206 



NA TURE 



[December 29, 1904 



degrees between the initial and the final boiling points. 

 With homologous hydrocarbons the lower-boiling 

 member vaporises more readily than the higher; con- 

 sequently, in practice, the vajwur from the second 

 spirit would in the early stages of a run contain an 

 excessive proportion of the more volatile constituent, 

 and in the later stages too much of that which is 

 less volatile. For satisfactory combustion these two 

 constituents require very different projxjrtions of air; 

 hence if the carburetter was initially arranged to give 

 the proper quantity it would not do so in the later 

 stages. The practical bearing is that, to avoid waste 

 of fuel or loss of heat, more jitlention must be paid to 

 the carburetter when the petrol has a wide range of 

 boiling points than when it is more nearly homo- 

 geneous. 



As already mentioned, the petrols in actual use 

 consist of several hydrocarbons ; there is none contain- 

 ing only one, or even only two. But the foregoing 

 examples typify the better and the inferior qualities 

 respectively. 



Products from Coal-tar. — These are known com- 

 mercially as benzol or benzole, benzine, and coal-tar 

 spirit, all of which terins mean nearly the same thing, 

 and toluol, which is a very similar liquid of lower 

 density. (Benzol or benzine should be distinguished 

 from benzoline, the petroleum product previouslv re- 

 ferred to.) In the first group the aromatic hvdro- 

 carbon benzene, CjH„, is the chief constituent, but 

 toluene, C.H,, and xylenes, CjH,„, also accompany it. 

 Benzol is commercial benzene, i.e. benzene with some 

 impurities and homologues ; benzine is a cruder 

 variety ; these differ only in the proportions of the 

 admixtures, and are often indistinguishable the one 

 from the other. Coal-tar spirit is a general term for 

 either. In .America and in France, as well as some- 

 times in this country, the term " benzine " refers to 

 the petroleum naphtha, not to the coal-tar product. 



Benzol has a greater density than petrol (about 0.883 

 at I5°.5 C), and a higher boiling point, viz. about 

 90° C. Nevertheless, it has the advantage of di-s- 

 tilling, as a whole, within much narrower limits than 

 most varieties of petrol do. Thus, while there mav 

 be a difference of more than 100° C. between the initial 

 and final boiling points of petrol, a good sample of 

 " go's benzol " will distil completelv within a range of 

 about js° C. or less. i.e. between qo° and 145° 

 Benzol is consequently more like the ideal homo- 

 geneous fuel than petrol is, and this, together with the 

 necessity of supplementing the supply of petrol by 

 some other fuel, has led to its frequent employment 

 abroad and to experimental trials in this country. 

 Deutz benzol locomotives have been used for some time 

 in Germany, and the tram-cars of the Saalgau- 

 Herbertingen-Riedlingen line are worked bv a 14 h.p. 

 benzol motor, whilst a mixture of benzol and alcohol 

 is used in some of the French racing cars. So far as 

 the German experience has gone, the results are said 

 to indicate that the benzol motor is about 10 per cent, 

 cheaper in working than the alcohol engine. The 

 British trials seem to show that benzol works more 

 uniformly than petrol, and is generally satisfactorv, 

 except that with too great a compression in the 

 cylinders there is a liability to pre-ignition. 



One disadvantage of benzol is the presence in it of 

 sulphur compounds, chiefly carbon disulphide and thio- 

 phene. These not only give an evil-smelling exhaust, 

 but may conceivably corrode the metal of the cylinder 

 through the formation of acid vajxiurs in the combus- 

 tion. Probably at a cost of about a pennv per gallon 

 the benzol could be sufficiently freed from sulphur, 

 and it is thought that, with a good demand, the purified 

 liquid inight be supplied at ,-i price of about yd. a 

 NO. 1835. VOL. 71] 



gallon, or less. Unfortunately, however, the 

 supply of benzol is even more limited than that of 

 petrol ; the yield from coal-tar is only some 0.6 per 

 cent., and much of what could be produced is already 

 absorbed by the chemical and dye industries. It seems, 

 therefore, very unlikely that benzol will ever largely 

 supplant petrol, though it mav usefullv supplement 

 this fuel. 



Toluol (crude toluene), of lower density but higher 

 boiling point than benzol, has also been recently tried, 

 though not on a sufficiently extended scale to give 

 much practical information. Benzol is essentially a 

 mi.xture of pure benzene and toluol, and in one respect 

 the mixture is better than pure benzene, because the 

 latter freezes at 0° C, and this is prevented by the 

 presence of toluol. 



Alcohols as Fuels. — The industrial side of the ques- 

 tion has encouraged the use of alcohol in France and 

 Germany, since, other things being equal, it is better 

 to support home agriculture than foreign oil-fields. 

 Strong alcohol can be bought in Germany at a cost 

 of Sid. to lod. per gallon, and at this price its use 

 is said to be economical compared with petrol. Pure 

 alcohol, of course, is heavily taxed — in this country 

 the duty amoimts to i~s. per gallon of 90 per cent, 

 alcohol — and that used for motor purposes is " de- 

 natured " by the addition of foreign substances. In 

 England the denatured product is methylated spirit, 

 obtained by mixing " spirits of \vine " with not less 

 than one-ninth of its bulk of wood-naphtha, and when 

 intended for retailing, with 0.38 per cent, of mineral 

 naphtha or petroleum oil in addition. In France the 

 denaturant is a mixture of heavy " benzine " and 

 malachite green. Ordinary methylated spirit, in some 

 experiments made a short time ago, was said to give 

 an exhaust with an odour so vile as would preclude 

 its general use; this is attributed to the denaturant, 

 and to obviate it one suggestion is that alcohol in- 

 tended for motor-fuel should be denatured with petrol. 

 There are, however, some fiscal difficulties in the way. 



Alcohol is a substance already partly oxidised ; it 

 contains rather less hydrogen than does petrol, and 

 onlv about one-half as much carbon, the difference 

 being made up of oxygen. Consequently its available 

 heat-energv, viz. the heat developed by the complete 

 oxidation of its carbon and hydrogen, is not much 

 more than one-half that of good petrol. Nevertheless, 

 it has some compensations. It is of nearly uniform 

 composition, and distils within much narrower limits 

 than petrol; in fact, strong alcohol, not denatured, is 

 an almost homogeneous body, which boils away com- 

 pletely at a practically constant temperature. More- 

 over, it is claimed that the alcohol engine has a much 

 greater efiiciency than the petrol motor. To get the 

 best results, hovvever, it has been found necessary to 

 use a higher compression than that given by the 

 ordinary petrol engine. In some cases both petrol and 

 alcoholare employed, with two'carburetters ; the petrol 

 is used for starting, and is automatically cut off by a 

 governor when the motor is sufficiently hot. The net 

 result of the alcohol trials at present seems to be that, 

 for equal volumes, petrol is appreciably more efficient 

 than denatured alcohol; but the difference is not con- 

 siderable, and fluctuations in price may yet make 

 alcohol a serious competitor with petrol where the fiscal 

 difficulties can be overcome. 



The cheaper higher alcohols of fusel oil (chiefly 

 .imvl and butyl alcohols) h.-ive also been proposed for 

 use as motor-fuels. But practical trials are lacking, 

 rmd in any case the supply of fusel oil is onlv a limited 

 one. For the principal motor-fuel of the future it is 

 probably to kerosene that we must look. 



C. SlMMONPS. 



