128 On the Detection of Bor acic Acid in Minerals. 
evaporated to dryness. The dry mass was boiled in alcohol, and 
the solution, so formed, burned with a green flame. The same 
process was repeated with the colophonite and axinite with a 
similar result. I have not yet had leisure to determine how 
much boracic acid is contained in axinite, but, judging from the 
quantity of colour communicated to alcohol, it must be consider- 
ably less than in the Brazilian tourmaline. 
Future observation must decide upon the value of the test 
here recommended. I know of no other substance but boracic 
acid that gives a green colour to the blowpipe-flame under the 
circumstances which have been described. A salt of copper 
tinges the flame green, but it does so without any flux at all. 
The mixture of fluate of lime and bisulphate of potash is appli- 
cable to saline as well as earthy minerals, since it causes the 
characteristic green colour, when fused with datolite and Hum- 
boldtite, equally well as with tourmaline and axinite. From the 
facility with which it acts on the latter, we may fairly presume 
that it would be equally efficacious in detecting the presence of 
boracic acid in any earthy mineral, if used in sufficient quantity. 
The proportion which seems best adapted for general use is two 
of the flux to one of the mineral, though in most cases much less 
of the former will suffice. 
I cannot speak precisely as to the smallest quantity of the acid 
which may be detected by the blowpipe. According to the ana- 
lyses of Arfwedson and Gmelin, some tourmalines contain only 
1 per cent, of it; and hence we may infer that some of the varie- 
ties included in the foregoing list are similarly constituted. If 
this is the case, then the test must be a very delicate one ; for I 
am satisfied, from the effect on the blowpipe-flame, that a less 
quantity of boracic acid could be detected, than exists in any of 
the tourmalines which have fallen under my notice. 
With respect to the mode by which the flux acts, it is remark- 
able that the bifluate of potash alone does not cause the green 
colour to appear, not even with datolite. The pure fluate of 
lime, and even the bifluate of potash, is also ineffectual. It is 
hence probable that pure fluoric acid is useful, not only in assist- 
ing to separate the boracic acid from the substances with which 
it was combined in the mineral, but perhaps by forming the fluo« 
tic acid gas. 
