A study was made of the density changes in the thermometer glasses, Corning 0041, 7560, 1720 and an experimental glass, Corning EXP175EK.Thermometers fabricated from these glasses were given similar heat-treatments in their respective annealing ranges. Measurements were then made of the ice point changes at various fixed temperatures from room temperature to the normal upper useful limits of the glasses. Holding periods extended to 1 year. The ice point change in a thermometer is a measure of the per cent density change in the glass from which the bulb is fabricated. The relation of this change in density to temperature for a given duration of roasting appears to be well represented by two curves of the form of a constant times a temperature to a power. The value of the power appears to change rather abruptly at some temperature, To, in the neighborhood of 150OC. below the strain point temperature and to be constant in the regions on either side of TO.At equal temperatures below the strain point the behavior of the glasses is quite similar.

The exchange reaction of bromine and radioactive hydrogen bromide in the gas phase has been found to fall just short of reaching equilibrium in two minutes. The very rapid rate of exchange would seem to be accounted for best by a chain reaction involving bromine atoms.

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Aging Changes in Clinical Thermometers 203as index equilitxium and the density-time curves were very similar to the refractive index-time curves, the density increasing or decreasing under the same conditions as the refractive index.The same samples as represented in Fig. 5 were used to investigate the density-time relationship when quenched irom the 590" and 620°C. holding temperatures. The samples that were sliced, in order to compare the physical properties a t the center and a t the edge oi the piece, were represented on Fig. 6 by crosscs. The results obtained from the 590°C. hold were shown by the solid line, and those from the 620°C. hold were shown by the broken line.From Fig. Ij it can bc seen that when a holding temperature of 590°C. is used samples again reach an equilibrium in about 4 hours with a density of 2.5035 when quenched to room temperature. If the holding temperature is 620°C., density equilibrium is achieved in hour as was index equilibrium, and the density of these samples when quenched to room temperature is 2.4970.The specific refraction of each sample was calculated from the refractive index and density which were determined for Figs. 5 and 6, respectively. The specific refraction-time relationship a t the holding temperatures could then be plotted. The results of the center and edge comparisons of the sliced samples are shown in Fig. 7 by crosses. The results obtained from the 590°C. hold were shown by the solid line, and those from the 620°C. hold were shown by the broken line. When these refractive indices and densities are used to calculate the specific refraction which is in turn plotted with time at a holding temperature, it is obvious that again an equilibrium must be reached for each holding temperature. However, the specific refraction rises to a maximum value in each case, when well-annealed pieces are used as a starting point, while the refractive index and density drop to minimum values. In the specific instances of 590" and 620°C. holding temperatures, the specific refractions a t equilibrium reached r = 0.12028 and r = 0.12040, respectively, as shown in Fig. 7 .