SEPTEMBER: 29, 1892] 



NATURE 



531 



This gas ii stated to have an illuminating power of fully 56 

 candles, and to lose little either by standing or by carriage to 

 considerable distances. 



As such petroleum gas has about 3-5 times the illuminating 

 power of i6-candle coal-gas, it follows that, so far as illumi- 

 nating purposes are concerned, the gas producible from one 

 gallon of oil by this process is equal to some 525 cubic feet of 

 coal-gas of i6-candle value. I shall later on refer to the heat- 

 ing value of this petroleum gas, but I have now justified the 

 statement with which this section commenced, viz., that petro- 

 leum is virtually liquefied gas in a peculiarly portable condition. 

 Hence in all states petroleum can be used as an illuminant as 

 well as a fuel, whereas coal and peat can only be used as illn- 

 minants in so far as they can afford carburetted gas. 



Let me now proceed to justify the further statement that 

 petroleum is the most concentrated, and, on the whole, the 

 most portable of all the natural fuels met with in considerable 

 quantities. 



Weight for weight the efficiency of liquid petroleum in steam- 

 raising is much greater than that of coal. The estimates of 

 relative value necessarily vary with different portions of the 

 crude material used, and with the quality of coal employed in 

 the comparative trials ; hence some of the statements of 

 results are often rather vague. Thus M. d'Allest found that one 

 pound of refined peiroleum evaporated I2'02 pounds of water, 

 while only 6-5 pounds were evaporated per pound of a rather 

 poor steam coal. The American results with crude petroleum 

 and Pittsburg coal gave respectively 15 and 7*3 pounds of water 

 per pound of fuel. Prof. Unwin has recently compared 

 petroleum with Welsh coal in steam-raising, the oil being 

 injected by a steam jet through a highly heated coil and then 

 burned perfectly witjfi a clear flame. In his trials with a not 

 particularly efficient boiler he found that I2'i6 pounds of water 

 were evaporated per pound of petroleum, and this result he 

 considers about 25 per cent, better than that afforded by the 

 steam coal. These results agree with those of M. d'Allest so 

 far as the effect of petroleum is concerned, but the coals com- 

 pared were different in value for steam-raising. Hence for an 

 average coal the proportion is nearly three to two ; in other 

 words the practical heating effect of one ton of coal can be ob- 

 tained by the combustion of only two-thirds of a ton of petro- 

 leum, while the comparison with the heavy oils would probably 

 be still more in favour of liquid fuel. Petroleum has another 

 advantage over coal in the matter of storage room, as one ton of 

 the liquid occupies only four-fifths of the space of the same 

 weight of coal, so that the bulk of the petroleum required to 

 perform the same work in heating as one ton of average coal is 

 little more than half that of the latter. It follows that a steamer 

 constructed to carry 1000 tons of coal [could, if provided with 

 suitable tanks, carry 1200 tons of petroleum, equal in fuel value 

 to about 1900 tons of coal. In addition, the liquidity of petro- 

 leum permits it to be pumped and conveyed long distances by 

 gravitation in tubes so that its transport in bulk and in detail is 

 easy. Therefore petroleum is not only a much more concen- 

 trated fuel than coal, but it is eminently portable as well and 

 convertible with much greater facility into permanent gas. 

 Against these advantages must, however, be set the inflamma- 

 bility of petroleum, and consequent greater risk of fire. 



Now we have to consider the question of relative cost of 

 petroleum used as fuel in liquid or gaseous form as compared 

 with coal — the latter being our standard for reference as in the 

 case of peat. We have already seen that about two-thirds of a 

 ton of petroleum can do the same amount of work in heating as 

 one ton of coal ; therefore petroleum, when burned directly, 

 cannot economically replace ccal unless two-thirds of a ton of 

 the liquid can be purchased for less than the cost of one ton of 

 coal. We know the cost of ordinary lamp petroleum in these 

 islands is at present far beyond that limiting value ; even the 

 heavy oils which are not good enough for lamps, and yet are 

 too ' thin ' for lubricants, only compare favourably with coal 

 where the latter has to be carried long distances, and is therefore 

 dear. However, all practical difficulties having been overcome 

 in the use of these heavy oils for steam-raising, a comparatively 

 small advance in the general price of coal would at once render 

 them economical for industrial use as fuel. 



