Phosphorus is a chemical element which finds itself used in many different applications.
.It is essential for the growth of plants and it is therefore a significant ingredient in fertilisers. The fertilisers themselves are made up of mineral phosphates rather than the actual pure element. Elemental phosphorus can exist as white phosphorus, red phosphorus or black phosphorus. Since red phosphorus is more thermodynamically stable than white phosphorus, it can be made by exposing white phosphorus to sunlight or by controlled heating.
Phosphorus can be alloyed with steel to make phosphor bronze, which is far harder than the original steel from which it is made. Phosphorus can be used as a flux in the production of copper since it reacts so readily with oxygen, thereby limiting the creation of copper oxide impurities. Phosphorus is also used to make a range of chemicals called organophosphorus compounds. These chemicals have a carbon atom bonded to a phosphorus atom or a phosphate group somewhere in its molecular structure. Organophosphorus compounds can themselves be used in the manufacture of pesticides and in the treatment of domestic water supplies.
Phosphorus was discovered accidentally by Hennig Brand in 1669 whilst trying to deduce a method of extracting gold from urine. It was believed at the time by some people that the yellow colour of urine was due to traces of gold rejected by the body. After boiling dry a sample of stale urine, a white glowing mass was left behind instead of the gold he had hoped for. This was white phosphorus. More than 18 litres of urine was needed to be processed for each gram of phosphorus obtained using this method. The technique for extracting phosphorus from urine was later sold to Robert Boyle, who was instrumental in publicising its manufacture. After being seen as nothing more than a curiosity at first, phosphorus-tipped pieces of wood were used as matches.
A far richer source of phosphorus than urine is in animal bones. Bones are made up to a large extent by calcium phosphate, also known as apatite, which is 10% phosphorus by mass. The method of extracting phosphorus from bone ash was developed by Gahn and Scheele in 1769. Gahn demonstrated that bone ash was a viable source of phosphorus by determining its composition. It was left to Scheele to devise the industrial chemical method.
The first step in the production of phosphorus from bones is to roast it to a high temperature in order that it should chemically decompose. The bone ash that results from this treatment contains almost a third by mass calcium phosphate. The next step is an intensive course of degreasing. Hydrochloric acid degreases and softens the bone ash. A weak solution of calcium hydroxide is then added to this. Mineral phosphates then precipitate out of the solution. These are collected and dried out. They can be roasted in the presence of charcoal in iron phosphorus retorts and the phosphorus vapour condensed and collected in a cooler place.