COAL-.SAPHTHA. ] 



UNDULATORY FORCES. LIGHT. 



107 



atmospheric air. In consequence of this property, the 

 greatest caution is necessary in manipulating with the 

 fluid ; for should an explosion take place, the most 

 dangerous results might follow. We are not likely to 

 employ the mixture in this country, on account of the 

 high price of spirits of wine ; but in France and Ger- 

 many, where alcohol is comparatively cheap, the fluid is 

 often used as an illuminating agent at railway stations in 

 country towns. 



(6.) Coal- naphtha. When coal is distilled for the manu- 

 facture of gas, a tar is obtained which is the source of 

 common naphtha. The tar itself is a very complex ma- 

 terial, for it contains a number of oily acids, alkalies, 

 and neutral bodies. As it comes from the gas-works, it 

 is a thick, dark liquid, of a most offensive odour. To 

 extract from it its various constituents, it is put into 

 large iron retorts or stills, and submitted to distillation ; 

 that which comes over first is of an aqueous nature, and 

 smells strongly of ammonia ; then follows a brownish 

 oil, which floats on the preceding. After a time, a 

 denser or heavier oil begins to make its appearance ; and 

 when this happens, the receiver is changed, and the first 

 product is set aside for the manufacture of light oil or 

 crude naphtha. The coal-tar generally yields from four 

 to five per cent, of this fluid. As the distillation of the 

 tar proceeds, a heavy oil, which falls to the bottom of 

 water, and is hence termed dead oil, comes over. This 

 is u*od, under the name of creosote, for the preservation 

 of timber. After this a yellowish semi-crystalline fat, 

 called naphthaline, makes its appearance ; and, finally, a 

 more solid material, named paranaphthaline, distils over. 

 Tk.it which remains in the retort is pitch. 



The crude coal-naphtha is rectified either by distilling 

 it a second time, or by driving steam through it and 

 collecting the condensed products. In this way it is 

 separated from another portion of heavy oil which re- 

 mains in the still. 



The light naphtha thus obtained is sent into commerce, 

 and sold for about 2*. 4d. per gallon, for combustion in 

 the common vapour-lamps which are so frequently to be 

 seen in the streets of London, lighting up the stalls of 

 the poor tradesmen. In this condition it is an amber- 

 coloured liquid, of a powerful gas-like odour, and 

 spirituous appearance. It has a density of from 860 to 

 900 usually it is about 887. It floats on water, like 

 turpentine, and becomes darker coloured by exposure to 

 the air. It mixes very freely with wood-spirit or with 

 spirits of wine; and may thus be burnt like the last- 

 named liquid, in an ordinary lamp. 



Tim light naphtha is further purified for commerce by 

 agitating it with a little oil of vitriol, thon washing with 

 water, and redistilling. In this condition it is sold as 

 rectified naphtha, and is used for combustion in the 

 naphtha spirit-lamps which have a flat wick and oval glass. 



Mr. Mansfield has shown that light coal-naphtha con- 

 tains a number of volatile oils, which may be separated 

 from it by fractional distillation. One of these namely, 

 benzole is of great importance. It is procured by 

 boiling the naphtha in a retort, to which there is adapted 

 a worm which coils through a vessel of boiling water ; the 

 worm is so constructed that all the vapour which con- 

 denses in it shall run back again into the still, while the 

 uncnndunsed vapour (that of benzole) passes on into 

 another receiver, where it is cooled and collected. The 

 benzoin thus obtained is rectified a second time in 

 a similar apparatus, the temperature of the worm 

 being kept at about 176 Fah. In this way a large 

 proportion of volatile oil is obtained, which is fur- 

 ther purified by agitating it with one-fourth its bulk 

 of strong sulphuric acid, or, better still, with about one- 

 tenth of strong nitric acid ; and then, after separating 

 the nitric acid, it is agitated with oil of vitriol as before. 

 The naphtha is now to be decanted and distilled a third 



tiiin-. 

 put . 



If it t>e 

 it is submitted 



required to have the benzole perfectly 

 mitted to a cold of 4 Fah. This is 

 produced by mixing salt and snow together. The benzole 

 s, ami leaves its impurities in a fluid condition, 

 from whii-h it may bo i>y moans of a filter. 



