It is less easy to describe the background to this third principal by-product. It might be said to have hardly existed before the gas industry began to produce it. 'Ammoniacal liquor' was an ammonia rich liquid that condensed on top of the tar after the gas was washed with water. Ammonia itself had been identified only thirty years previously when Priestly collected the gas from sal ammoniac. Some ammonia salts were known and commonly used but it should be noted that they were those commonly known by their older names - ‘sal ammoniac’ and ‘sal volatile’. Knowledge about the use of 'ammonia and its compounds' was thus confined to 'medical purposes and scientific investigations'. Nevertheless the promoters of the Chartered Gas Company claimed that it had potential.
Pamphlets produced before the opening of the first gas company made proposals for the use of by‑products. Winsor had advertised the uses of ammoniacal liquor by saying that it was for instance 'one of the strongest lyes for tanning skin'. 'Lye' was defined in a contemporary dictionary as 'a strong wash or lixivium made of ashes or other proper ingredients' - and was the alkaline solution used as part of the tanning process. It was also, Winsor said, suitable for smoking 'hams, bacons, beef' and 'very valuable in the fabrication of white lead, verdigris, copperas and alum'. In promotional literature Winsor suggested the manufacture of ‘chemical salts’. while at the 1809 Enquiry Accum talked at length about the various salts that could be made.
The new gas company would need to find both uses and customers for this bulky, almost unknown, product.
The company promoters however, while suggesting that the liquor had uses in dyeing and tanning also admitted that 'this has not yet been investigated'. This point was not lost on Boulton and Watt's lawyers who read the Chartered's advertising material with an eye to unsubstantiated claims. On copies of one particular pamphlet they highlighted extracts from a letter by Accum in which he said that ammoniacal liquor can be used for dyeing and calico printing - in particular they noted the words 'highly probable'. Their barrister, the future Lord Chancellor, Henry Brougham, was able to use these claims to some effect at the 1809 Enquiry.
What did the new company think they were going to do with this awkward and uninvestigated liquid? A point had to come when large quantities of it were being produced and the claims made by Winsor and Accum had to be turned into reality.
One advertised application for ammoniacal liquor was for dyeing. Ammonia itself was used to make cudbear, a lichen based dye. In London 'Cudbear' was also called 'archil'. There were two manufacturing works in Bethnal Green, that of Samuel Child, and that of Dent and Child. There was an even closer relationship with the industry in Westminster because the Great Peter Street Works of the Chartered Gas Company was to be built on the site of the Cudbear Company's works. A Mr. Grant had brought this enterprise from Scotland. It was the case however that the ammonia was often in the form of urine, nevertheless cudbear meant that dyers and those connected with the industry were aware that ammonia products were useful in the manufacture of at least one dye.
The new gas company promoters suggested, that rather than be used as a dye, ammonia could be 'applied as a mordant for dyers'. Hitherto sal ammoniac, the salt, had been used for this. A mordant - not defined in the eighteenth century dictionary - is the 'biting' solution used with some dyestuffs in order to 'fix' the colour.
A Mr. Bryan, described as a dyer from Spitalfields, had testified to the 1809 Enquiry on the usefulness of the liquor for dyers. Like others who testified on behalf of the gas company at this Enquiry he has not been traced. His tests had been for the use of the liquor as a potential colouring agent rather than a mordant. He had produced 'a number of neat shades of drab - which will stand wearing'. Asked about its use as a mordant, he said 'I'm sure.. it may be used .. as a substitute for potash'. There is ambivalence here about exactly what role ammoniacal liquor was to perform in the dyeing process.