4.  EXAMINATIONS IN THE PLATINUM FORCEPS.

Before the student attempts to make an examination in the platinum forceps or tongs, he should first ascertain whether or not it will act upon the platinum.  If the substance to be examined shall act chemically upon the platinum, then it should be examined on the charcoal, and the color of the flame ascertained as rigidly as possible.  The following list of substances produce the color attached to them.

A. VIOLET.

  Potash, and all its compounds, with the exception of the phosphate
  and the borate, tinge the color of the flame violet.

B. BLUE.

  Chloride of copper, Intense blue. 
  Lead, Pale clear blue. 
  Bromide of copper, Bluish green. 
  Antimony, Bluish green. 
  Selenium, Blue. 
  Arsenic, English green.

C. GREEN.

Ammonia,             Dark green. 
Boracic acid,        Dark green. 
Copper,              Dark green. 
Tellurium,           Dark green. 
Zinc,                Light green. 
Baryta               Apple green. 
Phosphoric acid,     Pale green. 
Molybdic acid,       Apple green. 
Telluric acid,       Light green.

D. YELLOW.

Soda,                Intense yellow. 
Water,               Feeble yellow.

E. RED.

Strontia,            Intense crimson. 
Lithia,              Purplish red. 
Potash,              Violet red. 
Lime,                Purplish red.

The student may often be deceived in regard to the colors:  for instance, if a small splinter of almost any mineral be held at the point of the flame of oxidation, it will impart a very slight yellow to the flame.  This is caused, doubtless, by the water contained in the mineral.  If the piece of platinum wire is used, and it should be wet with the saliva, as is frequently done by the student, then the small quantity of soda existing in that fluid will color the flame of a light yellow hue.

A. THE VIOLET COLOR.

The salts of potash, with the exception of the borate and the phosphate, color the flame of a rich violet hue.  This color is best discovered in the outer flame of the blowpipe, as is the case with all the other colors.  The flame should be a small one, with a lamp having a small wick, while the orifice of the blowpipe must be quite small.  These experiments should likewise be made in a dark room, so that the colors may be discerned with the greatest ease.  In investigating with potash for the discernment of color, it should be borne in mind that the least quantity of soda will entirely destroy the violet color of the potash, by the substitution of its own strong yellow color.  If there be not more than the two hundredth part of soda, the violet reaction of the potash will be destroyed.  This is likewise the case with the presence of lithia, for its peculiar red color will destroy the violet of the potash.  Therefore in making investigations with the silicates which contain potash, the violet color of the latter can only be discerned when they are free from soda and lithia.