calorimeter would have attained if there had been no loss of

heat.

Record the observations and calculations as in the previous section, and the additional calculation as follows:

Rate of cooling during third period = 0°-025 per half min.

Repeat the experiment, using a little more water in the calorimeter. If the two results obtained are concordant take the mean as the final result.

It is instructive to compare the results obtained by this approximate method of treating the cooling with the more accurate one given in the last section. It will be found that even in the case of a substance taking up the temperature as quickly as quartz the difference is appreciable.

SECTION XXVII.

LATENT HEAT OF WATER.

Apparatus required: Calorimeter, thermometer graduated in tenths of degrees, piece of ice.

The latent heat of water, i.e. the heat absorbed when 1 gram of ice melts, may be determined by adding ice at 0°C. to sufficient water to melt the ice completely, and determining the decrease of temperature of the water.

Weigh the calorimeter provided, place in it about 170 grams of water at about 18° C., and weigh again.

Select a piece of ice weighing about 10 grams.

Place in the water a thermometer graduated to tenths of degrees, and observe the temperature of the water every half minute for 6 minutes ("First period ") as explained in Section XXV.

Dry the surface of the ice thoroughly with blotting paper, and at the end of the next half minute drop it into the water of the calorimeter. By means of the stirrer keep the ice under water and the water stirred. Take half-minute observations of temperature till it reaches a minimum and then commences to rise-" Second period." Continue observations of temperature for 6 minutes after the rise has become uniform, these observations constituting the "Third period.”

From the observations taken in the first and third periods plot the curve from which the cooling at any temperature can be found, and apply the correction for cooling (or in this case heating) as described in Section XXV.

Weigh the calorimeter to determine the amount of ice

which has been added, and from your observations determine the latent heat of water.

Work out from elementary principles the formula applicable in this case and record the observations and calculations as in Sect. XXV, and the additional calculations as follows:

Repeat the experiment, using a little more ice, and if the two results are nearly alike take the mean as the final result.

SECTION XXVIII.

LATENT HEAT OF STEAM.

Apparatus required: Calorimeter, condenser, thermometer graduated in tenths of degrees, flask, stand and burner.

The latent heat of steam, i.e. the heat necessary to convert water at 100° C. into steam at the same temperature, may be determined by condensing a known weight of steam and observing the heat given up during the process to the liquid of the calorimeter, generally water, kept always below 100° C. The condensation takes place more regularly if the steam is allowed to condense in a separate vessel and not in the water of the calorimeter itself.

Weigh the calorimeter stirrer and condenser (Fig. 52) provided, first empty, then remove the condenser, weigh it to

01 gram, replace, fill the calorimeter to within about 2 cms. of the top with water at the temperature of the room, and again weigh.

Arrange the vessel in which the steam is to be generated, the delivery tube and the calorimeter as shewn in Fig. 53.

When this has been done, disconnect the tube from the condenser and place a burner under the boiler, regulating the height of the flame so that the water boils gently, the steam being allowed to escape from the end of the tube.

Observe the temperature of the water in the calorimeter for 6 minutes the "First period" of previous sections. Then replace the calorimeter, and insert the delivery tube into the head of the condenser tube so that the steam passes into the condenser and is condensed there. Keep the water well stirred, and observe the temperature every half minute, "Second period," till it has been raised about 10° C., then remove the delivery tube from the condenser.

Continue observations of temperature till the change of temperature has been uniform for 6 minutes, "Third period."

Weigh the calorimeter and contents, and for greater accuracy remove the condenser with its contents of condensed water from the calorimeter, dry its outer surface and weigh it again to 01 gram.

and

Determine the cooling during the first and third periods by means of the values found correct the observed temperature throughout the experiment for cooling, and find the latent heat of steam at the boiling point corresponding to the atmospheric pressure at the time.

Work out the necessary equation and record as follows: