Chemical garden

A chemical garden is an experiment in chemistry usually performed by adding metal salts, such as copper sulfate or cobalt(II) chloride, to an aqueous solution of sodium silicate (otherwise known as waterglass). This results in the growth of plant-like forms in minutes to hours. A chemical garden is an experiment in chemistry usually performed by adding metal salts, such as copper sulfate or cobalt(II) chloride, to an aqueous solution of sodium silicate (otherwise known as waterglass). This results in the growth of plant-like forms in minutes to hours. The chemical garden was first observed and described by Johann Rudolf Glauber in 1646. In its original form, the chemical garden involved the introduction of ferrous chloride (FeCl2) crystals into a solution of potassium silicate (K2SiO3). The chemical garden relies on most transition metal silicates being insoluble in water and colored. When a metal salt, such as cobalt chloride, is added to a sodium silicate solution, it will start to dissolve. It will then form insoluble cobalt silicate by a double displacement reaction (anion metathesis). This cobalt silicate is a semipermeable membrane. Because the ionic strength of the cobalt solution inside the membrane is higher than the sodium silicate solution's, which forms the bulk of the tank contents, osmotic effects will increase the pressure within the membrane. This will cause the membrane to tear, forming a hole. The cobalt cations will react with the silicate anions at this tear to form a new solid. In this way, growths will form in the tanks; they will be colored (according to the metal anion) and may look like plant-like structures. The crystals formed from this experiment will grow upwards, since the pressure at the bottom of the tank is higher than the pressure closer to the top of the tank, therefore forcing the crystals to grow upwards. The upward direction of growth depends on the density of the fluid inside the semi-permeable membrane of the 'plant' being lower than that of the surrounding waterglass solution. If one uses a metal salt that produces a very dense fluid inside the membrane, the growth is downward. For example, a green solution of trivalent chromium sulfate or chloride refuses to crystallize without slowly changing into the violet form, even if boiled until it concentrates into a tarry mass. That tar, if suspended in the waterglass solution, forms downward twig-like growths. This is because all the fluid inside the membrane is too dense to float and thereby exerts an upward pressure. The concentration of sodium silicate becomes important in growth rate.