180 
ME. G. GOEE ON HYDEOFLTT OEIC ACID. 
of hydrate of potash were then agitated occasionally with the gas at intervals during 
several hours, and the gas transferred to a graduated tube over mercury, and allowed to 
remain in contact with sticks of dry phosphorus during twelve hours, the phosphorus 
being used to remove oxygen introduced by traces of air adhering to the vessel, &c. 
About 15‘3 grains of fluoride of silver of a very high degree of purity (made from 
pure materials, viz. hydrofluoric acid, and carbonate of silver) was placed in the previ- 
ously heated and weighed platinum tube A (fig. 5), which was open at the top and closed 
at the bottom, and constructed without solder by the process of melting. The tube ^ 5 
was 6-| inches ( = 16‘6 centims.) long and jf- of an inch (=2T centims.) diameter, 
and had a capacity of 3’4 cubic inches (=55’716 cubic centimetres); in some of 
the experiments, where accurate weighing was not required, it was coated exter- 
nally for about 2 inches (=5'0 centims.) in length at its closed end with a thick 
layer of copper by the electrolytic process : the object of coating it thus was to a 
prevent traces of hydrogen passing through the platinum at a red heat; this 
may, however, be dispensed with by not applying more than a barely visible red 
heat in the subsequent reduction part of the process. The fluoride was now 
melted in it at a visible red heat until it formed a tranquil liquid, and the upper ^ 
part of the tube also heated to redness to expel all moisture*. The tube was then 
either at once affixed to the platinum receiver (see fig. 6), or as soon as possible corked, 
cooled, and reweighed ; the loss of weight upon the above quantity of salt was usually 
about 0T grain, arising from moisture expelled from the fluoride (which is a very hygro- 
scopic and deliquescent substance), and partly from the moisture of the air decomposing 
a little of the fluoride during the fusion. The tube A was 
now fixed tightly upon the open bent platinum neck-tube 
B of the graduated platinum receiver C, and the junction 
made perfectly gas-tight by a small quantity of the melted 
mixture of sulphur and lampblack, bound over tightly by a 
stretched ribbon of the thinnest vulcanized india-rubber 
secured by string. The platinum receiver, C, was 6 inches 
( = 15 - 3 centims.) long and 1-^inch (=3'8 centims.) diameter, 
open and flanged at the bottom end, and formed in one piece 
with the bent neck B without solder. Glass receivers were 
found to be corroded even when thickly and carefully coated 
with paraffin. (N.B. They were used before I succeeded in obta inin g the hydrofluoric 
acid in a perfectly anhydrous state.) They might perhaps be used provided moisture is 
perfectly excluded and the acid is not allowed to assume the liquid state. The entire 
apparatus, including A, B, and C, when put together had a capacity of about 15 cubic 
inches (=245 ’805 cubic centims.). 
The tubes A and B were now filled as quickly as possible with dry mercury, and 
* Oxide of silver was found to be decomposed at a temperature much below that of visible redness. H. Eose 
states that Ag 2 0 begins to evolve oxygen at 250° C. (Watts's Dictionary of Chemistry, vol. i. p. 792). 
Fig. 6. 
