# Alternative liquid for Galileo thermometer

So a friend of mine broke my Galileo thermometer recently. The glass tube and the liquid inside were lost, but the bulbs survived. I've cleaned out an old tall glass candle, and tried filling it with water. Even when the water is steaming hot the bulbs still float, so the liquid in there was definitely not water. It smelled somewhat like gear oil, so I'm guessing it might have been an oil, but I'm trying to think of low density (clear) liquids that I could acquire to fill the tube with. Preferably water soluble, so I can calibrate it by adding water until it's accurate.

Suggestions?

(No, I am not buying a new one. I am an intelligent human being, I have been presented a challenge, and I will use science to overcome it—not mere money.)

You would be wise to somehow determine the exact fluid used by the original manufacturer.

Consider that each of the floats has a fixed density, and has a temperature marked on its hanging tag. So you need a liquid which will have the correct, different density at each temperature marked on a tag. In short, the liquid you choose must match both the original liquid's density, and coefficient of volume expansion.

An alternate method would be to first settle on a liquid that has the correct density. You could adjust ethanol with water at $20^o$C until the appropriate float is suspended. Then slowly change the temperature, note when each of the remaining floats moves, and change the marking on the tag of that float...

Good luck...

You should be able to start with methylated spirits - ethanol with a bit of methanol mixed in to make it toxic and cheap (or ethanol if you can get your hands on it - but it will be expensive because of excise taxes unless you can prove "scientific exemption".) It is much lighter than water and highly miscible with it.

Once calibrated you do need to seal it in properly or the fumes will get to you.

WARNING - this is toxic and flammable stuff. Read safety data sheet for proper handling http://www.jmloveridge.com/cosh/Industrial%20Methylated%20Spirit%2095.pdf

I have broken one of these myself in the past - never thought to revive it. You inspire me...

Take one of the "floats" at the lower end of the temperature range, and find a way to accurately determine its mass (easy) and volume (harder), and calculate its density, noting the temperature tag that is attached. Take another float at the upper end of the temperature range and do the same. Just for grins, to ensure that your data are linear, choose a float in the middle of the range and do the same.

Plot the 3 data points, using density vs. temperature, and verify that the relationship is linear. Assuming that it is, and based on previous comments and postings, do an internet search on various hydrocarbons, and attempt to find the hydrocarbon that has the density vs. temperature relationship that you graphed. If you can't find that particular hydrocarbon, look for two or more hydrocarbons that are in the required density range, and back-calculate the mixture that is required.

I have no doubt that the data you are looking for is manufacturer's proprietary information, so you can't Google it. Thus, you either need to back-calculate it, or find a SMALL sample of it, and hire a laboratory to run an analysis on it. Good luck.

And, of course, there is an alternate method. Find a fluid that you like (assume water). Take all of the temperature indicators off of the floats. Attach new, light tags to the floats, that you can write on. Put all of the floats in the fluid of choice, and adjust the fluid temperature until only one float is neutrally buoyant and the rest are sunk. Pull that float out of the liquid and write the temperature on it. Change the temperature until the next float is neutrally buoyant, and write the correct temperature on that tag. Repeat until all floats have a number written on their tag. Admittedly, this is the "poor man's way" of getting the job done, but it is probably the most direct way.

Mine is broken too and water is not heavy/dense enough. The bulbs sinks to the bottom. So Ethanol will be too light too. The original liquid smells "oily". I created my own liquid with enough and high(!) density by solving more and more sugar in water. And you need a lot of sugar before it starts working more or less. Problem now is that the fluid is quit thick/syrupy. But it works and is save to drink (unless you are a diabitic patient).

I would say give it a try, Jos