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The benzaldehyde should be freed of benzoic acid by shaking with aqueous sodium carbonate solution.</div>
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 The mixture is stirred vigorously during the reaction, and one or two stout glass rods are clamped in the flask to act as baffles and to break up the lumps of benzalazine.</div>
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 Dimethylsulfate is extremely toxic. It should not be spilled; neither should the vapor be inhaled. Ammonia is a specific antidote.</div>
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 Unreacted hydrazine sulfate is removed by conversion to benzalazine. The filtrate should not give an appreciable precipitate when mixed with 5 cc. of benzaldehyde and left for four hours.</div>
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 From the mother liquors about 12 g. of less pure material, m.p. 133–136°, can be recovered.</div>