The extended use of gasoline as a lighting and heating agent, has brought about the development of a great number of mechanical devices that are intended to furnish the house with an efficient source of illumination and at the same time provide the kitchen with a convenient and relatively inexpensive fuel. These machines are generally simple in mechanical construction and so designed as to eliminate most of the dangers involved in the use of gasoline. In operation, they require a minimum amount of attention when suited to the purpose for which they are intended. That the object of the plants is attained is attested by the great number in use and the degree of satisfaction afforded the users. The three systems of gasoline lighting referred to above are known commercially by terms which are characteristic of the process involved: 1. The _cold-process_ system, in which the gasoline is vaporized, at the temperature of an underground supply tank, and after being mixed with the required amount of air is sent through the building in ordinary gas pipes exactly as in the case of city gas. 2. The _hollow-wire_ system, in which the gasoline is sent from the supply tank to the burners in a liquid form, where it is vaporized by heat and the vapor mixed with the necessary air to afford complete combustion. 3. The _central-generator_ or _tube_ system, in which the gasoline is sent to a central generator from a supply tank and there vaporized by heat, at the same time being mixed with air in sufficient amounts to render it a completely combustible gas without further dilution. THE COLD-PROCESS GAS MACHINE The gas machine of the cold-process type is so constructed that air is forced through a tank or carburetor, containing gasoline and remains in its presence until saturated with gasoline vapor. This saturated air is afterward diluted with additional air, to produce a quality of gas that contains proportions of air and gasoline vapor which will produce complete combustion when burned with an open flame. Combustion is a rapid chemical change in which heat is evolved due to the union of carbon and oxygen. If the carbon is completely oxidized, the combination produces carbon dioxide (CO₂) and the greatest amount of heat is evolved.