The efficiency of an alcohol engine may be assumed at this time to be unknown, but as alcohol can be burned in engines designed for gasolene, it may be assumed that such an engine will have with alcohol fuel the same thermal efficiency as with gasolene, 19 per cent, for fair working conditions.

From the above brief discussion of the efficiency of different methods of power generation from different fuels it appears that quite a range is possible, though not so great a range as exists in the case of cost of fuel energy. Efficiency is seen to lie, somewhere between 2 1/2 and 20 per cent for all the fuels under working conditions. It is known that actual thermal efficiency under bad conditions may be less than 1 per cent, and under the best; conditions as high as 40 per cent, but these are rare and unusual cases. The range given is sufficient to indicate that a highly efficient method may make the fuel cost per unit of power less with quite expensive fuel than it would be with cheaper fuel usel in a less efficient machine. It is also perfectly clear that without proper information on the efficiency of the machine or the efficiency of the plant it is impossible to tell what the cost of fuel per horse-power will be, even though the price of the fuel per ton or per gallon be known.

The following conclusions regarding the use of alcohol as fuel for engines as compared with gasolene are based on the preliminary results of the department's experiments, upon results of the European experiments and investigations which have been presented in the foregoing pages, and upon the general knowledge of the author:

(1) Any engine on the American market to-day, operating with gasolene or kerosene, can operate with alcohol fuel without any structural change whatever with proper manipulation.

(2) Alcohol contains approximately 0.6 of the heating value of gasolene, by weight, and in the department's experiments a small engine required 1.8 times as much alcohol as gasolene per horse-power hour. This corresponds very closely with the relatve heating value of the fuels, indicating practically the same thermal efficiency With the two when vaporization is complete.

(3) In some cases carburetors designed for gasolene do not vaporize all the alcohol suplied, and in such cases the excess of alcohol consumed is greater than indicated above.

(4) The absolute excess of alcohol consumed over gasolene or kerosene will be reduced by such changes as will increase the thermal efficiency of the engine.

(5) The thermal efficiency of these engines can be improved when they are to be operated by alcohol, first by altering the construction of the carbureter to accomplish complete vaporization, and second, by increasing the compression very materially.

(6) An engine designed for gasolene or kerosene can, without any material alterations to adapt it to alcohol, give slightly more power (about ten per cent.) than when operated with gasolene or kerosene, but this increase is at the expense of greater consumption of fuel. By alterations designed to adapt the engine to new fuel this excess of power may be increased to about twenty per cent.

(7) Because of the increased output without corresponding increase in size, alcohol engines should sell for less per horse-power than gasolene or kerosene engines of the same class.

(8) The different designs of gasolene or kerosene engines are not equally well adapted to the burning of alcohol, though all may burn it with a fair degree . of success.

(9) Storage of alcohol and its use in engines is much less dangerous than that of gasolene, as well as being decidedly more pleasant.

(10 The exhaust from an alcohol engines is less likely to be offensive than the exhaust from a gasolene or kerosene engine, although there will be some odor due to lubricating oil and imperfect combustion, if the engine is not skilfully operated.

(11) It requires no more skill to operate an alcohol engine than one intended for gasolene or kerosene.

(12) There is no reason to suppose that the cost or repairs and lubrication will be any greater for an alcohol engine than for one built for gasolene or kerosene.

(13) There seems to be no tendency for the interior of an alcohol engine to become sooty, as is the case with gasolene and kerosene.

(14) With proper manipulation, there seems to be no undue corrosion of the interior due to the use of alcohol.

(15) The fact that the exhaust from the alcohol engine is not as hot as that from gasolene and kerosene engines seems to indicate that there will be less clanger from fire, less offense in a rom traversed by the exhaust pipe, and less possibility of burning the lubricating oil. This later point is also borne out by the fact that the exhaust shows less smokiness.

(16) In localities where there is a supply of cheap raw material for the manufacture of denatured alcohol, and which are at the same time remote from the source of supply of gasolene, alcohol may immediately compete with gasolene as a fuel for engines.

(17) If, as time goes on, kerosene and its distillates become scarcer and dearer by reason of exhaustion of natural deposits, the alcohol engine will become a stronger and stronger competitor, with a possibility that in time it may entirely suplant the kerosene and gasolene engines.

(18) By reason of its greater safety and its adaptability to the work, alcohol should immediately supplant gasolene for use in boats.

(19) By reason of cleanliness in handling the fuel, increased safety in fuel storage, and less offensiveness in the exhaust, alcohol engines will, in part, displace gasolene engines for automobile work, but only when cost of fuel for operation is a subordinate consideration. In this field it is impossible to conveniently increase the compression because of starting difficulties, so that the efficiency can not be improved as conveniently as in other types of engines.

(20) In most localities it is unlikely that alcohol power will be cheaper or as cheap as gasolene power for some time to come.