144 



second process, in which ammonia is substituted for potass, and the 

 use of potassium is dispensed with. 



The following are the steps of the ammonia process. The si- 

 licated fluoride, such as trap-rock or the ashes of straw, is heated 

 with oil of vitriol, and the fluoride of silicon which is given off is 

 conducted by a bent tube into an aqueous solution of ammonia, with 

 which it forms the fluoride of silicon and ammonium (2 Si F^ -f 

 3 NH^ F). When this is evaporated to perfect dryness, the silicon 

 becomes insoluble silica, from which water dissolves out the pure 

 fluoride of ammonium. This ammonio-fluoride is dried up in a pla- 

 tina crucible, and after moistening the residue with sulphuric acid, 

 a piece of waxed glass, with lines traced through the wax down to 

 the glass, is laid as a cover on the crucible, so as to permit the hy- 

 drofluoric acid evolved to etch the lines. 



This process has been tried with Peterhead and Aberdeen gra- 

 nite, with basalt from Arthur's Seat, greenstone from Corstorphine 

 Hill, and clinkstone from Blackford Hill, all in the neighbourhood 

 of Edinburgh. It has also been tried wdth the ashes of barley-straw, 

 of hay, of coal, and of charcoal ; and in addition, with a fossil bone 

 containing much carbonate of lime ; and with the deposit from the 

 boiler of an ocean steamer. To the bone, and to the boiler deposit, 

 pounded glass was added. Most of the specimens obtained in this 

 way were shewn to the Society. These, the author stated, were not 

 selected successful ones, but represented the earliest trials. Where 

 the rocks under examination had been weathered, or the substances, 

 such as plant-ashes, contained salts of volatile acids, as chlorides and 

 carbonates, they were treated, first, with oil of vitriol, in the cold, so 

 as to evolve hydrochloric acid and carbonic acid. On afterwards rais- 

 ing the liquid to the boiling point, in a flask with a bent tube, a gas 

 was given off, if fluorine were present, which deposited gelatinous si- 

 lica when passed through water, and produced with it a solution 

 which gave a gelatinous precipitate with potash. The whole of the 

 fluoride of silicon is given oflf as soon as the oil of vitriol has reached 

 its boiling point. The author is at present engaged in applying this 

 process to a variety of substances, and in ascertaining its applica- 

 bility to the quantitative determination of fluorine. 



In conclusion, it was noticed that the discovery of fluorine in trap 

 and granite, threw much light on the production of minerals, such as 

 fluor spar and crystallised silica, which are found in those rocks ; 



