Magnesium also reacts with hydrochloric acid and produces heat and hydrogen when added to it. The magnesium will begin to bubble and become hot, too hot to touch comfortably. The reaction will occur faster with higher temperatures (see precautions). Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk.
Magnesium, when it burns in air, produces a brilliant white light (burning magnesium). This was used in the early days of photography when magnesium powder was used as a source of illumination (flash powder). Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is still used in the manufacture of fireworks and marine flares where a brilliant white light is required.
Magnesium, when glowing white, has many chemical properties that it does not possess at lower temperatures. It also becomes more toxic, although this is of little practical importance, because the high temperature alone generally prevents human contact.
Magnesium deficiency in humans was first described in the medical literature in 1934. The adult human daily nutritional requirement, which is affected by various factors including gender, weight and size, is 300-400 mg/day. Inadequate magnesium intake frequently causes muscle spasms, and has been associated with cardiovascular disease, diabetes, high blood pressure, anxiety disorders, migraines and osteoporosis. Acute deficiency (see hypomagnesemia) is rare, and is more common as a drug side effect (such as chronic alcohol or diuretic use) than from low food intake per se, but it can also occur within people fed intravenously for extended periods of time. The incidence of chronic deficiency resulting in less than optimal health, is debated.
The DRI upper tolerated limit for supplemental magnesium is 350 mg/day (calculated as mg of Mg elemental in the salt). (Supplements based on Amino Acid Chelates, Glycinate, Lysinate etc. are much better tolerated by the digestive system and do not have the side effects of the older compounds used.) The most common symptom of excess oral magnesium intake is diarrhea. Since the kidneys of adult humans excrete excess magnesium efficiently, oral magnesium poisoning in adults with normal renal function, is very rare.
Magnesium salts (usually in the form of magnesium sulfate or chloride when given parenterally) are used therapeutically for a number of medical conditions, especially the hypertension of eclampsia. See Epsom salts for a list of conditions which have been treated with supplemental magnesium ion. Magnesium is absorbed with reasonable efficiently (30% to 40%) by the body from any soluble magnesium salt, such as the chloride or citrate. Magnesium is similarly absorbed from Epsom salts, although the sulfate in these salts adds to their laxative effect at higher doses. Magnesium absorption from the insoluble oxide and hydroxide salts (milk of magnesia) is erratic and of poorer efficiency, since it depends on the neutralization and solution of the salt by the acid of the stomach, which may not be (and usually is not), complete.
Important magnesium compounds we can sort like:
- magnesium chloride, MgCl2, which is used in the preparation of cotton fabrics.
- magnesium bicarbonate, Mg(HCO3)2, which is produced in solution when water containing carbon dioxide dissolves magnesium carbonate. It is a cause of hardness in water.
- magnesium oxide, MgO, which is used as a refractory lining for metal, glass, and cement furnaces.
- magnesium peroxide, Mg2O2, which is used as a bleach for dyes and silks.
- magnesium sulfate, MgSO4, which is used as a purgative drug and as an antidote for barium and barbiturate poisoning. It is also used in dyeing and sizing of textiles, in man-made fibre production, and as a source of magnesium in fertilizers. One hydrated form, MgSO4.7H2O, is known as Epsom salt.