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candy. This fait is ufed in the curing of fifh,and is called fifliery-falt.

Much of the fined part of the rock felt dugout from the pits near NorthwicK in Chefhire(the only rock-pits in the kingdom) is exportedto Ireland , the Weft Indies and other parts,and of late years a plan has been adopted ofbruiting it by rollers and bringing the fragmentsto the fize of the common bay and fifhery fait,in which Hate it is found to anfwer well forcuring fifh and meat.

The chemical analyfis of the different brinesand produfts or impurities in falt-making willbe prefently mentioned.

The above method of falt-making has beenpra£tifed in the Chefhire works with fcarcelyany variation ever fince their firft eftablifhment,the methods employed in other countries ofconcentrating weak brine before boiling beingunnccefl'ary here, as there is abundance of ftrongbrine and a further opportunity of faturatingthe weak by the rock fait.

As the greateft inconvenience in falt-makingis the precipitation of the earthy impurities andthe difficulty of preventing them from mixingwith the fait; a plan has lately been adopted(under patent) in fome works near Northwich, ofheating the brine in a feparate pan to thedegree at which the earthy carbonats precipitate,before it is fent into the large faking pan. Itis found that the fame fire, by extending theflues, will heat this preparing pan which iscontiguous to the other, and the time in whichone pan-full is worked off is fufficient to bringthe frefh portion to the requifite heat, and topurify it confiderably.

We fltall now relate fome of the leadingcircumftances of the preparation of fait inforeign countries as far as they differ from thatabove deferibed.

When a weak brine is expofed to the at-mofpher-e the watery part gradually evaporates,and with it the carbonic acid which it contains,the effect of which is to'concentrate the lolutionand alfo to caufe the depofition of the earthand oxyd of icon which the carbonic acid helddiflolved. As evaporation much depends onthe furface expofed to the air, a very ingeniousmethod has been adopted of promoting this bycaufing the weak brine to fall fucceffivelythrough large bundles of faggots, whereby a vaftconfumption of time and fuel in the lubfequentevaporation is prevented. This operation iscalled graduation, and the place in which it isperformed a graduating hoitfe.

This confifts of a very long range of rows offaggots placed perpendicularly, and rifing tothe height of about 25 feet and difpofed incones, the fummits of which are about 6 feetin diameter, and the bafes about 10. Juftabove the faggots is a trough perforated withholes at frnall intervals, furnifhed with ftop-cocks, and the whole is covered with a pent-houfe roof. At the bottom of the faggots isanother trough to catch the brine. The lengthof thele houfes is determined by the quantity ofbrine wanted, fometimes it is enormous. Infome parts of Germany there are graduatinghoufes fix thoufand feet long, but in generalthey are from 200 to 1000.

The weak brine is firft raifed by pumps tothe upper trough, when the ftop-cocks areturned and the water made to fall like a fhowerof rain through the faggots into the troughbelow. It is then again forced up and under-goes the fame operation fucceffively till it isfulficiently concentrated. The date of theatmofphere has the greateft influence on thegraduation of the brine. The evaporation goeson the quickeft in a dry air with a moderate wind:when the wind is violent much of the brine iscarried away in the Hate of fpray or vapory,particularly when the column of faggots is notpyramidal but has the fame dimenfions through-out. As a proof of this wafte Haller obfervesthat in the neighbourhood of thefe graduatinghoufes the ground becomes in a few yearscovered with the falicornia and other plantswhich are known to require a fait foil andflourifh on the fea-fhore.

It has been mentioned that in proportion asthe brine becomes concentrated it parts with itscarbonic acid, and depofits carbonat of lime,and hence the faggots of the graduating houfesbecome gradually encrufted, over every twig,with a brown hard earthy matter, confidingchiefly of carbonat of lime. Thus in a courfeof years the faggots are entirely covered withftalactite as in the common petrefaflions,and the furfaces for evaporation become therebyfo much diminiftied that it is neceflary toreplace them with frefh faggots. The timethat one fet of faggots will laft, is about eightor ten years.

The effeft of graduation in concentratingbrine is very ftriking. Baron Haller in hisvaluable memoir on the fubjeft gives the refultof manv obfervations on this and other particu-lars relating to the falt-works in Switzerland ofwhich he was the director. 11

* Mem. dc l’Acad. for 1764,