The Orsat apparatus allows for the analysis of flue gases by passing them through three absorption bulbs containing different solutions. The first bulb contains potassium hydroxide and absorbs carbon dioxide. The second bulb contains alkaline pyrogallic acid and absorbs any remaining carbon dioxide and oxygen. The third bulb contains ammonical cuprous chloride and absorbs any remaining carbon monoxide. By measuring the volume changes in each bulb, the apparatus can determine the percentages of carbon dioxide, oxygen, and carbon monoxide in flue gases, providing information about the completeness of combustion.

1. ORSAT’s APPARATUS
Submitted to:
Dr. (Mrs.) Poonam Syal
Submitted by:
Mr. Dhruv Upadhaya
162510
ME [I&C] Regular

2. CONTENTS
• Introduction
• Orsat’s Apparatus
• Construction
• Working
• Precautions

3. INTRODUCTION
To have proper control on combustion process, an idea about
complete combustion of fuel is made by the analysis of flue gas.
CH4 + 2O2 CO2 + 2H2O
2CH4 + 3O2 2CO + 4H2O
If complete combustion of fuel takes place then Carbon Dioxide is
released. If incomplete combustion of fuel takes place then Carbon
Monoxide if released.

4. Thus,
• if the gases contain considerable amount of carbon monoxide, it
indicates that incomplete combustion is occurring (i.e. considerable
wastage of fuel is taking)
• Also indicates the short supply of oxygen for combustion
if the flue gases contain a considerable amount of oxygen, it indicates
the oxygen supply is in excess, though the combustion may be
complete.
The analysis of flue gases made with the help of ORSAT’S
APPARATUS.

5. ORSAT APPARATUS

6. CONSTRUCTION
• Consists of a water-jacketed measuring burette, connected in series to a set of
three absorption bulbs, each through a stop-cock.
• The other end is provided with a three-way stop-cock, the free end of which is
further connected to a U-tube packed with glass wool (for avoiding the
incoming of any smoke particles, etc.)
• The graduated burette is surrounded by a water-jacket to keep the temperature
of the gas constant during the experiment.
• The lower end of the burette is connected to a water reservoir by means of a
long rubber tubing.
• The absorption bulbs are usually filled with glass tubes, so that the surface
area of contact between the gas and the solution is increased.

7. • The absorption bulbs have solutions for the absorption of CO2, O2 and CO
respectively.
• First bulb has ‘potassium hydroxide’ solution (250g KOH in 500mL of boiled
distilled water), and it absorbs only CO2.
• Second bulb has a solution of ‘alkaline pyrogallic acid’ (25g pyrogallic
acid+200g KOH in 500 mL of distilled water) and it can absorb CO2 and O2.
• Third bulb contains ‘ammonical cuprous chloride’ (100g cuprous chloride + 125
mL liquor ammonia+375 mL of water) and it can absorb CO2, O2 and CO.
• Hence, it is necessary that the flue gas is passed first through potassium
hydroxide bulb, where CO2 is absorbed, then through alkaline pyrogallic acid
bulb, when only O2 will be absorbed (because CO2 has already been removed)
and finally through ammonical cuprous chloride bulb, where only CO will be
absorbed.

8. Flue gas
KOH(CO2)
Water reservoir
Rubber tube
Water tube
Fused Calcium
Chloride
Three way
stopcock
alkaline pyrogallic
acid (O2)
ammonical cuprous
chloride (CO)
ORSAT APPARATUS
graduated burette

9. WORKING
• Flue gas is passed through fused Calcium Chloride which absorbs the water
vapor present due to its hygroscopic properties.
• Three way stopcock is opened and the flue gas is filled in the graduated
burette.
• The whole set up is water jacketed to maintain a constant temperature.
• The stopcock of the KOH reservoir is opened and the water reservoir is
moved up.
• Water inflows in the graduated burette and pushes the gas to flow in the
KOH reservoir.

10. • In that reservoir carbon dioxide is absorbed. The whole CO2 in the sample is
absorbed.
• The water reservoir is brought down so that the air again can rush to the
burette.
• Again the stopcock of the alkaline pyrogallic acid reservoir is opened and
the water reservoir is moved up.
• Water inflows in the graduated burette and pushes the gas to flow in the
alkaline pyrogallic acid reservoir where the absorption of Oxygen takes
place.
• The same process is repeated with the ammonical cuprous chloride
reservoir.
• The Volume increase of all the reservoir is measured and the amount of
Carbon Dioxide, Carbon Monoxide and Oxygen are determined.

11. PRECAUTIONS
• The reagents in the absorption bulb 1, 2 and 3 are brought to the etched
mark levels one-by-one by operating the reservoir bottle and the valve of
each bulb. Then their respective valves are closed.
• All the air in the reservoir bottle is expelled to atmosphere by lifting the
reservoir bottle and opening the three-way to atmosphere.
• It is quite necessary to follow the order of absorbing gases: CO2 first, O2
second and CO last.
• This is because the absorbent used for O2 (i.e., alkaline pyrogallic acid) can
absorb only some CO2 and the percentage CO2 left would be less; while the
percentage of O2 thus-detected would be more. The absorbent used for CO2,
however, does not absorb O2 or CO2.
• The percentage of CO in the flue gas is very small and this should be measured
quite carefully.