Works blood in a fountain pen

Aha : Why does ink flow out of the fountain pen when I write?

Blood drawn from the earlobe. You know it. A puncture and blood flows from the vessels into a tube. The doctor doesn't need an injection. The blood rises in the cannula by itself if it is thin enough.

This is due to the fact that liquids like water like to wet a surface made of glass. The liquid molecules find attractive partners on the inner wall of the cannula due to their electrical charge distribution. The force with which they are drawn to the glass wall is greater than that with which the water molecules are bound together. They rise up in the hair-thin tube. The thinner the tube, the higher it is.

With the fountain pen you make use of this. "There are two thin capillary channels in the spigot that sticks into the cartridge from below," says Reinhard Probol, head of the development laboratory at Lamy in Heidelberg. The ink moves in these tubes towards the pen. It's slit in the middle. “The gap is wider at the back than at the front. So the ink reaches the tip. ”No further than that.

When writing, the nib bends slightly and the liquid comes into contact with the surface. If you put the filler on a plastic surface, little happens. Plastic cannot be described. Paper is different: it absorbs the liquid. Just like a mop absorbs water, the paper fibers pull the ink out of the cartridge - also due to surface forces.

While the cartridge is dispensing ink, air must be drawn into it at the same time. Otherwise a vacuum would be created in it, the cartridge itself would suck on the liquid and after a short time not let a drop out. A control valve takes care of the pressure equalization.

The inner workings of the fountain pen are even more complex. He should write at any temperature. If the temperature rises from 15 to 30 degrees, the air expands and the ink is pushed out of the cartridge more strongly. The filler could now leak if the excess liquid could not be collected in small chambers. These slats must first empty the next time you write. Another technical finesse. And all for a few clean lines. Thomas de Padova

A collection of the “Aha columns” was recently published by Piper-Verlag under the title “Wissenschaft im Strandkorb” (160 pages, 14 Euro 90).

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