Sensitive apparatus for obtaining freezing curves Purity of 4-aminopyridine.

Freezing curves of highly-purified 4-aminopyridine have been obtained with an instrument of new design employing a gold crucible, a platinum resistance thermometer, electrical heating elements on crucible and heat shield, and accessory electrical control devices such that the temperature difference between crucible and shield could be maintained constant within 0.005 degrees while the temperature of the 4-aminopyridine and crucible dropped through the freezing range. No stirring was used.