December 1965Viscosity and Density of Boron Trioxide 613 fixed composition decreases with increasing temperature The variation of activity shown in Fig. 3 , however, is, by virtue of the choice of standard states, relative to the activity in pure Na20 a t the same temperature. In reality the oxygen ion activities in pure sodium monoxide and in silicate or borate melts of fixed composition, all decrease with increasing temperature (daoZ-/dT is negative). The data in Fig. 3 now add to this knowledge and demonstrate that dao"/dT is approximately the same for the silicates and pure sodium monoxide but is numerically smaller €or the borates. Consequently, with pure sodium monoxide as the standard state, the activity of oxygen ions in silicate melts appears to be virtually indcpendent of tempcrature whereas for borate melts a positive value of da$-/dT is observed. IIence, a relation similar to Fig. 3 of Ref. 2 would have resulted for the present calculations if sodium monoxide a t some fixed temperature had been chosen as the skandard state instead of sodium monoxide at the tcinperature of interest.It is possible to rationalize the results as follows: Fincham and RichardsonlO postulated that since oxygen can exist in silicate melts in only three fornis (singly bonded 0-, doubly bonded 0", and oxygen ions 02-), the equilibrium between these tlirec forms can be exprcssed as follows:This forward reaction parallels the polymerization reaction, and the viscosity data indicate that, for a melt of given composition, increasing temperature favors depolymerization. IIence, it lollows that increasing temperature favors the back reaction of reaction (7) and thus reduces the oxygen ion activity as demonstrated in Figs. 5 and 2 of Refs. 1 and 2, respectively. The prescnt data would indicate therefore, that for binary borate and silicate melts with identical N N~~o , the complex borate ions are of greater thermal stability than the complex silicate ions. This is supported by the fact that the temperature coefficient of viscosity is greater in silicate melts. It does not follow, however, that the same degree of complexity exists in both melts. In fact the lower viscosities o€ the borate melts indicate that they are distinctly less complex than the silicate melts of the same quantitative compositions.Extensive and accurate viscosity values for molten BzOo a r e reported over the continuous range from 20 poises (at 1400°C) to 101Opoises (at 318°C). T h e measurements were made with a wide-range rotating-cylinder viscometer. The melts were pretreated by bubbling superdry nitrogen through them to ensure a minimum water content. Above 800°C the temperature dependence of the viscosity curve obeyed the Arrhenius equation ; below 800°C the curvature was smooth showing no breaks. At the low temperatures, although its curvature decreased, the viscosity curve did not obey the Arrhenius equation. Densities were determined between 41 l" and 1400°C. Over this range the volume expansion coefficient changed by 1 order of magnitude Prcsentcd in part at

The viscos ity o f a soda -lime-sili ca g lass has bce n m eas urcd a t t he Nat io na l B urcau of Stand a rd s a nd se ven oth er la bo ratories. D ete rmin atio ns wc rc mad e in t hc ra nge of 102 t o 10 15 p oises. The rotat in g cy lind er was u sed at t he hig her t em pcrat urcs (800 to 1450 °C) a nd t hc fib er elongation m et hod at t he lower te mpcratur es (52 0 t o 658°C) . T hc rcsul Ls ha ve bee n critically eva lu ated a nd t il e g lass has bee n issu ed as Stand a rd Sam p lc No . 710. This glass is a va ila ble fr om t he Nat ion a l Bureau of Standa rds.

A Wide-Range (up to 10 10 P) Rotating Cylinder Viscometer Albert Napolita no, Pedro B. Macedo, and Earl G . Hawkins (M ay 17, 1965) . 1~he ra nge of a hi g h temperature rota Ling cylinde r v iscometer has bee n extended so t hat VISCOSIty m easuremen.ts can be m ad e betwee n 10 0 to 10 10 p oises to within 2-p ercen t a ccuracy. ThiS lllvolves three different tec hniques . After a calibration consta nt has been determined for the apparatus III the stand ard oil range, the other two constants for t he hi g her viscosit ies \-v ere se lf~d etermlll e d . In ma klllg measurements at t he low viscosities, 10 0 to 10 5 poises, the o~ter e~l~nd e r J 7 S, ro t.ated at co ns tant sp ee~ a nd the torque measured on the inner cylinder ; flO~ 10 · to 10.·' pOIses the 111l1~1~ cyll11der IS rotated t hrough a n a ngle a nd timed as i t r eturns ~o Its zero pOSitIOn, and fr~m 10°. 0 to 10 10 poises the inner cy~incl er is drive n t hrough a n a ngle at co nstant to rque and tuned as It traverses t hiS a ng le. fhc Fulcher equation viscosity va lues obtall1ecl from prevIOus m~as ur e m e nts on Stan da rd Glasses No . 710 and No. 711 by t h e fiber elongat ion a nd rotatmg cylmclcr methods have been compared with the presen t results.