60 Laboratory Arts 



heat. Small jobs, however (keys, etc.), may be easily brazed 

 on a charcoal hearth, with a No. 5 Fletcher blower and 

 laboratory blowpipe. For this purpose make a sheet iron 

 trough, as shown in Fig. 56, by bending up a piece of ordinary 

 sheet iron, and fill it with pieces of compressed charcoal such 

 as are used for blowpipe analysis, or coarsely powdered hard 

 gas coke, of about J-" cube. Rest this on an asbestos mill- 

 board, and heat up. 



Place the job on the hearth in position and rake the 

 charcoal well round it. Smear the proposed joint with a paste 

 of powdered borax glass 1 and water, and heat up to red 

 heat, keeping the charcoal well heaped round the work. By 

 means of an iron wire flattened at the end, Fig. 57, sprinkle 



FIG. 56. Iron plate brazing FIG. 57. Spoon for adding flux 



hearth for small jobs. during brazing. 



a little white brass filings ("Spelter") on the joint, and con- 

 tinue heating until it " runs." More borax may be necessary ; 

 if so, it should be added dry, and more spelter then thrown 

 on the work. When the correct temperature has been reached, 

 and the brass has "run," the hearth may be cooled down, 

 and the job withdrawn. The work will usually require to 

 be filed up, and when first withdrawn will not have a very 

 attractive appearance. 



Copper may be brazed to copper, copper to iron, iron to 

 iron, but brass cannot usually be brazed, the job melting at 

 the same temperature as that required to melt the spelter. 



Spelter is made from soft brass; fine brass wire cut or 

 filed up makes good spelter, indeed brass wire may be used by 



1 Crystallized borax, which has been heated until all the water of 

 crystallization is driven off. 



