462 Mr. A. B. Northcote on the Brine-springs of Cheshire. 
‘incipient drying of the salt.’ In order to counteract this supposed 
.evil, acids were added, and it was imagined that the excellence of 
the Dutch salt was due to a skilful admixture of whey which the 
manufacturers were alleged to make with their brine during the 
evaporation, which prevented the injurious effects of the free alkali. 
Another very favourite class of adjuncts has always consisted of 
substances which contain constituents possessed of the property 
of coagulating upon the application of heat, which clarify a liquid 
by entangling all suspended particles of solid matter in the meshes 
of their coagulum, and carry them with it as it rises to the sur- 
face. Those substances which contain albuminous or gelatinous 
matters are peculiarly adapted for this purpose, and are constantly 
used in a variety of manufactures for the attainment of this end. 
Blood, white of egg, glue and cows’ or calves’ feet have long been 
used in this way in salt-making. In 1670 the Nantwich sait- 
makers are described as mixing twenty gallons of brine with two 
quarts of blood, and adding about two quarts of this clarifying 
liquid to a pan which held 360 quarts of brine. In 1810 this 
process was still adopted in some of the Cheshire works, but I 
am not aware that it is ever used at the present day. At Droit- 
wich the use of white of egg seems to have prevailed. Various 
vegetable infusions, still containing albumen, as linseed mucilage 
and ale, were, in the early days of the manufacture, in great re- 
pute, but have, I believe, now fallen almost entirely into disuse. 
In order to prevent that most unpleasant circumstance attend- 
ant upon the evaporation of all concentrated saline solutions,—the 
formation of a. pellicle upon the surface of the liquid, which gra- 
dually becomes a thick layer of salt, and seriously impedes eva- 
poration—another class of bodies are mixed with the brine; these 
are oils or butter, which, spreading over the whole area, by a 
peculiar molecular action prevent the formation of any pellicle, 
or “setting over” of the pan, as the workmen term it, and pre- 
serve that open surface which is most favourable to evaporation. 
The action of finely-powdered resin in effecting this is perfectly 
magical, the introduction of a very few grains being quite suffi- 
cient instantly to clear the surface of the largest pan, and to 
prevent any recurrence of the formation of the pellicle. This 
substance was also formerly thought to perform another function, 
viz. the production of a salt of finer grain; wheat-flour was also 
believed to exert the same action, whilst alum was added in order 
to facilitate the formation of larger crystals; but I believe it is 
now found that the regulation of the degree of heat employed in 
the evaporation will influence the size of the crystals with the 
utmost nicety, and that attention to that circumstance alone is 
sufficient to produce all the varieties which are found in the 
market. In Holland’s ‘General View of the Agriculture of 
