Water Gas.
—When the vapor of water is brought into contact with incandescent carbon, the water is decomposed and sufficient carbon is absorbed to produce a fuel gas. Its manufacture depends on the decomposition that takes place when steam is blown into a bed of incandescent coal. The gas made by this reaction is a water gas, but due to the fact that when burned it gives a blue flame, it is known as “blue gas.” It has a heating value of about 300 B.t.u. per cubic foot, and as compared with coal gas which gives 622 B.t.u. per cubic foot, would be reckoned at about one-half its value as a heating agent. Blue gas may be rendered luminous by the addition of some hydrocarbon that will liberate free carbon in the flame when burned. This is accomplished in the process of manufacture by the addition of vaporized oil.
The following table as stated by Fulweiler gives the heating values of the gases commonly used for domestic purposes in British thermal units per cubic foot.
| Coal gas. | 622 B.t.u. |
| Carburetted water gas | 643 B.t.u. |
| Pintsch gas. | 1,276 B.t.u. |
| Blau gas. | 1,704 B.t.u. |
| All-oil water gas | 680 B.t.u. |
| Acetylene gas | 1,350 B.t.u. |
| Gasoline gas. | 514 B.t.u. |
| Oil gas | 1,320 B.t.u. |
| Blue water gas | 300 B.t.u. |
The cost and calorific values as computed by Dr. Willard of the State Agricultural College of Kansas, given below, shows the relative values of various kinds of domestic fuels.
| Cost per pound cents | Cal. per Gram | Cal. for 1 cent | ||
| Wood, 20 per cent. H.O. | $ 5.00 per cord | 0.167 | 2.3 | 7,620 |
| Bitu. coal | $ 4.25 per ton. | 0.213 | 7.5 | 16,009 |
| Ant. coal | $12.50 per ton | 0.625 | 6.0 | 4,354 |
| Gasoline, sp. gr. 68 | $ 0.14 per gallon, 5⅔ pounds. | 2.470 | 10.0 | 1,846 |
| Kerosene, sp. gr. 80 | $ 0.11 per gallon, 6⅔ pounds. | 1.650 | 10.0 | 2,753 |
| Coal gas, 1.50 per 1000 cubic feet. | 3.100 | 20.0 | 2,927 | |
| Alcohol, 90 per cent., 50 per gallon, 7 pounds | 7.140 | 6.4 | 404 | |
| Electricity, 0.15 per kilowatt-hour | 57.4 | |||
The relatively high heat value of Blau gas (1704 B.t.u.) and the fact that it may be reduced to a liquid form for transportation has resulted in the manufacture of small lighting plants that may be used in places where other forms of liquid or gaseous fuel are not desirable.
For transportation the gas is compressed in seamless, steel bottles that contain about 20 pounds of liquid. The charged bottles are shipped to the consumer and when empty are returned to the manufacturers to be refilled.
The entire plant—ready to be attached to the distributing pipes in the house—is contained in a steel cabinet. The charged tanks are attached to a larger tank into which the liquid gas is first expanded. This expansion is accomplished by an automatic valve that maintains a constant pressure in the large tank. With this plant the lamps and burners of the stoves are operated as with city gas—no generating or preliminary preparation being necessary. As soon as the bottles are exhausted they are replaced by others and the empty bottles are shipped to the factory to be refilled.