Rate of Temperature Measurement (Effect of Salt)

[rencero]

Can anyone help me with our investigative project in physics? This is just a very simple project.
Our experiment is all about the effect of salt on the rate at which a glass thermometer measure a sudden change in the temperature of a solution.

The thermometer will first be allowed to be at thermal equilibrium with solution 1, then, the thermometer will suddenly be transferred to solution 2 (with different temperature). The time needed for the thermometer to reach 63% of ΔT (Tf-Ti) will be recorded. This will then be the thermal time constant.

One of my groupmates proposed this. Her assumption is that adding salt to water would affect the thermal time constant (the amount of time needed in order for the thermometer to read 63% of the expected change in temperature) of the glass thermometer. Is her assumption correct? Can anyone suggest on how can we improve this project?

 

[Andy Resnick]

why would adding salt to the solution affect the material properties of the thermometer?

 

[rencero]

yes. that is what i kept on explaining to her. But my groupmate insists that it has an effect.

We've done a different experiment. We obtained the thermal time constant of the thermometer at different ΔT. We were expecting that the value of the time constant would be the same. But based on our observations, the thermal time constant decreases as ΔT increases. Is this acceptable? We were expecting it to have the same value, but based on our observations, it varies. I am thinking is there really a change in its value or is the variation just due to errors? We've done several trials and the same results were obtained.