Phosphorous: from urine to fire
3. Food from old bones : the fertiliser connection
Peter E. Childs
|In the previous
articles we looked at the discovery of elemental phosphorus (#60, pp 55-58)
and the history of production of matches (#61, pp 25-28). In this article
the history of phosphoric fertilizers will be described.
The Irish connection
Who first discovered and patented synthetic manures (or fertilizers) containing phosphorus? Sir James Murray (Belfast and Dublin) should probably get the credit that usually goes to Lawes and Liebig (see below).
We take the use of artificial (synthetic) fertilizers for granted today, whether for gardening or intensive farming. However, the use of fertilizers (or manures) of inorganic origin, as distinct from manures from natural, usually animal, sources is only just over 150 years old. The beginning of the synthetic fertilizer industry is given in books to 1842 when John Bennett Lawes started making phosphate fertilisers at Deptford in England. However, as we shall see that is not quite the start of the story, which also has an Irish dimension.
For the majority of farmers soil fertility and the productivity of land could only be maintained or increased by using the traditional methods of animal manures, seaweed, leguminous crops and crop rotation. (What we would call today 'organic' farming.) The limited availability of these was a major limitation on agricultural production in the early 19th. century. Thus there was an impetus to produce better crop manures.
Figure 1 Sir James Murray
Sir James Murray of Belfast: unsung pioneer of synthetic fertilizers
(1788-1871) was born in Derry and died in Dublin (see Figure 1). He studied
to be a doctor in Edinburgh and became a member of the College of Surgeons
in Dublin in1807, and in 1808 set up practice as a doctor in Belfast.
He had a strong interest in chemistry and did research into better ways
of using magnesium carbonate to cure indigestion. He invented "Milk
of Magnesia", patented the production process and set up a manufacturing
plant in Belfast in 1817. His chemical works were producing wastes containing
sodium and potassium bicarbonates and silicates and he wanted to find
some way of using them, He remembered experiments done in 1808 to convert
bones to biphosphate of lime as a fertiliser, using sulphuric acid. His
first field trials were carried out in 1817. He mixed his wastes with
composts, phosphates and manure. In 1831 Murray moved to Dublin, where
he was to stay until his death in 1871.
"Many manufactories are preparing at certain distances, and several steam mills are at work for crushing and grinding materials in each district."
On May 12th, 1842 his son, John Fisher Murray, applied for a Scottish patent followed on the 23rd. May by an English patent. Murray's method was to react phosphorite of lime (calcium phosphate) with sulphuric acid for several days to produce a paste. This was then mixed with various plant materials (bran, sawdust, bark, dry earth etc.) to form a dry powder. This was easier to store, transport and it produced a slow-release fertilizer. Several different brands of fertilizer were produced for different crops. In 1842 trials were carried out in Dublin to compare the effect of the new fertilizers with manure, though these were on a small scale and did not relate to full-scale field trails.
In 1842 Sir James Murray gave a series of three lectures in Belfast on "Chemical Agriculture" (Figure 2) and followed these in 1843 with a book Trials and Effects of Chemical fertilizers with Various Experiments in Agriculture.
James Murray's main competitor was John Bennett Lawes in England, who turned out to be a better businessman and in 1846 he bought Murray's patent. Lawes has thus come to be known as the father of the fertilizer industry.
In 1849 Sir James went back to making fluid magnesia with his son Edward. In 1857 he took out a second patent on fertilizers and he retired from his medical duties in the same year. He died in Dublin on 8th. December 1871 and the Irish Times of 10th. December published his obituary, including the following:
"There was something truly liberal and dignified in his manners and his person. No-one could more effectively give a word of good advice to the young, or of encouragement to the deserving, or with a more pungent wit could rebuke the vain or the arrogant. A most perfect tolerance in matters of creed and party distinguished him. He was himself a Catholic, and a supporter of what is still called the Liberal party; but his friendships and benevolence were as wide as the fraternity of man."
Lawes and Liebig
Sir John Bennett Lawes (1814-1900) was born at Rothamsted, Hertfordshire. He studied at Oxford, though not in chemistry, but he became interested in the subject. He inherited his father's estate at Rothamsted and started experimenting with chemical fertilizers, following the ideas propagated by Justus von Liebig. In 1841/2 he patented a method of making superphosphate from bones, and later extended his process to mineral phosphates (coprolites) and later to imported apatite (calcium phosphate) with sulphuric acid. He started manufacturing fertilizers in 1844 in Deptford, London. He bought out Murray's patents in 1846 ensuring that Murray's contribution to the new synthetic fertilizer industry was forgotten.
In 1843 Lawes organised the Rothamsted Experimental Station, which has proved to be his most enduring legacy. Agricultural experiments have been carried out there since that date. It is the oldest experimental agricultural station in the world.
