series through a dry cell and voltmeter, or a telephone receiver and source of low-voltage alternating current. When contact is made, the voltmeter is deflected or the receiver buzzes. Take readings of micrometer and thermometer first with the rod at room temperature. Before heating the rod, turn back the micrometer several revolutions and slip the rod out of contact with the set-screw. Heating of these screws will expand them and lead to error. Pass steam through the jacket for several minutes till the thermometer ceases to rise. Find the boiling temperature by the method described in Experiment No. 201. Do not move the set-screw after the first micrometer reading has been taken. Dry the contact points before taking any readings of the micrometer. The expansion of the rod is given by the difference between the readings of the micrometer when the bar is hot and cold respectively. Measure the length of the rod with a meter stick. Having the expansion, the temperature change, and the original length of the rod, compute the coefficient of linear expansion. Test at least two different metals, taking them alternately and making two or more trials with each rod. Do the results show that different metals have the same or different coefficients of linear expansion? EXPERIMENT NO. 203 CUBICAL EXPANSION OF A LIQUID. References: Stewart, Physics, Sect. 200; Kimball, College Physics, Sect. 387; Duff, College Physics, Sect. 183, 184; Spinney, Text-Book of Physics, Sect. 163, 167. The coefficient of cubical expansion of a liquid is the amount of change in volume of unit volume for a change of one degree in temperature. In the method to be described the volumes are determined indirectly by weighing. A specific gravity bottle or pyknometer is used. It must first be cleaned and dried. Weigh the bottle, without the stopper, as accurately as the balance will permit. Fill the bottle with the liquid to be tested and place it in a bath of crushed ice and water for ten or fifteen minutes until the liquid comes to 0°C, leaving the stopper out. When this temperature is reached, insert the stopper, force out the excess liquid and wipe the bottle dry. Remove the stopper carefully and weigh the bottle and contents. The difference between this weight and the first weight is the weight of the liquid at 0° C. Call this Mo. Next suspend the pyknometer in a bath of water and heat to boiling point. (In case the liquid boils at a temperature lower than the boiling point of water, a temperature lower than the boiling point of the liquid must be used.) When the temperature has been constant for a few minutes, read the thermometer, and insert the stopper. Remove the bottle from the bath, dry the exterior and weigh without the stopper. The weight of the liquid left at this temperature is this weight minus the weight of the empty bottle. Call this weight M. If we represent the coefficient of apparent expansion of the liquid by B, then B = M-M M(T-To) For if V represents the volume of the pyknometer (considered the same for all temperatures), then V/M is the volume of unit mass at T°C, and V/M。 is the volume of unit mass at O°C, and But the true coefficient of expansion, A, of the liquid can be shown to be equal to the coefficient of apparent expansion, B, plus the coefficient of cubical expansion of the glass, called G. That is, A=B÷G. The value of G for glass may be taken as .0000267. Take two sets of observations, tabulate results as follows, and calculate A: Weight of Pyknometer| Temperature | M.=Q--P|M=R-P B EXPERIMENT NO. 204 THE CONSTANT-VOLUME AIR-THERMOMETER. References: Stewart, Physics, Sect. 211; Kimball, College Physics, Sect. 374, 375, 393; Duff, College Physics, Sect. 175, 188; Spinney, Text-Book of Physics, Sect. 163-166. Experience shows us that if a certain mass of gas has its temperature changed, but is prevented from expanding, the pressure increases in such a way that the increase of pressure is proportional to the increase in temperature; that is, if P, is the pressure at 0° C., and P1 that at t° C., then 1 P1 = P。