[research sos] Idea about the calorimeter

[Please give some useful suggestions or comments]

In my research, I'm trying to use some simple tools to replace traditional styrofoam calorimeter.

I came up with an idea to use two different size test tube and set up as a calorimeter as in picture.

Using the gap between two test tube to act as a heat insulator.

But, yet, it can't insulate heat well. The temperature drops so fast.

So I tried to make the gap vacumm, or silver covered (as in picture ). But they are not working.

I need some help, any idea would be good.

If I increase the space between test tube, or to fill the gap with some high specific heat material like water. would that do any good?

\&