Synthetic Inorganic Chemistry

268 ELEMENTS OF GROUP IV

and collect the silica on the suction filter, washing it well on the

filter. Dry the product and put it up in a 2-ounce cork-stoppered

bottle.

QUESTIONS

1. Quartz can be melted like glass, but at a much higher
   temperature, and many kinds of chemical apparatus are made
   of fused quartz. Dishes made of fused quartz are used for boiling
   concentrated sulphuric acid. Why cannot they be used equally
   well for concentrating caustic alkalies?


2. Mix 0.5 gram of the precipitated silica with 1 gram of pow-
   dered calcium fluoride. Place the mixture in a test tube, moisten
   it with 36 N H2SO4, and warm it gently under the hood. Dip a
   stirring rod in water and lower it, with a drop adhering, into the
   gas in the test tube. Note the precipitate that forms in the drop of
   water. Write equations for all the reactions, and state what
   rather unusual properties are shown by this experiment to be
   possessed by hydrofluoric acid and by silicon tetrafluoride.

PREPARATION 42
STANNOUS CHLORIDE, SnCl 2 -2H 2 O
This salt can be prepared by the action of hydrochloric acid
upon metallic tin, but since the action is exceedingly slow, it is
hastened by the addition of a very small quantity of nitric acid,
which oxidizes the tin. Nitric acid is ordinarily reduced only to
the oxide NO by its action upon a metal; but in the course of
this preparation no red fumes of oxides of nitrogen are found to
escape, because, under the influence of tin and stannous chloride,
the reduction does not stop at nitric oxide, but continues to the
lowest possible step, which is ammonia or in this case its salt,
ammonium chloride. Stannous salts are oxidized quite readily
to stannic by the oxygen of the air; to prevent this happening
during the evaporation of the solution, an excess of metallic tin is
kept in the liquid.

Materials: feathered tin, 100 grams.

12#HCl,175cc.

6N HNO3, 25 cc.

750-cc. casserole.