The reactions in reducing copper sulphate, CuSO4, with Na2CO3 and with KCN before the blowpipe, are here given:—
| CuSO4 | + | Na2CO3 | = | CuCO3 | + | Na2SO4 | } | (1) |
| 2CuCO3 | + | C | = | 3CO2 | + | 2Cu | } | |
| CuSO4 | + | Na2CO3 | = | CuCO3 | + | Na2SO4 | } | |
| CuCO3 | = | CuO | + | CO2 | } | (2) | ||
| CuO | + | KCN | = | Cu | + | KCNO | } |
After obtaining beads, it is well to obtain their coatings, for oftentimes it is only in this way that we can distinguish between the metals.
Examination in Tube with Na2CO3 and Charcoal.—If the substance in a finely pulverized condition be mixed with twelve parts, Na2CO3, and six parts of charcoal powder and the mixture be placed in an ignition tube and subjected to heat, the acid of the substance combines with the soda and the metal is set free.
If this metal is volatile, a sublimate is formed in the upper end of the tube.
Mercury deposits in minute globules, which may be seen with the magnifying glass. Arsenic forms a ring, which, when examined with the magnifying glass, is seen to be made up of minute crystals. Ammonia is recognized by its characteristic odor, and also by its turning a slip of moistened red litmus (held over the mouth of the tube) blue.
Examination on Platinum Wire.—Many substances possess the property of imparting to the colorless flame of the Bunsen burner characteristic colors.
The chlorides of these substances exhibit these flame reactions best, and hence before applying the flame tests we dip the wire which serves as a support into hydrochloric acid and then into the substance. When the substance has been taken up on the wire, it is placed in the edge of the long colorless flame of the Bunsen burner near the apex, when instantly the flame becomes tinged with the characteristic color of the substance.
Illustrations. Sodium compounds color the flame yellow, and a crystal of potassium dichromate appears colorless in the sodium light.