You may not feel the approach of impending storms, but the weather causes changes in the atmosphere that affect chemical reactions. You can use your command of chemistry to make a storm glass to help predict the weather.

Storm Glass Materials

2.5 g potassium nitrate

2.5 g ammonium chloride

33 mL distilled water

40 mL ethanol

10 g natural camphor

How to Make the Storm Glass

Dissolve the potassium nitrate and ammonium chloride in the water. Dissolve the camphor in the ethanol. Add the potassium nitrate and ammonium chloride solution to the camphor solution. You may need to warm the solutions to get them to mix. Either place the mixture in a corked test tube or seal it within glass. To seal glass, apply heat to the top of the tube until it softens, and tilt the tube so the glass edges melt together. If you use a cork, wrap it with parafilm or coat it with wax to ensure a good seal.

An advanced version of a cloud in a bottle, a properly prepared storm glass should contain colorless, transparent liquid that will cloud or form crystals or other structures in response to the external environment. However, impurities in the ingredients may result in a colored liquid. It's impossible to predict whether or not these impurities will prevent the storm glass from working. A slight tint (amber, for example) may not be cause for concern. If the solution is always cloudy, it's likely the glass won't function as intended.

How to Interpret the Storm Glass

A storm glass may present the following appearance:

Clear liquid: bright and clear weather

Cloudy liquid: cloudy weather, perhaps with precipitation

Small dots in the liquid: potentially humid or foggy weather

Cloudy liquid with small stars: thunderstorms or snow, depending on the temperature

Large flakes scattered throughout the liquid: overcast skies, possibly with rain or snow

Crystals at the bottom: frost

Threads near the top: wind

The best way to associate the appearance of the storm glass with the weather is to keep a log. Record your observations about the glass and the weather. In addition to the characteristics of the liquid (clear, cloudy, stars, threads, flakes, crystals, and the location of crystals), record as much data as possible about the weather. If possible, include temperature, barometer readings (pressure), and relative humidity. Over time, you'll be able to predict the weather based on how your glass behaves. Keep in mind, a storm glass is more of a curiosity than a scientific instrument. It's better to allow the weather service to make predictions.

How the Storm Glass Works

The premise of the functioning of the storm glass is that temperature and pressure affect solubility, sometimes resulting in a clear liquid and other times causing precipitants to form. In similar barometers, the liquid level moves up or down a tube in response to atmospheric pressure. 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.

History of the Storm Glass

This type of storm glass was used by Robert FitzRoy, the captain of the HMS Beagle during Charles Darwin's voyage. FitzRoy acted as meteorologist and hydrologist for the journey. FitzRoy stated "storm glasses" had been made in England for at least a century before his 1863 publication of "The Weather Book." He had started to study the glasses in 1825. FitzRoy described their properties and noted there was a wide variation in the functioning of the glasses, depending on the formula and method used to create them. The basic formula of the liquid of a good storm glass consisted of camphor, partially dissolved in alcohol; along with water; ethanol; and a bit of air space. FitzRoy emphasized the glass needed to be hermetically sealed, not open to the outside environment.

Modern storm glasses are widely available as curiosities. The reader may expect variation in their appearance and function, as the formula for making the glass is as much an art as a science.