We have so far followed, step by step, the various improvements undergone by internal furnace engines, from their first practical realization thirty-seven years ago by M. Lenoir. This improvement has continually tended, as one might naturally expect, to cheapen the cost of the motors themselves, and lessen the cost of the fuel consumption so that they might successfully compete against the steam engine, over which they have many advantages. As a rule, coal gas is pretty expensive, in some particular districts ruling as high as 4_s._ or 5_s._ per 1000 cubic feet. This price would be prohibitive were it not for the extreme economy which has been obtained in gas engines by such devices as compression and the lengthening out of the combustion. Inventors have sought to still further lessen the cost of power by replacing the expensive coal gas by other gases of lower illuminating power, produced by special gas plants attached to the engine, and which can be used in places where there is no coal gas laid on. Other engines have been devised, as we have already shown, which get over the difficulty by consuming petroleum oil or distillates of same, such as benzoline and other light hydrocarbons. Gas companies are, as a rule, heavily taxed, and if it were not for a vast amount of idle capital buried in the streets in the form of gas mains, they would probably supply gas at a very low price, especially as the sale of bye-products practically covers the cost of production. Some companies have even reduced the price of gas if used for driving gas engines, and have therefore slightly decreased the cost of production of power by this means. In France, the home of the oil motor, they are severely handicapped by having to pay double duties on all petroleum entering, first the country itself, afterwards the towns. Inventors have therefore sought a method of getting round these difficulties by producing a cheap gas, which would answer the same purpose as coal gas. First of all many manufacturers tried to cut down the expense by erecting their own coal gas plants, so as to be independent of arbitrary taxation. The system, although fairly satisfactory, had many drawbacks, and further experiments were made with a view to simplifying the process of production. The result has been to give us _water gas_ and also _poor gases_, whose great practical value we shall presently demonstrate. In order to produce what is called water gas, the process essentially consists of placing in contact with one another red-hot carbon and superheated steam. The result is to form a mixture of gases according to the following chemical equation— 3 H_{2}O + 2 C = CO + CO_{2} + 3 H_{2}.