178
JOURNAL OF CHEMICAL EDUCATION
JANUARY, 1930
A specific question comes up immediately. Is it necessary to insist on so much mathematics and physics if a student is interested in physiological or organic chemistry? If you think such problems are worth discussion I would be a most interested reader. BEN H. PETERSON CoE COLLEGE CEDAR RAPIDS, IOWA Ultra-Violet Windows Tested by Government. ]Tow to let the ultra-violet rays of thc sunliaht . through . the window into home and schoolroom was discussed by Dr. W.W. Coblentz, physicist of the U. S. Bureau of Standards a t Washington, in a report t o the Illuminating Engineering Society. He reported his tests upon various window glasses and other materials and suggested that for effective results the material should not transmit less than 45 t o 50 per cent of the ultra-violet rays in the sunlight. If only small amounts of the ultra-violet rays penetrate the windows they cannot be relied upon to effect cures of rickets, which are possible with large doses of ultraviolet rays as well as with sources of vitamin D. Dr. Coblentz quoted clinical reports that indicated that exposure of five to seven hours each day with light through glass with 25 per cent transmission would be necessary merely to prevent rickets in a normal, properly fed chid, and in view of the facts that such exposure of such lengths are not practicable, he believes that a t least 45 to 50 per cent transmission must be required in specifications. Even with this degree of transmission, the effect would he preventive only and in no sense curative. Various commercial makes of glasses: after being stabilized by exposure t o sunlight, ranged from only one-half of one per cent to 59 per cent transmission, with four out of nine greater than 40 per cent. Dr. Coblentz uped a wave length of 302 millimicrons as a division mint between the ultra-violet rays and the rest of the sunlight. ~ r a c i i gcloth, which has been suggested for window material because of a supposed trans~arencvt o ultra-violet rays, was found t o be actually no more transparent than other fabrics such as nainsook, batiste, or balloon cloth. Other studies of fabrics showed that those made of silk and wool yams compared favorably in transmission of ultraviolet light with cotton, linen, and rayon. Feathers have a fairly high transmission, apparently nature's provision for assuring chickens and other birds their supply of these vital rays. Unlacquered surfaces of metals, aluminum, nickel, and chromium, are good rdectors of ultra-violet radiation. Linseed oil and nitro-cellulose lacquer, especially after drying, are highly opaque t o ultra-violet radiation.-Science Senn'ce Survey Shows Plenty of Potash. The survey now being conducted by the United States Bureau of Mines and the U. S. Gealogid S u m y has disclosed the fact that we have in the Permian basin a sufficientreserve of potash t o make the nation independent in any future emergency such as that which arose in 1910 when German legislation voided all American potash contracts. It will be necessary t o solve certain problems of transportation, marketing, and mining engineering before the potash is available for commercial use, hut these problems are now being attacked by federal, state. and private agencies. The area in which the potash-bearing salts have been found occupies about 22 counties in Texas and New Mexico. Altogether it covers about 40,000 square milesScience Se&e
