M U R

MUR

( 126 )

effect. For this purpofe he made and fixed upvertically a tube of tinned iron, 33 feet high, andfilled it with brine containing 12 per cent, offait, and ciofed the top'. In two months it wasopened. Fifteen inches of liquid had oozed out,the brine at the furface (or 15 inches below thelevel when put in) gave only 9-)- per cent, of fait,at 11 feet lower it was nearly the fame, but atthe bottom, or 33 feet, it gave 12% per cent.This difference however is too fmall to promiteany advantage in concentrating weak brines bymere lubfidcnce.

The fame excellent obferver has given a feriesof accurate obfervations on the fpontaneousevaporation of brine expofed to the weather infummer in refervoirs of a given dimenfion, atAigle in the canton of Berne. h Though a moun-tainous country the climate is here warm enoughfor the vine and pomegranate. The heat inthe middle of fummer rifes from 140° to 144°in the fun. To contain the brine a refervoirwas made of the coarfe marble of the country,the joints of which were lined with afphal-tum to prevent leakage. This refervoir wascovered with a light moveable roof, which wasput up only in rainy weather. Another refer-voir was alio rqade of wood, but it is found thatthe founded: timber will not entirely Hand theprefi'ure of a column of fait water except ofa few inches, for after a time the brine oozesthrough, and covers the outfide with a ftalaCti-tical faline cruft. The particulars of thefe ex-periments which were carried on with greatattention for feveral years, need not be relatedat large, as they are calculated for a climatevery different from ours. In general it may heobferved that the utmoft exhalation for a fiugleday in fummer, was found to be 3 lines ori of an inch. Scarcely any thing exhaled inthe winter months. From October to February(4 months) the entire exhalation was only 10lines. In March, the average exhalation forthe whole month was 15 lines; in April 35;in May 48 ; in June 44 ; in July 47 ; in Auguft35 ; in September 25, and in OCtober 15. Themean exhalation from March to OCtober there-fore, was 261 lines, or 2if inches. Thefenumbers however do not give accurately therelative exhaling power in the different months,for the brine as it becomes more and more con-denfed, parts with its water with much moredifficulty, and the above experiments only givethe continued lofs by exhalation of the famebrine for many months confecutively.

The quantity of fait yielded by fpontaneous

k Mem <le l’-A

exhalation is nearly equal to that produced inexperiments in the fmall way on a few poundsof brine, which is far from being the cafe inaCtual manufacture. The fait obtained thusgradually is large-grained, of an opake white,very hard and lomewhat inclined to dampnCfs,and not very readily foluble. The common faiton the other hand is femi-traniparent, fofter,and more readily foluble.

During the evaporation of brine in a boilingheat the vapour that rifes is fenfibly faline, andgives a laltifh impregnation to wood and otherporous matter which it meets with. It hasbeen afferted that part of the acid alfo is fepa-rated in this heat and volatilized, leaving thefait therefore with a greater proportion of alkali,and to this has been attributed the inferior powerof the fmall-grained fait in preferving provifions.

Though the inferiority be undoubted it doesnot appear that any very accurate experimentshave been made on the relative quantities of acidin the large and fmall-grained fait, this hypothefistherefore is altogether doubtful. Neither doesthe large-grained fait owe its fuperior flrengthto any fuperior purity or freedom from the deli—quefeent earthy muriats, for the fine London bafket fait is fomewhat purer than the beltPortugal bay fait, though the quantity of earthymatter in each is fcarcely notable. On thewhole it is more probable that the hardnefs oftexture and flow folubility in water of bay orfifhing fait (which it owes to the flownefs ofcryflallization) is the chief caufe of its fuperiorefficacy.

Methods of procuring Soda by decompofttion ofCommon Salt .

Muriat of foda being the moft abundant ofthe neutral falts, and its alkaline bafe bearingfor the moft part a higher price in the marketthan potafh, has been fubjeCted to a vaft varietyof proceffes both on a fmall and large fcale,with more or lefs perfeCt fuccefs, for the pur-pofe of effecting its decompofition, fo as to ob-tain the alkali feparate, or at leaft only combinedwith carbonic acid. Thefe different methodsnaturally divide themfelves into two clafies, thefirfl: containing thofe that aim at the immediateextradition of the alkali, and the fecond thofethat feek the fame end, but by more complexmeans. Under the lirft clafs will be describedthe decompofition of fait by lime, by iron, byoxy.d of lead, and by potafh ; under the fecondclafs will be mentioned the different methods ofdecompofing fait after it has been previouflyconverted into fulphat of foda.

:ad. for 1764.