SOD

SOL

( 334 )

or unmanufactured Carbonat of Soda by pre-•cifely the fame methods which have been alreadyamply detailed in the article Potash , to whichwc refer our readers. In its general propertiesit fo clofely refembles potafh that it is with theutmoft difficulty that the two alkalies when ina pure uncombined ftate, are diftinguifhedfrom each other. To avoid ufelefs repetitiontherefore, we fliall only mention here thofe cir-cumftances in which foda differs from potafli.The affinity of foda for water is much inferiorto that which potafh exhibits for the fame fub-,fiance, hence when folid cauftic foda is expofed,to the air it prefently moulders to a moift pafte,.but as foon as it has abforbed carbonic acid.enough to form the fub-carbonat of foda, itparts again with its water and efflorefces to awhite powder. Potafh on the other hand,entirely deliquiates, and continues fluid tillquite faturated with carbonic acid. The fpeci-fic gravity of foda according to Haffenfratz ismi.33, whereas that of potafli amounts to1.70. Soda combines with filex and other vitri-■fiable ingredients into a glafs it) the fame manneras potafh does, but the glafs prepared with thelatter is harder than when the former is madeufe of. On the other hand the foaps producedby combining foda with oil or tallow are hardand folid, while thofe made with potafh arefoft and gelatinous. The two alkalies are ftillmore diftinguifhable when united to the differentacids, producing compound falts, and a con-fulerably fmaller proportion of foda than ofpotafh will faturate a given quantity of acid.The falts with a bafe of foda are for the modpart confiderably more foluble than the corref-ponding ones with a bafe of potafli, and in theforce of its chemical affinity foda appears .to befomewhat inferior to potafh, this however is nodoubt increafed by the fuperior folubility of itsfalts.

Soda is applied in general to the fame ufe aspotafh, and the preference given to either overthe other is often determined merely by theirrelative commercial value. In the preparationof hard foap and the fofter kinds of glafs thereis however an intrinfic ground of preference.SOLDER.

The art of foldering is that of joining togethertwo or more pieces of metal by means of ametallic cement: hence it is abfolutely requifitethat the folder employed fhould have the twofollowing qualities, viz. that of being fuflble ata lower heat than the metals which it is intendedto cement, and of adhering with confiderablefirmnefs to their lirfaces. The fo'der for gold

is compofed of fine gold with I or £ its weightof fine filver, mixed together accurately byfufion, and afterwards beat out into leavesfomewhat thinner than card paper, and renderedas foft as poffible by annealing. It is made ufeof in the following manner. A piece of folderof the proper fize and fhape being cut off, islaid on the part to be cemented and fprinkledover with pulverized borax; the flame from ablowpipe is then applied, and the borax andfolder both enter into fufion, the latterincorporating with and adhering firmly to thegold: when the jundlure is compleat the pieceis allowed to cool, and the borax is removed byboiling water, or what is Hill better a littledilute fulphuric or muriatic acid. The folderwill however appear confiderably paler than theother part, both on account'of the filver withwhich it is alloyed, and of the borax, whichalways lowers the colour of gold: this defetlmay be remedied by melting on the furface ofthe folder a mixture of two parts of nitre andone of burnt alum and afterwards wafhing it offwith a foft brufli and hot water, by which thenatural colour of the gold will be reltored andeven heightened.

For filver there are two kinds of folderemployed, the hard and the foft. The formeris compofed of equal parts of filver and finebrafs; and the latter is prepared by fufing thehard folder with T V of its weight of pure zinc.The mode of applying it is the fame as alreadydire£led for gold folder.

For copper, brafs, and the hard alloys ofcopper the bell hard folder is compofed of brafsand zinc in the proportion of from 8 to 16 ofthe former to one of the latter, according to therequired hardnefs. The foft folder is compofedof 3 parts of zinc and one of lead, and isapplied by means of a common foldering ironheated red hot.

The folder for tin, pewter, and lead, (or theplumber’s folder) is of two kinds: the leaftfuflble is compofed of equal parts of tin andlead; the more fuflble contains befides, bifmuthin various proportions. A very good foft folderis prepared by melting together 16 parts of tin,8 of lead, and 4 of bifmuth.

For delicate works in cut fteel the bed f®lderis gold with a high alloy of copper. For largerworks in iron and fteel copper is made ui' of,or an alloy compoled of equal parts of tin andiron.

SOLUBLE TARTAR, or Tartrhe of Pot -njh. See Tartareous Acid.