How would you set up a simple experiment to test whether salt crystal growth is affected by temperature

Question

It might help if you were clear on how an experiment is set up.

An independent variable is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable. (In your case, it would be the temperature.)

A dependent variable is the response or measure of results. (In your case, this would be the change in size, if any, of the salt crystals.)

Extraneous variables — other than the independent variable — potentially can affect the dependent variable, so they must be controlled. If possible, you try to keep them constant between the experimental and control group.

The experimental group receives the independent variable.

The control group is similar to experimental, except it does not receive the independent variable. Extraneous variables are balanced between experimental and control groups. (Here is where you need to do your research — online or otherwise — to find out what the extraneous variables are. One of them would be the type of salt you are using.
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As an example, suppose you want to find out if fluorides reduce dental cavities. You would find two groups, trying to control the extraneous variables. Extraneous variables are found by surveying previous research in the area. In this case, you would match the groups in terms of previous history of cavities, diet and dental hygiene habits including how and how often they brush their teeth.

The experimental group would get toothpaste with the independent variable, the fluoride, while the control group would not have the fluoride in their toothpaste. The toothpaste without the fluoride would be the placebo.

The dependent variable would be the number of cavities after participating in the experiment for a time. The dependent variable indicates the results, but it is not the results. At the end of the experiment, both groups could have no change in cavities or one of the groups could have a greater reduction in cavities. (Of course, if the fluoride increased cavities, you wouldn't want to use it.) All of these varied results would be indicated in terms of the dependent variable.

Since this is not my area of expertise, I searched Google under the key words "salt crystal growth" to get these possible sources for extraneous variables:

http://chemistry.about.com/cs/sciencefairideas/a/aa072903a.htm
http://www.newton.dep.anl.gov/askasci/chem03/chem03222.htm
http://www.creativekidsathome.com/science/crystals.html
http://www.selah.k12.wa.us/SOAR/SciProj2000/KaitlynS.html
(Broken Link Removed)

I hope this helps. Thanks for asking.