HEAT OF COMBUSTION

105

calorimeter itself. The weights of these (and the known specific
heat of the materials of the calorimeter), taken with the weight
of the substance burned and the temperature rise, furnish the
necessary data for the calculation.
Emerson Fuel Calorimeter.—Following is a description of the
Emerson calorimeter and also directions for making the deter-
mination of fuel value.
Bomb.—The bomb, made of steel, consists of two cups joined
by means of a heavy steel nut. The two cups are machined
at their contact faces with a tongue and groove, the joint being
made tight by means of a lead gasket inserted in the groove. The
lining is of sheet nickel, platinum or gold, spun in to fit. The
bomb is closed by a milled wrench or spanner. The pan holding
the combustible is of platinum or nickel, and the supporting
wire of nickel. (See Fig. 28.)
Calorimeter.—The jacket is a double walled copper tank,
the space between the walls being filled with water. The calo-
rimeter can is made as light as is possible, of sheet brass, nickel
plated.
Stirring Device.—The stirrer is directly connected to a small
motor and it is enclosed in a tube to facilitate its action in circu-
lating the water. The stirrer is mounted on a post on the calo-
rimeter jacket as is also the thermometer holder.
Ignition Wire.—Unless ignition of the fuel requires a very high
temperature a platinum resistance wire is suitable. For ignition
of such substances as are used in determining the water equivalent
of the calorimeter (naphthalene or cane sugar) or of anthracite
coal an iron wire is more certain in its action because it burns
and produces a higher temperature. When iron wire is used a
correction of 1600 calories per gram of wire is subtracted from
the total calories obtained from the fuel combustion. This
is the heat of oxidation of the iron.
Formation of Nitric Acid.—When any nitrogenous organic
matter is burned in air practically all of the nitrogen is liberated
in the elementary form. On account of the high concentration
of oxygen in the calorimeter bomb a considerable portion of the
nitrogen is oxidized and the products dissolve in the water which
is formed by the combustion of hydrogen. A dilute solution of
nitric acid is thereby formed. This gives rise to a positive error