Conventional Calorimeter Research Articles

A glass disk calorimeter for pulsed lasers

Because existing calorimeters are not adequate to measure Q-switched laser pulses accurately, we have designed a calorimeter in which the beam passes through two glass disks, one of green plate (absorbing from 0?6-1?6 ?m), the other of clear plate. A laser pulse creates a temperature difference which is sensed by thermocouples. 70% of the incident energy passes through the device and is available for experiment. Thermal drift is low enough to obtain 1% accuracy at 10 mJ input energy. For energies up to 0?1 J, any pulse length from 1 s to 0?1 ps can be used. Energies up to 50 J can be used provided the power density at the glass does not exceed 40 MW cm?2. The device is dependent on a conventional calorimeter for calibration (limiting the absolute accuracy to 2%), and the sensitivity is wavelength dependent, thus limiting its use to wavelengths where a free running laser is available; ways of overcoming this disadvantage are discussed.

Solid-liquid equilibrium diagram for the argon-methane system

The equilibrium between the solid and liquid phases of the argon-methane system has been investigated using the conventional calorimeter method of thermal analysis together with the heat capacity measurements. For the vapour pressure determination of solid and liquid mixtures a separate apparatus was constructed in which a metallic bellows operated as a pressure transducer at low temperatures. The measurements have shown an eutectic type of T-X equilibrium diagram with a miscibility gap between 23% and 67% methane. Two three-phase lines have been located between the quadruple point of the system and the respective triple points of the pure constituent components on the p-T graph. The qualitative behaviour of this system at different compositions is illustrated by means of a three-dimensional space model. Satisfactory agreement between the experimental results and theory could be achieved if we treated the solid phase as a regular solution and the liquid phase as a V a n L a a r solution.

Thermodynamic study of complex formation: 2,2′-bipyridine and some organotin and tin tetrachloride systems

The formation constants of 2,2′-bipyridine complexes of dialkyltin dichlorides, n-butyltin trichloride, and tin tetrachloride in acetonitrile have been determined spectroscopically. The heats of reaction in acetonitrile solution for these systems have been also determined by a conventional calorimeter of Dewar vessel type. From these results, free energy, enthalpy and entropy changes of these complex formations have been calculated. While, heats of solution of n-butyltin trichloride and tin tetrachloride in acetonitrile and heats of mixing of carbon tetrachloride solutions of some alkyltin chlorides with acetonitrile have been measured, and tin tetrachloride in acetonitrile has been found to be strongly co-ordinated by the solvent molecules. The order of co-ordinate bond strengths of 2,2′-bipyridine to alkyltin chlorides and tin tetrachloride is: SnCl 4 > n-C 4H 9SnCl 3 > (CH 3) 2SnCl 2 ≅ (C 2H 5) 2SnCl 2 > ( n-C 4H 9) 2SnCl 2. The u.v. spectra of complexes of 2,2′-bipyridine and tin chlorides have been discussed.

Thermochemistry of metallic alkyls. Part 15.—Heats of combustion of trimethyl-isopropyl tin, trimethyl-t-butyl tin and tetra-isopropyl tin

The heats of combustion at 20°C of crystalline Me3SntBu, and of liquid Me3SniPr and iPr4Sn have been measured using a conventional bomb calorimeter charged with O2 at 40 atm pressure, from which the standard heats of formation (in kcal/mole) were derived: ΔH°f(Me3SntBu, c)=–28.96±1.05, ΔH°f(Me3SniPr, liq.)=–20.91±1.0, ΔH°f(iPr4Sn, liq.)=–44.81±1.3.

