ceptacles to be filled, but fires to be enkindled." I do not recall who made this statement, but I am very anxious to get the original reference. If you can obtain same for me, I will greatly appreciate the cooperation.
Opticians Told of New "Artificial Sunlight." A method of changing the light from a nitrogen-filled incandescent lamp to the same color as that from the noonday sun, without the use of dyed filters, colored glass or solutions, or any of the usual devices, w a s described t o the members of the Optical Society of America by Dr. Irwin G. Priest, of the U. S. Bureau of Standards a t Washingan. Dr. Priest's apparatus was designed in order to permit "artificial sunlight," important in many industries which require accurate color matching, t o be standardized. It depends on the use of polarized light, which is light made to vibrate in one direction, instead of promiscuously, like ordinary light, by what the physicist calls a Nicol prism. If a beam of polarized light is allowed to fall on another such prism parallel t o the &st, it will pass through. If the two are a t right angles. however, the beam will not pass through unless some material is placed between them which has the power of rotating the plane of vibration. Quartz or "rock crystal" has this power, but does not rotate all colors t o the same extent. By arranging the quartz plate and the prisms properly, the apparatus will appear blue if one looks through it. If light from an incandescent lamp is passed through. i t will be converted into a light closely resembling daylight. As no actual colors are present in the system used t o filter the light, there is nothing t o fade, and it can be accurately standardized, said Dr. Priest.-Science Scnrice Sewage to Yield Valuable Gas Fuel. Cities of the future will have their gas works located near their plants for the disposal of sewage wastes, and scientific thrifts will recover for fuel a useful gas now wasted into the air. Light and heat from the gas obtained as a by-product in the treatment of sewage is a practicable possibility, according to the report made by the Illinois State Water Survey t o the Board of Natural Resources and Conservation of that state. Experiments conducted by the Survey indicate that in a city of fifty thousand inhabitants the quantity of combustible gas given off each day by the sewage in the treatment tanks is more than ninety thousand cubic feet. This gas contains 70 per cent methane, the chief combustible constituent of natural gas, and has a heating value equivalent t o 700 British thermal units per cubic foot, while the value of the common fuel gas is 550 to 600 units. The other constituents of the gas, carbon dioxide and nitrogen, are inert, and the gas itself has no more odor than ordinary fuel gas. The gas is produced in the digestion process which the sewage liquor undergoes in the Imhoff treatment tanks, and formerly escaped into the air. It has been known for a number of years that this product will hum readily, but city officials and sewage plant operators hive not heretofore realized the gross value of the gas that gws to waste each day. The Illinois State Water Survey, with funds assigned by the Chemical Foundation, is experimenting with the collection and utilization of this gas and is developing a new type of treatment tank which is designed t o give the maximum yields of gas.-Sc
