426 



THE INDIA RUBBER WORLD 



[April 1, 



Lithopone is used considerably in rubber, but its use is not as 

 great as zinc oxide. Many chemists do not recommend its use 

 at all, while others do. It is composed of about 29J/2 per cent 

 zinc sulphide and 69J4 per cent barium sulphate. This is the 

 reason it is generally sold as 30 per cent. There is a vast dif- 

 ference in the physical properties of this pigment. It possesses 

 very great covering power, and has a beautiful white color. It 

 also has a peculiar tendency to darken in the light, but will, how- 

 ever, regain its original color. There has been no one who 

 could satisfactorily understand this phenomena, although many 

 have tried and as many different theories have resulted. At any 

 rate, no one can control this change in lithopone or remedy it. 



Whiting or calcium carbonate is quite an important white 

 filler. It is inert and unaffected by vulcanization. Several grades 

 are employed, both imported and domestic. The imported is the 

 cliffstone or English chalk whiting, which is produced from the 

 great chalk cliffs of England. The domestic products are of 

 various qualities, and different colors, ranging from a brownish 

 or yellow gray to a beautiful white. 



Barium sulphate or barytes is generally of a white water-floated 

 grade, although large amounts of off color barytes are con- 

 sumed. The artificial barium sulphate or blanc fixe is not used 

 in any appreciable quantities. 



Soapstone and talc are used in certain compounds and in 

 dusting tubes, tires and rubber goods generally. It is essential 

 to get a product that is not gritty. Color does not make much 

 difference. 



It is extremely necessary that the quality of many of the pig- 

 ments and colors that are put into compounds of rubber should 

 be of a standard or recognized merit. Some sad experiences 

 have taught many rubber mills this lesson, and it is becoming 

 more apparent than ever, especially in view of the fact that so 

 many new rubber manufacturers are starting up in all parts of 

 the country. It is not always convenient or practical for rubber 

 firms to test out every ingredient that they employ, and for that 

 reason it is a good policy to direct their purchases in a direction 

 where their needs are understood, and where the possibility 

 of error is minimized. 



A NEW RAPID METHOD FOR THE DETERMINA- 

 TION OF SULPHUR IN RUBBER COMPOUNDS. 



By A. M. Munro M.A., A.I.C., F.C.S. 



THE ANALYTICAL METHODS for determining sulphur in manu- 

 factured rubber, in use at the present time, fall under two 

 heads: (1) those in which the finely divided sample is fused 

 with a suitable nitrate fusion mixture or with caustic potash and 

 sodium peroxide; (2) those where the rubber is decomposed with 

 fuming nitric acid and the sulphur completely oxidized by final 

 treatment either by a fusion process or by partial evaporation of 

 the residue with potassium chlorate and hydrochloric acid. In 

 both these cases the sulphur is finally determined by precipitation 

 with barium chloride. 



In this laboratory it has been customary to determine sulphur 

 by boiling the sample of rubber, cut into small pieces, with 

 fuming nitric acid, evaporating nearly to dryness, adding about 

 half a gram of potassium chlorate and a few cubic centimeters 

 of strong hydrochloric acid, and again evaporating. If the 

 sample showed incomplete decomposition the above process was 

 repeated. The mixture was then diluted with boiling water, 

 filtered, and the sulphate in the filtrate determined in the usual 

 way as barium sulphate. This method gives very accurate re- 

 sults, is more speedy than the fusion methods, and is free from 

 the danger of loss by spurting; a disadvantage almost inseparable 

 from the latter methods. 



In seeking a still faster method than the above for the rapid 



assay of sulphur, the writer devised the following, and strongly 

 recommends it as a routine method of analysis where extreme 

 speed combined with accuracy is required. Many carefully timed 

 tests have been made and it has been demonstrated that, with 

 practice, the whole analysis from weighing the rubber sample to 

 that of the precipitated barium sulphate can be carried out 

 within one hour. 



DETAILS or THE METHOD. 



One to one and a half grams of the sample, cut into small 

 pieces are placed in a large Erlenmeyer flask and covered with 

 about ten cubic centimetres of strong nitric acid. This acid 

 must be pure and free from traces of sulphuric acid. To this 

 about five grams of sodium peroxide are cautiously added in 

 small portions at a time. The reaction is often violent and the 

 rubber commences to decompose, but no loss need be feared if 

 the reaction is conducted in a large conical flask. The action is 

 completed by gently warming the mixture on a sand bath. 



After the first action is over and the rubber is more or less 

 broken up, a process occupying a few minutes only, the mixture 

 is boiled on the sand bath almost to dryness. Boiling water is 

 added and the liquid filtered through a fast filter paper ; the 

 paper is washed twice with boiling water and the washings 

 added to the filtrate. The sulphate in the filtrate is then pre- 

 cipitated in the usual way with a boiling solution of barium 

 chloride, and, after standing for a few minutes, filtered through 

 an ashless, fast filter paper, made to retain barytes. The pre- 

 cipitate is washed once by decantation and then on the paper 

 until free from chloride. The paper and its contents are then 

 removed from the filter, dried rapidly on a piece of wire gauze 

 supported in the open over an asbestos mat heated by a Bunsen 

 burner. 



The precipitate is detached as completely as possible from the 

 dry paper which is ignited separately. After the crucible has 

 cooled the precipitate of barium sulphate is transferred to it and 

 the crucible and its contents are again ignited at dull red heat. 

 .•\bout five minutes' heating is sufficient to bring the precipitate 

 to constant weight. 



OBSERVATIONS. 



The success and speed of the method outlined above depends 

 on the fact that the combined action of the hot nitric acid and 

 the hydrogen peroxide in the solution brings about a very rapid 

 decomposition of the rubber and completely o.xidizes the sulphur. 

 It is probable, too, that nascent oxygen is present in the mixture 

 and that this has a powerful action on the sulphur. Any loss of 

 sulphur in the form of fumes of sulphuric acid during the final 

 stages of the evaporation is prevented by the presence of sodium 

 salts which convert all the acid into sodium sulphate. The use 

 of a conical flask of large size precludes any loss due to spurt- 

 ing w-hen the peroxide is added. In the precipitation, speed is 

 attained by keeping all the solutions at boiling temperature and 

 using fast filter papers, and considerable time is saved by drying 

 the paper and precipitate as described on a wire gauze. 



^Research 



Du.-.loii Rubber Company of Australasia. Limited. 



VELOSAN ACCELERATOR. 



The English vulcanization accelerator Velosan is now avail- 

 able on the American market and is certain to elicit much in- 

 terest since adequate supplies of the popular hexamethylene 

 tetramine are not at present available. Velosan has been fa- 

 miliar for the past four years to the rubber manufacturers of 

 England. It is non-poisonous, free of objectionable odors, gen- 

 erates no extra heat and cures goods in one-half to one-fifth of 

 the usual time required. 



The quantity of Velosan to be used is one per cent of the crude 

 rubber weight in the mixing. It is added to the batch from a 

 sprinkling can or in a mixture with three or four times its bulk 

 of dry ingredients. Care is necessary to insure its uniform 

 distribution throughout the batch. 



