December 29, 1904J 



NA TURE 



205 



he says, " I have always thought that there must have 

 been a formative epoch, in which every creature had 

 the power of special adaptation to its own needs — nay 

 even to its own wishes or caprice. In this epoch of 

 ' plasmation ' when the so-called force of heredity — 

 which tends to reproduction according to the type of 

 the progenitor — had but little power, the world being 

 still young, the organism must have been far more 

 susceptible of modification by external forces (p. 36). 

 . . . The actual power of adaptation in organisms is 

 at the present day well nigh non-existent as compared 

 with what they must have possessed in the past (p. 211). 

 . . . The varied forms assumed by those groups of 

 individuals called by naturalists species, would be 

 merely the result of a plasmative force exerted by 

 surrounding conditions on primitive beings (p. 208). 

 . . . May it not be that the Rafflesia, and a host of 

 other aberrant species, both animals and plants, are 

 examples of the autocreation of organisms (derived 

 from exceptional circumstances of the environment) 

 and suddenly appeared a I'improviste, as it were, in 

 that primitive epoch during which organic mfitter was 

 easily plasmated, so as to adapt itself with facility 

 even to extraordinary conditions of existence? (p. 389). 

 . . . Therefore, contrary to the present prevailing 

 tendency to attribute a powerful action to variability 

 during the existing period, and to consider every species 

 as inconstant, I hold the opposite opinion, namely, 

 that at the present time species do not vary in Nature, 

 returning thus to the old idea of the nearly absolute 

 fixity of existing species (p. 210)." It is interesting 

 to compare these views with those arrived at by Alfred 

 Wallace, who wandered in the same jungles; and, as 

 Dr. Guillemard, the English editor, rightly observes, 

 " Whether the scientific reader does or does not admit 

 the validity of all Dr. Beccari's theories concerning 

 species-formation, he cannot call in question his 

 abundant experience of the country, or his knowledge 

 of the subjects of which he treats." A. C. H. 



OILS FOR MOTOR-CARS. 



POSSIBLY this article may be of interest to readers 

 of Nature who are not chemists, and therefore 

 no apology need be made for treating certain parts 

 of the subject in an elementary manner. The com- 

 mercial names for motor-oils are numerous and con- 

 fusing, and the automobilist may well be puzzled to 

 discriminate between them, even if his chemistry has 

 by no means become a mere schoolboy reminiscence. 



The various liquids in use at the present time as 

 fuels for motors are derived from three sources, namely, 

 crude petroleum, coal tar, and alcohols. By far the 

 largest quantity is furnished by the petroleum. Coal- 

 tar " spirit " is scarcely beyond the experimental stage. 

 Alcohol is somewhat largely used abroad, but at pre- 

 sent is almost out of the question in this country. 



Products from Crude Petroleum. — These, so far as 

 motor fuel is concerned, are two ; a light oil and a 

 heavier or " burning " oil. The light oil, in one grade 

 or another, is variously known as gasoline, petroleum 

 spirit, petrol, petrol spirit, motor spirit, mineral spirit, 

 motol, moto-essence, naphtha, petroleum-benzine, and 

 benzoline. Of these, gasoline has the lowest density, 

 benzoline the highest. The oil is obtained in the dis- 

 tillation of American crude petroleum, and may be 

 said generally to be the portion of the distillate pass- 

 ing through the still between the temperature-limits 

 of 60° C. and 150° C, and having a specific gravity 

 ranging from 0.68 to 074. The limits, however, vary 

 somewhat with the different refineries. To obtain a 

 good motor " spirit " this fraction of the distillate is 

 purified with sulphuric acid and with soda, and rectified 



NO. 1835, VOL. 71I 



by re-distillation. Such a spirit is clear, has no strong 

 odour, and leaves no residue when evaporated from 

 the hand. Two or three years ago the best English 

 petrol had a specific gravity of 0-680 ; but, for reasons 

 to be mentioned later, the density has been gradually 

 raised, and is now generally about 0-720 or more. 



Chemically, light oil or petrol is a mixture of several 

 members of the liomologous series of paraffin hydro- 

 carbons, C„H-,„ + 2- It is generally assumed to be 

 mainly heptane, CjHj,., and octane, CjH,j, but both 

 lower and higher members are usually present, and 

 some analyses indicate that the range may commonly 

 be from hexane, C^Hj^, to undecane, C,,H2.,. A point 

 to notice is that whilst petrol as a whole is a light, 

 volatile oil, it is by no means a homogeneous liquid. 

 The different hydrocarbons composing it have not the 

 same volatility cts one another, and they require 

 different quantities of air for their complete com- 

 bustion. 



The heavier oil obtained from crude petroleum corre- 

 sponds to what is ordinarily known as kerosene, petro- 

 leum oil, or paraffin. It is obtained by refining the 

 fraction which distils between 150° and 200°, and 

 has a density of about 0-78 to 0-81. This product con- 

 tains higher members of the paraffin series than those 

 of petrol. It is consequently less volatile, and has a 

 higher flash-point. 



Kerosene is not only cheaper than petrol, but safer 

 in the handling. Why, then, is petrol used so largely 

 as a motor fuel instead of kerosene? And why are 

 some kinds of petrol better than others? To answer 

 these questions we have to remember that, to form the 

 proper explosive mixture for the engine, it is necessary 

 to have the vapour of the liquid mixed with a particular 

 proportion of air. With too little air the mixture burns 

 too gently; with too much there is a diluent cn'ect. 

 and liability to failure of ignition. The ready volatility 

 of petrol allows of the requisite mixture being made 

 more easily, more certainly, and with a simpler form 

 of carburetter than when kerosene is used. Failure to 

 ignite is less frequent, and the combustion is cleaner. 



Nevertheless, since the supply of petrol is not limit- 

 less, attempts are being made, with some success, to 

 utilise kerosene as a source of motor energy. The 

 principle employed is that of heating up the vapour of 

 the kerosene, or the liquid itself, in order to allow of 

 a readier admixture with the air in the carburetter. 

 This is eft'ected either by the heat of the exhaust or 

 by some other special contrivance. A " smokeless 

 petroleum engine " has recently been described which 

 is said to run without smoke or smell, and without 

 " sooting " the cylinder. It will not, however, start 

 with the cold kerosene. Petrol is used for the first 

 revolutions in order to heat the vaporiser and raise 

 the kerosene to the necessary temperature. 



As regards differences of quality met with in motor 

 spirits (petrol), the first thing to notice is that the 

 higher the density of the liquid the nearer does it 

 approach to the character of kerosene and to the 

 possession of the disadvantages peculiar to the latter. 

 To meet the growing demand, makers have been u.ore 

 and more inclined to eke out their supply of petrol by 

 including a portion of the heavier fractions that were 

 formerly rejected. Hence many of the present oils are 

 to that extent of inferior quality. Next, the density 

 alone is not an infallible criterion, because a spirit 

 having a density of, let us say, 0-700, may be made up 

 in different ways. Ideally, it might consist of a single 

 hydrocarbon having the density in question. On the 

 other hand, it might be compounded of two hydro- 

 carbons having widely different densities, such as 0-660 

 and 0-740 respectively. In the first case it would distil 

 completelv at one uniform temperature, in the second 

 there would be a difference of perhaps a hundred 



