ANALYTICAL CHEMISTRY
1304 for carbon in the converter, to the simultaneous determination of carbon, hydrogen, and nitrogen. I t is hoped that interference from halogens or sulfur can be eliminated without undue difficulty. ACKNOWLEDGMENT
The authors Kish to express their thanks to J. u'.Henderson who carried out most of the analyses herein reported. LITERATURE CITED
(1) Aluise, V. A,, Hall, R. T., Stoats, F. C., and Becker, W. W., ANAL.CHEM.,19,347 (1947). (2) Chambers, W . T.,paper presented at the Rubber Technology Conference, London (June 23-25,1948). (3) Dinerstein, R. A,, and Klipp, R. W.,ANAL.CHEM.,21, 545 (1949).
(4) Elving, P. J., and Ligett, W. B., Chem. Revs., 34,129 (1944). Ibid., 43,69 (1948). (5) Emmett, P. H., (6) Gadsby, J., Long, F. J., et al., Proc. Roy. SOC.(London),A187,. 129 (1946);A193, 357,377 (1948). ENG.CHEM.,ANAL.ED.,6, 358 (1934). (7) Kirner, W.R., IND. (8) Wagman, D. D., Kilpatrick, J. E . , Taylor, W. J., Pitzer, K. S., and Rossini, F. D., J . Research Natl. Bur. Standards, 34, 143 (1945). (9) Smithells, C. J., "Gases and Metals," p. 94, New York, John Wley & Sons, 1937. (10) Meulen, H.ter, Chem. Weekblad, 19,191 (1922). (11) Taylor, R. C., and Young, W.S.,IND.ENG.CHEY.,ANAL.ED., 17,811 (1945). (12) Untersaucher, J., Ber., 73B,391 (1940). (13) Walton, W.W.. MoCulloch, F. W.,and Smith, W. H., J . Research Natl. Bur. Standards, 40,443 (1948). RECEIVED April 4, 1050. Presented in part before the Division of Analytical and Microchemistry a t the 116th Meeting of the AMERICAY CHEMICAL SOCIETY, iitlantic City, N. J.
Calorimeter for Some Corrosive Liquids B. H. SAGE A N D E. W. HOUGH' California Institute of Technology, Pasadena 4, Calif. The calorimeter described is suitable for measuring the heat capacity of corrosive liquids at temperatures up to 400" F. This instrument follows the general design utilized by Osborne and co-workers for the study of the heat capacity of water. The calorimeter appears to be capable of yielding results with an uncertainty of less than 170,provided the rates of corrosion and decomposition of the fluid under investigation are sufficiently small. The calorimeter was constructed of stainless steel containing a large amount of chromium and nickel and was
T
H E determination of the heat capacity of fluids by calorimetric techniques is not new. The general principles of such measurements were presented by White (IS),who discussed the more essential features of calorimeters and indicated the sources of error. It is believed that the greatest advances in the adaptation of these techniques to use a t elevated pressures were made by Osborne and co-workers ( 5 , 6), who developed a modern calorimeter capable of establishing the heat capacity and enthalpy of the saturated liquid and the enthalpy change upon vaporization of a pure substance over a wide range of temperatures. The calorimeter and associated equipment, the general features of which were similar to those employed by Osborne (6, B ) , are shown schematically in Figure 1. The assembly consisted of a vacuum jacket, A , within which the calorimeter, B , was suspended by small wires. A diffusiontype vacuum pump, C, with an appropriate forepump was connected to the vacuum jacket at D. A small centrifugal-type impeller was mounted a t E within the calorimeter. and served to agitate the Contents. A connection from the bottom of the calorimeter to appropriate equipment, F, was used to measure the pressure. The temperature of the bomb and its contents was determined by means of a resistance thermometer, G (Figure 1). The operation of the equipment involved the addition of a known weight of the material under investigation and the establishment of the energy added electrically by the heater, H, to raise the temperature of the calorimeter and contents a known amount. The rise in temperature was determined by means of resistance thermometer G . Significant gains or losses of energy from the calorimeter were revented by maintaining the wall of jacket A at substantially &e same temperature as the exterior 1 Present
address, Stanolind Oil and Gas Company, Tulsa, Okla.
gold-plated on the internal surfaces to decrease further the rate of corrosion by materials such as red fuming nitric acid. Agitation was provided in the calorimeter to ensure thermal and phase equilibrium, and the assembly was confined within an adiabatic vacuum jacket. Provisions were made for the addition electrically of known amounts of energy to the calorimeter and its contents and for measurements of the resulting change in state. From these and other data, the heat capacity of the liquid was established.
