A Simple Method for Detecting Cracks in Porcelain Crucibles Porcelain crucibles are frequently used in chemistry laboratories for igniting precipitates and heating small quantities of solids because of their low cost and their ability to withstand high temperatures without appreciable change in mass. Porcelain erueihles, when handled carefully, should last through many heat-cool cycles. However, even students with the best of intentions seem to shorten the expected lifetime of crucibles drastically. A number of crucibles end their lives in many pieces on the laboratory floor. Although frustratiug to the student, helshe usually has no one to blame hut himself1 herself. An equal number of crucibles seem to "self-destruct" while being heated. To the student this can be very frustratiug because, experimentally at least, nothing has been done wrong. Many of these latter breakages could have been eliminated h s checking the crucibles for cracks before use. To check a crucible. lace it on a hard. flat surface. hold a stirrine rod in a vertical oosition. and liehtlv .. , tan the uooer lip of the crucible with t h b end c.1 thestirring md. lf thirrurihle resphds w ~ t ha'.ping,:'thr i.rut.il,le isnot cmrked. If the h that ~.rucihlris cracktd. the sound IS a dull thud. This method, however, is not fuc,lpnwf. Owasiunally crucibles w ~ cracks arp rtftrwd to as"Crand Canyons" respond with a 'ping:" hwever, rartful wsual inspection should easily detect these.
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Jack F. McKenna St. Cloud State University St. Cloud, MN 56301
Volume 61
Number 9
Se~tember1984
817
