ROBERT C. PLUMB
chemical principles exemplified
Worce*ter Polytechnic lmlitule Worcerter, Massathu~lh01609
Cooking Succulent Roasts
Scuba Diving and the Gas Laws
/Nustrating principles of chemical kinetrcs and equilibrium Adapted from "Let's Cook it Right" by Adelle Davis1 Cooking a roast of heef so that i t is juicy and delicious is an art which many good restaurant chefs and some, hut by no means all, home cooks have mastered. A knowledge of the chemical dynamics of the process (and choosing prime heen can help any amateur equal the best restaurant roast sirloin. Are the complex chemical reactions in roasting best controlled by manipulating the rate of the overall reaction and the length of time that the reaction proceeds or by manipulating the balance of a chemical equilihrium? Certainly the overall roasting process can't he thought of as a chemical reaction a t equilihrium-it is obviously irreversible. However, experiments show that the quality of the product is far superior if the cooking process is thought of as an approach to equilihrium rather than as an exercise in chemical kinetics. Many cooks practice what we might call the "kinetic" method of cooking a roast. For example, a well-marbled tender cut of heef is placed in an oven set a t 300°F and the cooking time is estimated a t 20, 25, or 30 min/lb depending on whether the center is to he rare, medium, or well done. When a meat thermometer a t the center reaches 140. 155. or 165°F the roast is done. ~ o nearly t as common, but giving far superior results, is what we might describe as the "equilihrium" method. A roast is placed in an oven set at the temperature which the meat should reach when it is done and the meat is allowed to warm up to that temperature in the oven.2 It takes longer-3 times or more. However the cooking time is not critical as it is with the "kinetic" method. The meat does not get overcooked-the longer it cooks the more tender it becomes. It turns out rare, medium, or well done in accord with the temperature you choose, not the lenath of time i t cooks. The advantages of the "equilihrium" method (usually called slow roasting) are numerous. The meat is delicious. juicy and tender, slices beautifully and shrinks very little: Nutritionally the meat is superior; proteins and vitamins are not broken down at the lower temperatures, juices containing vitamins and minerals are not lost. Try roasting from the point of view of an approach to equilihrium -you will find that thereafter you will he able to identify slow roasted meat by sight and taste and will he raised to a higher level of culinary delight. ' Adelle Davis received a Master of Science degree in biochemistry from the University of California Medical School and is author of several books on cooking and nutrition. See Davis, Adelle, "Let's Cook It Right," Harcourt, Brace, Jovanich, Inc., New Yark, 1962, pp. 47-9 for further details. Conrad Baronowski is a senior at Worcester Polytechnic Institute, majoring in electrical engineering. Cooperman, E. M., et sl., "Mechanism of Death in ShallowWater Scuba Diving," Conod. Med. Assoc. J., 99,1128 (1968).
Illustrating Boyle's Law, Henry's Law and the thermodynamics of gas compressions Contribution by E. D. Cooke, Syncrude Canada Ltd. and Conrad Baranowski3 Since its development for military use in World War I1 SCUBA (self-contained underwater breathing apparatus) diving has rapidly developed as a sport; there are now an estimated one-half million divers in the U.S.A. alone. A large number of illustrations of physical-chemical principles can he drawn from the technology of this sport; three of these are discussed here. Getting Your Money's Worth When a diver goes to the dive shop to have his scuba tanks filled, the tank is connected to a compressor and filled to about 2100 psi (140 atm) while immersed in a tank of water. Why immersed in a tank of water?-so that the compression of air into the tank will he approximately isothermal rather than approximately adiabatic. If air could be compressed adiabatically from 300°K and 1 atm to 140 atms the final temperature would, from the following equation and the heat capacity of air
he approximately 1270'K; from the gas laws we see that the quantity of air in the tank would be only 300/1270 or 25% of that which would he present if this process were carried out isothermally. How hot does the water jn the cooling tank get? Using elementary thermodynamics it is possible to estimate only the minimum rise in temperature. If the gas is assumed ideal and the compression assumed to he reversible and isothermal w,,, = nRT In (PJP,)
and since L\E = 0
For a gas tank of volume 12.31 and a final pressure of 140 atm, n = 70 moles and qirr < -208 kcal. The thermal energy would raise the temperature of a cubic meter of water by a t least 0.20S°C, how much more depending on the extent to which the process is irreversible. Surviving the Training Program No activity is without hazards; the circumstances of the death of a novice scuba diver in a standard size indoor swimming pool4 are worth detailing, both to exemplify Volume 50.
Number 6, June 1973 / 425
Boyle's law and to help avoid similar accidents in the future. The victim was a 21-year-old Canadian flying cadet; he was learning the procedure known as "ditching." In this procedure the diver swims to the pool floor, takes a final breath from his tanks, abandons his equipment and rises to the surface; he then returns and redons the equipment. The victim failed to exhale as he was rising-it can happen through fear or lack of instruction or for physiological reasons, e.g., a bronchial obstruction. The pressure difference between 9 ft of depth and the surface is 0.28 atm. Thus when he reached the surface the air trapped in the lungs was a t a pressure nearly 30% higher than the fluids in the rest of the hody-memhranes separating the circulatory system from the air were ruptured and air was forced into the coronary arteries causing death within 24 hr. The Right Mixture for Deep Dives
Unlike sea creatures whose natural habitat is the high pressure of the deep, man's physiology has evolved so that
426 / Journai of Chemical Education
he gets along nicely breathing air a t 1 atm pressure. Are there physiological effects associated with breathing air under pressure? The problem caused by the increased solubility of nitrogen a t high pressures and its solution by substituting helium, a much less soluble inert gas, is well known. However there is another not-so-well-known effect which is important, that of oxygen pressure and solubility. Man's lungs and circulatory system are used to functioning a t an oxygen partial pressure of 0.20 atm. Increase the partial pressure of oxygen to, e.g., 1.M) atm by breathing compressed air a t a depth of 128 ft where the total pressure is 5.0 atm and the blood will become richer in oxyhemoglohin. This excess of oxygen oddly enough leads to carbon dioxide poisoning-the urge to hreatbe is reduced and carhon dioxide is not baled out of the system. The concentration of oxygen required to provide the physiological partial pressure of oxygen in the lungs is easily computed for a given depth. Cousteau's divers on Conshelf 111 used a mixture of 98% helium and 2% oxygen. For what depth would that mixture have been designed?
