60 
MICRO-CHEMICAL EXAMINATION OF MINERALS. Mar., 1889. 
AVliat is, however, perhaps even more to be desired by the 
working petrologist is the power to decide in a short time and 
without a quantitative analysis, the material for which can 
often be obtained onlv bv a series of very laborious and tedious 
operations, and, indeed, is often quite out of his power to 
obtain at all, as to the nature of a particular mineral grain 
which he may come across in the course of an investigation. 
Any analysis in this case must naturally be qualitative rather 
than quantitative, and must also of necessity be on a very 
minute scale, and it is with a short account of a few special 
methods devised for this purpose that I have the honour of 
occupying your attention this evening. 
The first method I have to mention has specially for its 
object the discrimination of the various members of the felspar 
group. It was devised by Dr. J. JSzabo, of the University of 
Buda Pesth, and depends on observations of the fusibility of 
grains of the substance in certain definite positions in the 
flame of a Bunsen burner, and on the flame colouration 
produced. 
In order that observations may be comparable, exact 
attention must be paid to the dimensions of the burner, the 
height and character of the flame, the thickness of the 
platinum wire which is used as a support, the position of the 
assay in the flame, and the duration of the experiment. The 
experiments are three:—Firstly, 5mm. above the burner in 
the outer zone of the flame; secondly, 5mm. above the 
chimney shield ; and, thirdly, in the same position as the 
last, but with the addition of a small quantity of gypsum to act 
as a flux, and render more of the alkalis volatile. During 
each experiment the flame is observed. The intensity of the 
yellow, due to soda, is estimated according to the scale given, 
and then the soda flame is eliminated by means of observing 
through glass coloured a deep blue by cobalt, and the violet 
colour, due to potash, similarly valued. The experiment lasts 
lmin. in the first two cases, 2min. when the gypsum has been 
added. At the end of the minute the assay is removed from 
the flame and examined through a lens for evidences of 
fusion. There will, in some cases, be only a very slight 
rounding of the sharp corners, at others a more or less com¬ 
plete fusion. The appearance of the grain is also observed 
with regard to the bubbles which form in it either in the 
interior or on the surface, and also for the condition of the 
surface, whether glassy or enamel-like. From the sum of 
these observations it is possible to arrive at very accurate 
results, but for the particulars I must refer to the original 
memoir. Anyone, however, may gain a very considerable 
