ME. Gr. GOEE ON HYDEOELU OEIC ACID. 
177 
or even of a limited amount of water added, as in the fifth experiment, and (2nd) that 
an equivalent, or 78 ‘13 parts, of the dry salt contains two equivalents, or 38 parts, of 
fluorine ; and therefore from these results, combined with the amount of potassium found 
as chloride in the foregoing determination, I conclude that the salt cannot contain more 
than a very minute amount, if any, of oxygen or water. 
I also checked the foregoing results by neutralizing a known weight of the distilled 
acid with carbonate of calcium. The first approximate and reliable result was obtained 
as follows. Into a weighed platinum bottle was poured 33 T8 grains of the acid; the 
stopper was reinserted, and the vessel and contents reweighed. The stopper was now 
taken out and replaced by a tightly fitting and open vertical tube of platinum about 
22 inches (=55-9 centimetres) high, with a stopper at its upper end, the junction of the 
tube with the bottle being made gas-tight by means of melted paraffin. The bottle was 
then immersed in ice, and about one-eighth of an ounce of distilled water added drop by 
drop through the tube. After awhile 102*7 grains of white marble in very fine powder 
was very gradually added ; the mixture stood about fifteen hours with occasional shaking, 
and was then heated. The mixture was now washed out into a large platinum dish (it 
was neutral to test-paper), and evaporated to dryness and weighed. The weight found 
was 84*92 grains=a loss of 17*78 grains=32*327 grains HF present. In this experiment 
a small quantity of the acid vapour escaped during the weighing, which would probably 
account for the amount missing, viz. 0*853 grain; it was almost impossible to prevent a 
slight loss by this method on account of the great volatility of the acid, the carbonic 
anhydride carrying hydrofluoric acid with it. 
I made several attempts to analyze the anhydrous acid by other means : thus, I gra- 
dually diluted the highly chilled acid, added to it an excess of a solution of acetate of 
lead, boiled the mixture, and filtered and washed the precipitate ; the result was a failure 
owing to the fluoride of lead being sparingly soluble in water and in spirits of wine. 
In a second experiment a portion of the diluted acid was added to an excess and known 
weight of nitrate of lead in solution, and the mixture containing the precipitated fluoride 
was evaporated to perfect dryness and weighed : in this case, on evaporating the mixture, 
a reverse decomposition occurred ; the whole of the fluoride of lead was reconverted into 
nitrate, and the hydrofluoric acid escaped ; indeed I found by a subsequent experiment 
that fluoride of lead was wholly converted into nitrate by evaporation to dryness with 
nitric acid. 
Another method I employed for analyzing the anhydrous acid was as follows. A six- 
ounce platinum bottle had a vertical open platinum tube about 4 inches (=10*2 centime- 
tres) high cemented into its mouth, the tube being perfectly closed by a well-fitting plug 
of paraffin. The bottle was placed for a short time in a thin tin case immersed in a 
freezing-mixture, then taken out and weighed, ^ and returned to the chilling-case; a 
small quantity of the acid, not exceeding 50 grains, was then poured into it through a 
long-necked platinum funnel, and the plug fixed securely and the whole reweighed. The 
bottle was now placed in the freezing-mixture itself at a temperature not above zero, 
