Plastic Crystals of Ammonium Nitrate. 7 



place chiefly at the point of maximum bending moment in 

 each case (as it appeared to), the deflexion produced by this 

 75 grams ought to have been about twice that produced by 

 the 400 grams in an equal time in the other experiment. It 

 will be seen that this is not the case. If, however, in place 

 of the load of 75 grams, one of about 55 or 60 grams had 

 been applied, the deflexions would have corresponded. 



When, in place of crystals of about 2 mm. thickness, con- 

 siderably thinner ones were placed on the two supports, the 

 non-recoverable immediate bend, that can be detected in 

 tigs. 3 to 6, was found to be much more pronounced. 



If the load be removed after this initial bend, and then 

 replaced carefully, no further bending will ensue. If, how- 

 ever, a larger load be applied a larger initial bend is produced. 

 Fig. 7 shows the deflexion produced by this method. A 









Fig. 7. 























'8 



















1 



f 



. -R 







O 







o 





k 



5-3 csm§, — *\ 







<B 













3 .A 













-1 .4 













< 







■2 



Or 

















» — n -* 





3>r 







10 



15 



20 



25 Grams. 



small load is first applied, and the deflexion noted. The 

 load is removed, leaving the crystal bent. A rather larger 

 load is applied ; this causes an increased deflexion. The 

 new deflexion is measured and the load again increased. 

 That this effect was not due to friction at the supports was 

 shown by repeating the experiments using the single support 

 method. Fig. 8 shows three curves obtained with a second 

 crystal. For the second of the three curves, the crystal had 

 been straightened by hand ; and yet again for the third. 

 The difference is thus an indication of the effect bending 

 has on the plastic properties. In this case, it has caused 



