SELECTION OF TECHNIQUES 57 



ties. The biologist cannot be expert in any of these fields, but at least he 

 should know what can be done and what is impossible. Otherwise he 

 might ask the machinist to bore a square hole, or he might ask the glass 

 blower to repair a cracked lens without damaging the optical perform- 

 ance. Crude sketches assist the mechanic, but drawings prepared accord- 

 ing to the practices of mechanical drawing, complete with all dimensions 

 and tolerances, will make his work easier. 



Assembly of components 



Because there is almost no limit to the types of parts and materials 

 available today, the assembly of parts or components is limited only by 

 the imagination of the biologist. If parts are to be made, they might be 

 constructed of metal, wood, plastics, glass, foam rubber or plastic foam, 

 cork, or almost any other material. Plastic or rubber tubing; assorted 

 wires; glass tubing and ground glass joints; metal tubing with connectors 

 and valves; and round, square, or rectangular rods of several materials 

 are easily available commercially. Distributors stock standardized items 

 such as screws, but also ball bearings, nylon spheres, precision gears, 

 and an infinite variety of other specialized parts. 



The parts of the apparatus may be held in place in several different 

 ways. Scientific supply houses furnish rods and fixtures for making 

 sturdy frames. The aluminum alloy rods are strong enough to support 

 rather heavy components, and the connectors available allow completely 

 flexible arrangement. Usually it is advantageous to build such a frame 

 on a sturdy table in such a way that both front and back are accessible. 

 Burette clamps, larger condenser clamps, and special devices for holding 

 thermometers, heaters, and other equipment are standard parts. 



Another type of supporting material consists of sheets of fiberboard 

 with rows of holes. Parts can be attached with screws, wire, or specially- 

 made hooks. Such boards are often used to display tools, but they work 

 as well to support laboratory apparatus. Much smaller pieces, with 

 smaller holes more closely spaced, also are available. These small boards 

 are useful as "bread boards" for temporary arrangements of parts. 



A number of items built originally as toys have also been used in 

 laboratories. You might arrange for a toy electric train to carry materials 

 to inaccessible places. Children's steel construction sets provide sheets, 

 bars, gears, and other parts that often are adequate for the purpose. Just 

 use your imagination. 



