January 1, 1921 



THE INDIA RUBBER WORLD 



253 



worthy that the inflexion in the extensibility curve occurs at a 

 vulcanization coefficient of 4 to 5, indicating that the first peak 

 in the tensile strength curve represents the ordinary "optimum 

 cure," and that the subsequent peak is the abnormal one. It may 

 also be observed that the maximum extensibility attained just 

 after the inflexion of the curve, has approximately the value of 

 650 commonly observed at the tensile optimum of a rubber- 

 sulphur mixing vulcanized under ordinary conditions. The ex- 

 planation of tliis unexpected irregularity in the alteration in the 

 physical characteristics of the rubber is not at all obvious. It 

 appears probable that the two sections of the extensibility curve 

 indicate two distinct processes causing alteration in the physical 

 characteristics of the rubber, the point of inflexion representing 

 the stage at which the one preponderating earlier is overtaken by 

 the other, which then becomes predominant. 



From the curve in Fig. 7 it will be seen that for one mixing 

 it may be possible within a small range of cure to apply three 

 distinct periods of vulcanization and yet to obtain identical ex- 

 tensibility in the resulting rubber in spite of the three different 

 vulcanization coefficients. Such a result, which is independent of 

 the further complications introduced into the relation between 

 the physical properties and the vulcanization coefficient bv sub- 

 sequent aging,' serves to emphasize more strongly than ever the 

 lack of simplicity in the relationship between the physical altera- 

 tion effected in rubber during vulcanization and the chemical 

 change by which this alteration is induced. 



LlTHOPONEi 



-Anhydrous zinc sulphide is prepared from hydrated sulphide 

 by treating zinc hydroxide, heated to 90 to 100 degrees C. by 

 means of steam, with suflicient sodium sulphite. The resulting 

 caustic soda is decanted ofT and is used to prepare a fresh amount 

 of zinc hydroxide from zinc sulphate. Periodically it is necessary 

 to purify the caustic soda by crystallization and to reject the 

 mother liquor which becomes charged with impurities. 



The precipitation of the zinc hydroxide is performed hot to 

 avoid the formation of a gelatinous product of low density, and 

 the sodium sulphate simultaneously produced is used to prepare 

 barium sulphate and sodium sulphide from barium sulphide. The 

 latter is obtained by the reduction of barium sulphate by means 

 of carbon, thus completing the cycle in which zinc sulphide and 

 precipitated barium sulphate are obtained from zinc sulphate, 

 barium sulphate and carbon. The hydrated zinc sulphide after 

 being washed free from alkali is filtered and dried at 100 degrees 

 C. or in a vacuum. It is then mixed with sulphur and heated 

 to 450 to 500 degrees C. in a muffle furnace, thereby volatilizing 

 any cadmium sulphide, and allowed to cool with exclusion of air. 



To prepare lithopone, the precipitated barium sulphate, after 

 washing and drying, is mixed with the desired proportion of zinc 

 sulphide in a revolving horizontal iron cylinder and finally passed 

 through a sieve. 



VULCAZOL 



The following is quoted from Andre Dubosc in Lc Caoutchouc 

 et la Guila-Percha, September IS, 1920: 



"Theoretically," says Spence, "the number of accelerators is in- 

 finite and probably the best have not yet been found." 



I will not say that Vulcazol, the latest of catalyzers of vulcan- 

 ization, the remarkable properties of which I have investigated, 

 may not be the ideal body to which Spence referred, but certainly 

 it is one of the most active and interesting among the accelerators 

 actually tested. This singular aldehyde is furfurol derived by 

 condensation with ammonia, and belongs to the group of hy- 

 dramides. These are neutral nitrogenous bodies formed by the 

 ■action of aromatic aldehydes and of furfurol on ammonia. 



Three molecules condense with two molecules of alkali, eliminat- 

 ing two molecules of water, and the action is reversible according 

 to the equation : 



3(C,H,0) -1-2NH,= (C,H,)3N,-|-2H,0 

 They are solid, crystalline, slightly soluble in water, soluble in 

 alcohol and ether and decompose by volatilization. 



By boiling with water or by the action of dilute acids many 

 of them decompose into aldehyde and ammonia, such as hydro- 

 benzamide, hydrosalicylamide and furfuramide. If held for some 

 time at a temperature higher than their melting point, or treated 

 with boiling potash, they are changed into basic isomers which act 

 as true alkaloids. 



Hydrobenzamide furnishes also amarine, anishydramide, ani- 

 sine, furfuramide and furfurine. Five hydromides are known, 

 namely: hydrobenzamide, cumiidiydramide, anishydramide, hydro- 

 salicylhydramide, and furfuramide or furfurol. * 



METHODS OF ANALYSIS 



COLORIMETRIC DETERMINATION OF LEAD DIOXIDE 

 IN LITHARGE 



THE following method, devised by W. V. Morgan, is taken 

 from the Journal of Industrial and Engineering Chemistry, 

 November, 1919. It is intended for the determination, in a semi- 

 quantitative way, of lead dioxide in the presence of litharge, and 

 has been used to advantage in connection with rubber work where 

 it is important to know the amount of oxidizing agent present. 

 The method with slight alterations is applicable to the determina- 

 tion of oxidizing agents in general where they occur as an im- 

 purity with non-oxidizing agents. 



METHOD 



.\ definite amount of litharge, for example, five grams, is 

 boiled for a minute with a solution containing two grams of 

 aniline hydrochloride dissolved in 10 cc. of water and five cc. 

 (if concentrated hydrochloric acid. The solution is then cooled 

 to separate any lead chloride which has formed, then filtered to 

 remove the lead chloride and any litharge which has not been 

 dissolved. It is not necessary to convert all or part of the litharge 

 into lead chloride as the action depends upon the oxidizing power 

 of the dioxide only. The filtrate is compared with standards 

 made by adding definite amounts of lead dioxide to the above- 

 mentioned solution. A colorimeter may be employed to estimate 

 the amount of aniline purple formed, or the solutions may be 

 compared in suitable receptacles. 



The lead dio.xide oxidizes the aniline to aniline purple. The 

 intensity of the color is pgoportional to the lead dioxide content. 



' British Patent No. 147,658. 



"Reports of the Progress of .Applied Chemistry, 1919, 4, 338. 



CHEMICAL PATENTS 



THE UNITEID STATES 



RUBBER Substitute and Proce.ss for Producing It, consisting 

 of treating by heat a mixture of fixed oils and sulphur 

 substantially free from air and moisture under pressure until the 

 period of the elements reacting has ceased. — Harry II. Haseltine 

 and Morton Gregory, Tacoma, Washington, assignors to Western 

 Rubber Co., Tacoma, Washington. United States Patent No. 

 1,360,744. 



the united kingdom 



Utilizing Waste Rubber. The separation and recovery for 

 re-manufacture of textile materials and rubber from such articles 

 as automobile or bicycle tires is effected by treating the coarsely 

 ground fragments with a solvent under heat in a closed drum. 

 The mass is worked mechanically until all the rubber is dissolved, 

 when the solution is run off and distilled to obtain the rubber. 

 The extracted textile material is adapted to paper making. — F. 

 Waitz, 78 Obernstrasse, Bremen, Germanv. British patent No. 

 19.585. 



