If the flask is not protected with an asbestos board or the equivalent,
decomposition occurs where the substance is super-heated on the side
walls of the flask. If crystals of the cyanide are allowed to remain
on the upper walls of the flask, they are not easily washed down
and so are not hydrolyzed.
The solubility curve of _p_-nitrophenylacetic acid is very steep
at temperatures near 100'0, so that the filtering of the boiling
solution should be rapid.
If a good grade of cyanide be used, it is not necessary to add
bone-black in order to obtain the acid in a pure state.
In making experiments with 500 g. of _p_-nitrobenzyl cyanide,
it was found that the time for hydrolysis was about the same as
when smaller amounts were used.