Studies on Glass. VI. Some Specific Heat Data on Boron Trioxide

STUDIES ON GLASS VI. Some Specific Heat Data on Boron Trioxide

Downloaded by UNIV OF CAMBRIDGE on August 25, 2015 | http://pubs.acs.org Publication Date: January 1, 1930 | doi: 10.1021/j150325a016

BY

s. BENSOX

THOMAS’ AND GEORGE

s. PARKS

In previous publications* heat-capacity data over a range of temperatures have been presented for a number of organic materials in both the glassy and liquid states. I n these studies the specific heat curves for the glass and liquid were found to differ greatly. Moreover, between the two states there invariably existed a characteristic transition interval of 8’ to z jo,depending upon the complexity of the glass-forming material. Within this interval the specific heat in every case underwent a rapid increase of 60% to 100%~altho the general character of the change and its sharpness, as measured on the temperature scale, were found to depend to some extent upon the previous heat treatment of the glass-forming material as well as upon the rapidity with which this transition interval was transversed in the course of the measurements. The question then arises as to whether inorganic glasses also exhibit these phenomena. The purely qualitative observations of Tool and Valasek* indicate that they do. Also certain results of White4 for silicate glasses might be interpreted as consistent with these phenomena, altho White’s data, obtained over intervals of 100’ by the “dropping method,” are in themselves hardly sufficient for the drawing of definite conclusions. Accordingly the present study of the specific heats of boron trioxide was undertaken in order t o throw further light upon this question. Boron trioxide was chosen for several reasons. I n the first place, as a glass-forming material it possesses a very simple empirical formula and is readily obtained in a state of purity. Then again it forms an extremely stable glass, which shows practically no tendency to crystallize. Equally important is the fact that this glass “softens” between zoo’ and 300’ C.; hence specific heat measurements need not be carried to as high temperatures as with most silicate glasses. Method and Apparatus The problem of finding a suitable method and apparatus for the present study a t first presented some difficulties. The method of mixtures, commonly employed for the measurement of specific heats at such temperatures (Le., 30’ to 400’ C.), was obviously undesirable here, since it does not permit of a Holder of a fellowshi on the Charles S. Coffin Foundation during the scholastic year 1929-1930;holder of the !hell Research Fellowship a t Stanford during the scholastic year 193-1931. We hereby wish to acknowledge the generous aid afforded by these fellowships in the present investigation. *Parks and Huffman: J. Phys. Chem., 31, 1842 (1927);Parks, Huffman and Cattoir: 32, I366 (1928);Parks, Thomas and Gilkey: 34, 2028 (1930);and Huffman, Parks and Thomas: J. Am. Chem. SOC.,52, 3241 (1930). a Tool and Valasek: Bur. Standards Sci. Paper, 15, 537 (1919). ‘White: Am. J. Sci., 47, I (1919).


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S. BENSON THOMAS AND GEORGE S. PARKS

series of determinations carried out on the same sample in a continuous manner. Moreover, it is not readily adaptable to the determination of a rapidly changing and irregular specific heat curve. On the other hand, the Nernst method, involving the measurement of “true” or instantaneous specific heats with an aneroid calorimeter, had proved extremely satisfactory in the preceding studies on organic materials at lower temperatures; and accordingly we finally developed a modification of it for use in the present investigation, The two chief objections to the use of the Kernst method a t these higher temperatures are ( I ) the difficulty encountered in insulating the heating coil which must be in good thermal contact with the aneroid calorimeter and ( 2 ) the inconveniently large cooling and heating corrections due to the large heat exchanges between the jacket and calorimeter a t temperatures much above that of the room. In the present case we really took advantage of this second point to avoid the first difficulty. In brief, we utilized the large rate of heat exchange between calorimeter and jacket as a means of heating (or cooling, as the case might be) our calorimeter and thus dispensed with electrical heating. The apparatus as finally developed might be termed a “radiation calorimeter.” In its development we profited greatly by the paper of Steiner and Johnston,‘ altho our apparatus differs considerably from theirs. The principle of our calorimetric method is very simple. If a calorimeter is suspended in air within a jacket maintained a t a small, constant, temperature difference with respect to the calorimeter, the rate of heat exchange between the calorimeter and its surrounding jacket a t any instant is a function of the two temperatures involved. Thus according to Newton’s law of cooling, q = KT(TJ - Tc) where q is the number of calories flowing to the calorimeter from the jacket per minute, TJ and - are the respective temperatures of the jacket and calorimeter and K T is the constant for Newton’s law of cooling. I t should be noted here that KT, while a constant a t any particular temperature, increases considerably with increase in temperature. We may also write the equation, T q=c d 2 dt where C, is the heat capacity of the calorimeter and contents, and dTc/dt is the rate of change of the calorimeter temperature per minute. Combining equations I and 2 , we then obtain dT C p L = KT (TJ-Tc) (3) dt If now the rate dTc/dt is first measured when the calorimeter is filled with a material of known heat capacity (in this case metallic copper), the constant KT may be readily evaluated for a range of calorimeter temperatures. Then, in turn, the heat capacity of the calorimeter and a second substance (in this Rteiner and Johnston: J. Phys. Chem., 32, 912(1928). In this connection the reader is also referred to White’s paper on ‘‘Calorimetry in Furnaces,” J. Phys. Chem., 34, 1121 (1930)which appeared after the present method was developed.