But when we compare petroleum gas with ordinary coal-gas 

 the comparison is much more favourable to the liquid fuel , 

 unlike coal, petroleum is already more than half-way on the 

 road to conversion into gas. As you know, one ton of coal 

 affords about 9500 cubic feet of i6-candle gas. On the other 



hand, one ton of oil of sp. gr. 0-85 can afford about 24,000 

 cubic feet of gas, having an average illuminating power of 60 

 candles, or the equivalent of about 70,000 cubic feet of 16 candle 

 value, and this rich gas admits of preparation on the small 

 scale suited to country places, while the retorts used in the pro- 

 duction of the gas can be heated by petroleum. The petroleum 

 gas of some 60 candle power is said to be producible at about 

 6j. per I003 cubic feet. If we were to assume that the calorific 

 value of the gas is directly proportional to its illuminating power 

 the cost would correspo id to about is. 7d. per 1000 cubic feet 

 of i6-candle coal-gas. But the facts do not justify the assump- 

 tion, as the calorific value of methane is known to be greater 

 than that of the heavier carbides to which the high illummating 

 power is due ; hence the comparison is probably less favourable 

 to petroleum gas by about 25 per cent., though further experi- 

 mental evidence is wanting on this point. However, even after 

 this deduction, pjtroleum gas is the cheaper fuel as well as 

 illuminant. 



The neceisiry links between the elements of the trilogy on 

 coal, peal, and petroleum are now, I think, sufficiently evident. 

 If we desire to use each fuel in such a way as to develop most 

 economically and conveniently its store of heat energy, we must 

 first partially or perfectly gasify it. The ne^ve-it m;mber of the 

 triad — petroleum — is the one which lends itself most easily and 

 completely to such treatment, in consequence of its physical 

 condition and chemical characters. It is also the material that 

 we must expect to facilitate the producion of cheap gaseous 

 fuels from coal and peat which shall at the same time possess 

 sufficient illuminating power for m >it purposes. Chemical in- 

 dustries would probalily benefit to a greater extent than others 

 by the supply of cheap fuel of the kind in que-tion ; hence I 

 have ventured to tax your patience by d>velling on this topic in 

 your presence to-day. 



SUGAR-CANE BORERS IN THE WESTINDIES. 

 A/TR. BLANDFORD'S report on suga'-cane borers, pub- 

 ■^*' lished in the Kew Bulletin for July and August last, 

 deserves more than a passing notice. 



The report contains a plate of the insects in question, which 

 will render their identification easy. 



The first is a caterpillar and moth, Chilo saccharalis ; the 

 second a weevil, Sphenophorus sacchari ; but the principal at- 

 tention in the report is paid to the shot liorer, Xylobortts per- 

 forans, a beetle which has lately caused considerable loss to 

 growers of sugar-canes in Trinidad. These losses have been so 

 large that on some estates thirty per cent, of the sugar crop has 

 been destroyed, and in some fields fifty per cent., presumedly 

 by the devastations of this beetle. 



This beetle X. perforans is to be found over a very large area 

 in the tropics ; it is the same species that has done so much 

 damage to wine and beer casks ; it has been found in India, the 

 Malay Archipelago, Madeira, Mauritius, North and Central 

 America, Brazil, Guiana, Peru, and probably in Australia, so 

 that no sugar-producing country can consider itself free from the 

 fear of its ravages. 



Mr. Blandford's report is interesting and valuable, not only 

 for the amount of information it gives relative to this most de- 

 structive insect ; but also for the way in which he points out 

 what remains still to be investigated on the subject ; so that it 

 not only furnishes valuable inlormation to the planter in the 

 West Indies, but also tells him what course his further investiga- 

 tions should take ; and it might w?ll serve as a model to future 

 observers in drawing up similar reports. 



" The chief subject for investigation," to quote Mr. Bland- 

 ford, " is the relation of the insect's attacks to the health and 

 condition of the canes, whether it (the shot borer, A', perforans) 

 is a true destroyer, or merely a follower and manifestation of 

 antecedent and more serious injury : " this question, Mr. Bland- 

 ford says, " I do not attempt to solve ; it can only be studied in 

 all its bearings by observers on the spot ; " and he further gives 

 a list of definite points which require inquiry and solution. 



There is no doubt that the presence of X. per/orans is usually 

 accompanied by the sugar-boring caterpillar, C. saccharalis, and 

 the weevil, .S". sacchari, and also with fungoid growths, which 

 may of themselves account for the acidification of the juices of 

 the cane, which is apparent in canes attacked by the shot borer ; 

 but whether or not the shot borer attacks healthy canes is a 

 question on which there is much diversity of opinion, and we 

 hope that bringing the question before our readers will lead to 



NO. 1196, VOL. 46] 



