Abstract
(1) Isolation of amino acid.
Mueller obtained the amino acid by precipitation
with mercuric sulphate after hydrolysis of
casein. The precipitate was decomposed with
baryta, the barium and mercury removed with sulphuric
acid and hydrogen sulphide respectively and the
solution evaporated to small volume. A second
precipitation, this time with mercuric chloride,
was brought about, and the precipitate was decomposed
by passing hydrogen sulphide into an aqueous
suspension. The silver oxide method was used to
obtain the free amino acid which was finally
crystallised from 75 per cent. alcohol. This
method did not give a pure product, the chief
contamination being apparently phenyl alanine. By
repeating the mercuric chloride precipitation, the
substance was obtained pure, but only at the expense
of a large loss. The yield of crude product varied
from 1 -2 grams per lb. of casein. The same method
used with gelatin gave smaller yields.
(2) Investigation of structure of amino acid.
The first experimental work carried out with
the amino acid was a repetition of Mueller's comparison
with ethyl cysteine. The results obtained
confirmed his statement regarding their relative
stabilities to alkali.
(3) Synthesis of amino acid.
The methods of synthesis of amino acids used
by Erlenmeyer and by Strecker were considered.
(4) Derivatives of amino acid.
The α-naphthyl isocyanate described by
Mueller was prepared and the synthetic and
natural products were again identical.
Further confirmation was obtained by the
preparation of the thio hydantoin and the picrolonpate.
In each case the products from the
synthetic and natural amino acid were identical.
