April 1, 1917.] 



THE INDIA RUBBER WORLD 



377 



The Nature and Uses of Rubber Solvents — II. 



By Lolhar E. JVebcr, Ph. D. 



[In the first iiislaliiii-nt of this article Dr. U'cbcr discussed gasoline, including casing-head and cracked gasoline, its characteristics, 

 more desirable methods of designation, uses in dipped goods and cements, and sokent recovery.] 



BENZOL. 



NEXT to gasoline the most important solvent which finds 

 commercial utilization in tlie rubber industr_v is benzcl. 

 While there is a definite chemical compound of this name, 

 the term benzol is used in a generic sense to denote certain 

 liquid hydrocarbons which are found in coal-tar. 



When bituminous coal is subjected to destructive distillation,* 

 there is obtained (1) illuminating gas, (2) an aqueous liquid, 

 the most important constituent of which is ammonia, (3) coal- 

 tar, and (4) a residue of col<e. The coal-tar is a viscous liquid 

 of characteristic odor. It is intense black in color, due to the 

 presence of suspended particles of carbon. This is the same 

 coal-tar which, as the basis of many dyestul¥s and medicinal 

 preparations, has been so widely discussed during recent years. 

 It is a highly complex mixture, containing as it does, substances 

 of widely difi^erent characteristics and properties. Amongst 

 them is ben.^ol, which is present to the e.xtent of only about 1.5 

 per cent. 



By suljjccting the coal-tar to distillation, the benzol is separated 

 irom the remaining substances. As has already been stated, the 

 term benzol is used to designate a group of generic hydrocar- 

 bons, which latter bear very much the same relationship to 

 each other that the paraffin hydrocarbons do. Fortunately the 

 gravity nomenclature is not used in designating these hydro- 

 carbons, they being referred to technically on a boiling point 

 basis. By "Benzol Pure" one infers a solvent consisting essen- 

 tially of the chemical substance known as benzol. This material 

 has a constant boiling point of 80.4 degrees C. (177 degrees F.) 

 Under "100 per cent Benzol" one designates the material which 

 is 100 per cent distillable at 100 degrees C. The material which 

 is 90 per cent distillable at 100 degrees C. is referred to as "90 

 per cent Benzol." This nomenclature is a logical and desirable 

 one, in that it enables a purchaser at a glance to know the com- 

 parative boiling points, and hence the volatility of the solvent. 



In the United States it is the 90 per cent benzol which prob- 

 ably finds the largest application in rubber manufacture. This 

 product consists of about 70 per cent pure benzol, the residue 

 being for the most part toluol. The 90 per cent benzol is seldom 

 used for spreading purposes, but it finds considerable applica- 

 tion in the manufacture of cements and dipped goods, and to a 

 certain extent in the cold cure. 



Benzol — meaning thereby 90 per cent benzol — is much to be 

 desired over gasoline as a rubber solvent. It is in the first place 

 a more uniform product, has a much narrower range of boiling 

 points, and largely increased solvent power. Whereas a gaso- 

 line solution is always opaque in appearance, a benzol solution 

 of rubber is clear and transparent. There is no indication of 

 any suspended matter being in the rubber solution, which is 

 always the case when gasoline is used as a solvent. Probably 

 on account of this homogeneity the film resulting from a benzol 

 solution of rubber is stronger in its physical properties, and at 

 the same time more transparent in appearance, than is the film 

 produced from a gasoline solution. The range of boiling points 

 being narrower, there is less chance for the formation of blisters 

 in the case of dipped goods and blowing in the case of cement 

 when benzol is the solvent employed. Under present conditions 

 the price of benzol is more than double that of gasoline, but 

 after cessation of hostilities the discrepancy in their prices will 



*By destructive distillation is meant the heating of a s\ih.stance, in the 

 absence of air, to a temperature at which decomposition results. 



probably be slight, owing to the vastly increased benzol produc- 

 tion in this country. When such is the case, it will be very 

 luuch to the advantage of the rubber manufacturer to substitute 

 the utilization of benzol for gasoline in dipped goods and 

 cements. 



SOLVEXT iVAl'IITIIA. 



This material is also obtained from coal-tar and has no rela- 

 tion v.-hatsocver to any petroleum product. Its boiling points 

 range from about 140 degrees C. to 170 degrees C. It consists 

 essentially of two hydrocarbons known as xylene and cumene. 



Solvent naphtha has never found wide application on the part 

 of the rubber manufacturer in the United States, though it is 

 used very extensively in Europe. Gasoline is used to a mod- 

 erate degree by the European rubber manufacturer, and scarcely 

 ever in the spreading operation, except in limited admixture with 

 solvent naphtha. The claim is authoritatively made that gaso- 

 line itself cannot be used with any degree of safety in England 

 for the spreading operation, the peculiar atmospheric conditions 

 which obtain creating an excessively precarious fire risk. It Js> 

 indeed, a fact that iu the days prior to the development of the 

 internal combustion engine when gasoline was a drug on the- 

 iTiarket, European manufacturers used solvent naphtha almost 

 exclusively as the spreading solvent, and this in spite of the fact 

 that the latter, as produced abroad at that time, had serious 

 objections in that it imparted an odor to the spread compound, 

 The odor is due to the very disagreeably smelling substance 

 known as pyridine, which even when present in the solvent to 

 the extent of less than 0.1 per cent, makes itself exceedingly 

 ofifensive. The solvent naphtha produced in America is almost 

 invariably free from even these minute traces of pyridine, as 

 also is tlie European product as usually marketed within recent 

 years. 



SH.\LE OIL. 



In Scotland, and to a certain extent in Germany, the destruc- 

 tive distillation of certain bituminous shales is carried on quite 

 e.xtensively. Shale is a rock formation, usually of a brownish 

 or gray color, which is permeated with bitumen. The shale is 

 heated in retorts, whereby the bitumen suffers destructive dis- 

 tillation. From the tar resulting on distillation there is ob- 

 tained shale naphtha, which has physical propertiss analogous to 

 the solvent naphtha obtained from coal-tar. While shale 

 naphtha has found very little application in America, it is used 

 quite extensively in Europe for purposes where the odor does 

 not militate against its use. 



CARBON BISULPHIDE. 



This solvent is made by the interaction of carbon and sulphur. 

 The older method of passing sulphur vapor over coke or char- 

 coal, heated to a red heat, has been practically superseded by 

 the electrical method, whereby the two components are heated 

 in an electric furnace. Carbon bisulphide, when strictly pure, 

 has a sweetish, pungent odor, although the article of commerce 

 is mo're or less evil smelling, owing to the presence of certain 

 sulphur impurities. Carbon bisulphide boils at 46 degrees C, 

 and even at ordinary temperatures is extremely volatile. Great 

 care has to be e.xercised in tlie handling of it, for the' reason 

 that its vapors are inflammalile when heated only to the rela- 

 tively low temperature of ISO degrees C. When carbon bisul- 

 phide burns, there is produced sulphur dioxide and carbon di- 

 oxide, both extremely suffocating and irritating gases. 



