How to Make Fitzroy's Storm Glass

Admiral Fitzroy (1805-1865), as commander of HMS Beagle, participated in the Darwin Expedition from 1834-1836. In addition to his naval career, Fitzroy did pioneer work in the field of meteorology. The Beagle's instrumentation for the Darwin Expedition included several chronometers as well as barometers, which Fitzroy used for weather forecasting. The Darwin Expedition also was the first voyage under sailing orders that the Beaufort wind scale was used for wind observations.

Storm Glass Weather Barometer

One type of barometer used by Fitzroy was a storm glass. Observing the liquid in the storm glass was supposed to indicate changes in the weather. If the liquid in the glass was clear, the weather would be bright and clear. If the liquid was cloudy, the weather would be cloudy as well, perhaps with precipitation. If there were small dots in the liquid, humid or foggy weather could be expected. A cloudy glass with small stars indicated thunderstorms. If the liquid contained small stars on sunny winter days, then snow was coming. If there were large flakes throughout the liquid, it would be overcast in temperate seasons or snowy in the winter. Crystals at the bottom indicated frost. Threads near the top meant it would be windy.

Italian mathematician/physicist Evangelista Torricelli, a student of Galileo, invented the barometer in 1643. Torricelli used a column of water in a tube 34 ft (10.4 m) long. Storm glasses available today are less cumbersome and easily mounted on a wall.

Make Your Own Storm Glass

Here are instructions for constructing a storm glass, described by Pete Borrows in response to a question posted on NewScientist.com, attributed to a letter published in the June 1997 School Science Review.

Ingredients for Storm Glass:

• 2.5g potassium nitrate
• 2.5g ammonium chloride
• 33 mL distilled water
• 40 mL ethanol
• 10g camphor

Note that man-made camphor, while very pure, does contain borneol as a by-product of the manufacturing process. Synthetic camphor doesn't work as well as natural camphor, perhaps because of the borneol.

1. Dissolve the potassium nitrate and ammonium chloride in the water; add the ethanol; add the camphor. It is advised to dissolve the nitrate and ammonium chloride in the water, then mix the camphor in the ethanol.
2. Next, slowly mix the two solutions together. Adding the nitrate and ammonium solution to the ethanol solution works best. It also helps to warm the solution to ensure complete mixing.
3. Place the solution in corked test tube. Another method is to seal the mixture in small glass tubes rather than using a cork. To do this, use a flame or other high heat to crimp and melt the top of a glass vial.

No matter what method is selected to construct a storm glass, always use proper care in handling chemicals.

How Storm Glass Functions

The premise of the functioning of the storm glass is that temperature and pressure affect solubility, sometimes resulting in clear liquid; other times causing precipitants to form. The functioning of this type of storm glass is not fully understood. In similar barometers, the liquid level, generally brightly colored, moves up or down a tube in response to atmospheric pressure.

Certainly, temperature affects solubility, but sealed glasses are not exposed to the pressure changes that would account for much of the observed behavior. Some people have proposed that surface interactions between the glass wall of the barometer and the liquid contents account for the crystals. Explanations sometimes include effects of electricity or quantum tunneling across the glass.