143 



" I shall therefore close this paper (Mr Robins' words) with pre- 

 dicting, that whatever state shall thoroughly comprehend the nature 

 and advantages of rifled barrel pieces, and, having facilitated and 

 completed their construction, shall introduce into their armies their 

 general use, with a dexterity in the management of them ; they will 

 by this means acquire a superiority which will almost equal any- 

 thing that has been done at any time by the particular excellence 

 of any one kind of arms, and will perhaps fall little short of the 

 wonderful effects which histories relate to have been formerly pro- 

 duced by the first inventors of fire-arms." 



4. On two New Processes for the detection of Fluorine when 

 accompanied by Silica, and on the presence of Fluorine 

 in Granite, Trap, and other Igneous Rocks, and in the 

 Ashes of Recent and Fossil Plants. By Dr George 

 "Wilson. 



The author, after alluding to his previous communications to the 

 Society in reference to fluorine, stated that he had always attri- 

 buted the slight indications of the presence of this element in plants, 

 which his own investigations and those of others had yielded, to the 

 amount of silica which was contained in vegetable ashes. The pre- 

 sence of silica, which throws special difficulties in the way of de- 

 tecting fluorine, had also prevented him from seeking for it in trap 

 rocks and other mineral masses. Recently, however, he had put in 

 practice two processes, which were applicable to all bodies containing 

 silica and a metallic fluoride, which are decomposed by boiling oil of 

 vitriol. When this acid is heated along with a silicated fluoride, it occa- 

 sions an evolution of the fluorine in combination with silicon, as the 

 well-known gaseous fluoride of silicon (Si Fg). In the first process, 

 this gas is conducted into a solution of caustic potash, in which it 

 occasions a precipitate of the fluoride of silicon and potassium (2 Si 

 Fg + 3 K F). This precipitate is heated in a metallic crucible with 

 potassium, so as to separate the silicon, and convert the double fluo- 

 ride into fluoride of potassium. When moistened with oil of vitriol, it 

 evolves hydrofluoric acid, the escape of which is easily recognised by 

 its etching glass. This process gave good results, but was tedious, 

 and sometimes unsuccessful. It was accordingly abandoned for the 



