COMPOUNDING. 155 



every other substance. It may be mixed with other gums, oils, 

 coal-tar carbon, and with the earths and oxides, or pulverized 

 metals and ores ; and it can be combined with all fibrous sub- 

 stances, although it is not made like some of the gums, to ad- 

 here firmly to any smooth surface of metal or wood, or even of 

 cloth. It is compounded in the manufacture with many of the 

 above substances, for the purpose of obtaining particular advan- 

 tages for special uses. Lampblack is often used to cause the 

 gum to endure the effects of the sun and weather. Ground cork 

 and other light substances are sometimes combined with the 

 gum, to increase the bulk and make the articles light. 



Earths are used as color, for cheapness, and to increase the 

 weight of the fabric, as in the case of carpeting. Bitumen and 

 resin are sometimes used to give the articles a finish or high 

 lustre. Oxides of some of the metals are used in the manufac- 

 ture ; among these, white lead and litharge are commonly 

 preferred. From two to four ounces of either of these metals 

 to the pound of gum, cause the articles, and particularly those 

 that are thick or massive, to be more readily changed, or vul- 

 canized, and more completely, or with greater uniformity. 



In the process of vulcanizing, the sulphur is applied through 

 the medium of heat, in different ways, for the manufacture of 

 different articles or fabrics for different uses. It is sometimes 

 mixed with the gum in the process of crushing or grinding the 

 gum, in the proportion of half an ounce of sulphur to the pound 

 of gum ; at other times it is dusted upon the goods in the form 

 of flour of sulphur, before the goods are placed in the heater, or 

 oven ; this is commonly done when the mixture contains white 

 lead, or when the coat of gum is thin and the goods light, in 

 which cases the gum is more easily penetrated or impregnated 

 with the sulphur, without its being mixed with the gum. 



Another mode of applying the sulphur, or impregnating the 

 gum with it, is that of generating the sulphurous gas in the oven 

 or heater which contains the goods, or of introducing it into 

 the oven after it is generated. 



