822 



THE INDIA RUBBER WORLD 



August 1, 1921 



all of the volatile oreanic solvents is designated as free carbon 

 to distinguish it from that carbon which is chemically combined 

 with other clicmical elements. In the examination of coal-tar, a 

 determination of this carbon is found to be of great value. 

 Among the solvents which have been u.sed by coal-tar chemists 

 for the test are : carbon disulphide, aniline, glacial acetic acid, 

 benzene, toluene, and xylene. 



NATURAL ASPHALT PITCH 



Trinidad asphaltum with 56 per cent bitumen is obtained from 

 Asphalt Lake on the island of Trinidad, off the coast of Venezuela 

 in South .\merica. Bermudez asphalt contains about 75 per cent 

 bitumen, and is found in Venezuela. The analysis of refined 

 Bermudez asphaltum .^hows in round numbers : 



Per Cent 



Bitumen soluble in carbon disulphide 75.0 



Organic niattei nor bitumen 3.5 



Non-volatile mineral matter 21.5 



lOO.O 



Carefully retined Bermudez asphaltum shows as high as 90 

 per cent of actual bitumen. These asphalts are by some con- 

 sidered to I.e alteration products of petroleum hydrocarbons, re- 

 sulting from evaporation and oxidation. 



Another type of rather pure solid bitumen is known as gil- 

 sonite. and is found on the Uintah Indian reservation in Utah. 

 As early as the year 1900, the annual production was approxi- 

 mately 7,000,000 pounds, and the demand for the material as a 

 waterproofing agent and as a raw material in rubber works has 

 increased this figure. The chemical analysis of gilsonite shows 

 that the amount of matter soluble in carbon disulphide varies 

 from 90 to 95 per cent. 



An examination of natural pitches should invariably include a 

 determination of "Loss on heating to ISO degrees C. (about 300 

 degrees F.) for fire hours," as it has been found that some of 

 them contain a considerable amoimt of volatile organic matter. 



COAL-TAR PITCH 



Coal-tar is a thick, viscous liquid obtained in gas-works when 

 bituminous coal is heated to high temperatures in retorts. By 

 this operation gas is driven off and after purification it is col- 

 lected in suitable tanks : aiumoria is also driven off as a gas and 

 is absorbed by sulphuric acid. Some of the fumes which distil 

 off are very heavy and for that reason they condense shortly 

 after leaving the hot retorts, as a tarry mass which is collected 

 in suitable "tar-wells." From here the molasses-like tar is 

 pumped into tank cars and delivered to the coal-tar refinery, a 

 separate and distinct industry. The coal-tar refiner subjects the 

 material to a series of distillation processes whereby he removes 

 (1) water, (2) light oil. cut at 200 degrees C, (3) middle oil, 

 cut at 270 degrees C, and heavy oil, cut above 270 degrees C. 



The hard pitch which remains in the still after the third or 

 anthracene oil fraction is distilled off, constitutes the material 

 known in commerce as "hard pitch." If the distillation is stopped 

 at 270 degrees C. the material which remains in the still will be 

 "soft pitch," with a melting point below 90 degrees C. (195 de- 

 grees F. ). 



TESTS 



The tests usually applied to coal-tar pitch are mostly physical. 

 Specific gravity is determined in the manner used for solids. 

 Evaporation loss is determined by exposing in an air bath at 160 

 degrees C. for seven hours. Melting point is determined by heat- 

 ing a cube of pitch in water while it is suspended from a wire. 

 Free carbon is determined by extraction with toluene and ben- 

 zene in an Underwriters' extraction flask. 



Coal-tar is a mixture of hydrocarbon distillates, mostly un- 

 saturated ring compounds, and coal-tar pitch, being a solid resi- 

 due of this material, contains the same type of chemical sub- 

 statices. It will be recalled that the petroleum pitches contain 

 tnostly cyclic and bridge compounds. 