James Muspratt, an Irish-born chemical industrialist, who started making chemicals in Dublin in 1816 and moved to Liverpool in 1822, has been called 'the father of the British chemical industry'. He was a friend of Liebig and took out an English patent for Liebig's Patent Mineral Manure and tried manufacturing them in Newton, near Liverpool, in 1843-44. They were not successful as Liebig's idea to prevent loss of nutrients by making the phosphate insoluble turned out to render them useless and the venture was abandoned.
Figure 3 Goulding's manure factory in the Glen, Cork
The fertilizer industry quickly returned to Ireland when W. and H.M. Goulding started making phosphate fertilizers in Cork in 1856 (Figure 3). At their centenary in 1956 they had 8 fertilizer plants in Ireland, North and South. They are still in existence but no longer make fertilizers. They only blend, package and sell branded fertilizers.
Mary Daly (1984) wrote about the fertilizer industry in Dublin at the end of the 19th. century, located near the mouth of the Liffey:
"The chemical and manure industry .. expanded to fill agricultural needs. The growing use of artificial manures provided many commercial opportunities. .. In 1870 there were apparently four artificial manure plants, by 1895 this had risen to seven while employment had risen from 347 to 463. The most successful firm was W. and H.M. Goulding, founded in Cork in 1858 (sic), which opened a Dublin plant in 1869."
In 1898 there were sixteen manure works in Ireland, giving an idea of how substantial the Irish fertilizer industry was in the late 19th./early 20th. century. NET (now IFI) was not the first firm to start making fertilizers in Arklow. In the 1860s the Wicklow Copper Mine decided to set up a chemical plant to make sulphuric acid from pyrites and this was used to make artificial manures i.e. phosphate fertilizers (see Figure 2 below). The factory was taken over in 1894 by Kynochs to supply acids and acetone for their explosives factory (Childs, 1998).
Over the years there have been several other fertilizer manufacturers in Ireland e.g. McDonaghs of Galway, Albatross of New Ross, but none of these synthesizes fertilizers any more, they merely compound and sell them from bought-in materials. However, there is much more to be said about the Irish fertilizer industry ,which goes back at least 150 years. Richardsons in Belfast, part of IFI since 1988, was originally started in the 1860s and NET was started in 1965.
From bones to rock
Phosphorus is one of three essential plant nutrients, along with nitrogen and potassium, together forming the big three: N,P,K. Phosphorus is often the limiting nutrient both in soils and in water due to its limited solubility. Phosphate is easily precipitated out of solution by calcium (or other divalent or trivalent ions). This explains why the major resources of phosphate in the world occur as calcium phosphate ('phosphate rock') deposits. This is often found in the form of fluorapatite, Ca5(PO4)3F.
Bone meal from ground up bones is a traditional slow-release fertilizer, as it contains phosphorus in an insoluble form. Murray's great achievement (later taken up by Lawes and others) was to find a way of solubilizing bones by dissolving them in sulphuric acid. This converts calcium phosphate, Ca3(PO4)2, into calcium hydrogenphosphate, CaHPO4, and calcium dihydrogenphosphate, Ca(H2PO4)2). These last two compounds have lower charges on the anion and thus lower lattice energies and are more soluble in water.
Initially the process of acidulating bones or phosphate rock was used to produce calcium dihydrogenphosphate-1-water, also known as superphosphate because it contains a greater % of phosphate. This was done by adding just less than the required amount of conc. sulphuric acid, and the solid product contains superphosphate, unreacted phosphate rock and calcium sulphate. Fluoride present in the rock comes off as HF and SiF4, much much remains in the fertilizer.
2Ca5(PO4)3F + 7H2SO4 + 3H2O
3Ca(H2PO4)2.H2O +2HF + 7CaSO4
Triple superphosphate is made by dissolving the phosphate rock in phosphoric acid (obtained from phosphate rock by using excess sulphuric acid) so that the product contains only calcium dihydrogenphosphate and no calcium sulphate, with an even higher % of phosphate.
Ca5(PO4)3F + 7H3PO4 + 5H2O
5Ca(H2PO4)2.H2O + HF
Ammonium phosphates and potassium phosphates are made by neutralising phosphoric acid with ammonia or potassium hydroxide, respectively. These compounds deliver two plant nutrients at the same time.
Blended fertilizers are made by combining the various fertilizer compounds containing nitrogen (as ammonium or nitrate), with phosphates and potassium salts.
Mary Daly, Dublin: The Deposed Capital, Cork: Cork University Press, 1984
Peter E. Childs, 'Ireland's early chemical industry', Chemistry in Action!, #55, 10-20, 1998
"Phosphorus, Phosphoric acid and inorganic phosphates" A.F.Childs 375-402 in The Modern Inorganic Chemicals Industry ed. R.Thompson Special Publication no. 31 The Chemical Society, London 1977
Phosphorus chemistry in everyday living 2nd. ed. A.D.F.Toy and E.N.Walsh ACS, Washington 1987
In the next issue:
Other uses of phosphorus - from fire-retardants to detergents