The most traditional chemicals used for cloud seeding comprise of silver iodide, potassium iodide and dry ice (solid carbon dioxide). Liquid propane, which develops into a gas, has similarly been used. This can create ice crystals at higher heats than silver iodide. After contracting research, the use of hygroscopic substances, such as table salt, is becoming more popular. Cloud seeding to improve snowfall takes place when temperatures within the clouds are between 19 and −4 °F (−7 and −20 °C). The installation of a substance such as silver iodide, which has a crystalline composition comparable to that of ice, will produce freezing nucleation. In mid-latitude clouds, the typical seeding strategy has been determined on the fact that the equilibrium vapor pressure is lower over ice than over water. The formation of ice particles in supercooled clouds allows those particles to gain at the cost of liquid droplets. If sufficient swelling takes place, the particles become heavy rather fall as precipitation from clouds that otherwise would produce no precipitation. This method is known as “static” seeding. Seeding of warm-season or tropical cumulonimbus (convective) clouds seeks to utilize the latent heat discharged by freezing. This strategy of “dynamic” seeding estimates that the additional latent heat adds buoyancy, strengthens up-drafts, ensures more low-level confluence, and ultimately causes accelerated growth of suitably selected clouds. Cloud seeding chemicals may be dispersed by aircraft or by distribution devices towed into positions on the ground (generators or canisters fired from anti-aircraft guns or rockets). For discharge by aircraft, silver iodide flares are ignited and dispersed as an airplane flies through the inflow of a cloud. When released by equipment on the ground, the fine particles are carried downwind and upward by air flows after release. An electronic device was tested in 2010 when infrared laser pulses were directed to the air above Berlin by researchers from the University of Geneva. The experimenters posited that the pulses would encourage atmospheric sulfur dioxide and nitrogen dioxide to form particles that would then act as seeds.Referring to 1903, 1915, 1919, 1944, and 1947 climate alteration experiments, the Australian Federation of Meteorology reduced “rain making”. By the 1950s, the CSIRO Division of Radiophysics switched to investigating the physics of clouds and had hoped by 1957 to understand better these processes. By the 1960s, the visions of weather making became faded only to be re-ignited post-corporatisation of the Snowy Mountains Scheme to achieve “above target” water. This would provide enhanced energy generation and profits to the public agencies that are the principal owners.