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case boron trioxide) may be determined by measuring the corresponding value of dTc, dt, when the calorimeter is filled with this substance. As the heat capacity of the calorimeter itself is known, the specific heat of the second substance can be easily calculated. Heats of fusion and of transition aiso may be determined by this method by simply multiplying the time required

FIG.I A Croea-section of the “Radiation”

Calorimeter System.

for their completion by the predetermined rate of heat transfer for the temperature involved. Thus, AH = KT (TJ - Tc)t (4:, where AH is the heat of fusion, or of transition, of the amount of substance in the calorimeter and t is the time required for the Completion of the melting or transition process. A cross section of our apparatus designed to operate on the principles outlined in the preceding paragraphs is shown in Fig. I . A calorimeter, A, is centrally suspended within a heavy copper block, B, by means of two small glass tubes, el and e*. The calorimeter (capacity about I 5 cc) is constructed of silver tubing, 2.2 cm outside diameter and 4.4.cm. long, having a wall thickness of 0.05 cm. The ends are also of silver o . o j cm. in thickness. In the measurements on poor thermal conductors, such as boron trioxide, twelve


2094

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BENSOS THOMAS AXD GEORGE S. PARKS

to fifteen perforated silver disks 0.02 cm. in thickness are equally spaced within the tube to promote thermal equilibrium throughout the calorimeter. Two light nickel tubes of 0.24 cm. inside diameter, placed in direct contact with the side wall and sealed into the top, serve as thermocouple wells. The chromel-alumel thermocouple, C Z , with one junction imbedded in the first tube and the other junction in the copper jacket, is used for temperature control (to be described later) , while the platinum-platinrhodium thermocouple, C1, in the second tube is used for measuring the temperature (Tc) of the calorimeter and the thermal head (TJ - Tc). The exterior of the calorimeter is polished and the interior cavity of the copper block is heavily silver plated so as to preserve a constant surface and cut down radiation to a minimum, since it is desirable to effect the heat transfer largely by conduction thru the air space because radiant heat transfer varies considerably with the temperature. The copper block, B, was made from a piece of 34 inch rolled copper rod 2 2 inches long, which was hammered to approximately the final dimensions. The hammered copper was then turned to a diameter of 1 2 . 7 cm. and a length of 20.3 cm. The cavity containing the calorimeter was machined out of the block. It has a diameter of 3.5 cm. and a total length of 8.6 cm. This chamber is closed by a copper plug, D, ground to fit the block. The plug is drilled to accommodate the glass support, ez, and four small alundum tubes thru which the thermocouple wires are led. Imbedded in the copper block are nine alundum, threaded furnace cores, F, each wound with 3.8 meter of No. 2 5 nichrome I V resistance wire and plastered over with alundum cement. The heating coils are connected together in series of three, the three groups being connected in parallel. Copper rods are cemented in the center of the heating coils in order to further improve the heat transfer. Copper plates, GI and Gz,cover both ends of the block and provide for heat transfer between the rods and the block. The copper block is mounted within a heavy brass can, hf, zo cm. in diameter and 35 cm. high. The intervening space is packed with silocel insulating powder. The various electrical lead wires are led out of the can thru 1.6 cm. copper tubes. The can is immersed in a Izo-liter water bath in order to keep its temperature approximately constant. In order to maintain a given temperature difference between the calorimeter and its surrounding block, use was made of a photoelectric system similar to that employed by Southard and Andrews' for the regulation of a low temperature thermostat. The regulation of the temperature difference depends upon maintaining a constant electromotive force in the differential thermocouple, C z , one junction of which is in contact with the wall of the calorimeter and the second is imbedded in the copper block. This electromotive force is balanced across a potentiometer set to correspond to the desired temperature difference. The thermocouple and potentiometer are 1 Southard and Andrews: J. Franklin Inst., 207, 323 (1929). For further information concerning the use of ghotoelectric cells the reader is referred to the following papers: Styer and Vedder: Ind. ng. Chem., 22, 1 0 6 ~McMaster: ; 1070 (1930).