of calorimeter B. Any difference in the temperatures of the two surfaces was ascertained by means of copper-constantan thermocouples. From a sequence of measured increments in temperature. each of which resulted from the addition of a known amount of energy, the change in internal energy of the calorimeter and contents was established as a function of temperature. Upon the completion of such a set of measurements, the quantity of material in the calorimeter could be altered and the measurements repeated. From two such series, the change in the internal energy of the fluid in the calorimeter could be determined without knowledge of the heat capacity of the calorimeter or of the nuisance volumes ( 1 ) . The measurements were carried out in the heterogeneous region and corrections were made for the changes in phase associated with the change in temperature of the calorimeter and contents. However, in order to avoid the need for two sets of measurements with unusually corrosive materials, procedures requiring knowledge of the heat capacity of the colorimeter and nuisance volume were often employed. METHODS O F MEASUREMENT
The evaluation of the heat capacity of a fluid by the methods just discussed consisted of two principal steps: first, evaluation of the net quantity of energy added to the calorimeter and contents and, second, determination of the resulting change in state. The first step involved little that was thermodynamic in nature, inasmuch as it included the determination of energy transfer to and from the calorimeter and the means of evaluating the energy added electrically to the equipment. The second step was primarily a thermodynamic analysis of the resulting processes.
V O L U M E 2 2 , NO. 10, O C T O B E R 1 9 5 0
1305 of the calorimeter was established from two sets of measurements upon water, utilizing the enthalpy data of Osborne and co-workers ( 2 , 5 ,7). Good agreement was obtained between the present set of heat capacity measurements and those of Osborne et al. ( 7 ) .
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DESCRIPTION OF APPARATUS
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The general arrangement of the calorimeter assembly is shown in Figure 2.
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Figure 1.
Schematic Arrangement of Calorimeter
The methods employed in establishing the net quantities of energy added to the calorimeter were similar to those used by Osborne and co-workers (5, 6) and followed by other investigators in this field (9) with but slight revision. Corrections were made in the conventional fashion for the energy loss from the calorimeter as the result of radiation and for the gain in energy associated with the mechanical agitation of the contents. These determinations in conjunction with the measured electrical input yielded values of the net energy additions with an uncertainty of not more than 0.1%. The quantity of material in the calorimeter was considered to be constant for a particular loading, as the change in weight of material within the connecting lines was negligible. This variation in weight might have been taken into account, but it materially complicated the calculation of the results without significantly increasing their accuracy. This "nuisance volume" was less than 2% of the total volume of the calorimeter and was filled \\-ith liquid. In these circumstances it appeared that a change in weight of material within the calorimeter during a set of measurements was usually less than 0.05% of the total material present, thus permitting an average value to be used safely. One of the more accurate means of evaluating thermodynamic properties involved similar measurements with two different quantities of material in the system. This approach was used bj- Oshorne (6) and others (12) to good advantage. The basic expression was prasented recently ( l a ) for evaluating the change in internal energy of the calorimeter and contents in terms of the properties of the phases and the relationships applicable to the estimation of the isobaric heat capacity. This method, when applied to a pure substance, necessitated measurements with two rather widely different quantities of the liquid and gas phases present, as well as data concerning the volumetric properties of each phase. Such information need not be highly accurate and in many instances may be estimated satisfactorily from the la11 of corresponding states. The calorimeter described here was not well suited to the measurement of the heat capacity of gases, except those of fairly high molecular weight at elevated pressures. The technique outlined above cannot be used in some instances without excessive deterioration of the calorimeter because of the lengthy contact of the corrosive fluids with the apparatus. However, the heat capacity of the calorimeter may be ascertained, thus eliminating the need for more than a single set of measure. ments. This procedure is believed to be somewhat less desirable, but was followed by Osborne and Van Dusen (8) and others (IO). In the present instance the apparent heat capacity
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The calorimeter, A , was constructed of stainless steel of moderately high tensile strength and was machined in two parts to be joined by a tapered acme thread. Figure 3 is a photograph of the calorimeter prior to assembly. The vessel was designed for an operating pressure of 1000 pounds per square inch, a t which presSure the steel was stressed to a maximum value of 20,000 pounds per square inch, well below the ultimate strength of the metal. The interior of the calorimeter was plated with gold to decrease the rate of corrcsion by the material under investigation. The total thickness of gold of a p p r o x i m a t e l y 0.015 inch was applied in five successive operations. The gold was burnished b e t ween each plating to attempt to fill the small pores. I t is probable that even with this laminated structure of the gold plate a substantial part of the corrosion of the c a l o r i m e t e r with nitric acid resulted from its reaction with the stainless steel t h r o u g h pores. Lugs were provided on the outside of the bomb to facilitate assembly and disassembly and t o reinforce t h e s p h e r i c a l walls a t t h e points where the leads to the internal heater were brought through the wall of the calorimeter. Agitation within the calorime t e r was o b t a i n e d b y means of the impeller, B , Figure 2, which induced c i r c u l a t i o n through the ports, C, over a heater which is not shown. and up around the circulation shield, D. T h e fluid flowed down around the resistance thermometer, E , and returned to the impeller along the radial guide vanes, F. Provision also was made k~ circulate a small part of the total flow through the space below impeller B. A photograph of the principal internal parts of the calorimeter including the impeller, shield, and guide vanes is shown in Figure 4. These parts were also coated with a fairly heavy gold plate.
