ME. Gr. GrOEE ON HYDEOELEOEIO ACID. 
179 
grains of HF present. By these means the loss of acid vapour did not exceed 005 
grain ; the residue was alkaline to test-paper, and the gain of weight found was 55 parts 
for every 100 parts of liquid acid taken. The following are the numbers experimentally 
found: — in the first reliable experiment 31-61 grains of the acid and 54-56 grains of 
lime were taken, and the weight of ignited residue found was 71-93 grains = a gain of 
17*37 grains= 31-58 grains of HF present=99-90 per cent, of HF in the acid. In 
another experiment 50-26 grains of the acid and 77-54 grains of lime were taken, and 
the weight of ignited residue was 105-18 grains=a gain of 27"64 grains=50-27 grains 
of HF= 100-01 per cent, of HF. 
In an analysis by the above process of a portion of non-rectified acid obtained from 
some double fluoride of hydrogen and potassium which had not been sufficiently fused, 
and which from the weight of acid obtained from a given quantity of the salt was sus- 
pected to contain traces of the double salt and a small quantity of water not exceeding 
at the utmost 3-47 per cent, (see page 176), 39-39 grains of the acid-1-66-74 grains of 
lime gave 87-78 grains of ignited residue=a gain of 21-04 grains = 38-25 grains of HF 
= 97-09 per cent, of HF present. These results confirm all the former ones, and further 
support the conclusion that the liquid obtained by distilling properly prepared fluoride 
of hydrogen and potassium, and rectifying the product at a temperature not exceeding 
100° Fahr., is anhydrous hydrofluoric acid. The lime for the above process was pre- 
pared as follows : — an excess of clear lime-water was added to a solution of nitrate of 
calcium, the filtered solution precipitated by a mixture of solution of ammonia and ses- 
quicarbonate of ammonium ; the precipitate was washed and dried, and repeatedly ignited 
to an incipient white heat in an open platinum crucible in a small gas-furnace. The 
presence of magnesia in the lime does not affect the numerical relation of the gain of 
weight to the amount of acid present. Various attempts were made to employ pure 
oxide of magnesium in place of the lime, but its power of neutralizing the acid was 
found to be too slow. 
Molecular Volume of the Anhydrous Acid in the gaseous state. 
I have made fourteen separate attempts to ascertain the volume of gaseous product 
formed by the chemical union of one volume of hydrogen with fluorine. The method I 
have adopted has been to heat pure anhydrous fluoride of silver to fusion in a platinum 
vessel containing an equivalent quantity of pure and dry hydrogen. The experiments 
were extremely difficult owing to the destructive nature of the substances, and the con- 
sequent difficulty of eliminating the numerous interferences which presented themselves. 
The following are the particulars of the method finally employed. Fragments of the 
purest magnesium were introduced into the neck of an inverted bottle full of previously 
boiled and partly cooled dilute sulphuric acid, consisting of one measure of the purest 
acid, and about forty or fifty of distilled water. The mixture was stirred with a rod of 
magnesium immediately before use. When the bottle was quite full of hydrogen, the 
gas was transferred to a dry bottle filled with mercury and inverted over mercury ; sticks 
