AND ITS APPLICATIONS. 373 



supernatant liquid decanted. The liquor is not tlirown away, but preserved 

 to wash, the impure borax ; the solid matters held in suspension being first 

 separated by settlement and decantation. The washing is continued with 

 the same liquid, clarified by subsidence as often as applied, until it is no 

 longer rendered turbid. In this way a great portion of the . fatty matter 

 may be washed away as an insoluble soap of lime. The salt thus purified 

 is dissolved in two and a half pints of boiling water, and mixed with a 

 solution of chloride of calcium, containing two parts of that salt to one 

 hundred parts of tincal. A precipitate is thereby produced, consisting 

 chiefly of the insoluble soap of lime ; the liquor is separated from the 

 precipitate by filtration, and evaporated down to the density of 1"14 or 

 ri6. It is then run off in crystallising vessels, and cooled very gradually, 

 in order to obtain large crystals. — The preceding process has received 

 various modifications. There are several works in England and on the 

 Continent where they purify and crystallise tincal, producing from it the 

 finest borax. Some manufacturers, however, prefer tincal to borax, as the 

 latter frequently contains large quantities of soda and moisture. Very 

 fine borax, such as should contain 85 per cent, of pure borax, is scarcely 

 to be met with ; whereas very fine purified tincal will refract 98 to 99 per 

 cent, of pure borax. 



The most considerable consumption of borax at present is at the 

 potteries, chiefly in the formation of a porcelain and earthenware glaze — an 

 application dependent on the vitreous character of most combinations of 

 this salt with metallic oxides and earthy bases. The particular composition 

 of the borax glaze is varied at different potteries ; but the essential con- 

 stituents, besides borax, are felspar and soda. Nitre is sometimes added in 

 small quantity, and a mixture of powdered flint-glass and flints is 

 occasionally substituted for felspar. 



The following information has been supplied me by a manufacturing 

 chemist in the Potteries district : — 



The use of tincal or borax in the manufacture of earthenware is to 

 give increased fusibility to the glass or glaze, which is composed of silica 

 or felspar, lime, and soda : lead is also added to the above, when run down, 

 to increase its fusibility and density. The finer the quality of the glaze 

 required, the greater the quantity of borax must be used. After it is run 

 down into a glass, it is called by the potters " frett," and the operation is 

 called "fretting." 



This frett is ground in water until it is very fine and smooth, and about 

 the consistence of cream, when it is ready for use. The calcined or biscuit 

 porous ware is then dipped into it, and absorbs a portion of it ; the ware is 

 then dried, and again fired, when the glaze on the surface fuses and covers 

 the ware with a thin coating of glass. 



It is also used in preparing the colours of the earthenware manufac- 

 turer, to increase their fusibility, and to make them a little softer than 

 the glaze with which the ware is covered. 



Borax is also used for domestic purposes, by the laundress, who finds 



