488 



THE INDIA RUBBER WORLD 



Apri-- 1, 1921 



case ot waterproof cloth, the finished cloth will curl toward the 

 rubberized surface." Obviously the outer layer or surface of 

 rubber coating will dry before the lower or inner layer has a 

 chance to dry. The surface layer contracts long before the sol- 

 vent has left the lower layer, and the cloth wrinkles, warps or 

 ■"cockles," as the workers say. 



As a thinner or solvent for sulphur chloride, coal-tar benzene is, 

 liowevcr, used successfully to a large extent today. 



Solvent \.\phtha. The oil obtained from coal-tar might bet- 

 ter be called "160-degree coal-tar naphtha." It consists of a mix- 

 ture of benzol, toluol, xylol, styrol and pseudo-cumol, so that 

 90 per cent boils below 160 degrees C. (320 degrees F.). This 

 material resembles gasoline in that it boils over a wide range 

 aud for that reason it does not evaporate superficially as does 

 benzene. On the other hand, it boils similarly to turpentine (160 

 to 170 degrees C), and for that reason it has been used as a 

 substitute for turpentine in many cases where thinners are need- 

 ed. In England and Europe the oils obtained from the distilla- 

 tion of coal-tar have for years been the logical solvents and 

 thinners for the rubber industry because of the lack of extensive 

 petroleum deposits. 



Xumerous experiments have proved that rubber which has been 

 thiraied down with "volatile solvents" loses much of its value 

 ■when it is recovered from the cement thus formed. The rubber 

 -remaining after evaporation of the "solvent" has lost considerably 

 in tensile strength. Now it is also found that the loss in tensile 

 will vary with the "solvent" which has been employed. This may 

 be due in a measure to the fact that the distribution of resins in 

 the rubber ha.< changed, or a residue of very high boiling oil has 

 been left in the rubber after the major portion of the "solvent" 

 has disappeared. The coal-tar naphtha at present on the market 

 in .\merica is of such a quality that the impurities which were 

 mentioned in specifications twenty years ago have now practically 

 disappeared. The one thing which should invariably be given 

 consideration is its boiling point and the (volume) percentage 

 which is non-volatile at 160 degrees C. (320 degrees F.). 



C.\RB0x DrSLXPHiDE. Bccause of its ability to dissolve large 

 amounts of sulphur, this material was one of the first to be used 

 as a solvent and thinner in rubber work. Virtually all of the 

 carbon disulphide used in America today is made in special elec- 

 tric furnaces. One shaft of the furnace is kept filled with char- 

 coal, while the outside ring contains sulphur. The hot vapors 

 of sulphur rise and pass through the heated charcoal, forming 

 vapors of carbon disulphide, which are then piped off and con- 

 densed. The material has a boiling point of 47 degrees C. 

 (116 degrees F.) and its vapors are unusually heavy. This, 

 coupled with the fact that it is highly inflammable, makes it so 

 undesirable that its use is extremely limited at the present day 

 in all plants where scientific management is used. Up until about 

 1910 it was used quite a little as a thinner for sulphur chloride. 



Turpentine. The distillation of resinous woods may be car- 

 ried out in as many as five different ways and by means of de- 

 structive distillation turpentine, wood-tar and charcoal are ob- 

 tained. If distilled by means of steam under a pressure of 

 twenty pounds, a very high-grade turpentine is obtained. As far 

 "back as 1819 Thomas Hancock in Manchester, England, conducted 

 experiments for the purpose of dissolving rubber in turpentine, 

 but he found that the "solution" dried very slowly because the 

 iturpentine contained some high-boiling constituents. Experience 

 lias shown that the conversion of rubber and rubber compounds 

 into "cements" is facilitated by first grinding the material in a 

 ■chum or masticator. In this way the fiber of the rubber is 

 *broken down somewhat and the solvent is enabled to act more 

 effectively. It is interesting in this connection to note that it is 

 almost impossible to incorporate such materials as rubber sub- 

 stitutes (sulphurized oils) by merely mixing them in the cement 

 in the churn. The only practical way to add these substitutes to 



a rubber compound seems to be to grind them into the rubber 

 on the usual mixing mill. In this way the particles are spread 

 through the whole mass uniformly. 



