The finale of the weekly physics department seminar series at my college is my annual demonstration lecture. Normally, the front of the room is filled with apparatus, but in May 2008 I had only a giant kaleidoscope and a leaning tower of Pisa (Fig. 1) on display. Instead, there was a pile of overhead projector transparencies that showed examples…

Describes a lecture teaching technique called lap-dissolve projection in which two slide projectors are operated alternately so that one visual image fades away while the next appears on the same screen area. (MLH)

Discusses the use of lap-dissolve projection to give students pre-laboratory instruction on an upcoming experiment. In this technique, two slide projectors are operated alternately so that one visual image fades away while the next appears on the same screen area. (MLH)

The construction and uses of a device to facilitate the use of an overhead projector to show chemical reactions is presented. Materials and instructions for construction as well as reactor vessels are discussed. (CW)

Provides two demonstrations: (1) electrolyte migration of ions using colored ions which cross a strip of gelatin allowing for noticeable migration; and (2) photochemical reduction of Fe+3 by the citrate ion. Points out both reactions can be done in a Petri dish using common lab materials. (MVL)