the Limit of Elasticity in Metals. 



203 



place with 980 pounds in all. The load was now increased to 

 1040 pounds and upwards. The curve for the permanent elon- 

 gations (fig. 5) has now the same direction which it had before 

 using the equal loads of 980 pounds. Fig. 1 shows quite 

 the same phenomenon with the loads 850 and 966 pounds. 

 Before the curve again assumes its old direction the bar appears 

 to give up as much to the permanent elongations as it had 

 previously been stretched. Hence an increase of 50 pounds on 

 the square dec. line in the load, immediately after repeated stretch- 

 ing-experiments with equally great or smaller loads, did not 

 produce the same elongation as before. Thus it is seen that 

 the form of the curve is ultimately quite independent of the 

 manner in which the bar has been treated. 



Such a property of the curve for the permanent elongations, 

 that is, its independence of the treatment of the bar in the 

 stretching-experiments, is worth particular attention ; for it pos- 

 sibly justifies us in regarding the curve either wholly or partially 

 as representative of the quality of the material. 



§ 8. On the Curve for Permanent Elongations. 



As a type of the curves which represent the permanent elon- 

 gations of iron and of the softer kinds of steel, fig. 6, constructed 

 according to the following Table, may be taken : — 



Table VI. 

 Steel. A= 17-41. 



No. 



P. 



AL. 



No. 



P. 



AL. 



1 



237 



00 



20 



536 



20 



2 



260 



00 



21 



547 



2-3 



3 



283 



00 



22 



559 



3-2 



4 



306 



00 



23 



570 



4-8 



5 



329 



00 



24 



582 



88 



6 



352 



01 



25 



593 



181 



7 



375 



0-3 



26 



605 



45-3 



8 



398 



0-5 



27 



616 



53-4 



9 



409 



0-7 



28 



639 



63-3 



10 



421 



0-8 



29 



662 



72-3 



11 



432 



0-9 



30 



685 



81-4 



12 



444 



10 



31 



708 



91-4 



13 



455 



11 



32 



731 



102-2 



14 



467 



1-2 



33 



754 



111-8 



15 



478 



1-3 



34 



766 



120 



16 



490 



1-3 



35 



789 



1326 



17 



501 



1-4 



36 



812 



1470 



18 



513 



1-6 



37 



835 



161-6 



19 



524 



1-8 



38 



858 



180-6 



The curve takes first an ascending direction, by which the per- 



