METHOD OF INVESTIGATION 



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to measure in the field, it is advisable to 

 take a series of samples to measure at home. 

 Samples of different types of clay also make 

 valuable material for museum exhibit and 

 teaching. The samples are taken in tight 

 troughs of zinc plate, 50 centimeters long, 5 

 centimeters wide, and 2 centimeters high. 

 The face of the clay bank is carefully 

 smoothed, and the trough is cautiously 

 pressed in, a knife being used to cut away 

 the clay just outside the edges, until the 

 trough is entirely filled. The samples are 

 taken so that they overlap each other 5 

 centimeters. The troughs are then cut loose 

 from the bank, and part of the clay which 

 projects above the edges is removed. If 

 moistened and wrapped in wax paper, such 

 samples keep in good condition for months. 

 In the laboratory the clay is carefully cut 



Fig. 4 — Sample of measurement made in the field and curve constructed from 

 it in the office. Actual scale. 