STCDIES OK GLASS

209.5


connected in series with a high sensitivity Leeds and Xorthrup galvanometer. When the temperature difference varies from that corresponding to the electromotive force set on the potentiometer, the galvanometer is deflected. This deflection of the galvanometer mirror causes an image of a projection-lantern lamp with concentrated filament to be reflected off from a General Electric PJ-23 photoelectric cell, placed 2 meters from the galvanometer. The operation of this cell then causes relays to actuate which appropriately change the resistance in series with the heating coils and so bring the temperature of the To White Potentlometer.

Pt-Rh

a

v v $ locK ,

BlocK Calorimeter

,

FIG.2 Temperature-Control Circuits

block back to its proper relationship with respect t o the calorimeter. The sensitivity of the galvanometer is such that a difference of one degree causes a deflection of j o cm. a t a distance of two meters. With this arrangement the maximum deviation from a definite, predetermined difference is always less than 0.02’ under actual operating conditions. The various electrical circuits used in controlling the temperature of the block are schematically shown in Fig. 2 . Tho this photoelectric system serves admirably in maintaining a temperature difference which is almost constant throughout a moderate temperature range, small variations due to thermoelectric inequalities in the chromelalumel thermocouple are encountered when working over a range of several hundred degrees. The repeated “setting up” of the calorimeter causes further


2096

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BENSON THOMAS A S D GEORGE S. PARKS

variations in the thermocouple e.m.f. due to unavoidable bending of the wires. For these reasons the actual temperature measurements are made by the platinum-platinrhodium thermocouple system (diagramed in the upper left-hand section of Fig. 2 ) in conjunction with a White double potentiometer and a sensit,ive galvanometer, since the platinum-platinrhodium couple has been found to remain more constant thermoelectrically than the chromelalumel couple. By this noble-metal system' the temperature of the calorimeter (Tc), the temperature difference (TJ - Tc) and the temperature of the jacket (TJ) may be readily measured at regular time intervals. Also from these readings the values of dTc 'dt' may be easily computed. During our studies these two platinum-platinrhodium thermocouples were frequently checked against each other. The method of checking consisted of measuring the electromotive forces of the two thermocouples when the calorimeter and jacket are at the same temperature, this condition being determined by observing the point a t which the temperature of the calorimeter remained constant. The empty calorimeter when fitted with 14 silver disks, as in the nieasurements on the boron trioxide, weighed 23.6 gm. It's heat capacity was readily calculated from the specific heat values of silver and nickel as given in the International Crit,ical Tables,* and varied from 1.61 cal. a t oo to 1.84 cal. a t 4ooOC. I n the evaluation of the constant KT of equations, these disks were removed and a copper cylinder (weight, 96.3 gms.), machined to fit within the calorimeter, was inserted in their stead. The heat capacity of this copper cylinder was calculated by use of the following equation, suggested by Maier,c for the atomic heat of copper as a function of the Centigrade temperature:

C, = 4.89

+ o.oo~36T- o.oooooo67T2

As calculated in this manner the total heat capacity of the silver calorimeter and copper cylinder varied from about 10.0 cal. at oo to 11.9 cal. a t 400' C. I n obtaining the results for boron trioxide, which are given in the next section, a 18.05 gm. sample was sealed into the calorimeter. Under these conditions the total heat capacity of the calorimeter and contents was found to be 6.1 cal. a t 100' and 9. j cal. at 3 jo°C. With the apparatus as described we were usually able to obtain specific heat values reproducible to 0.5% or better. Such a degree of concordance is very satisfactory and, we feel, serves t o indicate the possibilities in applying this "radiation" calorimeter to measurements at moderately high temperatures, However, there are several possible sources of systematic errors in our measurements and these reduce the reliability of our results in an absolute sense. As a rather conservative estimate, we judge the absolute errors in our specific heats to be within zyoat rooo and 4y0a t 350'. The temperature scale used is that given in the "International Critical Tables," 1, 5;. Suitable percentage corrections (about 0.25% for our couple) are employed to correct this scale t o directly calibrated oints. * International Critical 5, pp. 92 and 93. a Maier: Reports of Investigations, U. S. Bureau of Mines, Serial 2926, April, 1929.

