
DR GEORGE WILSON ON NEW PROCESSES FOR FLUORINE, &o. 485 
ammonia instead of potass, and then evaporated to dryness, which has the effect 
of rendering the silica produced insoluble. On digesting water on the residue, 
fluoride of ammonium is dissolved, and the solution requires only to be evaporated 
to dryness and moistened with sulphuric acid to give off hydrofluoric acid, which 
readily etches glass. The stages in the ammonia process are thus :— 
1st, Distillation of the substance with oil of vitriol, so as to produce fluoride of 
silicon, Si F,. 
2d, Neutralisation of the aqueous solution of the distillate, with ammonia in 
excess, so as to produce fluoride of silicon and ammonium, 2 Sif, +3 NH,F. 
3d, Evaporation of the neutralised liquid to dryness, so as to separate silica, 
and render it insoluble. 
4th, Exhaustion of the residue with water, and evaporation to dryness, so as 
. to leave fluoride of ammonium. 
5th, Moistening of the ammonio-fluoride with oil of vitriol, so as to liberate 
hydrofiuoric acid; which will act upon glass. 
I have tried this process with Aberdeen and Peterhead granite; with three 
trap rocks from the neighbourhood of Edinburgh, namely, basalt from Arthur 
Seat, greenstone from Corstorphine Hill, and clinkstone from Blackford Hill; 
with a deposit from the boiler of the Atlantic steamer, Canada; with a fossil 
bone; with the ashes of charcoal, of barley-straw, and of hay; and in all with such 
success that the applicability of the process to the end proposed is certain. The 
pieces of glass, etched by hydrofiuoric acid evolved from the substances referred 
to, which I lay upon the table, are not selected successful specimens, but repre- 
sent the whole of the trials made by the ammonia process. The etchings on the 
majority of them are as deep as could be obtained from pure fluorspar and oil of 
vitriol; and, with the experience which I have now acquired, I have no doubt 
that I shall be more successful in succeeding trials with vegetable ashes, which, 
for reasons to be presently mentioned, require more precautions than fragments 
4 _ of rock do. 
The examination of a hard crystalline mineral, such as granite, or an un- 
weathered trap, presents no difficulties. It must be reduced to a tolerably fine 
powder, and employed in considerable quantity. A little sulphurous acid is 
always evolved during the action of the oil of vitriol, from the dust which is 
_ gathered during a protracted process of powdering ; but the presence of this acid 
in small quantity is of no importance, and the powdering of the rock is the most 
_ troublesome part of the investigation. 
It is otherwise with weathered granite and trap, which containe hlorides and 
carbonates, and give off hydrochloric and carbonic acids when treated with sul- 
phuric acid. These gaseous acids materially interfere with the processes described 
by the frothing which they occasion, and by their tendency to sweep away the 
hydrofluoric acid which may accompany them. In my earlier trials, accordingly, 
