EXPEPJMENTAL PESEARCHES ON DPvAWN STEEL. 
9 
drawing cold both tend to diminish the magnitude of a negative coefficient, whilst 
drawing the wire several times after tempering, and without re-annealing, completely 
reverses the sign of the coefficient, which then becomes positive. But extreme 
drawing bends the curve again to the zero line, and, in the case of the twelfth wire, 
50 diameters long, the coefficient actually becomes zero ; thus the curve for a dimension 
ratio of 50 cuts the zero line twice, namely, between the 8th and 9th stages and at 
the 12th stage. 
The diminution of the positive coefficient observed in the exjDerlments on the first 
set of wires received from Messrs. W. Smith and Sons is now explained, for it is 
evident that that series must have commenced beyond the final bend in the curve. 
This bend also marks a distinct change in other properties of tire wire, for steel 
wire when drawn too far loses the qualities of strength, elasticity, and electrical 
conductivity"*^ which moderate drawing confers to a high degree. 
The temjiering or patenting process in the 4th stage does not seem to lie essential 
to the production, by subsequent drawing, of an incremental coefficient; for if the 
curve belonging to the larger dimension ratio were continued backwards, following 
the same path as its companion curve, it nearly, if not quite, reaches the zero line at 
the 3rd stage, Avhere the wire is drawn after annealing, but before tempering, and if 
the exjieriments had been made on endless wires it is certain that the zero line would 
have been crossed at the 3rd stage. Hence the production of a positive temperature 
coefficient is entirely due to cold drawung, if not carried to an extreme stage. 
6. In Table III. the initial residual intensities have ' been calculated as the 
magnetic moment per unit volume, the volume being obtained from the mass and 
density. From the figures giA^en in the table, or more clearly from the curve given 
m Diagram III., it is seen that the intensity steadily mounts upAvards as the draAving 
proceeds. The maximum intensity reached is about 930 units; altogetlier the 
residual intensity, after magnetisation, has been increased from 469 at the first 
drawing to 930 at the last, for magnets 100 diameters long, an increment of no less 
than 100 per cent. Thus the magnetic properties of steel can be modified to an 
extraordinary degree by the simple operation of cold drawing through successive 
holes. 
7. Nevertheless, considerable skill and judgment are required in conducting the 
operation of drawing, if the peculiar qualities which piano wire possesses are to be 
developed in the highest degree. One fact in connection Avith the process of 
manufacture, which may be mentioned here because of its physical interest, is that 
a Avire after draAving through one hole diUAvs more satisfactoiily through the next if 
giAmn a period oj rest between the operations, and the longer the period of rest, 
extending even to many weeks, the more satisfactory is the subsequent draAving. f 
* Part II., §§ 2 and 4. 
t Tomlinson remarks that rest after strain diminishes internal friction, ‘Roy. Soc. Phil. Ti'ans.,’ 
vol. 177, Part II., p. 835; also vol. 174, p. 5; vide EwiNG, ‘Roy. Soc. Proc.,’ vol. 30, p. 510. 
VOL. CCI.—A. 
C 