The use of sulphuric acid in this process is to remove 



all the basic substances, and to oxydise the brown 

 colouring matter of the naphtha ; the nitric acid assists 

 the oxydation, and at the same time forms a small 

 quantity of nitro-benzole, which gives a fragrant, 

 almond-like odour to the product. 



Benzole is a limpid colourless liquid, of a rather 

 ethereal odour ; its density is 850 consequently it floats 

 on water. It boils at a temperature of 177 Fah., and 

 gives off a vapour which is very inflammable, burning 

 with a sooty flame. It solidifies at the freezing-point of 

 water, and then looks like camphor. So volatile and 

 combustible is the liquid, that when a current of hydro- 

 gen gas is passed through the fluid, or through a sponge 

 moistened with it, the gas will burn with an intensely 

 white light. Atmospheric air charged with the vapour 

 also burns with a smoky flame and a bright light : the 

 flame is sometimes of a violet-blue colour when the 

 apertures of the jet are very small. 



Benzole mixes freely with alcohol or with wood-spirit, 

 and the compound so formed burns in common lamps with 

 a very powerful light. It is necessary that the mixture 

 should be made with proper proportions, or else the 

 light of the flame is not good ; for if there be too much 

 spirit the light is blue, and if too little it is smoky. The 

 mixture which is found to give the best results, is about 

 one part benzole and two of spirit, of specific gravity 840. 

 This mixture, when burning at the rate of 160 grains an 

 hour, gives a light of from one-and-a-half to two sperm 

 caudles. 



The extreme volatility of benzole gives to coal-naphtha 

 the property of naphthalising air or bad gas ; for if a 

 little of the liquid be placed in the gas-meter, or in a 

 chamber containing some pieces of sponge through which 

 the gas passes, it will acquire increased illuminating 

 powers. Mr. Lowe, of the Chartered Gas Company of 

 London, has taken out a patent for this mode of 

 naphthalising gas. Beale's lamp is also a contrivance 

 for naphthalising atmospheric air. It consists of a cup 

 of naphtha, through which a stream of air is made to 

 pass ; and to facilitate the volatilisation of the naphtha, 

 a hot cap is placed over the cup, so as to communicate 

 its heat to the air and liquid. The other constituents 

 of coal-naphtha are not so volatile as benzole, and hence 

 they are not fit for the purpose of naphthalising. 

 Mansfield states, that the oil which distils over from the 

 crude naphtha at a temperature of 230, will take fire at 

 its surface ; but it yields so little vapour to cold air, that 

 the Utter, when passed through it, burns with but a 

 focble blue flame; and the oil which distils at a tem- 

 perature of 300 is still less inflammable, for it will not 

 take fire at the surface, or furnish any combustible 

 vapour to atmospheric air. In these respects it re- 

 sembles turpentine, which requires a heat of 314 Fah. 

 to boil it. 



A fluid like coal-naphtha is also obtained from the 

 distillation of certain oily matters, or petroleums, which 

 exude from the earth. In many places in the neigh- 

 bourhood of the Caspian Sea, in Ava, at the Tegernsoe 

 in Bavaria, at Amiano in Italy, at Neufchatel, at Saint 

 Zibio in the Grand Duchy of Modena, at Clermo^it and 

 Gabian in France, at Val di Noto in Sicily, at Rangoon, 

 Barbadoes, Trinidad, Lake Gencka in New York, and 

 many other places, an oily matter called rock-oil oozes 

 out of the ground, and is collected in pits dug in the 

 earth to receive it. When distilled, it furnishes a 

 volatile oil called naphtha, of which Persian naphtha 

 may be taken as a good example. It is colourless, 

 limpid, very combustible, and burns with a sooty flame. 

 In some places it is used for illuminating purposes. 



(e.) The OH of Fermented Lie/up*, Oil of Grain, or 

 Fusel-oil. In the process of fermentation, all the 

 saccharine fluids produce a volatile oil, which can be 

 separated fronj the spirit by distillation. Pellitan, in 

 1825, first noticed this fact; and as he obtained the oil 

 from spirit of potatoes, he called it potato-spirit oil. It 

 was subsequently examined by Dumas (1834) ; and in 

 1839 it was investigated by Cahours. More recently 

 Buchner obtained it from corn-spirit. For a long time 

 it was obtained as a waste product by Mr. Bowerbank, 



