210 



THE INDIA RUBBER WORLD 



[January 1, 1920. 



a "volume i)f pigment" base lor constant elongations of 50 per 

 cent and 100 per cent. These curves arc really a more distinct 

 representation of the growth of agglomerated masses of pigment 

 as the volimie of pigment is increased. It will be noticed that at 

 100 per cent strength the whiting and zinc 

 oxide curves tend to approach the barytes 

 curve, due to the more rapid formation of 

 agglomerated masses of these pigments 

 than that of the barytes. Since the aver- 

 age particle of whiting has only one-eighth 

 the volume of the average particle of 

 barj'tes, it would require an agglomera- 

 tion of the whole body of whiling into 

 average groups of eight particles each to 

 cause the whiting curve • to meet the 

 barytes curve, or multiples of eight, if "' 



there already existed an agglomeration ^ 



of the barytes particles. This agglomeration of the pigment 

 particles and the phenomena connected with it are of vital 

 importance, since the sudden growth of agglomerated par- 

 ticles at certain volumes may be coincident with a rapid increase 

 of hysteresis, due to the friction when the rubber body is dis- 

 torted, amongst those particles which are in dry contact with 

 each other. Conversely, any means of reducing the agglomera- 

 tion of pigment 

 should also be the 

 means of reduc- 

 ing the hystere- 



shown for the three pigments barytes, whiting, and zinc oxide, lie 

 approximately on a circle having the origin as center. The lamp- 

 black curve cannot be extended sufficiently far to reach the maxi- 

 mum volume increase due to the inability of the rubber to ab- 

 sorb large quantities of lampblack. The 

 curves for china clay, red oxide, and 

 carbon black are not shown, but as far 

 as they have obtained, the fall between 

 whiting and zinc oxide, the china clay 

 lying highest and the carbon black lowest 

 of the three. 



Fig. 11 undoubtedly shows the real ex- 

 planation of the variability of the pig- 

 ments from the volume increase stand- 

 point. They show that, with the excep- 

 '"""*'""' tion of zinc oxide, the greater the mean 



• • diameter of the pigment' particles, the 



greater is the volume increase under strain. A confirmation of 

 this statement was the result of a test on four samples of barytes 

 compounds, containing equal volumes of barytes of diflferent 

 degrees of fineness. The different grades were prepared by 

 allutriation in water. The compound containing the finest grade 

 of barytes showed the least volume increase under strain. This 

 was a critical test which eliminated every other variable but the 

 size of the pigment. 



A NEW FIELX) FOR RUBBER CULTURE. 



Papua or British New Guinea is entering the plantation rub- 

 ber field in earnest. One company has 

 nearly 2000 acres with 152,000 trees, over 



Fig. 9. Fig. 



sis. such as the method of milling, and the use of solvents to re- 

 duce the viscosity of the rubber while mixing in the pigment. 



Fig. 10 shows the percentage volume increase at failure on a 

 base of percentage pigment, plotted up to the point of maximum 

 volume increase, which takes place, as mentioned before, when 

 local contraction of area occurs. These maximum points, as 



10. Fig. 11. 



50,000 of which are tappable ; it produced 89,938 pounds of rub- 

 ber in 1918 as compared with 54,303 pounds in 1917. Another 

 company has 920 acres planted with Hcvca. With the rise in 

 the price of rubber, or if Australia will establish preferential 

 trade conditions, the Papuan rubber may compete in Australia 

 with that from Singapore. 



NEW ZEALAND TIRE IMPORTS. 



The value of New Zealand's tire imports for 1916 was £639,719, 

 for 191 7 £453,893, for 1918 £702,026, and for the first four months 

 of 1919 £334,472. 



United Kin^flom 

 United Kinydoni 



Canada, via wfs't 

 Canada via Wtst 



Austral 1 1 

 Austral 1 i 



The following tabulation shows the total value of 

 tires imported at each port in New Zealand and the 

 shipments and origin during the month of May, 1919: 



motor car 

 :ountry of 



13,959 



322 410 19,061 



193 20,845 



£1,947 £3, ICO £117,656 



