In PART THIRD of this work, commencing at page 109, the student will find a sufficiently explicit description of the blowpipe reactions of those principal substances that would be likely to come beneath his attention.  The following tabular statement of those reactions—­which we take from Scheerer and Blanford’s excellent little work upon the blowpipe—­will be of great benefit, as a vehicle for consultation, when the want of time—­or during the hurry of an examination—­precludes the attentive perusal of the more lengthy descriptions in the text.

In the examination of minerals, before the student avails himself of the aid of the blowpipe, he should not neglect to examine the specimen rigidly in relation to its physical characters, such as its hardness, lustre, color, and peculiar crystallization.  It is where the difference of two minerals cannot be distinguished by their physical appearance, that the aid of the blowpipe comes in most significantly as an auxiliary.  For instance, the two minerals molybdenite and graphite resemble each other very closely, when examined in regard to their physical appearance, but the blowpipe will quickly discriminate them, for if a small piece of the former mineral be placed in the flame of oxidation, a bright green color will be communicated to the flame beyond it, while in the latter there will be no color.  Thus, in a very short time, these two minerals can be distinguished from each other by aid of the blowpipe, while no amount of physical examination could determine that point.  The blowpipe is equally an indispensable instrument in the determination of certain minerals which may exist in others as essential or non-essential constituents of them.  For instance, should a minute quantity of manganese be present in a mineral, it must be fused with twice its bulk of a mixture of two parts of carbonate of soda, and one part of the nitrate of potassa, in the flame of oxidation upon platinum foil.  The manganate of soda thus formed will color the fused mass of a bluish-green tint.

Or a slight quantity of arsenic may be discerned by the following process recommended by Plattner:[4] one grain of the finely pulverized metal is mixed with six grains of citrate of potassa, and slowly heated on the platinum spoon.  By this means the metals are oxidized, while the arseniate of potassa is obtained.  Then boil the fused mass in a small quantity of water in a porcelain vessel till all tho arseniate is dissolved.  The metallic oxides are allowed to subside, and the above solution decanted off into another porcelain vessel.  A few drops of sulphuric acid are added, and the solution boiled to expel the nitric acid, after which it is evaporated to dryness.  In this operation, the sulphuric acid should be added only in sufficient quantity to drive off the nitric acid, or, at the utmost, to form a bisulphate with the excess of potassa.  When dry, the salt thus obtained is pulverized in an agate mortar, and mixed with about three times its volume