Mar., 1889. MICRO-CHEMICAL EXAMINATION of minerals. 
65 
may be recognised on examining the flame through a solution 
of indigo instead of through a blue glass, as when testing for 
potash. The glass cuts off the lithia flame as well as the soda 
flame, but through the thinner parts of the indigo solution, 
which completely stop the yellow light due to soda, the lithia 
flame is still visible, but gradually disappears before the 
thicker parts are reached. 
With the help of a pocket spectroscope I have detected 
lithia in the great majority of micas from granites which 
I have examined, not only in lepidolites, but even in dark 
micas which would, no doubt, come under the division of the 
biotites. 
It is obvious that before coming to any conclusions on the 
constitution of a mineral by these micro-cliemical methods, 
the reagents used must be most carefully tried by blank 
experiments, so that we may be quite sure that there is no 
trace present of the base the presence of which we wish to 
determine. For instance acetate of uranium, as usually 
bought, must be recrystallised, and probably twice over, 
before it ceases to show on evaporation the yellow tetrahedra 
due to the presence of soda. Chloride of platinum must be 
carefully examined as to the absence of potash (or ammonia), 
which would make itself unpleasantly manifest on slight 
evaporation. The best method for purifying this reagent is to 
dissolve the solid salt in as neutral and dry a state as possible 
in absolute alcohol, filtering off any small quantity of 
undissolved double salts and evaporating the filtrate to get rid 
of the alcohol. 
In the next place it is of course essential for the beginner to 
proceed methodically—testing, first, known salts of the various 
bases, then known minerals. Fragments of the different felspars, 
augites, hornblendes, micas, &c., of which the composition is 
at least approximately known, should be first examined, and 
the results obtained compared with those of the ordinary 
analysis. The student is then in a position to proceed to the 
examination and determination of minerals in a rock ; first of 
all, those which he can detach as being more easily 
manipulated ; finally, as he acquires practice with small 
quantities of material, attacking the cases where only a thin 
section is available and the grain has to be isolated by means 
of a perforated screen as above described. 
In conclusion, I may refer to my authorities:— 
Szabo, “Ueber eine neue Methodedie Feldspathe auch in Gesteinen zu 
bestirnmen.” Buda Pest, 1876. 
v 
Boricky,“Elemente einer neuen chemisch-microscopischen Mineral-und 
Gesteinsaualyse.” Prag., 1877. 
Streng, Neues Jahrbuch fur Mineralogie und Geologie. 1885, I., p. 21. 
Behrens, “ Chemical News.” 1886, Oct. 15 to Dec. 24. 
