﻿444 Barus and Strouhal — Viscosity of Steel. 



Art. LIII. — The Viscosity of Steel and its Relations to Temper ; 

 by C. Barus and V. Strouhal. 



Introductory. 



In an earlier number of the Journal, we expressed the belief 

 that the qualities of retaining magnetism exhibited by steel 

 would probably stand in relation to the viscous properties of 

 the metnl. In the present paper we make a first search for such 

 a relation. The work is restricted to torsional viscosity be- 

 cause it usually exists in larger amount, and is much more 

 accurately measurable than any of the other manifestations of 

 viscosity. Possibly it may be brought more rationally into 

 comparisons with magnetic phenomena. We therefore de- 

 velop partially (i. e. so far as is necessary for our especial pur- 

 poses) a new and verj 7 sensitive differential method for the 

 study of torsional viscosity. Having applied it to steel, we 

 compare the results obtained with the known behavior of per- 

 manent linear magnets, tempered under like conditions. Dur- 

 ing the course of the experiments we incidentally come upon 

 certain ulterior results (viscosity of iron, glass). 



In our magnetic comparisons we have endeavored to avoid 

 prematurity. Many inferences of the original draught have 

 been cropped. We do not wish to ignore the magnetic effect 

 of the chemical changes of steel. We have merely endeavored 

 to circumscribe the magnetic effect of carburation, by exploring 

 the magnetic importance of certain mechanical properties of 

 steel. To do this we have studied, abstractly as it were, the 

 occurrence of permanent magnetism in a medium of continu- 

 ously varying viscosity, without insisting on an inherent rela- 

 tion between retentiveness and viscosity. 



Literary notes. — The necessary existence of viscosity in solids 

 was pointed out, discovered, and its nature described by Weber;* 

 but it is to Kohlrausch'sf extensive researches that we owe the 



* Weber: Gotting. Gelehrt. Ariz., St. viii, 1835; Pogg. Ann., xxiv, p. 247, 

 1835; ibid., liv, p. 1, 1841; i'omm. Soc. Gotting., iii, p, 45, 1841. Weber's re- 

 searches express the amount of viscous deformation in terms of time by a hyper- 

 bolic formula with three coustants. 



fKohlrausch: Pogg. Ann., cxix, p. 33*7, 1863; ibid., cxxviii, pp. 207, 399, 1866;, 

 ibid., civ, p. 579, 1875 ; ibid., clviii, p. 337, 1876. The author subjected fibers of a 

 great number of substances to torsional, tensile and flexural stress, and discusses 

 the amount of deformation in each case in its dependence on time and on tem- 

 perature. The results are too elaborate to be excerpted here. The author finds 

 it necessary to use exponential relations with three and even four constants to 

 describe the results completely. In this place we advert, moreover, to the papers 

 of Neesen (Pog. Ann., cliii, p. 498, 1874; ibid., clvii, p. 579, 1876; Wied. Ann. r 

 vii, 460, 1879), of Braun (Pogg. Ann., cxix, p. 337, 1876), of Wiedemann (Wied. 

 Ann., vi, p. 496, 1879) which supply important details of critical discussion. 

 Perhaps we may even add Pernet's well-known thermometric researches (Carl's. 

 Rep., xi, p. 257, 1875, and elsewhere). 



