Storm glass
A storm glass is a type of weather forecasting device, composed of a sealed glass container, filled with liquid, that allows the user to forecast the weather by observing the appearance of the liquid in the glass.
The liquid within the glass is a mixture of several ingredients, most commonly distilled water, ethanol, potassium nitrate, ammonium chloride, and camphor. This specific mixture was developed by Admiral Robert FitzRoy and used on his voyage with Charles Darwin on HMS Beagle.
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 be used for wind observations.
During the historic voyage, FitzRoy carefully documented how the storm glass would predict the weather:
• If the liquid in the glass is clear, the weather will be bright and clear.
• If the liquid is cloudy, the weather will be cloudy as well, perhaps with precipitation.
• If there are small dots in the liquid, humid or foggy weather can be expected.
• A cloudy glass with small stars indicates thunderstorms.
• If the liquid contains small stars on sunny winter days, then snow is coming.
• If there are large flakes throughout the liquid, it will be overcast in temperate seasons or snowy in the winter.
• If there are crystals at the bottom, this indicates frost.
• If there are threads near the top, it will be windy.
Ingredients
• 2.5 g potassium nitrate
• 2.5 g ammonium chloride
• 33 ml distilled water
• 40 ml ethanol
• 10 g camphor
Warm the water and dissolve the potassium nitrate and ammonium chloride; add the ethanol; add the camphor. Place in corked test tube.
Mark Ford, who has been making storm glasses for years, e-mailed me to add that man-made camphor, while very pure, does contain borneol as a by product of the manufacturing process. His experience is that the synthetic camphor doesn't work as well as natural camphor, perhaps because of the borneol.
Mr. Ford advises dissolving the nitrate and ammonium chloride in the water, then the camphor in the ethanol. Next, slowly mix the two solutions (adding the nitrate & ammonium solution to the ethanol solution works best). It also helps to warm the solution to ensure complete mixing. Mr. Ford never uses a cork, preferring to seal the mixture in small glass tubes.
No matter what method is selected to construct a storm glass, the reader is advised to use proper care in handling the chemicals.
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.

瓶子里的溶液是几种物质的混合溶液，通常包括蒸馏水、乙醇、硝酸钾、氯化铵和樟脑。这种独特的配方是由作为小猎犬号的指挥官的罗伯特•菲茨罗伊陪同查尔斯•达尔文进行航行时发明的。海军上将罗伯特•菲茨罗伊在1834〜1836年间陪同查尔斯•达尔文探险。除了海军的工作，菲茨罗伊也是气象学的先驱。小猎犬号上达尔文所使用的部分仪器，包括精密计时器和晴雨表，也被菲茨罗伊用来指示天气。这次探险在航行中将蒲福氏风级作为风力观测单位也开创了一个先河。
在那次历史性的航行途中，菲茨罗伊认真地纪录下了暴风瓶对于天气的预测：
如果液体很澄清，说明天气将会是晴好的；
如果液体是朦胧的，有时伴有沉淀，那么天气也会像溶液一样多云；
如果溶液中有沉淀悬浮，就预示着潮湿的天气或者下霜；
如果悬浮的沉淀和朦胧的液体并存，说明暴风雨将会到来；
如果在晴朗的冬日里液体中有沉淀悬浮，就说明要下雪了；
如果在暖和的日子里或者下雪的冬天，液体中有大块的沉淀，说明将会阴天；
如果在杯底有晶体析出，说明要下霜了；
如果在顶部有螺旋纹，说明要起风了。
以下为暴风瓶内容物的配方和配置方法
2.5g硝酸钾
2.5g氯化铵
33ml蒸馏水
40ml乙醇
10g樟脑
将蒸馏水加热，并溶解硝酸钾和氯化铵，加入乙醇，专门制作暴风瓶很多年的马克•福特给我，即便很纯净的人造樟脑，在制作过程中或多或少会有冰片杂质混入。经验告诉他，天然樟脑的效果要比人造樟脑的效果好，也许与人造樟脑里的杂质有关。
暴风瓶的原理或许是温度和气压影响了溶解度，于是溶液澄清，有时又会沉淀。不过，它的原理尚无准确定论。和它很相似的，液面通常被染色的晴雨表，也会因大气压而在试管里上下移动。显然温度能影响溶解度，但是因为外界大气压的缘故导致密闭瓶子内气压的改变并不会非常明显。有些人认为瓶壁和溶液之间的某种作用导致了结晶，有时不同的解释甚至会牵扯到静电和玻璃的量子通道。

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