!abies,

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Heat-Capacity Data I n all we have completed four independent groups of specific heat measurements on boron trioxide. The first two groups each included several series of determinations with a copper calorimeter (instead of the silver calorimeter described in the preceding section) and with a chromel-alumel thermocouple system for measuring the calorimeter temperatures and the thermal head. In the third group this copper calorimeter was then replaced by the silver one? which provided a surface less subject to oxidation and to a consequent chaiige in its emissivity. On the whole these first three groups of measurements must be considered as rather preliminary in character, since the results of successive series of determinations showed more or less of a trend with time, which was finally traced to changes in the t,hermoelectric value of the chromel-alumel thermocouples employed to measure TC and the quantity TJ-Tc. However, the general character of these results was such as to indicate in an unmistakable fashion the nature of the curve for the boron trioxide glass and liquid, leaving possibly an uncertainty of 4 to 8% in the absolute magnitude of the specific heat values. In the fourth group of determinations t8hechromel-alumel thermocouples were replaced by the platinum-platinrhodium thermocouple system mentioned before, whereupon the trend in the results disappeared. In this group we carried out three entirely distinct and rather complete series of determinations, as well as a nuniber of partial series, which were designed to satisfy us regarding the reproducibility of the values obtained. Accordingly, the results of this last group constitute our final and, we think, our most reliable values. For this reason we shall omit all data obtained in the preceding three groups, since these are merely confirmatory. The material studied was Merck's C. P. anhydrous boron trioxide, with impurities guaranteed to be less than 0.01%. A sample of this was heated in a platinum crucible for eight hours a t about goo0 C. in order to drive off the last traces of water. The molten oxide was then poured directly into the silver calorimeter which was maintained a t a temperature around 500'. The calorimeter cover w& immediately put into place and the contents of the calorimeter were cooled to about, j o " C. within a period of half an hour. The heat capacity of the glass formed by this comparatively rapid cooling process was then measured in a continuous series of determinations, starting at 33' and going up to 345' C. In covering this temperature range the heating process required 1.1hours. The experimental values so obtained are given in Table I, where Column I shows the mean temperature of each determination, Column 2 the corresponding specific heat in IgO-calories per gram of the boron trioxide and Column 3 the heat capacity at constant pressure per mean gram atom. As the oxide is really a very viscous liquid above 2 7 jo, this sample was next cooled very slowly and regularly down to room temperature in order that we might determine the differences between a glass sample formed by slow cooling and one formed by rapid cooling. This slow cooling process required

2098

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TABLE I The Heat Capacities of Boron Trioxide Glass and Liquid


(Determinations made while heating after the formation of the glass hy very rapid cooling) Cp per gram Cp per gram Temp., "C Temp., "C Cp per gram atom Cp per gram atom

0 . 2 1 4 cal.

2 . 9 8 cal. 3.07 3.14

22j.6

0 . 2 6 3 cal.

235.5 244.3

0.281

3.22

252.3

0.385

260. j 266.4

0.448 0.4j1 0.440

0.257

3.32 3.41 3.46 3.05 3.54 3.57 3.57 3,56 3.58

0.257

3.58

33.6 46.3 58.6 72.3 84.0 104.9

0.245

120.9

0.248

129.5 142.9 159.3 176. I 191. I 210.4

0 . 2jI

2 1 7 .I

0.220

0.22j

0.231 0.238

0.2j4

0.256 0.2j6 0.25j

272.2

281, I 294,s 309.2

324.5 338.1 345.3

0.320

0.439 0,436 0,438 0.436 0.437 0.436

3 . 6 6 cal. 3.92 4.46 5.37 6.24 6.28 6.13 6.12 6.07 6.10 6.08 6,0g 6.08

TABLE 11 The Heat Capacities of Boron Trioxide Liquid and Glass Temp., "C

332.4 318,s 303.3 285.2

(Determinations made while cooling from the liquid condition) Cp per gram CP per gram Cp per gram atom Temp., 'C Cp per gram atom

0 . 4 3 7 cnl. 0.438 0,439 0,437

278.3 271.4 261.4

0,434

255.3 248.9

0.413 0..398 0.383 0.360

242.6

234.3

0.430 0.424

0 . 3 4 4 cal. 0.333 0.3'4 0,304 0.293

4 . 7 9 cal. 4.64 4.38 4.24 4.08

0.285

3.97 3.82 3.78 3.64

6 . 0 9 cnl.

