Weather in a Crystal Drip
An introduction to Storm Glass
Origin of Storm Glass can be traced back to 17th century in Europe for sailors to predict weather by observing crystal with a mixture five accessible chemicals with a formula. In a 100 ml of Storm Glass content, there are 3.8 g Ammonium chloride (NH4Cl), 10 g Camphor (C10H16O), 40ml Ethanol (C2H5OH), 3.8 g Potassium Nitrate (KNO3) and 33ml water. As development in weather forecasting in the past centuries, Storm Glass no longer a tool, but an art work for its fascinating crystal formation.
Structural formula of Camphor
Crystal formation inside Storm Glass
The crystal formed insides the Storm glass is white, but what is the composition of these crystal? The answer is Camphor, with using X-ray diffraction method in a research in 2008. The addition of two salts and water as minor components, NH4Cl and KNO3, are used in the nucleation of Camphor crystal. Yet, there are factors causing the formation of various crystal forms insides Storm Glass.
Factors affecting the crystallization Changes in atmospheric conditions of temperature and pressure, crystal formation is affected. The amount and state of camphor crystal formed are related to the solubility, density of camphor crystal and also the rate of temperature change. Inside Storm Glass, solubility varies with temperature and vapor pressure of aqueous ethanol solution in the sealed glassware. The solubility of camphor increases with increasing temperature and results in a clear solution with little amount of crystal. On the other hand, the cooling of Storm glass results in the decrease solubility and makes the solution cloudy. Meanwhile, you can observe the different levels of the crystal form which is related to density and the process of the crystal formation. Camphor has density of 0.990 g/cm which is between the density of pure ethanol and pure water. Yet, the density of solution (~55% ethanol by weight) is 0.903 g/cm, the crystal formed is slowly sinking to the bottom due to greater density and presented as suspended. For example, at windy air condition, vertical needle shaped crystal forms and sinks slowly toward the bottom. The sudden change in temperature and pressure affecting the size of crystal formed inside. The rapid decrease would decrease the solubility as mentioned above, which the solution being supersaturated. Due to presence of two salts as nuclei, the nucleation of camphor occurs rapidly, and forms small starry crystal. On a contrary, the gradually decline in temperature, the solution can only be saturated. The nucleation of camphor occurs slowly and camphor deposit on the crystal forms. As the crystal sinks slowly, branches forms, results in feather shaped crystal.