52 MEASUREMENTS 



Even if the value of k is unknown, the results give relative values of 

 M'^ater content. 



The reasoning demonstrated is generally applicable. If you know that 

 A = kB, and if you know the value of the proportionality constant, it is 

 possible to compute the value of B from measurements of A. Even if the 

 value of the constant is unknown, relative values for B can be obtained 

 by measuring A. 



Micro-methods: Biologists and biochemists have found it necessary to 

 develop a set of microanalytical methods. These methods, in general, 

 follow the same physical and chemical principles as ordinary analytical 

 procedures, but working with very small quantities may introduce special 

 difficulties. Pipetting 10 ml of water is easy, but pipetting 10/^1 is more 

 difficult because the surface tension of the water has more influence in 

 the smaller pipette. Certain micromethods are limited by the random 

 fluctuations or movements of molecules. Obviously special care is re- 

 quired when working with extremely small quantities of materials. 



Some other micromethods depend upon physical and chemical prin- 

 ciples which are not ordinarily used on a larger scale. Several of the tech- 

 niques described in the later chapters qualify as micromethods by dealing 

 with small quantities and commonly used principles or by using prin- 

 ciples not ordinarily used on larger amounts of material. 



SELECTED REFERENCES 



No separate publications specifically covering Measurement are 

 recommended here. 



From the Bibliography: 



Wilson, E. Bright, Jr., An Introduction to Scientific Research. 

 Measurements and the execution of experiments are discussed in 

 great detail. 



Richards, James A., Francis Weston Sears, M. Russell Wehr, and 

 Mark W. Zemansky, Modern University Physics. Several discussions 

 of the theory and practice of physical measurement are included. 



