sulfide, decomposes into copper sulfide and hydrazine sulfate.
After the copper salt has been filtered off, the solution
is concentrated until the hydrazine sulfate crystallizes.
The yield of product is small, so that it is hardly advisable
to undertake this recovery in the laboratory.

It is possible for one man, simultaneously evaporating six dishes
of the hydrazine mixture, to turn out from 20 to 25 runs in nine hours.
The time for the evaporation of a solution, such as is mentioned
in the experimental part, with a four-flame Bunsen burner, is two to
three hours; if the evaporation is carried out more slowly than this,
the yield of product is distinctly diminished.


3. Other Methods of Preparation

Hydrazine salts have been prepared by the action of hypochlorites on
ammonia[1] or urea;[2] by the hydrolysis of salts of sulfohydrazimethylene
disulfonic acid;[3] by the hydrolysis of triazoacetic acid;[4] by the
reduction of diazoacetic ester;[5] by the reduction of nitroguanidine
followed by hydrolysis;[6] by the reduction of the nitroso derivatives
of hexamethylene tetramine;[7] by the reduction of nitrates or nitrites
with zinc in neutral solution;[8] by the action of sodium bisulfite
on hyponitrous acid followed by reduction;[1b] by the reduction
of K2SO3N2O2;[2b] by the action of ammonia on dichlorourea;[3b]
by the reduction of nitrosoparaldimin;[4b] by the action of copper
sulfate on ammonia at high temperatures;[5b] by the reduction of
methylene diisonitrosoamine;[6b] by the hydrolysis of the addition
product of diazoacetic ester and fumaric or cinnamic esters.[7b]