The same method I used before, now let's restrict temperature of Sulfuric acid and Potassium nitrate to less than 200°c. To test I will use thin copper wire. If it survives we can move forward and use real IC.

It might look easy but MOSFETs cannot be used. Since they are better suited for DC not AC. So Triac or electric relay must be used. But the thermostat thing with Arduino can stay as is.

I've always wanted to make Arduino regulated power socket. 

It went surprisingly smooth. 

Also changed gasket to Viton rubber. I hope it will withstand Nitric acid. 

Also replaced cooling rubber tube as few Nitric acid drops felt on it and it cracked. 

What's reminds me not to play with Nitric acid to much few drops and dispose of it. 

I've started from range of  160-170 when I measured the temperature of the plate but nothing happened. So I've increased gradually to 200 and nothing happened. Some sites said 200 some 180. So I targeted the sensor to the upper part of boiling mixture the temperature was only 50°c as I did that owen started (as it was set to about 200°c) until I realized what happened the temperature on the plate rised to more than 300°c and flask was filled with red fumes. I've checked the quality by dipping fine copper wire in it. It desolved as usually, too much heat killing Nitric acid. 

Re-watched and re-read everything I could find on DIY nitric acid acid and RFNA (Red fuming nitric acid) only now I got where the 200 or 180 degrees coming from. It's fahrenheit! And in Celsius it 83°c which the temperature which Nitric acid decomposing to water and something else.

Got it! I've decided to re-run the experiment with my last portion of Potassium nitrate. This time I've pointed the sensor to the mixture not the plate.

 The test was pretty much the same with red fumes now I tried to change the direction of the sensor the temperature jumped to 180°c! Alas! I aimed to high! I throwed waht I've got in the output flask and restarted again, knowingly it already contaminated with some water got few drops their color was more transparent (no yellow) 

I didn't expect too much as I knew the temperature was wrong but the result surprised me! Instead of usual dissolving which typically looks like this:

This time I got only few drops and same amount of ultra thin 0.02mm copper wire but it dissolved in such a vigorous/violent way! I saw red plums of fumes and it was boiling. My first thought was OMG how do I turn it off. Luckily there was so little of copper and Nitric acid so it stopped after few seconds. 

I don't have video of this as it happened so fast and it was my last portion of Potassium nitrate. I will redo the experiment only for the sake of making this chemical reaction 😝

One thing was clear this time it was much more concentrated acid.