literature of
the paper-making industry.[12]

It is not a little remarkable that the main by-product of these
bisulphite processes--the sulphonated derivatives of the lignone
constituents of the wood--is still for the most part an absolute waste,
notwithstanding the many investigations of technologists and attempts to
convert it to industrial use (see p. 149). Seeing that it represents a
percentage on the wood pulped equal to that of the cellulose obtained,
it is a waste of potentially valuable material which can only be termed
colossal. Moreover, as a waste to be discharged into water-courses, it
becomes a source of burden and expense to the manufacturer, and with the
increasing restrictions on the pollution of rivers it is in many
localities a difficulty to be reckoned with only by the cessation of the
industry. The problem in such cases becomes that of dealing with it
destructively, i.e. by evaporation and burning. In this treatment the
obviously high calorific value of the dissolved organic matter (lignone)
appears on the 'credit' side. But where calcium and magnesium
bisulphites are used, the residue from calcination is practically
without value. It appears, however, that by substituting soda as the
base the alkali is recoverable in such a form as to be directly
available for the alkaline-sulphide or 'Dahl' process. As a more
complicated alternative the soda admits of being recovered on the lines
of the old black-ash or Leblanc process, and the sulphur by the now
well-established 'Chance' process, for which, of course, an addition of
lime is necessary to the fully evaporated liquors previously to
calcining. The engineering features of the system, so far as regards
evaporating and calcining, are the same. For economic working there is
required (a) evaporation by multiple effect and (b) calcining on the
continuous rotary principle. For the latter a special modification has
been devised so that the draught of air is concurrent with the movement
of the charge in the furnace, securing a progressively increasing
temperature within the furnace. This interesting development of the
chemical engineering of wood-pulp systems has been elaborated by two
well-known technologists, Drewson and Dorenfeldt, and readers who wish
to inform themselves in detail of these developments are referred to the
various publications of these inventors.

Assuming the present necessity of a destructive treatment of the
by-products of the bisulph