Design and use of aneroid bomb calorimeters

(1) The object of a bomb calorimeter is to absorb the heat released from an accurately measured amount of chemical reaction and convert it into a temperature rise which can be measured with corresponding accuracy. Questions associated with the chemical reaction are often difficult, but will not be discussed here. This paper is concerned with the purely physical questions associated with the temperature rise. It is also concerned, in part, with the physical problem of producing a comparable temperature rise by introducing accurately measured Joule heat within the calorimeter. This procedure is necessary when the calorimeter is used for evaluating a thermochemical standard material, such as benzoic acid, with the intention of using it to measure the equivalents of other bomb calorimeters in which heat will be generated by combustion only. Reasons will be put forward for believing that aneroid bomb calorimeters are capable of higher accuracy than conventional calorimeters in which the heat is absorbed in well stirred water. It will be contended that aneroid calorimeters can be designed which are simpler, and quicker in use, than stirred-water calorimeters. (2) Apart from chemical considerations, the first requirement of a calorimeter is that its equivalent should be repeatable every time it is assembled, except for small variations in mass of substance, platinum, fuse and auxiliary material for which corrections can be made. The presence in the conventional calorimeter of water, whose heat of evaporation is very high, means that great care must be taken in design and assembly to minimize the evaporation and condensation of water, and to reproduce in every experiment any movements of water which are unavoidable. (3) The rate of transfer of heat Q between the calorimeter and its surroundings, during the period of the experiment, must obey an unchanging law such as Q. = k( T Tc) where T is the temperature of the thermometer in the calorimeter, and k and T c remain constant throughout the experiment. Corrections can be applied, for example, if Tin the equation differs for part of the time from the temperature of the thermometer; but errors are unavoidable if k and Tc do not remain constant. It is clearly an advantage if k is small, and this is best achieved by evacuating the space between the calorimeter and its outer jacket, and by lengthening the electrical leads which cross this space. Vacuum spaces are not usually possible round stirred-water calorimeters. As to the problem of keeping k constant, investigations by White l and others have shown that k is affected mainly by water vapour movement and by convection of air in the space surrounding the calorimeter. The

Aneroid bomb calorimeter for determining the heat of combustion of thermochemical standard benzoic acid

An electrically calibrated bomb calorimeter is described which has no stirred water, and is mounted in an evacuated outer jacket. Its departures from the ideal are investigated. The heat of combustion of samples from a batch of specially pure benzoic acid is found to be 26431·7 J/g under ‘standard bomb conditions’, with an estimated standard error of 2·2 J/g. This result is compared with those of conventional calorimeters. Considerably less time per determination is needed with the new calorimeter than with a typical conventional calorimeter.

A new high precision calorimeter for the measurement of heats of combustion: and the heat of combustion of succinic acid

The construction, calibration and use of a high-precision bomb calorimeter of the aneroid type are described. It consists of a stainless-steel combustion bomb as designed by Garlton-Sutton (I933) in a mantle of aluminium alloy, the temperature of which is measured by a platinumresistance thermometer. A simple means of measuring the electrical ignition energy has been devised. Because the time required for the attainment of a thermal steady state is greater for this type than for the conventional water calorimeter, the theory underlying methods of allowing for heat loss from the calorimeter to its surroundings has been critically re-examined, and the limitations of the commonly used Dickinson method (1914) have been clearly stated. For high precision to be attained, it proves to be particularly necessary that the conditions under which calibrations and measurements are performed shall be as similar as possible. Working under optimum conditions, chosen after systematic trials, it is possible to reduce to 0.012 % the standard deviation of the values for the calibration constant, with benzoic acid as the standard substance. The heat of combustion of succinic acid has been redetermined as — A.US = 3020-57 +0-43 cal/g (vac.). This agrees very well with the high-precision determination by Huffmann (1938) 3020-47 ± 0.43. Succinic acid is suitable as a secondary standard for combustion calorimetry; and the best value is taken to be 3020.5 ± 0.5 cal/g (vacj <.

A Rotating Combustion Bomb for Precision Calorimetry. Heats of Combustion of Some Sulfur-Containing Compounds

To obtain accurate heat of formation data for organic sulfur compounds, a heat of combustion calorimeter has been developed in which it is possible to rotate the bomb after the combustion. Rotation of the bomb tends to produce a thermodynamically defined final state for the combustion process, because the stirring action hastens the attainment of (a) homogeneity of the bomb solution and (b) equilibrium with respect to solution of the bomb gases in the solution. Uncertainties inherent in the use of conventional calorimeters for heat of combustion studies of sulfur compounds are thereby minimized. Results, comparable in precision to those possible in similar studies of hydrocarbons, have been obtained. The indications are that the rotating bomb will have many other applications in combustion calorimetry, particularly in cases in which it is advisable to add a large amount of liquid to the bomb. The following values in kcal. mole/sup -1/ are reported for the standard heats of formation, ..delta..H/sup 0//sub f/(25/sup 0/), of some organic sulfur compounds from graphite, hydrogen gas and rhombic sulfur: 1-pentanethiol, (1) -36.1, (g) -26.2; 3-thiapentane, (1) -28.9, (g) -20.4; 2-methyl-2-propanethiol, (1) -33.7, (g) -26.3; thiacyclopentan, (1) -17.3, (g) -8.0; thiacyclobutane, (1) +6.2, (g) +14.7; and thianthrene,more » (s) +43.6.« less