I bought a $3 regular thermometer at Walmart today and am marveling at the precision that it required to make. How do they make thermometers with such an inner diameter of the tube, and how do they fill it so accurately? This is, also, quite old technology, so it must be rather simple.
I did find references to glass thermometers being regularly produced in europe as early as 1666.
I don't know how they are made in mass production, but if I was challenged to guess how it "could" be done I'd say:
The tubing is made by drawing out a larger diameter glass tube. There may be a strip of opaque colored glass fused to the side first to provide the backdrop. The bulb may well be "blown" by heating that end until it closes over and then blowing in the other end in typical glassblower fashion.
You could probably fill them through the open top end by submerging them in the filling liquid, pulling a vacuum so all the air leaves the thermometer, then bringing them back up to room pressure.
I'd expect you could establish the right amount of liquid in them by heating them to a temperature you want to correspond to the full length of the tube, so the excess spills out, then letting them cool so the column retracts, and finally fusing the top end closed.
Sounds like something even I could learn to do if I absolutely positively had to.
Of course. As far as how to fill it accurately, I would imagine the whole filling system is at a temperature at the top of the scale - fill it to the top, and as it cools it'll shrink down. But the volumes have to be very precise. I'd also like to know how it's drawn, but the filling I think is the easy part.
Try to imagine HOW they would be filled to the top. In fact, the part of the tubing with the uniform hole is not all that difficult to make with proper practice because of the way glass behaves when it has a hole in it and is pulled. The descriptions I have read for older methods involve pulling the capillary tube, sealing one end, adding the reservoir end, open, pulling a vacuum inside the whole thing, sealing the bottom. Not something I would like to try with alcohol inside.