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110 QUANTITATIVE AGRTCn/rrRAL AXALYSIX

The terminals of the electric, circuit used for tiring arc now attached,
Care should be taken that neither the bomb nor tin* stirrcr in
allowed to touch the sides of the can. Th(* Htirrcr is now si ailed and
allowed to run 3 or 4 minutes to equalize the temperature throughout
the calorimeter.

Readings of the thermometer are. now taken for 5 minutes (muling
to 0.001° or 0.002° every minute) at the end of which time fin* switch in
turned on for an instant only, which will he found sufficient, to fire* the
charge. In course of a few seconds the temperature begins to rise rapidly
and approximate readings are takon every minute* until the rise become**
slow, more accurate readings then being taken. After a maximum temper-
ature is reached and the rate of change of temperature is evidently due only
to radiation to or from the calorimeter, the readings arc continued for an
additional 5 minutes, reading every minute. These readings, before the
firings and after the maximum temperatures, are m*ci*ss»ry in the com-
putation of the cooling correction. The time- elapsed from the time of
firing to the maximum temperature .should be, in no case, more than 0
minutes.

When through with the run, replace the bomb in the* holder ami allow
the products of combustion to escape through the valve at the top of the
bomb. Unscrew the large nut and clean the interior of the bomb. The
inside of the nut should be kept greaned, also the* threaded part, at the top
of the lower cup.

Immediately after each run, the lining of the bomb should be washed
out with a cloth moistened with a dilute solution of ammonium hydroxide
and then with water. When the apparatus after using;, is to be left for
several hours or more before making another test, the lining should be
removed and the inner surface of the bomb slightly coated with oil. This
oil under the linings should be removed when next preparing the bomb for
use, as an excess of it may be ignited with a possible resulting injury to the*
linings.

Heavy Qih, Coke and Hard C'oal—The determination of the heat of
combustion of heavy oils, such m crude petroleum, and ulno of eoke and
extremely hard coals, is best made by mixing with u ready burning com-
bustible, such as a high-grade bituminous coal or pure earbon. This
auxiliary combustible facilitates the complete combustion of the whole
mixture in the case of coke, and hard coal, and with the* heavy oil it acts its
a holder and prevents rapid evaporation of the oil. The uuxiliary rornbuH-
tihle should be placed at the bottom of the pan and the coke, roal or oil
sprinkled over it. It should be dried with extreme cure mul carefully
standardized as to the resulting rise in temperature, per gram in the calori-
meter when completely burned.

Calculation,—First plot a smooth curve, using temperatures

as ordinates and time as abscissas, line only the* ntniight por-
tions of the ends of the graph for calculating K\ and #2.

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