227.8

6.10 6.12 6.09 6.05 5.99 5.91

221.0

207.6 200.8 190.4 177.4 161.8

5.75

153.9

0.271

5.54

135.0 124.8 112.6

0.261

5 .34 j .02

0.274

0.2jj

3 .55

O.Z\jI

3.50

about 18 hours and during it a series of heat capacity determinations was made upon the material by keeping the jacket temperature below the calorimeter temperature by a regulahed amount and measuring the rate of cooling of the calorimeter. This procedure illustrates one of the great advantages of our "radiation" calorimeter over one which employs electric heating as in the Kernst method: it is possible to study the heat capacity of a substance during cooling as well as during heating. The heat capacity values obtained in this cooling procedure are given in Table 11.

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.5 .4


.3 .2

.I

---- Determined from U" ~

__-_

heating curve following rapid cooling. Determined from heating curve follo slow cooling. Determined from coolinq curve.

0

200

300

400

FIG.3 The Heat-capacity Curves for Boron-trioxide Glass and Liquid

TABLE I11 The Heat Capacities of Boron Trioxide Glass and Liquid (Determinations made while heating after the formation oi the glass by dow cooling) C p pergram Cp per gram Temp., "C Cp per gram atom Temp., ' C C p per gram atom

35.3 46.5 61.8 75.5 87.2 118.6 130.8 143.6 159.5

0 . 2 1 5 cal. 0.221 0.228

0.234 0.240

0.254 0.259 0.262 0.267

1j5.6 190.3 199.7

0.28j

207.I

0.289

214.3

0.294

0.273

0.279

3.00 cal. 3.08 3.18 3.26 3.35 3.54 3.61 3.65

223.6 230.8 237.7. 246,4 252.3 258.6 265.3

0.308cal. 0.318 0.341

271 . o

0.447

3.72

276.0

3,80 3.89 3.97

283.4 310.6

0.438 0.436 0.436 0.435

323.1

0.434

4.03 4 . IO

295,9

0,397 0.448

0.479 0.466

4.29cal. 4 43 '

4.75 5.53 6.24 6.67 6.49 6,23 6.10

6,07 6.07 6.06 6.0j

A third complete series of determinations (given in Table 111) was then made upon this newly formed glass by heating it up gradually from 35' to 32j oC. These particular results might, perhaps, be considered as the normal or standard values for a carefully annealed boron trioxide glass. The three series of determinations are represented graphically in Fig. 3, where the heat capacity (at constant pressure) per gram of boron trioxide has been plotted against the Centigrade temperature. Below 100' and above


2100

S. BENSO?; THOMAS AND GEORGE 5. PARKS

280' the three curves practically coincide. On the other hand, in the intervening range they show marked differences, which were also found in the three preliminary groups of determinations. For comparison with our experimental results the literature' contains very few values. Regnault has reported a specific heat value of 0.237 cal. per gram a t a mean temperature of 57'; this lies about 4.3% above our curve. Russell by the method of mixtures has obtained a series of three interval specific heats covering the temperature range, - 13 joto f40'. His highest point, 0.217 cal. per gram a t a mean temperature of 40' C., falls within 0.1% of our curve. Considering the differences in the experimental methods, these agreements are really very satisfactory. On the other hand, Samsoen and Monval* from the results of a discontinuous series of determinations by the method of mixtures believe that the transition between the glassy and liquid states takes place at 218" C. with a heat of transition of 2.3 cal. per gram. They report 0.302 cal. per gram for the specific heat of the glass below 218" and 0.344 cal. per gram for that of the liquid above this point. Our data indicate that this transition is spread over the temperature interval from 220' to 2 7 5 ' and that the specific heat of the glass is steadily increasing with temperature while that of the liquid is practically constant a t 0.43j cal. per gram. Thus there are several points of discrepancy between our investigation and that of Samsoen and Monval. We feel, however, that our method, which gives a continuous series of values on the same sample, is far more reliable than theirs. Discussion of the Curves

