Packaging and storage—
Preserve in well-closed containers.
Identification—
A:
Dilute 10 mL with 90 mL of water, and stir for 5 minutes with a magnetic stirrer. Add 25 mL of hydrochloric acid, and mix: a heavy, resinous precipitate is formed. Remove the liquid by decantation, and wash the precipitate with 2 N hydrochloric acid until the last washing is nearly colorless. Transfer the precipitate to absorbent paper, allow it to stand for 10 minutes, and then transfer 10 mg of the precipitate to a 250-mL conical flask. To the flask add 100 mL of ether, attach an air condenser to the flask, and stir for 30 minutes with a magnetic stirrer: the precipitate does not dissolve completely.
B:
To a solution (1 in 10) add 1 N sodium hydroxide, and heat to the boiling point: ammonia is evolved.
Loss on drying 
731
—
Dry it at 80
for 8 hours, and continue the drying at 100
for constant weight: it loses not more than 50.0% of its weight.
Limit for ammonium sulfate—
Accurately weigh about 1 g, transfer to a 100-mL beaker, and add 25 mL of alcohol. Stir, filter, and wash the filter with a mixture of equal volumes of ether and alcohol until the last washing is clear and colorless. Air-dry the filter and residue, and pass 200 mL of warm water, slightly acidified with hydrochloric acid, through the residue on the filter. Heat the filtrate to boiling, add barium chloride TS in excess, and heat for 1 hour on a steam bath. Collect the precipitate of barium sulfate on a filter, wash it well, dry, and ignite to constant weight. Each g of barium sulfate is equivalent to 566.1 mg of (NH4)2SO4. Ichthammol contains not more than 8.0% of ammonium sulfate.
Assay for ammonia—
Dissolve about 5 g of Ichthammol, accurately weighed, in 100 mL of water, transfer the solution to a distillation flask, add 3 g of paraffin, and add 20 mL of sodium hydroxide solution (4 in 10). Connect the flask to a condenser by means of a spray trap, and immerse the lower outlet tube of the condenser in 30.0 mL of 0.5 N sulfuric acid VS. Distill slowly, collect about 50 mL of distillate, and then titrate the excess acid with 0.5 N sodium hydroxide VS, using
methyl red TS as the indicator. Perform a blank determination, and make any necessary correction. Each mL of 0.5 N sulfuric acid is equivalent to 8.515 mg of NH
3.
Assay for total sulfur—
Transfer from 500 mg to 800 mg of Ichthammol, accurately weighed, to a Kjeldahl flask with the aid of 20 mL of water. Add 3 g of potassium chlorate, then add slowly 30 mL of nitric acid, and evaporate the mixture on a hot plate to about 5 mL. Cool, repeat the oxidation with 3 g of potassium chlorate and 30 mL of nitric acid, and evaporate to about 5 mL. Add 25 mL of hydrochloric acid, and again evaporate to about 5 mL. Add 100 mL of water, heat to boiling, filter, and wash well. To the hot filtrate add 25 mL of
barium chloride TS, and heat on a steam bath for 1 hour. Collect the barium sulfate on a previously ignited and tared filtering crucible, wash, dry, and ignite, then cool, and weigh. Each g of barium sulfate is equivalent to 137.4 mg of S.
