186 



THE INDIA RUBBER WORLD 



[January 1, 1913. 



tion, has greater elasticity and tensile strength, enabling the 

 manufacturer to obtain tlie greatest yield when being made into 

 the final product. 



As different grades oi rubber must be subjected to varying 

 temperatures, the temperature of the heating medium is easily 

 regulated without overheating or materially affecting the time of 

 drj'ing, so that the vacuum process offers many advantages over 

 the old method of drying rubber, whether it be line Para or 

 Pontianak. 



Owing to the drying period only taking a few hours, varying 

 according to grade of rubber, the crude rubber can be washed, 

 dried and pressed in a fraction of a day. Consequently, there is 

 no deterioration between drying and using. 

 ' With an average establishment of today, with a consumption of 

 two tons, if the old hot air method is used and six weeks con- 

 sumed in drying the washed and sheeted rubber, there would be 

 72 tons of rubber banging in the drying lofts, representing an idle 

 investment of $144,000 on raw material, besides insurance, fac- 

 tory space, etc. The same tjuantity of rubber could be more 

 thoroughly and permanently dried by one or two vacuum cham- 

 bers in a day of ten hours, thus working up the requirements of 

 each day's output, with an initial cost of installationn less than 

 that of the old-fashioned drying rooms for the same quantity. 

 Besides paying for itself the vacuum chamber gives an otherwise 

 unattainable flexibility to the factory for its daily production. A 

 vacuum drying chamber having a capacity of two tons of dry 

 sheeted rubber every ten hours, occupies a space S'^ ft. high, 

 15 ft. wide X 9 ft. long, its auxiliaries, the condenser and pump, 

 being conveniently located in any place in the factory near the 

 dryer. 



While not more than one-third of the heat units are utilized by 

 any hot air system — by the vacuum process practically every heat 

 unit is transmitted to and comes in direct contact with the mate- 

 rial being dried. The apparatus itself is practically indestructi- 

 ble and only requires one operator. There is a considerable 

 saving of fuel and the time of drying is shortened from 

 weeks to hours, combined with higher efficiency. The condenser 

 connected with the vacuum chamber (as well as the vacuum 

 pump) should be of the proper capacity for condensing the 

 vapors given out during drying; while the necessary heating sur- 

 face must be balanced in order to transmit a certain temperature, 

 and if the condenser is burdened with a much larger quantity of 

 vapor than it is calculated to cool, the result is detrimental, both 

 to the product and the working of the pump. 



Basing his view on the foregoing and other facts quoted, the 

 author submits the opinion that it is w-rong to subject apparatus 

 to work for which it is not intended, and attribute the unsatis- 

 factory results to the principles of drying under vacuum, viz. : 

 rapidly and thoroughly at a low temperature. 



While the use of the vacuum drying process was first adopted 

 by manufacturers to dry washed rubber, much thought has of 

 recent years been given to the preparation of crude rubber on 

 the plantation. This fact is especially noticeable in the quality of 

 the rubber reaching the market from the Malaysian, Straits Settle- 

 ments and Congo Plantations, where this process has been in- 

 stalled and found of great value. This is somewhat reflected in 

 the moisture content of plantation rubber, which reaches the 

 market with a low percentage of moisture, as compared with 15 

 per cent, or more in Upriver Para. Planters will understand in 

 the future that the price is based on actual rubber, and tliat they 

 will serve their purpose by adopting the very latest metliod for 

 the treatment of the raw material, so as to free it from inpurities 

 and let it contain a minimum percentage of moisture. 



This improvement in quality of the raw material will not cause 

 the discontinuance of the process of drying at the factory, but will 

 restrict its use to the removal of the final percentage of moisture 

 only, thus simplifying factory operation. 



The results of scientific and research work in the laboratory 

 have materially contrilmted to the advancement of the industry. 



and its further progress can and will be accomplished by a closer 

 and more intimate relationship between the manufacturer or pro- 

 ducer and the appliance manufacturer. The author asks in con- 

 clusion why users and makers of machinery should not recognize 

 their mutual obligations to co-operate, so that a maximum pro- 

 ductiveness by newer and better methods may be secured. 



LITHOPONE AND OXIDE OF ZINC IN THE RUB- 

 BER INDUSTRY. (Abslract.) 

 By G. C. Sloiie and Gilbert Rigg. 



■ I 'HE zinc oxide of commerce is a white amorphous pow- 

 ■*• der, the purity of which depends on the character of 

 the ore from which it is produced. With the exception of 

 those from Franklin Furnace, New Jersey, zinc ores contain 

 considerable lead and usually cadmium. Their presence, 

 when the object is to make a white product, is inadmissible, 

 while their absence insures regularity in the composition of 

 oxide of good color. For example, the oxide made by the 

 New Jersey Zinc Co. contains upwards of 99 per cent, zinc 

 oxide. 



Zinc oxide is made by two processes, the direct or Amer- 

 ican, and the indirect or French. The first drives off the 

 zinc from the ore by the action of carbon at a high temper- 

 ature, the zinc vapor being burned direct to oxide. In the 

 second, metallic zinc or spelter is first produced by smelt- 

 ing, tliis metal being then burned to oxide. The latter is the 

 more costly and the products of the two differ in certain 

 material points. 



Purity is the first essential of a zinc oxide for rubber pur- 

 poses, wliile imiformity of composition is likewise very de- 

 sirable for arriving at a good result. The authors believe 

 that users of oxide should confine their analytical work to 

 testing for adulteration and suitability for a particular pur- 

 pose by a practical laboratory compounding test, rather than 

 spend much time and effort in attempting to determine the 

 zinc contents of the oxide. 



Commercial zinc oxide consists of extremely minute parti- 

 cles, forming more or less coherent aggregates resembling a 

 slightly elastic sponge entangling considerable air. 



It is necessary to distinguish clearly between the coherence 

 of an oxide and the true specific gravity, these two prop- 

 erties being sometimes confounded under the term "density." 

 The determination of the actual specific gravity requires con- 

 siderable care, as the o.xide tends to retain its entangled air, 

 a good vacuum pump being used to insure that the air has 

 been completely expelled. 



While screening is often useful for breaking up aggregates, 

 this method is, according to the view of the authors, useless 

 for sizing oxide of zinc, owing to its extreme fineness. This 

 can best be done in a bolting machine. Revolving screens 

 without heaters tend to form balls, while shaking screens 

 have a like tendency. 



Oxide of zinc, the use of whicli is rapidly increasing, is 

 one of the most important ingredients of manufactured rub- 

 ber. It is remarkably constant in chemical composition and 

 physical properties, and is also rarely adulterated. 



LITHOPONE. 



Lithopone is an amorphous white pigment obtained by 

 mixing solutions of barium sulphide and zinc sulphate, which 

 causes a transfer of the acids and produces an intimate mix- 

 ture of zinc sulphide and barium sulphate. In properly made 

 lithopone every particle of the barium sulphate appears coated 

 with zinc sulphide; the opacity being much higher than that 

 of a mixture of the dry salts in the same proportion. It is 

 largely used in the manufacture of rubber goods, but in the 

 opinion of the authors, oxide of zinc is preferable for giving 

 strength and resilience in the product. 



