224 



Mr. J. T. Bottomley. On the Effects of [June 19, 



The following tables contain a considerable part of the results of 

 these experiments. 



Two kinds of wire were used both of pure soft iron wire, drawn 

 for the purpose of these experiments, but differing slightly in the 

 treatment during the annealing process. They are distinguished in 

 our note books as " Black annealed wire " and " Bright annealed 

 wire." Tables I and III show the results of qnick breaking of these 

 two wires, and Tables II and IV the results of slow breaking. It will 

 be seen that the slow and long- continued application of stress has in- 

 variably strengthened the wire, a result in itself of great importance. 

 It should tend to correct some of the views commonly held as to the 

 danger of applying severe loads, as tests to iron structures, such as 

 steam boilers. It appears that the iron wire here employed was in 

 more than one case actually improved in strength by about 10 per 

 cent. As the wires tested were about 16 feet long and very uniform, 

 it is very unlikely that the wires 8, 9, 14, 15, in Table II, were ab- 

 normally strong over such a length ; while the wire 12, in Table II, 

 the only one which is not strengthened, may readily have contained 

 some slight flaw, or may have been broken by some jar in putting 

 on the weights. 



The result as to amount of elongation is no less important. Wires 

 broken rapidly receive an elongation of over 25 per cent, on the 

 average ; while the same wire broken slowly is only elongated by 

 about 7 per cent., and in the case of the bright annealed wires so 

 small elongation as 4' 79 per cent, was found with a breaking weight 

 increased by 5 J per cent. 



A specimen curve showing the relation between stretching weight 

 and elongation is here given. It will be seen that the stretching does 

 not go on uniformly. At the beginning the wire resists stretching 

 very much, till the weight of 32 lbs. is reached. If, however, a 

 weight of 29 lbs. be put on at first this resistance is overcome, and the 

 curve goes uniformly down till a weight of about 35 lbs. is reached. 

 About this point the wire appears to become abnormally stiff again, 

 and resists weights up to about 42 lbs. This stiffness is again broken 

 down by this weight and the wire runs rapidly down with increasing 

 loads. These features are noticed in every curve and at very nearly 

 the same loads. 



It might be supposed that the stiffness at the very beginning is due 

 to a skin of oxide acquired in the drawing and annealing process. 

 This is not the case however. The wire may be cautiously elongated 

 in such a way that the skin must be broken through and the stiffness 

 is still retained. The stiffness acquired after loading to the extent of 

 35 lbs. could not ri any case be accounted for by skin-stiffness. 



