Explanation:
The principle used in the preparation of these salts is to dissolve
the cystine in an alcoholic alkali solution to which just sufficient
water to effect solution has been added, and, after filtering from
excess cystine, to precipitate the salt by addition of a suitable
indifferent solvent. While various solvents, such as acetone,
ether, or large amounts of alcohol caused precipitations, these were
either oily or amorphous. Only acetonitrile was found to possess
the power of initiating regular crystallization in the salt solutions.
While the solutions of the different salts require different amounts
of the solvent for complete precipitation, a partial substitution of
absolute ether for acetonitrile was found expedient in the case
of the most soluble of the salts, the K salt.
