SELECTION OF TECHNIQUES 55 



(4) Precautions. What are the major sources of error? How can these 

 errors be minimized? What kind of measurement should not be at- 

 tempted? Does the technique give only one kind of information, or is 

 it more versatile? Are there safety hazards? 



The safety hazards deserve special mention. Because many modern 

 instruments are electrical, severe shocks are possible. Any large capacitor 

 might store its charge for some time after the instrument is turned off, 

 and discharge through a human body may produce a flattening jolt. 

 Many of the chemicals used in laboratory studies are more or less poison- 

 ous; some are extremely dangerous. Carbon monoxide is used in some 

 metabolic experiments, and its presence in the air is not easily detected 

 until it is too late. Poisonous materials are produced in some chemical 

 reactions, one of which might occur as a side reaction along with the 

 reaction being studied. Some pieces of glass apparatus are extraordinarily 

 fragile. Hard glass such as Pyrex breaks with especially sharp edges and 

 may give nasty lacerations. If an instrument or technique involves safety 

 hazards, it might be well to ask "Is there a safer way to do it?" 



(5) Precision. Of what degree of precision is the technique capable? 

 Is this precision adequate for the problem? Does this technique offer 

 more precision than the problem requires? Would a less expensive, 

 more convenient technique be as effective in providing answers to 

 problems? 



(6) Requirements of operation. What must the operator know about 

 the instrument in order to make the measurements? Does the technique 

 require any special dexterity or any difficult manipulations? Can the 

 operator reach all the controls easily? Does the technique contribute to 

 excessive fatigue by causing the operator to work in uncomfortable 

 positions? Is there a possibility of eye strain? Is nervous tension a usual 

 result of operating the instrument for long periods? 



(7) Cost. Will the budget stand the original expense, as well as the 

 cost of maintenance and operating supplies? Is the instrument adaptable 

 to various kinds of measurements? Can a higher initial cost be justified 

 because a versatile instrument can be used for many purposes? 



Instrument design 



Occasionally it becomes necessary to build an instrument in the 

 laboratory, especially if a measurement is to be made for which no 

 commercial instrument is available. Physical scientists are more likely 

 to build their own instruments than are biologists. The biologist does 



