**Calibration of bomb calorimeter **

**PURPOSE **

The purpose of

this standard operating procedure is to provide the guidelines of calibration

of bomb calorimeter.

**SCOPE**

The

scope of this standard operating

procedure includes the guidelines of calibration of bomb calorimeter.

**PROCEDURE**

The

effective heat capacity of the system is determined by burning pure and

dry benzoic acid weighing not less

than 0.9 and not more than 1.1 gram. Determine the corrected temperature rise T

, from the observed test data , also titrate the bomb washings to determine the

nitric acid correction, and measure the unburnt fuse fire ,compute the energy

equivalent by substitution in the following equations:-

** H
M +
E1 + E2**

** W
= ——————————**

**
T**

** **Where

W

= energy equivalent of calorimeter in calories per degree centigrade.

H

= calorific value of standard benzoic acid/ sample in calories per gram

M

= mass of standard benzoic acid/samples in grams.

T = corrected temperature rise in degrees C.

E1 = correction for heat formation

of nitric acid in calories, and

E2 = correction for heat of combusting of

firing wire, in calories

# Pharmacology: Prep Manual for Undergraduates

**CORRECTIONS TO BE MADE**

**1. Cooling Correction**: Cooling correction

includes the effects of the heat interchange between the vessel and the jacket

due to conduction, convection and radiation, and of the heats of stirring and

evaporation. This is minimized by having the temperature of the

water in the vessel below that of the water in the jacket

at the time of firing and within ±1 ^{o} C, preferably ± 5^{o}C,

of it at the end of the chief period a low heat of stirring and a low loss by

evaporation. The correction shall be determined as follows by the use of the

Regnault – Pfaundier formula or the Whitaker Formula which gives, for a

representative series of coals, a mean correction differing by not more than

one part in 1000 from that given by the Regnault – Pfaundier formula.

**2. Whitaker Correction**: In place of the Regnault –

Pfaundier cooling correction, which s cumbersome, the Whitaker correction may

be adopted, provided that it has also been employed to find the water

equivalent or the heat capacity of the apparatus. The heat capacity will be

found by the Whitaker correction to be about to be 0.25 to 0.3 percent lower

than the value given when R-Pcorrection is used – a difference of 7 to 9 in

3000.

To employ the Whitaker correction ten temperature

readings are taken in the after period in order to obtain a more reliable value

of the cooling rate per minute. If this rate be denoted by the dt and the time

from the instant of firing to any chosen temperature reading in the steady

cooling period be x minutes, then the cooling correction is simply (X x dt)^{o}C.

The “observed rise” is the difference between the temperature at the instant of

firing and the temperature taken x minutes later in the cooling range. It is

not necessary, nor is it desirable , to take the actual maximum temperature

reading. Generally , a temperature taken 2 or 3 minutes later in the steady

range of cooling forms a more reliable and definite “observed maximum”. The

temperature value at x, of course , depends upon the magnitude of x, but the

same corrected temperature rise is obtained provided that dt is constant.

**3. Heat of Ignition**: The heat release from the cotton and

firing wire is subtracted from the total heat release. The heat release from

the cotton is calculated from the weight, after drying at 105^{o}C, of

a known length of cotton thread, and using the calorific value of cellulose

(4180 cal/g). Determine the weight of piece of

wire equal in the length to the distance between the poles of the bomb, and

calculate the heat release by allowing 335 cal /g for platinum wire.

**4. Heat of formation of Acids**: The heat gain due to the

formation of sulphuric acid and nitric acid is subtracted from the total heat

released. These corrections amount to 3.60 cal/ml of 0.1 N sulphuric acid 1.43

cal/ml of 0.1 N nitric acid presents in the bomb washings and are calculated as

follows: –

Sulphuric

acid correction = 3.60(a+b-20) cal

Nitric

acid correction = 1.43 (20-a) cal

Where

a=

vol in ml of 0.1 N hydrochloric acid used

b=

vol in ml of 0.1 barium hydroxide used

**5. Correction for Unburned Carbon**: If unburned carbon

is suspected, its heat equivalent on the basis of 1 mg of carbon equals 8

calories shall be added to the determined heat release. Unburned carbon is

determined as the loss in weight on ignition of the residue from the crucible.

**Calculation**:

The following example illustrates the method of calculation using the Whitaker

corrections:

Calculation

using Whitaker correction:

Weight

of crucible + thread

= 5.298 g

Weight

of crucible + thread + coal

= 6.301 g

Weight

of air – dried coal = 1.003 g

Mean

Calorimeter temperature

= 26.5^{o}C

Effectivemean

heat capacity at 26.5^{o}C

= 2.863 cal /^{ o}C

Correction

for sulphur in coal

= 16 cal

Temperature of calorimeter jacket = 26.7 ^{o}C

Temperature of thermometer settings =

24.6 ^{o}C

Room Temperature = 26.6 ^{o}C

Moisture in coal = 1.90

%

Ash

= 12.1

%

Uncorrected temperature rise = 2.480^{
o}C

Add cooling correction = 0.048^{ o}C

Add thermometer correction = 0.014^{ o}C

Corrected temperature rise =

2.542^{ o}C

Heat Liberated = 7.278cal

Subtract nitric acid corrected = 8 cal

Subtract correction for heat of Ignition = 21 cal

Heat from 1.003 3g coal = 7249 cal

Heat from 1.000 0 g coal = 7225

cal

Subtract sulphur correction = 16

cal

Calorific value of air dried coal = 7209

cal/g

**Rounding Off**

– Round off the mean of the values or the single value4 to the nearest 10 cal /

g

**Precision**

– The results of duplicate determination in one laboratory should agree to

within 50 cal/ g and those between different laboratory to within 100 cal / g.** **

**PRECAUTIONS**

1. Do not use too much sample .the bomb

can not be expected to withstand the effects of combustible charges which

liberated more than 10,000 calories. this generally limits the total weight of combustible

material (sample plus gelatin firing oil or any combustion aid) does not more

than 1.10 gram .Do not charge with more

oxygen than is necessary and do not fire the bomb if an overcharge of oxygen

should accidentally be admitted.

2.

Keep all parts of the bomb especially the insulated electrode assembly

in good repair at all times Do not fire the

bomb if gas bubbles are leaking from the bomb when it is submerged in

water.

** **

3. Proceed with

caution and use only a fraction of the allowable maximum sample when testing

new materials, which burn rapidly, or have explosive characteristics.