I n their general form the two heating curves, especially the one made with the annealed boron trioxide glass, are remarkably similar to those which were obtained previously in the studies upon organic glass-forming materials. Thus it is quite evident that the organic and inorganic glasses are essentially the same in character, the former merely showing softening, or the transition into the liquid condition, at a considerably lower temperature. As suggested in previous papers,3 the rather sudden increase in heat capacity on changing from the glass to the liquid condition may be explained on the assumption of a great decrease in the magnitude of the interatomic constraints or attractive forces within the material. If we may suppose that these constraints are fairly large within the glass, the resulting mean atomic heat capacity, according to the Einstein or Debye functions, should be much below the limiting value of 3R (Le. 5.96 calories) at moderate temperatures, as in the present case, altho it should exhibit a marked increase with rising temperatures. On the other hand, a relatively large decrease in these internal constraints throws us a t once into the region where Cv approaches Landolt-Bornstein-Roth-Scheel: "Tabcllen" 5th Ed., p.

* Samsoen and Monval: Compt. rend., 182, 968 (1926).

1252

(1923).

Huffman, Parks and Thomas: J. Am. Chem. Sac., 52. 3246 (1930); Parks, Thomas and Gilkey: J. Phys. Chem., 34, 2032 (1930).


STUDIES ON GLASS

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j.96 calories and where Cp, of course, is somewhat 1arger.l In this region (above 280’ C in the present case) the heat capacity should exhibit little or no change over rather wide intervals of temperature. The actual process of loosening up the interatomic constraints2 within the glass should require energy; and in our opinion this requirement accounts for the very marked maximum or “hump” in the heat capacity curve (corresponding to the data in Table 111) of the annealed glass around 2 6 0 “C. The excess energy represented by this “hump” thus serves to some extent the same function as the latent heat of fusion in the transformation of a crystalline solid into the liquid state. However, its magnitude is much less than the heat of fusion of a crystalline solid, indicating that probably the strong interatomic constraints in a glass are far less numerous. I n the specific heat curve obtained during the slow cooling process we find evidence of a thermal hysteresis effect. I n this case no “hump’‘ appears, altho the energy given up during cooling is clearly equal to that represented in the subsequent heating curve with its hump. Evidently we have here a temperature lag or undercooling effect in the process of tightening up the interatomic constraints, i.e. in the vit’rifaction process. This situation is again analogous to the undercooling so frequently observed in a liquid prior to crystallization. The heating curve for the glass formed initially by very rapid cooling also presents some interesting features. If we are permitted to apply the adjective a t n b k to the annealed glass, this particular glass might properly be described as ?vetasi‘nble. Apparently its formation has been so rapid that the interat,omic constraints wit,hin it show a wide variety of magnitudes and those of great strength are perhaps much less numerous than in the well annealed product. Accordingly, on heating up this metastable glass to 140’ C., mnrked internal readjustments take place. Strains are to some extent relieved, probably with the evolution of some energy and the production of a larger number of rather strong const’raints. These, however, are much less numerous than in the well annealed glass, as evidenced by the relative sizes of the two “humps” involved. In short, the behavior of this metastable glass may well be likened to that of an incompletely Crystallized solid. Frequently the latter, on heating up, reaches a temperature at which further crystallization proceeds with the evolution of heat and, possibly, with an apparent decrease in the specific heat,. Moreover, if the melting point is reached before crystallization is complete, the heat of fusion (or fusion hump) is found to he less than for a completely crystallized sample of the same substance. 1 We are here assuming that the motions of the component atoms in liquid boron trioxide are primarily vibrational in character as in a crystalline solid. While these vibrations are undoubtedly more or less anharmonic, becoming more 90 a t higher temperatures,, the Einstein or Debye heat capacity formulas can probably be applied here as first approximations. Rosenhain calls this “the rupture of interatomic bonds.” We here have borrowed quite freely from the picture and idea6 presented by this author in his splendid article on “The Structure and Constitution of Glass,” Trans. Soc. Glass Technology, 11,77 (1927).

2 I02

8. BENSON THOMAS AND GEORGE 6 . PARKS

summary

A fairly accurate “radiation” calorimeter has been developed for use between room temperature and 500’ C. With this apparatus the heat capacities of boron trioxide glass and 2. liquid have been measured between 35’ and 350’ C. with a probable absolute error of less than 4% and with a reproducibility for comparative purposes of about 0.5%. 3. The heat capacity curves obtained (a) by heating a “metastable” glass, (b) by heating a well annealed glass and (c) by slowly cooling the liquid to produce the annealed glass have been compared and discussed.


I.

Department of Chemistry, Stanford Unaversity, California, Febrwlrq 8,1991.

Studies on Glass. VI. Some Specific Heat Data on Boron Trioxide

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