INSTRUMENT FOR MEASURING TENACITY. gg 



piece of brass passing through a hole in the lower extremi- The apparatut 

 ty of the nut, and having its ends secured in the standards de,c " bed - 

 C C, is intended to steady the motion. G the tube contain- 

 ing the spiral spring represented fig. 2. Down the middle 

 of this spring passes the rod or slide, fig, 3. a is a button 

 of brass of the same diameter as the interior of the tube G, 

 and screwed on the end of the slide, so that, when in its 

 proper situation, it may rest on the extremity of the spring. 

 b, fig. 3, a round piece of brass, which screws in and closes 

 the end of the tube after the spring is in ; it has a perfora- 

 tion in the middle, through which the extremity c of the 

 slide freely passes, and is connected to the slider g of the 

 nut e, fig. 1. 



By this arrangement it will be seen, that as the tube G, 

 containing the spring, is attached to the movable nut e, and 

 freely supported by the end of the brass plate B B, which is 

 turnedup at a right angle for this purpose, it must move al- 

 together back ward or forward *as the nut is moved ; but if the 

 wire i have one end coiled round the pin Ar, which is made to 

 turn for this purpose in apiece of brass screwed into the end 

 of the tube, and the other round a similar pin /, which is in- 

 serted in a brass slider, that moves horizontally, through the 

 standard o for the purpose of adjusting its length ; and, 

 while in this position, if the screwy be turned so as to 

 move the nut back, the slide will be drawn out, and the 

 tube held in its original position by the wire i; which will 

 acquire a tension equal to the resisting power of the spring, 

 as compressed between the round piece of brass b and the 

 button a fig. 3. If the screw continue to be turned slowly, 

 the tension of the wire will consequently increase, till the 

 cohesive attraction of its particles be overcome by the ex- 

 pansive force of the spring. 



This expansive force, being the measure of tenacity in the 

 wire, will be indicated by the index m t consisting of a small 

 brass quadrant and pointer as at fig. 4, fixed on the quad- 

 rantal scale nnn, round which it moves as the screw turns, 

 in consequence of teeth on the edge, which work in the 

 threads of the screw. The index moving in this way is 

 not influenced by the recoil of the tube, when the wire 

 breaks, but remains at the degree it has been carried to on 

 G 2 the 



