%66 Mr . J. Davy's Account of some Experiments 
nearly sufficient to occasion the ebullition of the sulphuric acid,, 
and the proportions just recommended are used, the retort will 
not be injured, and pure fluoboracic acid g as will be produced 
in abundance. When the gas ceases to come over, if the heat 
is raised, more will be evolved, and there will be distilled 
over at the same time, a viscid fluid, which is a compound of 
sulphuric acid and fluoboracic acid gas. Now the operation 
should be stopped, if the object is to obtain merely pure fluobo- 
racic gas, a long continuation of the heat producing some siii- 
cated fluoric. Before quitting the subject, it should be observed 
that the quantity of sulphuric add employed is of considerable 
consequence to the success of the experiment. If too much is 
used, there is a great loss of gas from the property which 
sulphuric acid has of absorbing fluoboracic acid gas ; and if 
too little is employed, it soon becomes diluted, and loses the 
power of generating the gas, though it may still decompose 
the fluor spar. Both extremes, therefore, are to be avoided, 
and the proportion of acid mentioned above, as far as my ex- 
perience goes, appears to be the best. 
I have endeavoured to ascertain the specific gravity of fluo- 
boracic gas. 
The flask exhausted weighed 14500.5 grains. 
Filled with common air - 1400.5 -j- 6. 2 
Again exhausted - - 1400,5 
Filled with pure acid gas - 3 400.5 -f* * 4 - 7 - 
Thus it appears that 100 cubic inches of fluoboracic gas are 
equal to 73.5 grains. 
M M. Gay Lussac and Thenard have described the com- 
pound of this gas and water, a fuming fluid, in many respects 
similar to concentrated sulphuric acid. Like this acid, I have 
