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as to make the colour of the folder correfpond, as nearly as 

 may be, to that of the piece. A mixture of gold and cop- 

 per is alfo a folder for fine copper as well as for fine gold. 



Gold being particularly difpofed to unite with iron, this 

 metal, with a high alloy of copper, proves an excellent fol- 

 der for the finer itinds of fteel inftruments. 



For larger works in iron and fteel, copper, or an alloy 

 compofed of equal parts of tin and iron, is employed. 



The folder ufed by plumbers ia made of two pounds of 

 le»d to one of block-tin. Its goodnefs is tried by melting 

 it, and pouring the bignefs of a crown-piece on a table ; 

 for, if good, there will arife little, bright, (hining ftars 

 in it. 



For filver, two kinds of folder, viz. the hard and foft, are 

 ufed and applied like the gold folder. The hard folder is 

 compofed of equal parts of filver and fine braf'i, and the 

 foft is prepared by fufing the hard folder with -r^th its 

 weight of pure zinc. Another folder for filver may be 

 formed of two parts of fine filver and one part of brafs, 

 taking care that thefe are not long kept in fufion, leil the 

 brafs fly ofi" in fumes. For coarfer filver, a folder is pre- 

 pared by melting four parts of fine filver and three of brafs, 

 throwing in a little borax, and pouring it out as foon as it is 

 melted. 



The folder for copper is made like that of the plumbers ; 

 only with copper and tin ; and for very nice works, inftead 

 of tin, they fometimes ufe a quantity of filver. 



For copper, brafs, and the hard alloys of copper, the 

 beft hard folder, fays Aikin (Dift.), is compofed of brafs 

 and zinc, in the proportion of from eight to fixteen of the 

 former to one of the latter, accordingto the required hardnefs. 

 The foft folder is compofed of three parts of zinc and one 

 of lead, and is applied by means of a common foldering 

 iron, made red-hot. 



Solder for tin is made of two-thirds of tin and one of 

 lead, or of equal parts of each ; but where the work is any 

 thing delicate, as in organ-pipes, where the junfture is 

 fcarcely difcernible, it is made of one part of bifmuth, and 

 three parts of pewter. 



The pewterers ufe a kind of folder made with two parts 

 of tin and one of bifmuth : this compofition melts with the 

 leaft: heat of any of the folders. 



The folder for tin, pewter, and lead (or the plumber's fol- 

 der), fays Aikin (ubi fupra), is of two kinds : the leaft 

 fufible is compofed of equal parts of tin and lead ; the more 

 fufible contains, befides, bifmuth in various proportions. A 

 very good foft folder is prepared by melting together fixteen 

 parts of tin, eight of lead, and four of bifmuth. 



Spelter folder is made of one part of brafs and two of 

 fpelter, and is ufed by the braziers and copper-fmiths for 

 foldering brafs, copper, andiron. This folder is improved 

 by adding to each ounce of it one pennyweight of filver. 

 But as this folder does not melt without a confiderable de- 

 gree of heat, it cannot be ufed when it is inconvenient to 

 heat the work red-hot ; and therefore, in this cafe, copper 

 and brafs are foldered with filver. 



Though fpelter folder be much cheaper than filver folder, 

 yet workmen in many cafes prefer the latter. And Mr. 

 Boyle informs us, that he has found it run with fo moderate 

 a heat, as not much to endanger the melting of the dehcate 

 parts of the work to be foldered ; and if well made, this 

 filver folder will lie even upon the ordinary kind itfelf ; and 

 fo fill up thofe little cavities that may chance to be left in 

 the firft operation, which is not eafily done without a folder 

 more eafily fufible than the firft made ufe of. Works 

 Abridged, vol. i. p. ijj. 



As to iron, it is fufficient that it be heated red-hot, and 



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the two extremities, in this ftate, be hammered together. 

 By this means they become incorporated one with the other : 

 when it is foldered it is ufually done with brafs ; good 

 tough brafs, with borax applied, mixed with water to the 

 confiftence of parte. 



The duke of Florence's nail, anciently fo much admired, 

 as being half iron and half gold, whereas thofe two metals 

 were deemed irreconcileable, wasjoined by a kind of folder 

 made by Turneifler, an ingenious chemift of Venice ; the 

 fecret of which was never difcovered till publilhed by Tache- 

 nius. This folder is nothing but a little copper, or cypru» 

 vitriol, put between the gold and the iron. For, naturally, 

 the great acidity of the gold reduces the iron into a fcoria or 

 ruft, when the two are applied over one another ; but this 

 inconvenience is removed, by the interpofition of a little 

 copper, be it in the fmalleft quantity imaginable. See the 

 next article. 



SOLDERING, orSoDOERlNO, among Mechanics, the 

 joining and faftening together of two pieces of the fame 

 metal, or of two different metals, by the fufion and appli- 

 cation of fome metallic compofition on the extremities of 

 the metals to be joined. 



In foldering, fome artifice is necelTary to make the folder 

 and metals adhere. All the metals, except filver and gold, 

 upon melting, or before, are covered with drofs : and all the 

 folders have fome of thefe metals in them : this drofs hinder* 

 the folder and metal from uniting, and it is neceflary to re- 

 move it. This is not performed in every kind of foldering 

 by the fame materials. The plumbers effeft this by greafing 

 the lead, laying on the folder, and melting it with a hot 

 iron, and thus the drofs, generated in fufion, unites with 

 the greafe, and flows away from the melted metal. The 

 glaziers and tin-men ufe rofin in powder for the fame pur- 

 poie ; for all inflammable fiibftances that will melt are 

 equally conducive to this ufe. When copper and brafs are 

 foldered with pewter, the work is firrt waftied with a folu- 

 tion of fal ammoniac in water," then heated jull hot enough 

 to melt the pewter, and the pewter applied to the joint to 

 be foldered. In foldering that requires a greater heat, 

 borax is ufed. 



Thus, in foldering gold, and alfo filver, take a piece of 

 folder of the proper fize and fiiape, and lay it on the part 

 to be cemented, and fprinkle it over with pulverized borax ; 

 then apply the flame of a blow-pipe, which will caufe both 

 the borax and folder to fufe, the latter incorporating with, 

 and adhering firmly to, the gold. When the juncture is 

 complete, the piece is left to cool, and the borax is removed 

 by boiling water, or, what is ftill better, a little dilute ful- 

 phuric or muriatic acid. It is obferved, that the folder 

 will, in this cafe, appear confiderably paler than the other 

 part, both on account of the filver with which it is alloyed, 

 and of the borax, which always lowers the colour of the 

 gold. This defeft, however, may be remedied by melting 

 on the furface of the folder a mixture of two parts of nitre 

 and one of burnt alum, and afterwards wafliing it off" with a 

 foft brufh and hot water ; by which the natural colour of 

 the gold will be reltored, and even heightened. Other* 

 direft this operation to be performed by joining together 

 the pieces propofed to be united with fine foft iron wire, 

 and touching the joint to be foldered with a camel's hair 

 pencil, dipped in borax finely powdered, and well moiftened 

 with water ; and then placing a little folder upon the joint, 

 and applying upon it a large piece of charcoal, and, with a 

 blow-pipe and lamp, blowin'.r upon it through the flame, 

 until it melts the folder ; and thus the work is finiftied. In 

 order to cleanfe filver or gold, after it is foldered, make it 

 juft red-hot, an4 let it cool; then boil it in alum-water, in 



an 



