SINTERED PYREX GLASS AERATORS

Sintered glass aerators have been found to be of great value in water culture experiments. A few years ago PLANT PHYSIOLOGY carried a paper on sintered pyrex glass aerators.' This paper, however, did not treat of the actual steps involved in the making of the aerators. The present paper describes a technique for the rapid and economical production of such aerators. A sintered glass aerator is essentially a baked disk of fine glass particles, having suffikient porosity to allow the passage of fine air bubbles; this disk when sealed into a tube constitutes a complete aerator. The first requirement in the production of an aerator is a quantity of pyrex glass particles of minute size and uniformity, free from impurities. A porcelain ball mill with quartz pebbles will reduce pyrex glass scraps to a fine size when rotated rapidly for a few hours. Particles of uniform size may then be obtained by means of an elutriator, as used by FURNSTAL and JOHNSON,' or by sifting through a wire screen, or a piece of silk bolting cloth. By the use of two pieces of cloth, one of 125 mesh per inch and one of 173 mesh per inch, a suitable size may be obtained. By rejecting all particles that do not pass through the larger mesh, and all that pass through the smaller mesh, an appropriate range is obtained. After washing with distilled water and drying, the ground glass is then poured into nickel rings (solid nickel) set on a plate of pure nickel, and the whole baked in a muffle furnace at a temperature of. about 780° C. for about 20 minutes. If the furnace is not provided with a thermometer, the temperature may be estimated by observing the color of the heated interior; after a little experience one may safely trust this empirical method. By using a nickel ring cut from tubing of relatively small diameter, 14 mm., a greater number of disks may be accommodated at one time. There are two ways of assembling the component parts of the aerator, one method requiring special skill in the art of glass blowing; the other, requiring no special skill, yields a product of less presentable appearance, but equally as good in point of service. In the first method, a short piece of tubing is selected, an 8to 10-cm. length with an inside diameter about 1 mm. less than the diameter of the sintered disk which is to be sealed in. This difference in diameter is important in facilitating rapid production in the disk-sealing phase. To each end