OF DENISON UNIVERSITY. 
129 
fumes, the objective may be protected by a thin glass cover tempora- 
rily fastened to the end by glycerine. 
As an example of the micro-chemical process we may mention the 
process of distinguishing apatite from nephelin. If the grain of 
apatite can be isolated it is dissolved in a concentric nitric acid solution 
of molybdate of ammonia. As the solution is slowly affected, a 
multitude of yellow octahedrons of 10 Mo O3 + PO4 (NH4)3 appear 
about t^ie edges. This detects the phosphoric acid. The lime may 
be demonstrated by dissolving the grain in nitric acid, to which is then 
added a drop of sulphuric acid producing small crystals of gypsum. 
In case the questionable grain is in a section the acids may be 
applied with a glass rod and then removed by a pipette to a glass slip 
and there evaporated. 
Nephelin fails to produce the reactions described but its solution 
in concentric hydrochloric acid affords, on evaporation, minute cubes 
of common salt which are very readily recognized. 
Boricky has applied Fluo-silicic acid in the micro-chemical analysis of 
many minerals. The reagent must be chemically pure and about 
13 per cent, strong. It cannot, of course, be preserved in glass 
vessels. Its availability arises from the fact that nearly all rock- 
forming minerals are attacked by it and the resulting compounds afford 
characteristic crystals. 
A slide is covered with a thin protecting layer of balsam and upon 
this the particles to be examined are placed. When the substance is 
very slowly affected the best results are obtained by applying the 
reagent to the section itself If the mineral is easily dissolved the 
various components appear approximately in their relative proportion 
in crystals of various form. In cases where the mineral is but slightly 
attacked, some of its components may first separate and thus make 
necessary a repetition of the process, or it may be faciliated by first 
dissolving these soluble substances in fluoric acid. The fluo-silicates 
crystallize most perfectly when evaporated and the watery solution 
permitted to again evaporate on a second slide. 
1. Fluo-silicate of postassium crystallizes in the isometric system, 
usually in i-i in skeleton groups, also in i, and I. The reaction is 
masked by presence of sodium, when apparently rhombic crystals i-n . m-i 
are formed. 
2. Fluo-silicates of sodium give short hexagonal columns with * 0 , 
