Cobalt chloride, or CoCl2, is a compound of cobalt and chlorine. It is more correctly known as cobalt (II) chloride or cobalt dichloride. The compound is blue when it is anhydrous, or contains no water. When wet, cobalt chloride is the colour magenta. Because of its chemical properties, including its ability to change colour when it comes into contact with water, cobalt chloride has several uses.
Cobalt chloride can be used to make invisible ink. Chemistry teachers Barker North and Norman Bland explained the procedure as long ago as 1920. If you dissolve cobalt chloride in water and use the substance to draw or paint on a sheet of white paper, the markings will be almost invisible when the substance dries. To make the markings visible again, you simply have to warm the paper in front of a source of heat.
Cobalt chloride is used in the T.R.U.E. test, or Thin-layer Rapid Use Epicutaneous Test. Allergic contact dermatitis is an inflammation of the skin that can occur when people come into contact with a substance to which they are allergic. These substances, which include foods, plant pollens and metals, are called allergens. The T.R.U.E. test is a patch test used on contact dermatitis sufferers to determine the causes of the inflammation. Three panels of surgical tape, or plaster, containing 29 allergens or allergen mixes, are applied to the sufferer's skin. Cobalt chloride is on panel 1 and is allergen 12. After a patient has worn the panels, if the skin shows signs of contact dermatitis where the panel 1, allergen 12 patch was, it is clear that cobalt chloride is the cause. Physicians can then advise the patient about avoiding contact with things that contain the compound.
Computer Memory Devices
Because of the magnetic properties of cobalt, it is useful as a coating for computer memory storage devices. There are two main types of coating, hard and soft. The latter has very rapid response, allowing fast data storage and retrieval. The hard magnetic coatings are usually alloys of 20 per cent nickel and 80 per cent cobalt. Electroplating using the chlorides of these metals is one of the ways used to coat the devices. The process involves manipulating the metal ions in solution. Ions are atoms or molecules with positive or negative charge. An electric field is used to transfer the nickel and cobalt chloride ions from the solution onto an immersed object, thereby depositing a thin layer of nickel-cobalt upon it.
Cobalt and cobalt chloride may also be used in the making of building materials, paints, pigments and printing inks, vitamin B12 supplements, tattoo inks, soaps and silica gel.