HARDWOOD PITCH 



In the process of distilling sudi woods as oak, beech and maple, 

 a number of products are obtained as in the case of coal distilla- 

 tion. Acetic acid, alcohol, and wood-tar are obtained as liquids, 

 while charcoal remains in the retort at a tcmix^rature of about 

 427 degrees C. (800 degrees F.). 



The tar is later distilled separately and the oils which come 

 off are collected and fractionated up to a teni|)eraturc of about 

 200 degrees C. At the end of this distillation the hard-wood 

 pitch remains in the retort. It can be produced in grades which 

 melt at 100 degrees C, or as high at ISO degrees C. The former 

 would show about 95 per cent of matter soluble in chloroform, 

 while the latter would contain not much more than 50 per cent 

 of matter soluble in that liquid. .\ pitch of melting point 100 

 degrees C. may contain as much as 40 per cent of matter soluble 

 in (denatured grain) alcohol, and will show about 1.250 specific 



gravitv. 



PETROLEUM PITCH 



Wlien liquid native bitumens (petroleum) are treated with a 

 current of air while they are being heated, the volatile parts of 

 the petroleum are driven off and an asphalt-like product known 

 as "blown petroleum pitch" is obtained. This is sometimes called 

 Byerlite. Thomas T. Gray, the American petroleum expert, 

 claims that the asphalt residues from crude petroleum so closely 

 resemble the natural asphalts that the two cannot be distinguished 

 with certainty. 



The melting point of these pitches is determined by the ball 

 and ring method. This depends on the use of a steel bicycle 

 ball weighing five grams, which is allowed to drop through a 

 disk of asphalt 16 millimeters in diameter. In the petroleutn in- 

 dustry, the bitumen soluble in petroleum spirit has been desig- 

 nated as "petrolene," and the part soluble in carbon disulphide 

 has been called "asphaltene." 



Pennsylvania petroleum is a "paraffine base" oil, as it yields 

 solid hydrocarbons of the parafiine series, while California pe- 

 troleum has an "asphalt base." It is rich in asphalt and con- 

 tains practically no solid parafHnes, although it contains a large 

 proportion of nitrogen bases of the pyridine and chinoline series. 



The penetration test is carried out to determine the consistency 

 or hardness. To this end, a sample is subjected to the impression 

 of a weighted standard needle for a specified time at a specified 

 temperature. The penetration of the needle is then recorded on 

 a dial of the penetrometer. 



The buyers of petroleimi asphalt usually specify the propor- 

 tion of petrolene and asphaltene which they desire in the prod- 

 uct, and these specifications depend upon the use to which the 

 asphalt is to be put. The petroleum spirit extraction is first con- 

 ducted and the carbon disulphide extraction is then made on the 



residue. 



STEARIN PITCH 



In the meat packing industry this material is otherwise known 

 as "candle pitch" or "candle tar." It is obtained as a retort resi- 

 due in the manufacture of distilled fatty acids. In modern soap 

 manufacture it is customary to first separate the valuable glycerol 

 (glycerine) from the tallow or the vegetable oils. The remaining 

 part of the oil or fat is the fatty acids. In order to obtain them 

 in a state of relative purity they are distilled, preferably in 

 vacumn retorts. 



In certain cities the recovery of grease from kitchen garbage 

 has been introduced. The grease expressed from garbage is very 

 dark-colored, and the fatty acids split off from the grease are like- 

 wise rather dark-colored, so that they must be distilled two or 

 three times in order to obtain the crisp, white, stearic acid of 

 commerce. The pitch which remains in the retort as a residue 

 will have a melting point anywhere from SO to 100 degrees C, 

 and will contain appreciable amounts of saponifiable matter. This 

 is in fact the characteristic of the pitch obtained from the fatty 

 acid refineries. The ash or non-volatile mineral matter will be 

 less than 5 ))er cent, and tlie matter soluble in carbon disulphide 



