The ancient Romans, of course, didn’t have washing machines. But they had the next best thing. They had fullonicae, laundries where servants called fullones washed clothes. Don’t picture some sort of hand-washing operation though. In a fullonica it was mostly feet that did the work. Clothes were sprinkled with wood ashes and then piled into tubs filled with the prime cleaning agent of the day — urine! The fullones would trudge around the tub, trampling the clothes, doing essentially the work that the agitator does in a modern washing machine. Why the ashes? Treating greasy stains with alkaline materials converts the grease into soluble salts of fatty acids. Wood ashes contain potatsium hydroxide, an alkaline substance. And urine? That has alkaline ammonia, a decomposition product of urea.
After sufficient trampling, the clothes were transferred to basins containing fresh water for rinsing. Trudging around in a vat of urine was undoubtedly an unpleasant job, but not necessarily damaging to the skin. In fact, urea is an emollient that is included in some moisturizing creams today and it was not unusual for Roman ladies to take baths in urine to soften the skin.
After the clothes had been rinsed of urine, they were often spread on an inverted basket-like structure that was placed over burning sulphur. Sulphur dioxide is a noxious gas but an effective bleaching agent. A classic mural found in Pompeii depicts the use of sulphur in a fullonica and archeological digs in Pompeii have unearthed 11 of them. