George III, indigo and the blue ring test

Analysis of George III's urine at the height of his insanity revealed a deposit in the shape of a blue ring, characteristic of indigo. But what could have been the source of indigo and was it linked to his dementia? 

Most of us pay little regard to the colour of our urine. The various shades of yellow are caused by the presence of a variety of pigments - urobilins - the degradation products of haemoglobin. But other colours are possible: red, orange, and even green, purple, brown and blue. The first of these should necessitate a visit to the doctor. Blood tints the urine red, and needs early investigation. But what about shades of blue and green? Possibly the most famous report of blue-tinted urine is that of George III (1738-1820) just before he became too ill to rule. Does the colour give us any clues to the cause of his eventual fall from power? 

Shades of blue

Shades of blue, purple and green in the urine could originate from either ingesting a blue dye or pigment, or from the biochemical conversion of food into indigo, well known now as the blue dye used to colour jeans.  

Prussian blue (an artists' pigment, formerly used in some inks) or the water-soluble methylene blue were possible dye candidates in the 19th and early part of the 20th century. Methylene blue was also used during this period in minute amounts in patent medicines - eg Boots Back and Kidney Pills - to persuade the gullible, from the tint imparted to their urine, that good was being done. The dye was also used to treat malarial fever, gonorrhoea, diabetes and even in experimental therapy to control mania in disturbed patients.¹  Here the dose was large and the patients' urine assumed the colour of writing ink. 

Edward Schunck investigates

The connection of blue urine with indigo, a product from the woad plant or the shrub, Indigofera tinctoria, was investigated most persistently by Edward Schunck, a rich Manchester chemist who spent much of his life (1820-1903) investigating dyes of natural origin (see Box 1).²

In 1855 Schunck investigated the colourless indigo precursor in plants, indican. Encountering purple urine, he suggested the tint came from the presence of indigo (blue) and its isomer, indirubin (red), and eventually devised a test to confirm the presence of indigo. This involved: 

1. treating the evaporated urine with boiling ethanol to dissolve out the indirubin and leave the insoluble blue/black indigo; 
2. decolourising the latter by reducing with tin(II) oxide and alkali. This formed a solution of leuco-indigo, which deposited indigo as a blue film on its surface on exposure to air. The blue pigment was filtered and dried; 
3. treating the pigment with concentrated sulfuric acid to form a dark blue soluble product which remained blue after dilution with water;
4. heating the product in a test tube - the indigo produced a purple vapour which condensed to form a blue solid on the cooler parts of the tube. 

(The last three reactions are characteristic of plant-derived indigo.) 

With these tests available to confirm the presence of indigo, Schunck then devised a method for detecting the indigo precursor in urine. He added basic lead(II) acetate (ethanoate) solution to the urine and filtered off the white precipitate (lead sulfate, chloride and urate). He then added ammonia to the filtrate which again gave a white precipitate, which he removed and added to dilute sulfuric or hydrochloric acid, sufficient to neutralise the lead hydroxide, and filtered. When indigo was present it formed a film of blue solids on the surface of the liquid, sometimes only after 24 hours if a small amount was present.  

Using this procedure, Schunck examined the urine of 40 individuals, all apparently healthy, aged between seven and 55 years, mostly of the working class. In all but one case the result was positive. The largest amount of indigo was obtained from a man above the age of 50, a publican by trade.  

In Schunck's self-experimentation he found his amount 'varied most capriciously from a tolerable quantity to a mere trace'.³  He thought this variation might be caused by different types of diet, but after many experiments he found one which was really effective: 'I took on the next night, before going to bed, a mixture of treacle and arrowroot, boiled with water in as large a quantity as the stomach could bear, and the effect was that the urine of the following night gave a large quantity of indigo-blue'.³

And the link to George III?

George III was born on 4 June 1738 in London, became king in 1760 and died after a reign of nearly 60 years in 1820. He is widely remembered for two things: losing the American colonies and going mad. He had four bouts of insanity, the first in 1788, after the declaration of American independence on 4 July 1776 and the end of the American war with surrender by British forces in 1782, followed by reoccurrences in 1801, 1804 and 1810. Throughout these periods he also showed many of the symptoms of porphyria (see Box 2). George became permanently deranged after the 1810 episode. He was blind and mentally unfit to rule so his eldest son - who later became George IV - acted as Prince Regent from 1811. 

A report in the British Medical Journal  (BMJ) in 1966 by a mother and son team of psychiatrists, Ida MacAlpine and Richard Hunter,⁴ claimed that King George III's insanity was a classic case of porphyria.This prompted the play by Alan Bennett The madness of George III,⁵  which in turn prompted Wilfred Arnold, writing in The Lancet  in 1996, to re-examine the original 1811 reports which mention a blue colour of the King's urine.⁶

On the 6 January 1811, Sir Henry Halford, one of the attending physicians, wrote of the King's urine: 'The water is of a deeper colour - and leaves a pale blue ring upon the glass near the upper surface.' ⁶  The blue ring may have been indigo, and as Edward Schunck showed, it is not an uncommon physiological phenomenon. There may have been no connection between this and the King's insanity, which may have had other causes.  

Although some medical writers choose to connect urine containing indigo and indirubin with illness (notably Crohn's disease and acute myelomonocytic leukaemia),⁷  we have not found it linked to mental instability. 

Possible source of indigo?

And what would have been the source of the indigo? Physicians treating John Good in 1901, who had among other symptoms 'peacock blue' urine, had a theory: 'It was due to the formation of indigo through oxidation of the indican that results from the putrefactive activity of the Bacillus coli upon the products of tryptic digestion (see Scheme 1).⁸

This view has been recently amplified by Professor Wilfrid Arnold: 'Because the patient was constipated, putrefaction during stasis (sluggish performance) of the bowel led to indole formation from dietary tryptophan by the normal intestinal flora. Some indole was absorbed into the blood stream and converted in the liver first to indoxyl and then to the sulfate ester (see Scheme 2). The colourless, water-soluble indoxyl sulfate (metabolic indican in the older published research papers) was excreted in the urine. In the presence of a sulfatase of bacterial origin, either from urinary tract infection or as an environmental contamination of the chamber pot, indoxyl was slowly released by hydrolysis and oxidatively dimerised to indigo, which precipitated on the porcelain', (see Scheme 3). ⁶

The later stages of this hypothesis were vividly demonstrated by using urine fortified with indoxyl sulfate and Providencia stuartii - a bacterium associated with urinary tract infections and known to have sulfatase activity). Sir Henry Halford's blue ring was thus seen again.⁶

And King George III?

Initially, MacAlpine and Hunter thought George III had the most common type, intermittent porphyria, but they changed the diagnosis to variegate porphyria after learning that some of George's descendants were abnormally sensitive to sunlight, a characteristic of this type of porphyria. This view was generally supported by Wilfred Arnold⁵  30 years later, but there are still critics who claim 'not proven': 'Arnold perpetuates the fable that King George III had acute porphyria'.⁹ 

Chris Cooksey is retired; Alan Dronsfield is professor of the history of science in the faculty of education, health and sciences at the University of Derby, Kedleston Road, Derby DE22 1GB.