Inexpensive, low-density polyethylene tubing has physical characteristics about midway between glass and rubber. For many laboratory uses it may be superior to both. (BB)

An easily constructed apparatus that models the effect of penicillin on the structure of bacterial cells is described. Background information and procedures for using the apparatus during a classroom demonstration are included. (JN)

A relatively simple opto-electronic setup is described that utilizes a cadmium sulphide (CdS) photoconductive cell to detect resonance of a stretched vibrating string or wire. The display may be either an oscilloscope or a frequency counter. Also describes an inexpensive socket for flanged-base light bulbs. (JN)

A high-impedance comparator suitable for monitoring the resistivity of a deionized or distilled water line supplying water in the 50 Kohm/cm-2 Mohm/cm range is described. Includes information on required circuits (with diagrams), sensor probe assembly, and calibration techniques. (JN)

Discusses the theory, design, and availability of laboratory recorders. (MLH)

Discusses the conditions under which stereoscopic photographs and drawings may be produced and viewed, and which will show the results of some experimental work. (DF)

Reports comparison of three models of apparatus designed to collect gas evolved by a photosynthesizing water plant. Problems of design and operation are reported for each model. (AL)