It is manifest that, but for this later compound, we might double the quantity of hydrocyanic acid from the yellow salt." The decomposition just described is the one usually received; but too much reliance must not be placed on its accuracy, for the analysis of the several compounds is too difficult for the results to be fully admitted.

The residue left in the retort speedily turns to one of the blues, identical with, or allied to, Prussian blue.

This is at best a disagreeable process to conduct, for the hydrocyanic acid formed adheres so strongly to the glass, that, instead of being freely given off, bubbles are evolved suddenly with such explosive violence as occasionally to crack the vessel.

This may be remedied as far as possible by the insertion of plenty of waste pieces of platinum--if platinized, so much the better, as that facilitates the escape of the gas.

The heat should be applied to every part of the vessel, and the flame should not be allowed to play upon one single part alone.