Gas making has probably been the most extensive and important of all the commercial chemical operations of the Nineteenth Century, and with it has come a great array of minor inventions as accessories. Among these first came the gas meter and pressure regulator. With the introduction of gas into houses some means of determining the amount consumed as a basis of payment was required, and for this purpose the gas meter was devised. The first gas meters were known as wet meters, and effected a measurement by passing the gas through a liquid and rotating a wheel therein. The wet meter was invented by Clegg (British patent No. 3,968, of 1815), and the dry meter, by Malam (British patent No. 4,458, of 1820), and improved by Defries (British patent. No. 7,705, of 1838). The gas regulator is simply a little automatic apparatus whereby the variation of pressure in the gas main is reduced and the flow rendered perfectly uniform at the burner. It effects a saving of gas by preventing it from blowing when the pressure is too great, and also gives a more steady and uniform light. Among the great number of mechanical devices which have grown out of the use of gas may be mentioned the gas range for heat, the gas engine for power, and the Welsbach burner for light. The gas range has contributed much to the domestic economy of the city house. It gives an immediate heat in the kitchen for all culinary and domestic purposes, without the incidental objections of having to transport fuel and remove ashes. It is put into or out of action in an instant, saves labor and time, and avoids the heat and discomfort of a coal stove during the hot months of summer. It is organized in principle after the Bunsen burner, whereby a perfect combustion of the carbon is obtained with maximum heating effect and without smoke or deposits of lampblack. [Illustration: FIG. 226.--OTTO GAS ENGINE.] The Otto gas engine, seen in Fig. 226, is a pioneer and representative type of a great number of explosive gas engines, which in recent years have become active competitors of the steam engine where only small power is required. The Otto engine is covered by patent No. 194,047, August 14, 1877. Patents No. 222,467, 297,329, 336,505, 358,796, 320,285, 386,211 and 549,160 represent important developments in this art. [Illustration: FIG. 227.--WELSBACH GAS BURNER.]