486 DR GEORGE WILSON ON NEW PROCESSES FOR FLUORINE, &c. 
I treated the powdered pieces of rock with hydrochloric acid, and washed them 
with water, then dried them, and heated them with oil of vitriol. The prelimi- 
nary treatment, however, risked, and I have no doubt occasioned, the loss of the 
fluorides present in the mineral, which were soluble in water or in hydrochloric 
acid; and latterly I abandoned this process. J refer to it here only because it ex- 
plains certain of the less perfect etchings which are exhibited. 
Tn later trials, a simpler and more satisfactory process has been put in prac- 
tice. The powdered rock has been added to oil of vitriol in the cold, in small 
quantities at a time, so as to prevent any great rise in temperature. So long as 
the heat evolved is not considerable, there is no risk of fluorine escaping, either as 
hydrofluoric acid or as fluoride of silicon, whilst any chlorides or carbonates pre- 
sent are decomposed, and the hydrochloric and carbonic acids evolved, are carried 
away, before their escape can interfere with the evolution of fluorine. When the 
oil of vitriol is afterwards raised to its boiling-point, the fluoride of silicon is 
liberated, and little difficulty attends its collection and identification. 
The ashes of plants are somewhat less easily examined. They almost inva- 
riably contain charcoal, which occasions the evolution of sulphurous acid with 
hot oil of vitriol. Sulphurous acid, however, does not very materially interfere 
with the detection of flucrine, as it can be expelled by heating the distillate before 
adding ammonia, which is the process I have hitherto generally followed. It may 
also be converted into sulphuric acid by the cautious addition of nitric acid, and 
then its presence is quite immaterial. But in several quite successful trials no 
steps were adopted to separate the sulphurous acid. 
The specimen laid upon the table, of glass etched by fluorine from barley- 
straw, will illustrate the applicability of the process to plant-ashes largely charged 
with silica, and which yielded, with oil of vitriol, carbonic and hydrochloric acid, 
besides much sulphurous acid. 
The glass etched by the fluorine of charcoal-ashes is still more deeply cor- 
roded, although they were subjected to no preliminary process to remove the;vola- 
tile acids which they contained, or to set free or separate the sulphurous acid 
which they yielded. : 
In truth, the ammonia process has succeeded with every substance upon 
which I have tried it. The worst result has been with the ashes of hay, but they 
had been washed with water and hydrochloric acid to remove chlorides and car- 
bonates ; and in former papers I have shewn that such washings remove fluorides. 
Notwithstanding this, the evidence of the presence of fiuorine in hay, afforded by 
the specimen, is such as has not hitherto (so far as | am aware) been afforded by 
any analyst, and the omission of the washings will, I have no doubt, yield a still 
more satisfactory result on a repetition of the analysis. The same remark applies 
to coal-ashes, by the fluorine of which I have only one etching to shew. It is not 
a favourable specimen ; the ashes were washed with a considerable volume of 

