Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

ANTIMONY SULPHATE. 129

rate at which air is drawn through the apparatus. The total air

admitted is regulated by a screw clamp placed between the safety-

bottle and the water-pump, and the proportion passing over the

pyrite and through the nitric acid is governed by the clamp shown

at the end of the combustion tube.

First heat the pyrite in a slow stream of air until it takes fire.

Then warm the nitric acid and, by partially closing the clamp at

the end of the " pyrite-burner," cause air to enter also through the

capillary in the distilling flask, and thus carry nitric acid vapors

into the large bottle. Heat the pyrite strongly and continuously;

regulate the current of air laden with nitric acid so that red fumes

are always present in the bottle. If insufficient nitric acid is pro-

vided, the walls of the flask become coated with colorless crystals

of nitrosyl sulphuric acid (" chamber crystals "; cf. No. 152).

When the pyrite is completely burned, disconnect the apparatus,

and wash the contents of the bottle into a beaker with a little

water. Test the solution qualitatively, and determine by titration

the yield of sulphuric acid.

87. Reduction of Barium Sulphate and Preparation of Barium
    Nitrate.

Mix thoroughly 47 g. of finely powdered heavy spar with 12 g.

of fine sifted charcoal, and place the mixture in a Hessian crucible

which should be two-thirds to three-quarters filled by it. Spread

a layer of charcoal on top, and place a cover on the crucible.

Heat to a red heat for two hours in a charcoal furnace. After

cooling break up the reddish-gray, porous contents of the crucible,

and add it little by little to 600 c.c. of a solution containing 25 g.

of nitric acid. Boil, filter, and evaporate the solution to crystalli-

zation. Separate the crystals on a filter, wash them with a little

water, and dry them at a moderate temperature on a porous plate.

Recover more crystals from the mother-liquor. Yield, 45 to 50 g.

of Ba(NO 3 ) 2.

88. Antimony Sulphate Sb 2 (SO 4 ) 3.

Antimony sulphate is an example of a salt which is very easily hydrolyzed.

In spite of the fact that it can be crystallized from concentrated sulphuric

acid, it is impossible to obtain it pure without adopting some special expe-

dient. The sulphuric acid adhering to the crystals cannot be removed by