PAINTS, DYES, AND VARNISHES 



industry in itself, and even varnish of very high quality 

 is made in large quantities in such factories. The 

 apparatus for manufacturing is very simple, consisting 

 essentially of a large copper kettle mounted on wheels 

 for convenience in handling, and a chimney with a kind 

 of hooded fireplace at its base. The fireplace serves for 

 heating the contents of the kettle, while the chimney 

 carries off the dangerous fumes and smoke. The copper 

 kettle has a closely fitting cover, with an opening through 

 which a stirring-rod may be inserted an arrangement 

 that has been in vogue for at least a thousand years. 



The first step in the manufacture of varnish is the 

 melting of the resin. Lumps of this substance are placed 

 in the copper kettle and run under the hood over 

 the fire. As the resin melts it gives off a pungent and 

 highly inflammable vapor, which is conducted off 

 through the chimney by means of the opening in the 

 cover of the kettle to which a pipe is attached. As the 

 heat in the kettle increases and the lumps disappear, the 

 liquid resin tends to foam, this tendency being controlled 

 ordinarily by vigorous use of the stirring-rod. If the 

 heat is so intense, however, that boiling-over is immi- 

 nent, the kettle is pulled quickly out of the fireplace and 

 allowed to cool a little. It is to meet such an emergency 

 that the varnish kettles are mounted on wheels. 



During the melting-process from ten to twenty-five 

 per cent., by weight, of the resin is driven off in the 

 form of vapor. The temperature of the liquid resin 

 rises to at least 650 F. by the time the mass is com- 

 pletely melted. But both these things vary greatly in 

 different resins. And it is not a common practice among 



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