Figure 2. General Arrangement of Calorimeter
The rate of corrosion of the AISA Type 320
ANALYTICAL CHEMISTRY
1306
Figure 3.
Calorimeter Bomb Prior
to
Assembly
stainless steel employed in the construction of the calorinlotei under the action of red fuming nitric acid was established as a function of temperature. This rate w&sdetermined hyaseriesof measurements at a given temperature, from which the rate of loss of the stainless steel with time was fixed. The influence of separation and drying followed hy re-exposure was not large. Most of the expoaure times were for a period of 24 hours. It was found that the average corrosion rate at 235' F. was approximately 0.71 inch per year a t a volume-to-area ratio of 1 inch. At this rate, i t would he difficult t o obtain accurate heat capacity data because of the enthalpy changes resulting from the reaotion between red fuming nitric acid and stainless steel. It is also necessary to avoid rapid deterioration of the calorimeter. The corrosion rate of red fuming nitric acid upon a gold-plated sample of this stainless steel a t 235" F. was 0.21 inch per year at about the sam6 volume-to-area ratio. This rate represents the conditions after approximately 36 hours' exposure. The impeller, B, Figure 2, was driven by the shaft, G, enclosed in tube H which emerged from the vacuum jacket through a seal, I. B was mounted upon platinum-glass hearings shown in Figure 2. Smdl ports that do not appear in this figure were used to connect the annular space between shaft G and the interior of tube H with the lower part of the calorimeter, These ports were so located that substantially all the liquid in the calorimeter could be removed through H . A string-free platmum resistance thermometer within the stainless steel tube, E, Figure 2, was used to measure the temperature of the calorimeter and contents. Conventional four-lead eon-
The oil bath, K, Figure 2, was surrounded by an adiabatic jacket, which is not shown and which was msintained by manual control a t substantially the same temperature as the oil bath. This shield was desirable in order to avoid the need for the large energy additions which otherwise would be required to maintain the oil bath a t the appropriate temperature. Photographs of the magnetic drive for the odorimeter agitator and the belt drive for the oil bath agitator appear in Figure 6. The magnetic drive was operated a t approximately 200 r.p.m. and afforded adequate torque to rotate the impeller st this speed. The entire calorimeter was housed in a separately ventilated structure in order to prevent damage to other parts of the laboratory and t o personnel in case of a complete failure of the apparatus when being operated a t elevated temperatures. Figure 7 indicates the general arrangement of the calorimeter wit,h the sssociated control equipment. The calorimeter was placed upon a steel frame covered inside and out with Trausite sheeting, and the control room, which was adjacent to the calorimeter, housed almost all of the electrical control equipment required. The odorimeter was located in the room which comprised the right half of t,he housing shown in Figure 7. This room was maintained a t a slightly reduced pressure by a blower discharging to the atmosphere. Various other pieces of apparatus were contsined in the lefthand room shown in Figure 7. The mechmicrtl vacuum pump and a three-stage jet pump, with capacities of about 0.15 and 8 cubic feet per second, respectively, were used to evacuate the adiabatic jacket of the calorimeter. One of the potentiometers was used in conjunction with B thermocouple, a galvanometer, a photoelectric circuit, and a light source to govern the temperature of the oil bath. The difference in temperature between the oil hath, A, and the calorimeter, B, Figure 1, was kept small enough by this arrangement t o minimize thermal transfer. The mer y for the internal calorimeter heater wm furnished electricjly by four 6-volt storage b&teries. The potential difference across and the current through the heater were measured by a Type K-2 otentiometer shown in Figure 7. The temperature ditference getween the adiabatic jacket snd the oil bath was measured by a White double potentiometer. The resist8nces of the two platinum resistance thermometers in the calorimeter were determined by B Mueller-type bridge. The material was added to the calorimeter through a tube entering the bottom of E', Figure 2. Conventional high-vacuum techniques utilizing weighing bombs (9) were employed in adding or withdrawing materid. It is believed that these techniques have been so refined that weight of material added to the calorimeter was determined with an uncertainty of less than 0.8%.
block tin because of the fairly low corrosion rate of this material in contact with red fuming nitric acid. The calorimeter was supported within J by means of three small wires. The jacket, J , Figure 2, was constructed of stainless steel and immersed in the oil bath. K . The imoellw., L.~diaehnrnerl ~ , _-.__.._ . . the ~ oil tbrouEh the ports. M, aud circulated i t around the outside of the shield, N , upon which two electric heaters were mounted to aid in the control of the temperature of the oil bath, The flow of the oil ww upward around N, through the opening, 0, The pressure within the calorimeter was established t hrouah down around the vacuum jacket. DSSt the mide vanes. P. and a stainless-steel diaphragm attached to E' and oil-filled t ubing which led to a pressure balance (11). The stainless-stee1 diaphragm was necessary in order to avoid reaction between th e materials under investigation and the oil in the pressure ba.lance. appeared that, by appropriate control of the position
