Concerning the annealing and characteristics of glass

240

U. S. BUREAU OF STANDARDS NOTES.

[J. F. I.

a balistic galvanometer, the normal induction is measured by the throw of the galvanometer upon reversal of the magnetizing current. By connecting either the inner and middle or middle and out’er coils in opposition the value of the magnetizing force is determined. Normal induction curves obtained for a number of specimens of different materials show very good agreement! with similar curves obtained by the Burrows method within the range of the latter. Hysteresis values, however, have not proved so reliable and are being studied further with the hope of satisfactory improvement. Fro’m the normal induction data, the intensity of magnetization and reluctivity are calculated and discussed from the point of view of revealing in some specimens the presence of two constituents of different degrees of hardness which reach the maximum intensity of the magnetization for different values of H. NOTE ON METHODS OF COMPUTING AND INTERCOMPARING RADIATION DATA. By W. W. Coblentz. [ABSTRACT.]

A SIMPLE method is given for computing spectral energy A table of values of log curves using the Planck formula. By means of this table, a (e” - I ) is given for this purpose. table of logarithms and a slide rule, a complete spectral energy curve can be computed in an hour. The paper gives also a chart for the intercomparison of thermal radiabon constants with similar data, obtained indirectly from ionization potential, photo-electric and X-ray measurements. CONCERNING THE ANNEALING AND CHARACTERISTICS OF G&ASS.’ By A. Q. Tool and J. Valesak. [ABSTRACT.]

THE characteristics involved in annealing were investigated The glasses for a number of glasses of\ different composition. ‘Scientific Paper No. 360. ’ Scientific Paper No. 358.

l:cb.,

rgro.1

U.

S. EURE_\U OF ST~\~-~ARDS NOTES.

241

studied were chiefly those produced by the Bureau of Standards at Pittsburgh. Any common process of annealing may be considered as made up of three factors, namely: the annealing temperature, the time allowed for’the reduction of the stresses, and the rate and mode of cooling. One method which appears very dependable for determining the’ practical range of annealing temperatures consists of locating the temperature interval in which the glass on being heated shows a distinct and fairly sharp increase in the heat absorption. All glasses investigated showed this effect. It always occurred in a temperature range in which the glass was soft enough to allow a practically complete relaxation of the stresses in an unThe rapidly increasing annealed sample in a very short period. softness of tihe glass at these temperatures and the increase in the heat absorptioln are undoubtedly related, but the nature of the relationship is as yet undetermined. The rate of the relaxation of the stresses in the glass was determined at different temperatures by the use of two methods; first, by measuring the rate of deformation elf loaded strips on rods; and, second, by determining the rate at which the double refraction in unannealed glass disappeared. The data thus obtained, as previous investigations also show, aid greatly in determining the practical annealin g temperature, the time the glass should be held at this t’emperature. and a satisfactory cooling procedure. THE

CONSTANTS

OF RADIATION OF HEATED ENCLOSURE: By W.

W.

A

UNIFORMLY

Coblentz.

[ABSTRACT.]

EXPERIMENTAL data are given on atmospheric absorption. The paper gives also a recalculation of the coefficient o,f total radiation of a uniformly heated enclosure, or so-called black body, giving a value of 0=5.72

The

effect

‘Scientific

x

of atmospheric Paper No. 357.

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watt cm’ deg-’

absorption

is discussed,

and

the