Climate in cities

Basics

Worksheet: Wind in the city

Sheet 4: Ways to produce smoke for the experiment

For the experiment, shown on Worksheet 3, you need smoke.

This page shows you different possiblities to produce smoke:

1st possibility: Usage of dry ice

Dry ice (frozen CO2) is used to cool food during transport, to produce fog on stages and discos, and to cold-shrink certain objects.
Dry ice can be bought at different stores and costs between 5 and 10 €. However, the problem with dry ice is that it sinks when frozen, in contrast to fog which rises. Additionally, as dry ice is quite dangerous (burnings), it shouldn’t be used for this experiment.

2nd possibility: Usage of a fog machine

Fog machines, which are often used in discos can either be bought or rented. It is important that the fog machine only blows in one direction. If it doesn’t, it might be converted with a fitting attachment (diameter of about 3 cm).

3rd possibility: Usage of fog from model railways

Furthermore, little smoke-producers in stores, where model railways can be bought. They are very cheap and only vaporize harmless oil. The smoke only has to be blown by a fan into the direction of the model.

4th possibility: Usage of fog candles / tablets / powder

Fog candles / fog tablets / fog powder can be bought in magician stores. However, as they produce gases which may be harmful to health, these things shouldn’t be used. Alternatively, the smoke of cigarettes might be used.

5th possibility: production of salmiac

Salmiac can be produced in the chemistry lab. And this is the best way to produce smoke for this experiment. Do you know why?
The following instruction will help you produce it:

Chemical production of salmiac:

1. Which measures of precaution have to be taken when doing the following experiment?

Any chemical experiment hast to be carried out under high safety precautions in the chemistry lab.

When using acids and bases there is the danger of etching.

When using substances which are easily inflammable there is a high danger of fire.

Toxic and irritating substances must be dealt with care.

Certain chemical reactions are in the danger of exploding.

For your safety you should always wear protective glasses.

A plan in case of emergency should be set up.

The teacher should consider whether the learning effect and the use for the pupils is higher than possible side effects like the harm of health.

Security note when producing salmiac:

From the chemical point of view smoke can easily be produced with the help of hydrochloric acid and the vapour of ammonia.
However the production in big amounts is harmful to health. Only when the smoke is needed in little amounts it is justifiable to health.

2. Production of salmiac:

The reaction of the vapour of hydrochloric acid and the vapour of ammonia produces the fog of sal ammoniac.
(Only use very little amounts!)

Attention: Hydrochloric acid and the vapour of ammonia are toxic and etching and harmful to health.
To get rid of the substances prepare for a neutralization of SO4 and NH4.

Ammonium hydroxide and hydrochloric acid react to ammonium chloride and water:

NH4OH + NH4CL + H2O

Production of Salmiac, picture taken by G. Bauer

The following things are needed:

1. standing cylinder with 2 cover plates

2. 2 wash bottles

3. rubber hoses

4. T-piece

5. rubber blower

6. concentrated ammoniac

7. concentrated hydrochloric acid

3. Other chemical ways to produce smoke:

- Production of white phosphorus (dangerous)

- Green and red fireworks used for a garden party (dangerous)

- Bengalis fire (very dangerous)

About this page:

- Author: - G. Bauer, B. Wohlhöfer - University of Nürnberg - Germany
- scientific reviewing:
- educational reviewing: Dr. Schrettenbrunner / Dr. Schleicher / J. Heres
- last update: 09.09.03