left for at least twenty-four hours in contact with sul- 

 phuric acid. If they contain, as they generally do, some 

 compound of calcium, the pasty sulphate of lime produced, 

 will obstinately retain the hydrofluoric acid, so that unless 

 the mass is occasionally stirred, and the glass left for some 

 period exposed to the vapour evolved, no etching may be ob- 

 tained, although an appreciable quantity of fluorine is present. 



On the extent to which Fluoride of Calcium is soluble in water 

 at 60° F. By George Wilsoi^, M.D., F.R.S.E. Com- 

 municated by the Author. t 



In 1846, I reported to the Chemical Section of the British 

 Association the result of an enquiry into the extent to which 



* Chloride of sodium, and, therefore, hydrochloric acid, are liable to coii- 

 tain fluorine derived from sea water. Phosphorus, phosphoric acid, and 

 phosphate^ are associated in nature with it ; and so, though to a much smaller 

 extent, are the insoluble salts of lead and the alkaline earths. 



t Read to the British Association, at its Meeting at Edinburgh, August 6th, 

 1850. 



