Storm Glass

Modern reproduction storm glass


 The storm-glass, sometimes known as the chemical barometer or camphor glass, is an ancient weather forecaster. It consists of a sealed glass bottle containing a mixture of chemicals that undergo interesting and unusual crystal growth in response to changing weather conditions. It has been around since around 1750 but was not in common use until the 19th century. 

 Robert Fitzroy described the storm-glass in The Weather Book published in 1863. In this book he offers some interesting thoughts on the operation of the storm-glass suggesting atmospheric pressure, temperature, electrical disturbances and even the direction of the wind being the cause of the changes in crystal formation.

In 1860, Admiral Fitzroy introduced the Admiral Fitzroy Barometer, an instrument including a mercury barometer, thermometer and storm-glass. This was a self-contained weather station with the instruments mounted in a glass fronted wooden frame with Fitzroy’s remarks written on the backboard to assist the user. Examples of this instrument can still be found in antique shops throughout the world.

A storm glass fitted to an original 10th century Fitzroy oak-cased weather station


 Some Recent Experimentation
Over the past 10 years I have constructed about fifty of these instruments but I have been only able to identify one physical cause of the variation in crystal growth – temperature history. It may indeed be possible to predict the weather using the storm-glass. Just as the direction of movement of a barometer’s indicator (rising or falling) often says more about the weather than the actual reading (after all, this is why we tap an aneroid barometer), it may be the variation and rate of change of temperature that provides the rich complexity of crystal growth in the storm glass and the intriguing possibility that the weather might be predicted with the instrument. In practice it is probably only slightly better than reading tea leaves but let’s not spoil the romance of the instrument by surrendering to skepticism.

How to Make a Storm-glass
The storm-glass consists of a mixture of chemicals sealed in a hermetically sealed glass bottle. The proportion of the various chemicals is quite critical and may need to be adjusted to suit your local climate (more on that later). Also, the operation of the instrument seems to be affected by the size of the jar; for a given mixture, a storm-glass made using a small phial will react quite differently to one made using a pickling jar. When mixing the chemicals it is necessary to warm the mixture slightly so that they all dissolve. This can be done by placing the ingredients in a sealed glass container and immersing it in warm water and then vigorously shaken.

Some Recipes
Here is a description of a practical storm-glass taken from the book Pharmaceutical Formulas by Peter MacEwan, published in 1908. The article includes notes to assist in the reading of the instrument.

Chemical Barometer Recipe 1 from Pharmaceutical Formulas

Camphor - half ounce
Ammonium chloride - half ounce
Potassium nitrate - half ounce
Rectified spirit - one ounce
Distilled water - two ounces

Weigh the spirit into the bottle and dissolve the camphor, then add the salts and the water (warm). Shake, and when dissolved filter.
Long narrow tubes of glass are filled with this solution and hermetically sealed or corked. The tubes are then affixed to boards by means of wires in the same way as barometers are fixed. The changes of the solution signify the following:
Clear liquid : Bright weather.
Crystals at bottom : Thick air, frost in winter.
Dim liquid with small stars : Thunderstorms.
Large flakes : Heavy air, overcast sky, snow in winter.
Threads in upper portion of liquid : Windy weather.
Small dots : Damp weather, fog.
Rising flakes which remain high : Wind in the upper air regions.
Small stars : In winter on bright, sunny days, snow in one or two days.
The higher the crystals rise in the glass tube in winter the colder it will be.

Interestingly, in a supplementary chapter to this book, another storm-glass recipe was given including a more descriptive set of notes to aid in the prediction of the weather:

Chemical Barometer Recipe 2 from Pharmaceutical Formulas

Nearly fill a glass tube 10 in. long and ¾ in. diameter with the following liquid, then hermetically seal:-
Camphor - 2 drachm
Potassium nitrate - ½ drachm
Ammonium chloride - ½ drachm
Absolute alcohol - 2 ounces
Water - 2 ounces


Temperature is the main factor in changing the appearance of the solution. The indications are as follows:-
(a) During cold weather beautiful fern-like or feathery crystallization is developed at the top, and sometimes throughout the liquid. The crystallization increases with cold, and if the structure grows downwards the cold will continue.
(b) During warm and serene weather the crystals dissolve, the upper and greater part of the liquid, becoming perfectly clear. The greater the proportion of clear liquid, the greater the probability of fine dry weather.
(c) When the upper portion is clear and the flakes of crystals rise to the top and aggregate, it is a sign of increasing wind and stormy weather.
(d) In cold weather if the top of the liquid becomes thick and cloudy, it denotes approaching rain.
(e) In warm weather if small crystals rise in the liquid, which still maintains its clearness, rain may be expected.
(f) Sharpness in the points and features of the fern-like structure of the crystals is a sign of fine weather ; but when they begin to break up and are badly defined, unsettled weather may be expected.

Note: 1 drachm = 3.89 grams. For more information about the apothecaries system of weights and measures go to

An American book by Henry B. Scammell published in 1897 entitled Cyclopedia of Valuable Receipts gives an interesting variation of the description of the Stormglass. Here the action of the instrument is attributed to, at least to some degree by variations in atmospheric pressure. Notable is the lack of water in this recipe as proof spirit is in fact a mixture of alcohol and water (50% by volume in the US).

STORM-GLASS - A thin glass tube, about 12 inches long and 3/4 inch in diameter, about 3/4 filled with the following liquid, and covered with a brass ear, having an almost capillary hole through it, or else tied over with bladder. Take of camphor, 2 dr.; nitre, 1½ dr.; sal ammoniac, 1dr.; proof spirit, 2 ¼  fl.oz.; dissolve and place in the tube. When the liquid is clear in all but the lower portion of the tube, it denotes clear weather; when the cloudy appearance arises in the middle, a change in the weather is indicated; when the whole contents of tube become clouded with the mixture, rainy or stormy weather is to be betokened. Thus a simple barometer may be made for home or office use. This invention will be more reliable in action if the glass is kept in the outer air, under shelter.

After constructing many storm-glass instruments using recipes from various old texts, it soon became apparent that they were all designed for use in regions with a colder climate than the mild winters of Perth, Western Australia. Consequently, the quantities of the ingredients were altered to give good results for warmer climes. The end result is a storm-glass that gives results very similar to those described in the old texts.

Another problem relates to the comfort of the modern home. As the storm-glass is an instrument that reacts to environmental temperature changes, it works best in a draughty, un-insulated and unheated home. This makes finding the optimum mounting position of the storm-glass an interesting problem. It should preferably be placed in the shady part of the home near a large window where direct sunlight will not fall on the instrument.

The following storm-glass mixture, when placed in a glass tube 25mm diameter and 150mm long works well in Perth, Western Australia.

Camphor - 4.2 gm
Methylated spirit - 23.5 ml
Potassium nitrate - 1.2 gm
Ammonium chloride - 0.8 gm
Distilled water - 23.5 ml

You may need to adjust the mixture for your local climate.

Some notes on the use of methylated spirits:

I was recently contacted by Ted Griffith, a storm glass maker in the US who has had problems using methylated spirits instead of ethanol. It seems that unlike the methylated spirits available in Australia, the product available elsewhere is often denatured with substances that will spoil the operation of the storm glass. For more information, see the Wikipedia article on methylated spirits.

 Some other useful links:

Wikipedia article on the stormglass

Wikipedia article on Robert Fitzroy

Owl Technologies, a Stormglass maker

To purchase a storm glass, the following links to Amazon might be useful: