A Laboratory Hand Book JUST ISSUED CAMBOSCO Chemical Catalog, 94. The most complete and most usable Chemical Catalog in the trade. DESIGNED for your Laboratory Hand Book. An aid in teaching as well as most convenient in the preparation of lists and orders. ratus. CONSULT Chem. Cat. 94 whenever you are in need of appa A WORD ABOUT GLASSWARE. WAVERLEY GLASS is Made-in-America. It is a genuine. Boro-Silicate Glass with an extremely low coefficient of expansion and a maximum resistance to sudden changes of temperature and a maximum chemical stability. WAVERLEY GLASS has a minimum solubility in acids and alkalies. It is adequately suited to technical work and has met with the highest approbation of the chemist. WAVERLEY GLASS has had a long and severe testing in actual service and stands on a par with the highest grade of chemical glass ever produced. (See Cat. 94, pp. 31-68.) THE CAMBOSCO uses this Adv. to ask you to write for 94 Cambridge Botanical Supply Company LABORATORY EQUIPMENT-ALL SCIENCES 1-9 Lexington Street 1884-1918 Waverley, Mass. IOWA ACADEMY OF SCIENCE. President, S. W. Beyer, Iowa State College, Ames; First Vice-President, T. C. Stephens, Morningside College, Sioux City; Second Vice-President, R. Monroe McKenzie, Parsons College, Fairfield; Secretary, James H. Lees, Iowa Geological Survey, Des Moines; Treasurer, A. O. Thomas, State University, Iowa City.-318. IOWA ASSOCIATION OF MATHEMATICS TEACHERS. President, E. E. Watson, Parsons College, Fairfield, Iowa; Vice-President, Maria M. Roberts, Iowa State College, Ames, Iowa; SecretaryTreasurer, Ira S. Condit, Iowa State Teachers College, Cedar Falls, Iowa.-118. IOWA ASSOCIATION OF SCIENCE TEACHERS. President, F. E. Goodell, University High School, Iowa City, Iowa; VicePresident, F. W. Berninghausen, Superintendent, Pocahontas; SecretaryTreasurer, Frances Church, East High School, Des Moines; Section Leaders: Chemistry, Charles A. Mann, Iowa State College, Ames; First-Year Science, H. E. Ewing, Iowa State College, Ames; Physics, H. L. Dodge, State University, Iowa City.-118. KANSAS ASSOCIATION OF MATHEMATICS TEACHERS.` President, T. E. Mergendahl, College of Emporia, Emporia, Kan.; Vice-President, Miss Eleanora Harris, Hutchinson, Kan.; SecretaryTreasurer, J. A. G. Shirk, State Manual Training Normal, Pittsburg, Kan.-118. ILLINOIS ACADEMY OF SCIENCE. President, Rollin D. Salisbury, University of Chicago; Vice-President, Secretary, J. L. Prices, State Normal University, Normal; Treasurer, T. L. Hankinson, Normal School, Charleston. MATHEMATICAL ASSOCIATION OF AMERICA. President, E. V. Huntington, Harvard University; Vice-Presidents, D. N. Lehmer, University of California, and J. W. Young, Dartmouth College; Secretary-Treasurer, W. D. Cairns, Oberlin College; additional members of the Council to serve until January, 1921: Florian Cajori, Colorado College; Elizabeth B. Cowley, Vassar College; G. A. Miller, University of Illinois; E. J. Wilczynski, University of Chicago. MATHEMATICS TEACHERS ASSOCIATION OF RHODE ISLAND. President, Alden E. Hodgkins, Technical High School, Providence; Vice-President, Henry K. Sears, Hope St. High School, Providence; Secretary-Treasurer, Professor Clinton H. Currier, Brown University, Providence.--118. MISSOURI SOCIETY OF TEACHERS OF MATHEMATICS AND SCIENCE. President, O. M. Stewart, Columbia; Secretary, B. F. Finkel, Springfield; Treasurer, A. J. Schwartz, St. Louis. Mathematics Division: Vice-President, Wm. A. Luby, Kansas City; Secretary, Miss Eula A. Weeks, St. Louis. Science Division: Vice-President, H. L. Roberts, Cape Girardeau; Secretary, Miss Loula VanNeman, Kansas City.-118. NATIONAL EDUCATION ASSOCIATION. President, Mary C. C. Bradford, Denver, Colo.; Secretary, J. W. Crabtree, Washington, D. C.; Treasurer, A. J. Mathews, Tempe, Arizona. NEW ENGLAND ASSOCIATION OF CHEMISTRY TEACHERS. President, George A. Cowen, West Roxbury High School, Jamaica Plain, Mass.; Vice-President, William W. Obear, High School, Somerville, Mass.; Curator, Lyman C. Newell, Boston University, Boston, Mass.; Secretary, S. Walter Hoyt, Mechanic Arts High School, Boston, Mass.; Treasurer, Alfred M. Butler, High School of Practical Arts, Boston, Mass.-118. NEW JERSEY SCIENCE TEACHERS' ASSOCIATION. President, Earl Eastman, Atlantic City High School, Atlantic City; Vice-President, Merton C. Leonard, Dickinson High School, Jersey City; Secretary-Treasurer, Raymond S. Blodgett, Caldwell High School, Caldwell; members of Executive Committee: Dr. Melville T. Cook, Rutgers College, New Brunswick; Miss Agnes V. Luther, State Normal School, Newark; H. Morgan Campbell, Bayonne; Section Chairmen: AgricultureBiology, Dr. C. H. Robison, State Normal School, Montclair; Chemistry, Charles E. Dull, South Side High School, Newark; Elementary Science, Miss Caroline G. Howe, South Side High School, Newark; Physics, E. R. Vactor, West Hoboken High School, West Hoboken.-118. NEW YORK STATE SCIENCE TEACHERS' ASSOCIATION. President, H. A. Carpenter, 1736 Church St., Washington, D. C.; Vice-President, M. C. Collister, 2303 Sunset Ave., Utica, N. Y.; SecretaryTreasurer, E. E. Ford, West High School, Rochester, N. Y.; Council members: Prof. R. C. Gibbs, Cornell University, Ithaca, N. Y.; C. Caulkins, Elmira, N. Y.; Edward L. Long, High School, Saugerties, N. Y.; Chairman of the Physics and Chemistry Section, R. A. Crumb, High School, Binghamton, N. Y.; Chairman_of_the_Biology Section, Mrs. Roberta Parke, Masten Park High School, Buffalo, N. Y.; Chairman of the Earth Science Section, Melvin E. Coon, West High School, Rochester, N. Y. -1117. OHIO ASSOCIATION OF TEACHERS OF MATHEMATICS AND SCIENCE. President, J. D. Boldt, Stivers High School, Dayton; Vice-President, Prof. William Holt, State Normal, Bowling Green, Ohio; SecretaryTreasurer, H. M. Beatty, Columbus, Ohio.-118. THE PHYSICS CLUB OF NEW YORK. President, Roland H. Williams, Horace Mann School for Boys, New York; Vice-President, Fred F. Good, Teachers' College, New York; Secretary, Arthur L. Yoder, Richmond Hill High School, New York; Treasurer, John O. Scudder, Morris High School, New York.-118. SOUTHERN CALIFORNIA SCIENCE AND MATHEMATICS ASSOCIATION. President, Agnes Wolcott, High School, Long Beach; Vice-President E. E. Chandler, Occidental College; Secretary-Treasurer, Harriet S. King, High School, Pasadena.-118. WASHINGTON ACADEMY OF SCIENCES. President, Lyman J. Briggs, of the Bureau of Plant Industry; Corresponding Secretary, Robert B. Sosman, of the Geophysical Laboratory; Recording Secretary, W. R. Maxon, of the National Museum; Treasurer, William Bowie, of the Coast and Geodetic Survey. Hawkes, Luby, and Touton Algebras have come to have significant meaning in school mathematics They fix one algebraic idea in the pupil's mind before a new one is introduced. They make the subject really interesting and help, through their portraits and historical notes, to bring out the human side of the subject. They give pupils a firm grasp of the processes of algebra. They introduce the equation early and frequently. They develop factoring gradually. They furnish the pupil systematically with methods of checking results. They grade exercises and problems carefully, and correlate algebra with arithmetic, geometry, and physics. Caldwell and Eikenberry's General Science (Revised) Recent important scientific discoveries are responsible for this revised edition, which follows the same excellent style and form that made the first edition so widely popular. In addition, there has been a thorough rewriting of the text; new chapters have been added on electricity; a set of important application problems for each chapter; and much new material on household industries and art. $1.28. GINN AND COMPANY Boston New York Chicago London Atlanta Dallas Columbus San Francisco EDUCATIONAL PRESS ASSOCIATION OF AMERICA President, Henry G. Williams, Columbus Ohio; Vice-President, H. R. Pettingill, Lansing, Michigan; Secretary, G. L. Towne, Lincoln, Nebraska; Treasurer, S. Y. Gillan, Milwaukee, Wisconsin; Executive Committee: O. T. Corson, Columbus, Ohio; H. T. Musselman, Dallas, Texas. Members. American Education, Albany, N. Y., C. W. Blessing, Editor; American School Herald Columbus, Teacher, Columbus, Dr. Henry G. Williams, Editor; Oklahoma City, Mrs. Sibyl Dunn Warden, Editor; Pennsylvania School Journal, Lancaster, Dr. N. C. Shaeffer, Editor; Popular Educator, Boston, Mass.; Primary Education, Boston, Mass.; School and Home Education, Bloomington, Ill., Geo. Brown, Editor; School Bulletin, Syracuse, N. Y., S. Y. Bardeen, Editor; School Century, Oak Park, Ill., Geo. W. Jones, Editor; School News, Taylorville, Ill., L. L. Parker, Editor; School Science and Mathematics, Chicago, Charles H. Smith, Editor; Sierra Educational News, San Francisco, Cal., Dr. Arthur Chamberlain, Editor; Southern School Journal, Lexington, Ky., R. S. Eubank, Editor; Teachers' Monograph, Jamaica, N. Y.; Texas School Journal, Dallas Texas, H. T. Musselman, Editor; Southern School Work, Alexandria, La. C. R. Reagan, Editor; Utah Educational Review, Salt Lake City, H. R. Driggs, Editor; Western Teacher, Milwaukee, Wisconsin, S. Y. Gillan, Editor; Wisconsin Journal of Education, Madison, W. N. Parker, Editor. RADIUM LUMINOUS COMPOUNDS. The use of radium luminous compounds has only recently been recognized in connection with commercial apparatus, but is now widely known through the enormous sale of watches and clocks with "radium dials." It was as recent as 1910 that Marsden made the first measurements of the brilliancy of zinc sulphide under the action of the radiations from radium products, but it was not until several years later that advantage was taken of this fact to make instruments which must be read at night, self-luminous. Radium luminous compounds consist almost exclusively of specially prepared zinc sulphide, with which is mixed about four parts per 10,000 of radium bromide or its equivalent in gamma ray activity. To apply the paint, in practice, the powdered material is mixed with a minimum possible quantity of varnish or other suitable binding material, and laid on either with a brush or by filling in the figuring which has been engraved into the surface of the object to be painted. The luminosity of the material is due to the action of a particles from the radium impinging on the crystals of zinc sulphide. The light is of a decidedly greenish hue and in the visible region lies between λ =5,920 and λ = 4,250, with a fairly sharp edge toward the red. The degree of brightness is of the order of 10 microcandles per square centimeter, or .03 equivalent foot-candles.1 This is about one-hundredth of the brightness of a newspaper satisfactorily illuminated for comfortable reading by artificial light. It is of the order of the brightness of white paper illuminated by the light of the full moon. The luminosity of radium compounds falls off with time. The radium itself decays to half its value in about 2,000 years, and it has sometimes been assumed that radium paint will retain its luminosity for a similar period. But this is not the case, for decay is mainly due to action on the zinc sulphide itself, which loses its power to luminesce in the course of time. In general, the material attains a maximum brightness in ten to twenty days after mixing. The intensity then falls off gradually and probably becomes almost constant after a couple of years. Thus we may conclude that a watch dial which is satisfactorily brilliant after a year or two will continue to remain so. When the material is applied as paint the rate of decay of luminosity is noticeably lower than that of the compound before application, and the initial luminosity is also smaller, being of the order of one-third to onefourth of that of the compound before application. The reason for this is not clear, but it seems reasonable to suppose that the effect of the varnish or other medium is to impede the activity of the a= ray bombardment from the radium, and in this way cause an effective lowering of the radium content of the compound with a subsequent reduction of both the initial luminosity and also the rate of decay. απ The initial brightness is in the ratio of the radium content, but the rate of decay of the compound of smaller content is slower, so that the ratio of the luminosities gradually approaches unity as time goes on. This question is of considerable commercial importance, for it is clear that if the compound is required for use after the lapse of several years, there is very little advantage, except from the point of view of initial brightness, in increasing the radium content beyond a certain point. For painted dials the maximum useful content for a life of over six months will not be more than .6 mg. per gram, and the minimum useful content about .2 mg. per gram. The factor of cost cannot be ignored for a compound containing .4 mg. of radium per gram of zinc sulphide costs about $30 to $35 per gram. This is mainly due to the amount of radium present. This unit is the brightness of a perfectly diffusing surface with a coefficient of reflection of 100 per cent when illuminated to an intensity of a one foot candle, i.e., by a source of one candle placed one foot away. |