THE EFFECT OF DRAWING ON THE CRYSTAL STRUC- 
TURE OF TUNGSTEN WIRES. 
L. P. SIEG 
The writer has in various places published results of tests on the 
coefficient of rigidity of drawn tungsten wires. The latest ^ re- 
sults indicated clearly that in a series of wires drawn down from 
the same original stock the coefficient of simple rigidity progres- 
sively increased as the diameters of the wires decreased. For ex- 
ample, the value of “n” ranged in the case of two extremes of five 
such wires from 14.15X10^^ to 15.10X10^^ dynes per square 
cm., for corresponding radii of 0.0227 cm., and 0.00240 cm. The 
hypothesis was put forth at that time that a change in the crystal 
structure which was limited to the surface, and which yielded a 
greater rigidity for the wire would account for the results. This, 
because as the wires become progressively smaller the effect of the 
surface would become more and more pronounced. 
No opportunity came for testing this suggestion until after the 
war. Last year the five wires were again tested for their rigid- 
ities, the results from which tests have not yet been reported. How- 
ever, the tests agreed excellently with those taken two years pre- 
viously, establishing incidentally that the changes were very likely 
permanent. 
The examination involved a photomicrographic study of sec- 
tions of the wires. To accomplish this short lengths of wires were 
embedded in two copper plates by squeezing together the plates, 
with the wires between them, exerting great enough pressure to 
mould the copper around the wires. The copper plates were then 
dressed down, first roughly with a file (which failed to make much 
impression on the tungsten), then with successively finer grades 
of carborundum paper. The last stage of the polishing was done 
with rouge. Great patience and care is required throughout all 
this operation, greater even than for most metals on account of the 
extreme hardness of the tungsten. One must have the patience 
not to progress to a finer grade of the abrasive until he is sure that 
all scratches of a size larger than the grade he is using have been 
obliterated. After the polishing was completed the surfaces were 
1 la. Acad. Science, Proc. 24, p. 207, 1917. 
