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naval war they will probably play an important part in coast defense, and here again the advantages of alcohol over petrol would, I think, be very great. In England alcohol has practically never been experimented with as a fuel for high-speed motors, although it has been successfully adapted to slow-running engines by Messrs. Tan- gyes, this being due to the fact that all the time petrol or petroleum spirit could be obtained at ls or less per gallon, alcohol handicapped by state restrictions and duties could never come into competition with it, and for this reason only it has been experi- mentally neglected. On the continent, however, the de- sire to foster industries which would keep labor on the land has in several countries led to the encouragement rather than the hampering of the pro- duction of alcohol for industrial uses, and in Germany and France the use of alcohol for motors was made a commercial success, and many hun- dred vehicles employing alcohol as a fuel were in constant use. The alco- hol used in these was made from po- tatoes, and in 1902 and 1903 its price was about 8d to 9d per gallon, and in Germany, there being a tax on pe- trol, it was cheaper to use the potato spirit; the failure of the crop in 1904, however, caused a rise in price to Is 1d per gallon, with the consequence that the economic advantages disappeared, and with them alcohol as a fuel. In England petrol is free fsom any import tax, whilst alcohol is _ so hedged around with legislative precau- tions that the methylated, or some prefer to call it, "denatured," spirit al- lowed to be sold duty free for indus- trial purposes costs 2s per gallon, so that, although the price of petrol is rapidly rising, alcohol is unlikely to be employed generally in the place of petrol for a long time to come. These considerations, however, do not enter into the question I am now raising, as any extra safety we can give in the submarine is far more im- portant than any question of cost, and it must be remembered that alcohol is a native product, while in the event of a long war we might find ourselves considerably hampered by the failure of the petrol supply, and it appears to me that, if the feasibility of using alcohol as effectively as petrol can be shown, nothing should stand in the way of its adoption. In comparing the relative values of petroleum spirit and alcohol, the first point that must be taken into consid- eration is their thermal value, and in doing this.with alcohol it is only the TAE Marine REVIEW methylated spirit which need be con- sidered. Taking samples spirit, having a 0.722, as representing the petrol, de- terminations were made of its thermal value, with the following results: of Pratt's motor Calories. British Thermal Units. Gross. Net. Gross. Net. (a) 11,514.6 10,818.6 20,726.3- 19,473.5 (b) 11,146.9 10,624.9 20,064.4 19,124.8 (c) 11,174.4 10,742.4 20,113.9 19,336.3 Aver..11,278.6 10,728.6 20,301.5 19,311.5 In the same way samples of com- mercial methylated spirit gave: Calories. Gross. Net. Gross. Net. (a) 6,491.5 6,011.5 11,684.7 10,820.7 (b) 6,089.0 5,489.0 10,960.0 9,880.2 (c) 6,285.0 5,805.0 11,313.0 10,449.0 Aver.. 6,288.5 5,768.5 11,319.2 11,383.3 It is evident, therefore, that, weight for weight, alcohol has not much more than half the califoric value of the petrol, whilst by volume the heat of combustion of the vapors would stand to each other as follows: Pe- trol, 50.8 calories per c. c. of vapor. Alcohol, 14.8 calories per c. c. of va- por. So that, if thermal value were the measure of the value of liquid and gaseous fuels in the internal-combus- tion engine, alcohol would have a very poor chance of ever competing with petrol. There are many factors, however, which play an important part in determining the percentage of thermal value which can be converted into power, such as the degree of compression that can be employed without fear of premature ignition, the amount of air needed to produce com- plete combustion, the rate at which the vapor diffuses through the air cre- ating a uniform mixture, the range over which the mixture is explosive, the possibility of keeping down the cylinder temperature, and other, but little studied points. It so happens that nearly all these are in favor of alcohol, the use of which enables a higher compression, a cool cycle in the engine, the use of a moderate volume of air, and a greatly-increased range of explosibility of the mixture of alcohol vapor and air, this resulting in making alcohol nearly as effective a fuel as petrol. Experiments were made in Vienna at the time of the last exhibition there upon two 8 H. P. engines, one de- signed for petrol and the other for alcohol, and the following results were obtained: Petrol, 340 grams per brake horsepower hour; alcohol, 373.5 grams per brake horsepower hour, the ef- ficiency calculated for the petrol be- ing 16.5 per cent, and for the alcohol 28 per cent; while M. Cheveau, work- ing with a 16 H. P. motor running at 180 revolutions, obtained with alcohol an efficiency of 38 per cent. The chief specific gravity of British Thermal Units. ; causes of the higher efficiency of the alcohol are: (1) Compression; (2) amount of air needed for combus- tion; (3) increased range over which mixture is explosive. Compression--It is well known that in the gas or vapor engine efficiency increases with increase of compres- sion, and that using petrol as a fuel it is inadvisable to use a compres- sion greater than 90 Ibs., while with alcohol 150 lbs. to 200 lbs. can be employed. Amount of air needed for combus- tion--As air only contains 20.9 per cent of its volume of oxygen, a va- por which needs a large proportion of air wastes heat by having to raise the temperature of a larger volume of in- ert gas (nitrogen and products of combustion) than is the case with a vapor requiring a smaller proportion. Petrol, theoretically, requires for each volume of vapor 45.5 volumes of air to give the necessary oxygen to com- plete combustion and give the high- est explosive power, and this means that there should be 2.5 per cent of petrol vapor in the gaseous mixture entering the cylinders; if there be less, the mixture is weaker in explo- sive power, and there is a _ large amount of inert products and residual nitrogen to carry off the heat; if there be more, incomplete combustion is the result, and the delicate aroma of the motor is at once recognized. In order to avoid incomplete com- bustion an excess of air is mostly supplied, so that generally one and one-half times the theoretical propor- tion of air is admitted, and each vol- ume of petrol is diluted with about 68 times its own volume of air, four- fifths of which is inert nitrogen tak- ing no part in the action, but so hin- dering the combustion by dilution that the mixture would not burn at atmospheric pressure, and only be- comes explosive under compression. With alcohol, however, one volume of the vapor will only require 14.3 volumes of air, or about one-third the volume needed by the petrol, and it is much easier with the smaller pro- portion to get a good mixture, espe- cially as the degree of compression can be so much increased. <s When a mixture of petrol vapor and air is made at atmospheric pres- sure and a light is applied to the mix- ture, it will just burn when there is 1.25 per cent of the vapor present, and the combustion increases in vigor un- til it reaches its maximum power with 2.5 per cent, and after that the ex- plosion gets weaker with increase of vapor, until when there is 5.3 per cent it is non-explosive.