In turpentine we have an example of a solvent which has an 

 almost constant boiling point, 160 to 170 degrees C. (320 to 338 

 degrees F. ). In other words, it contains no oils which boil at 

 about 100 degrees C, and the result is that the evaporation is not 

 facilitated. This is a problein in vapor tensions which will be 

 recognized by students of physics. 



It may be added that turiicntine is today of no practical interest 

 for most of the industrial rubber processes, but in those cases 

 where its boiling point is not an objection it will be found to be 

 desirable and effective as a thinner and solvent. Turpentine is 

 interesting to rubber chemists, as it has the same empirical for- 

 mula as Hevea rubber hydrocarbon (C,oH,o). 



P.xra-Cymene. In the manufacture of sulphite spruce pulp 

 certain liquors are obtained which on distillation yield a crude 

 oil. The oil is allowed to stand over lime for about one week 

 and is then subjected to steam distillation. This distilled oil is 

 now washed repeatedly with sulphuric acid imtil a sample of 

 it when .shaken in a small bottle imparts very little color to an 

 equal volume of sulphuric acid. The oil is finally washed with 

 water, dried and purified by distillation. The product so ob- 

 tained boJls at almost exactly 175 degrees C. Its chemical name 

 is l-methyl-4-isopropyl benzene ; its specific gravity at 16 de- 

 grees C. is 0.8623, and its flash point, 42 degrees C. 



The liquid bears quite a little resemblance to turpentine (boil- 

 ing point 160 to 170 degrees C.) but it is much more fragrant, 

 and for that reason is used to a considerable extent in perfumes. 

 In 1918 Andrews took out a United States patent covering the 

 use of amino-cymene as an accelerator of vulcanization, but the 

 cymene itself has up to the present been used in the rubber in- 

 dustry chiefly as a solvent for rubber in the laboratory. In 

 order to avoid confusion, it should be repeated that cymene is 

 chemically a derivative of coal-tar benzene (benzol), but is ob- 

 tained on an industrial scale from sulphite spruce pulp liquors. 

 Its market price today is approximately $2 a gallon, in 110-gaIlon 

 drums. 



Denatured Grain Alcohol. To chemists this material is 

 known as ethyl alcohol (CsHiOH), to which a small percentage 

 of foreign matter has been added to render it unfit for drinking. 

 It is generally made by fermentation of Indian corn or maize with 

 a small percentage of malt. More recently, however, it has been 

 made by treating sawdust with dilute sulphuric acid. In this 

 way the carbohydrates are changed to fermentable sugars, and 

 the sugars are later fermented by means of distillers' yeast. 



A finished alcohol which contains 90 per cent alcohol by vol- 

 ume is known in the trade as "180 proof," and this would show 

 a specific gravity at 16 degrees C. of 0.8340. A United States 

 proof-gallon (of alcohol) is one which consists of 50 per cent ab- 

 solute alcohol by volume— the other £0 per cent being water. 

 This is known as "lOO proof." 



With 180 proof alcohol at about 65 cents per gallon, and with 

 70 degrees Be. gasoline rising each day from 38 cents per gallon, 

 the question has frequently been raised by rubber factory super- 

 intendents as to whether the former liquid could be used as a 

 thinner in admixti're with the gasoline. Experiment shows that 

 100 gallons of 95 per cent denatured alcohol will mix with 30 gal- 

 lons of a 70-degree gasoline to form a perfectly clear, water-white 

 liquid. 



BuTVL Alcohol. One corporation has recently put on 

 the market almost pure butyl alcohol. In solvent power 

 this resembles amyl alcohol, or refined fusel oil to some 

 extent. It shows 0.814 specific gravity, and 90 per cent of it boils 

 between 115 and 117 degrees C. (239 to 243 degrees F.). The 

 chemical formula of butyl alcohol is CH3.(CHj)5.CH:OH. It 

 contains no water or acetic acid whatever and can readily be 



