Vol.. XIV. No. 348. 



THE AGRICULTURAL NEWS. 





VULCANIZATION EXPERIMENTS ON 



PARA RUBBER. 



The cause of variabilit} in I'ara rubber has for 

 man} years been the subject ol much discussion and 

 investigation. In the Fi It-rated Malaj States, 

 during rei i nt yi ars, the work don has been consider- 

 able, bul it seems that il is onl} now thai real light is 

 being thrown upon the subject The following is 

 a sum mar} ol recent results obtained bj Eaton and 

 ( irantham: — 



(I i Considerable variati 'curs in plantation Para 



rubbei case ot 'first latex' rubbers, both From 



rubbers from the same i tndfrom different estates. 



(•_') This variation is connected principally with the 



behaviour of the rubber on vulcanizati i.e. its rate of cure, 



.•Hid not in respect to its strength, elasticity and general 

 properties,- especial!} in the case ol properly prepared 'first 

 latex samples. 



(3) [f the rate of cure- be known or ascertained under 

 specific conditions, vulcanized rubber having similar mechani 

 ca] pro] cai m ide from all good s imples ol 'first 



1 i 



ili A difference in mechanical properties does exist, 



even among led first quality rubbers, but these 



differences an greater between high and low grade plantation 



rubbers; some rubbers never attain the maximum mechanical 



properties reached by others, whatever period of cure is 



adopted. These < ! es in the case of 'first latex' rubbers 



ire not so important to the -manufacturer as the 



difl rences in the rate ol cure, and are not of the same order. 



The rate ol cure is due to the presence of some 



chom u in the latex, possibly the proteins 



,,]■ some other constil cu nt. or to soi di t adation produi I 



,1 ,1, d from thesi substances whicl icts as a catalyst and 



i the rate ol cure. 



(6) lin substanci ma} be already- present in the latex, 

 ind its amount in the raw rubber determined by the mode of 



ration and coagulation, or it may be subsequently 

 formed in the latex b} decomposition, and taken'up by the 

 i, ,n iable quautit g to mode of preparation, 



or alternatively it may be formed in the coagulum in van ible 

 iding on the amount of serum (or moisture) 

 left in the coagulum or the presence of preservatives which 

 hinder or prevent its formation. The alternative theories 

 await investigation. 



(7) Smoking, removal of excess of 'serum (or moistui 

 in the washing and machining processes and preservative are 

 imong the artificial factors which either hinder the forn 



substance or, il it already exists in the pn pared rubber, 

 > it. The natural differences in latex due to 

 i .1 causes maj also have a simil n effect. 



(8) Tin catalytic substance is probably not affected 

 greatly bj heat, since in the process of mixing and vulcani 



the rubber i- subjected to considerable temperatures, 

 although heal ma} prevent its formationjn the latex or freshly 

 i o igulated rubber. 



Th rate ol cure of a rujbber in der spi cified 

 conditions, is not indicated in an} way 1 > \ the apparent 

 mechanical or any other apparent properties ol the raw 

 material, hence the absurdity ol the present 'methods' of 

 valuation ol rubber. 



(10) Oneleris pantos, a manufacturer probably prefers 

 a rapidly curing rubber, as it i its economy in heat, 



labour and time costs, and dly, a rubber which cures 



rapidly is said to hai ei keeping qualities after vulcani 



zation Rapidly curing amples should therefore obtain 

 a premium in the market and probably would do so, it valuation 

 n ' irried out on a :ii ntifii basis, provided uniformity in 

 rate of cure is maintained at the same time. 



(Ili I nifoi mil j I ween r fii 3l latex rubbers from 

 different estates will proljaWy be very difficult of attainment 

 with present methods, owing to the number ol I 

 involved, but should not be difficult of solutii n among such 

 rubbers from the same est ti 



(12) Two alternatives are suggested: (1) the issue of 

 certificates giving correct rate of cure and mecha 

 properties at this cure (2) the attainment oi more 

 uniformity by the method suggested in this paper and 

 elsewhere, in which rubber from late: collected during 

 a scries of days forms part of one ball or block, whii b m 

 described as the method of averages. 



THE INHERITANCE OF SIZE IN 



TOMATOES. 



The Ohio Naturalist for April L915 contains an 

 interesting paper on the above subject, a summary of 

 which is reproduced below. Although the paper i 

 only with the currant pear tomato cross the results 

 ma) have a much wider application. 



A more accurate representation ol the size of tomato 

 fruits can be obtained from their weights than from their 

 linear dimensions. 



The size of fruit of the F I generation of the currant- 

 I" H cross is the geometrical mean between the parental sizes. 



From an examination of all available data upon the 

 inheritance of fruit size in the F 1 generation, it appears 

 that, when two varieties are crossed which differ widely in 

 fruit size (the size of fruit of one parent being probably 

 about two, three or more times the size of the fruit of the 

 other parent), the V 1 fruit size will be nearer to the geomet- 

 rical than the arithmetical mean; but when two parents 

 similar in fruit size are crossed, the size of fruits of the 

 offspring will approach more nearly to the arithmetical than 

 to the geometrical mean. 



The average fruit size of the F '_' generation .Iocs not 

 exceed and is even slightly less than the average fruit-size 

 of the F 1 generation. The segregation of size factors and 

 the incomplete dominance of the small size (actors of the 

 red currant parent may be explained by the assumption of at 

 least four size factors. It no parental sizes can be ever 

 obtained, there may be more than multiple factors involved. 



The fruits of the F 2 and F 3 generations agree fairly 

 well with respect to variability and average generation size. 

 The F I fruits- show diminished variability and size. 



In connexion with the prevention of cotton reaching 

 any of the enemy countries Professor Dunstan, Dii 'Cto I 

 the Imperial Institute, writes to J% Times to the effe 

 should any stringent measures such as the declaration of 



., as contraband betaken, due consideration should be 

 given to the interests ol cotton growers within the British 

 Empire. The principal point raised however is in connexion 

 with the idea that the whole of next year's siipplx si Id be 



bought Tom America in advance. This would obviously 

 affect adversely the British cotton-growing industries in 

 Egypt and Ah e a 



