102 



The following table gives p tor every fifth degree of latitude • — 



2. On the Extent to which Fluoride of Calcium is Soluble in 

 Water at 60' F. By Dr George Wilson. 



Dr Wilson stated, that the object of his communication was to 

 supplemerit a paper read to the Royal Society, April 6, 1846, on 

 the solubility of fluoride of calcium in water. He was not then able 

 to state the extent of its solubility in that liquid, but he has since as- 

 certained the weight of the salt in question, which water at 60° can 

 dissolve. The solutions referred to in the following statements were 

 prepared from native well-crystalhzed fluor-spar. This was first di- 

 gested in warm dilute aqua regia, to remove any trace of metallic 

 oxides, soluble lime-salts, or other foreign matters, and afterwards 

 carefully washed till it exhibited no acid reaction. Distilled water 

 was then boiled on the purified fluor till it became saturated ; the 

 solution filtered whilst warm, and left at rest for some days in stop- 

 pered bottles, at a temperature of about 60°, till it deposited the ex- 

 cess of salt soluble above that temperature. It was then filtered a 

 second time. A certain volume of this solution, measured at 60°, 

 was evaporated to dryness on the vapour bath, in a counterpoised 

 platina basin. 



Twenty-four pints of the solution were thus made use of. In six 

 experiments, 1 imperial pint of the solution (16 fluid ounces, or 7000 

 grs.) was taken at each trial. In four trials, 3 pints were evapo- 

 rated at each experiment. In one, 6 pints were employed. 



The following are the results : — 



Exp. 1. Evaporated 1 pint of solution. 



Exp. 2. 



Exp. 3. 



Exp. 4. 



Exp. 5. ,, ., 



Exp. 6. „ „ 



Average, 0-265 per pint. 



Per Pint. 

 Residue, 0-27 grs. 

 0-28 „ 

 0-28 „ 

 0-24 „ 

 0-27 „ 

 0-25 ,. 



