EXERCISE 70 

 TENSILE STRENGTH OF BARK 



Materials. Strips of bark from the branches peeled in the pre- 

 ceding exercise, as well as strips of fresh bark from other kinds of 

 trees. 



Directions for work. Cut the bark into strips of uniform 

 width. Clamp one end of a strip in a vise and attach a spring 

 balance to the other end by means of a small portable vise, as 

 a wooden cabinet-maker's clamp. Pull upon the spring balance 

 until the strip of bark tears, noting the reading of the balance 

 at the time the bark gives way. Repeat with several pieces of 

 bark of the same kind in order to get an average result. Secure 

 similar data for bark from other species of trees. 



Does the tensile strength of bark appear to you to be rela- 

 tively great ? Is there any marked difference in bark from 

 various kinds of plants ? Do you know of any textile or cord- 

 age fibers that are secured from bark, and, if so, what are they ? 

 What materials are manufactured from them? 



References 



, BERGEN and CALDWELL. Practical Botany, p. 47. 

 BERGEN and CALDWELL. Introduction to Botany, p. 65. 



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