(1+at), where a is called the pressure-coefficient of the gas. Its value for any ordinary gas is nearly 1/273. The object of this experiment is to find the value of a for air, and to use the value so determined for finding the temperature of the room. The air-thermometer consists of an elongated glass bulb full of dry air, connected by a fine-bore tube to a short wider tube. into which is sealed a platinum wire to serve as a marker. This tube leads to a long piece of rubber tubing which connects with another parallel glass tube, open at the top. Mercury stands in the rubber tubing and in the two upright glass tubes, but must not on any account be allowed to get into the bulb. First place the bulb in a vessel containing a fine mush of ice and water. Be sure that the mush is thick enough so that the ice is not floating above the water, for in that case the temperature near the bottom of the vessel may be several degrees above zero. Also be sure that the ice and water cover the top of the bulb. As the air cools, it will tend to suck mercury into the bulb. This must be prevented by lowering the open tube at the other end of the rubber hose, so as to reduce the pressure in the bulb. When the bulb has been in ice long enough for the air-temperature inside to become constant, raise or lower the open tube till the mercury in the side next to the bulb just touches the end of the platinum wire. Then read by the verniers the heights of the mercury in each arm. Also read the height of the barometer, and then calculate the total pressure of the air in the bulb. This gives Po and calculate the new pressure, P1. Immedia the readings of the heights of the mercury co removing the bulb from the steam, lower the bulb side so that, when the bulb cools, mercury over into the bulb. The temperature of boil existing barometric pressure (see Experiment N Hence we can calculate a, since the volume has both cases. To determine the temperature of the roo to stand and cool to the room temperature, mercury is not sucked into the bulb. The b stand about half an hour to insure a const Then adjust the mercury level as before, deter and calculate the new t. EXPERIMENT NO. 205 SPECIFIC HEAT. References: Stewart, Physics, Sect. 215-220; Physics, Sect. 396-399; Duff, College P 196; Spinney, Text-Book of Physics, Sec The purpose of this experiment is to deter heat of one or more metals by the method of specific heat is defined as the number of calori to raise the temperature of one gram of the sub Centigrade. The calorimeter furnished consists of two nickel-plated cups, one supported inside the conducting ring at the top. The inner cup is proper; the outer one serves to prevent the gai by radiation. A metal stirrer is also provi inner cup and stirrer together and multiply specific heat of the material of which they ar the water equivalent. The material of which the specific heat is to be found should be in small pieces; lead shot, copper or aluminum pellets. A sample of the metal must be weighed out and put into a small copper cup with a handle, and this cup set in a boiler of water to heat. Bury the bulb of a thermometer in the mass of metal particles and place cotton around the stem to prevent the loss of heat by convection. Continue the heating until the reading of the thermometer ceases to change, and then note the highest degree reached. While the metal is being heated, weigh out in the calorimeter a mass of water a few degrees below room temperature and of sufficient volume to cover the metal particles when they are poured into it. A second thermometer, preferably one reading to fifths of a degree, is used to take the temperature of this cool water. Set this calorimeter and water inside the jacket. When the metal has reached a stationary temperature, near the boiling point, read the temperatures of both the metal and the cool water, remove the cotton and thermometer from the copper cup and quickly pour the metal into the cool water. Stir the mixture and record the temperature after it becomes uniform throughout the mass. Determine the fall in temperature of the metal. Multiply this change of temperature by the mass of the metal and by S, the unknown specific heat of the metal. This indicated product is the amount of heat given off by the metal in cooling. Heat has been absorbed by the water, by the cup and stirrer, and by the submerged part of the thermometer, That absorbed by the water is found by multiplying its mass by its rise in temperature. The product of the water equivalent of the cup and stirrer times the same rise in temperature gives the heat absorbed by the calorimeter and stirrer. The quantity absorbed by the thermometer can be found as follows: Since glass is a poor conductor of heat, we may safely assume that only the submerged part of the thermometer is heated. It takes 0.46 calories to heat one cubic centimeter of either glass or mercury one degree Centigrade, so if we can find the volume of the submerged part of the thermometer, we can calculate the heat absorbed by it. Set the calorimeter cup and water on one pan of a balance and enough weights for equilibrium on the other pan. Place the thermometer in the water, not allowing it to touch the cup, but |