Synthetic Inorganic Chemistry

276 ELEMENTS OF GROUP IV

ments is a vigorous one, and usually it is necessary to cool the

mixture to prevent the loss of bromine. Stannic bromide boils at

a relatively low temperature (203°), and it can be purified by

distillation. Since stannic bromide reacts with water, care

must be taken to exclude moisture during the distillation, and the

product must be preserved in a dry, well-stoppered tube.

Materials: bromine, 12.5 cc. = 40 grams = 0.25 F.W. Br 2.

feathered tin, 25 grams.

Apparatus: 125-cc. separatory funnel.

125-cc. distilling flask,

thermometer, 250°.

Pyrex test tubes,

ring stand,

burette clamp.

Bunsen burner.

Procedure: Place 24 grams of feathered tin in a 125-cc. dis-
tillling flask which has been warmed to expel all moisture. (Save
1 gram of the smallest pieces of tin for use later in the preparation.)
In a 125-cc. separatory funnel place 12.5 cc. of bromine. (Before
pouring the bromine into the separatory funnel, make sure that
the stop cock has been lubricated and that the bore is not ob-
structed.) Insert the stem of the funnel in the neck of the flask.
Regulate the stop cock of the separatory funnel so that the
bromine falls at the rate of 1 or 2 drops a second. Observe the tin
when a drop of bromine first falls on it. If bromine vapor comes
out of the side arm, stop the addition of bromine and immerse the
bulb of the flask a moment in a pan of water.

When all the bromine has been added, shake the flask and allow

it to stand 5 minutes. Then add the gram of tin saved at the

beginning of the preparation and allow it to stand 5 minutes. If

the mixture commences to boil, cool the flask again with water.

When the reaction is apparently complete, replace the separatory

funnel with a 250° thermometer arranged so that the bottom of

the mercury bulb is 1 inch below the side arm of the distilling

flask. Adjust the clamp holding the flask so that the side arm of

the flask dips into a dry test tube. Warm the stannic bromide

in the flask with a very low flame until it begins to boil. Grad-

ually increase the temperature until uncombined bromine has