(3.) Carbon (C).—­Carbon is found in nature in the pure crystallized state as the diamond.  It occurs likewise in several allotropic states as graphite, plumbago, charcoal, anthracite, etc.  It exists in large quantities combined with oxygen as carbonic acid.

The diamond, although combustible, requires too high a heat for its combustion to enable us to burn it with the blowpipe.  When excluded from the air, it may be heated to whiteness without undergoing fusion, but with the free access of air it burns at a temperature of 703 deg.  C, and is converted into carbonic acid.  If mixed with nitre, the potassa retains the carbonic acid, and the carbon may be thus easily estimated.  If a mineral containing carbonic acid is heated, the gas escapes with effervescence, or a strong mineral acid as the hydrochloric will expel the acid with the characteristic effervescence.

(4.) Phosphorus, Phosphoric Acid (PO^{6}).—­This acid occurs in a variety of minerals, associated with yttria, copper, uranium, iron, lead, manganese, etc.  Phosphoric acid may be detected in minerals by pursuing the following process:  dip a small piece of the mineral in sulphuric acid, and place it in the platinum tongs:  this is heated at the point of the blue flame, when the outer flame will become colored of a greenish-blue hue.  This color will not be mistaken for those of boracic acid, copper, or baryta.  Some of the phosphoric minerals, when heated in the inner flame, will color the outer flame green.

If alumina be present with the phosphoric acid, the following wet method should be adopted for the detection of the latter:  the substance should be powdered in the agate mortar with a mixture of six parts of soda, and one and a half parts of silica.  The entire mass should now be placed on charcoal, and melted in the flame of oxidation.  The residue should be treated with boiling water, which dissolves the phosphate and the excess of carbonate of soda, while the silicate of alumina, with some of the soda, is left.  The clear liquor is now treated with acetic acid, and heated over the spirit-lamp, and a small portion of crystallized nitrate of silver added; a lemon-yellow precipitate of phosphate of silver is quickly developed.  Previous to the addition of the nitrate, the liquor should be well heated; otherwise, a white precipitate of dipyrophosphate of silver will be produced.

If the examination be of any of the metallic phosphides, the substances should be powdered in the agate mortar, and fused with nitrate of potassa on the platinum wire; the fused mass should be treated with soda in the same manner as any substance containing phosphoric acid.  The metal and the phosphorus are oxidized, while the phosphate of potassa is fused, and the metallic oxide separates.

(5.) Sulphur (S).—­Sulphur is found native in crystals It is frequently found associated with lime, iron, silica, carbon, etc., and combined extensively with metals.