110 



Selectioyis. 



[No. 7, NEW SERIES, 



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 

 Droitwich the use of white of egg seems to have prevailed. Vari- 

 ous vegetable infusions, still containing albumen, as linseed, mucil- 

 age and ale, were, in the early days of manufacture, in great re- 

 pute, but have, I believe, now fallen almost entirely into disuse. 



In order to prevent that most unpleasant circumstance attendant 

 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 evapo- 

 ration — another class of bodies are mixed with the brine ; these 

 are oils or butter, which, spreading over the whole area, by a pecu- 

 liar molecular action prevent the formation of any pellicle, or 

 " setting over" of a pan, as the workmen term it, and preserve that 

 open surface which is most favorable to evaporation. The action of 

 finely-powdered resin in effecting this is perfectly magical, the 

 introduction of a very few grains being quite sufficient 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 regula- 

 tion of the degree of heat employed in the evaporation will influ- 

 ence the size of the crystals with the utmost nicety, and that atten- 

 tion 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 Cheshire," to which I am so much in- 

 debted, and to which such frequent reference has been made, will 

 be found a list of the varieties produced at different temperatures ; 

 according to it, the finest table-salt is deposited from the brine at 

 its boiling temperature (220° F.), and the coarsest description by 

 slow evaporation conducted at from 100° to 110° F. 



The derivation of the brine in Cheshire is too well known to 

 require any observation : the immense beds of rock-salt which oc- 

 cur in the new red sandstone of that county are familiar to every 



