Sulphuric acid, commonly called oil of vitriol, a common, yet very
important, acid. Although not used to any great extent in ostrich
feather dyeing, it occurs in commerce in various states and degrees
of purity. It was at one time prepared by distilling dried copperas
at a high temperature. It is now obtained in greater purity from the
alkaline bisulphates. It is a clear colorless oily fluid, weighing
about eighteen pounds to the gallon. If mixed with cold water, a great
increase of temperature takes place. It rapidly destroys organic
bodies, depriving them of their oxygen and hydrogen, and leaving
the carbon behind, as a blackish mass. If any particle of organic
matter falls into a carboy of acid, it is decomposed, and imparts a
dark color to the liquid. It takes up water from the air rapidly, if
left uncorked, and thus dilutes itself. Its use in feather dyeing is
principally to extract colors that are too dark.