Page 13 - A HANDBOOK OF ORGANIC ANALYSIS QUALITATIVE AND QUANTITATIVE

IO ORGANIC ANALYSIS
sodium and carbon into sodium cyanide, nd by boiling the
alkaline cyanide solution with ferrous hydroxide, sodium
ferrocyanide will have been produced. Now if on addition
of an excess of hydrochloric acid a blue coloration or precipi-
tate of ferric ferrocyanide is formed, it may be taken as
proof that both carbon and nitrogen are present in the sub-
stance:- •
Fes0, + 2NaCN = Fe(CN), + Na,SO,
Fe(CN), + 4NaCN = NaFe(CN),
3Na,Fe(CN), + 4Fel, = Fe[Fe(CN)], + 12NaCl.
'
Should the substance be very volatile, it may be found
difficult to make the sodium react sufficiently with it. In
such a case it is advisable to support the tube, which should
be of hard glass, in a piece of asbestos board so that it hangs
in a vertical position by the flange around the open end.
The sodium is then to be heated by itself, and the substance
dropped in small portions upon it, thus giving it a better
opportunity to react. The sodium may with advantage be
replaced by potassium.
In the absence of carbon of course no cyanide is produced,
although nitrogen may be present. In carrying out this test,
only a faint greenish-blue coloration may occasionally be
produced, which forms a blue precipitate on prolonged
standing. In such a case it is advisable to repeat the test
with great care, employing larger quantities. The presence
of sulphur occasionally tends to obscure the. cyanide test,
owing to the reduction of ferric iron to the ferrous condition
by the hydrogen sulphide liberated on the addition of acid.
In such cases black ferrous sulphide is precipitated on the
addition of the ferrous sulphate solution, and it will be well
to make sure that enough of this reagent has been added, and
to filter the solution after boiling, before adding the ferric
chloride and hydrochloric acid.
To another portion of the filtrate a drop of sodium plumbite
solution is added. A black precipitate or dark coloration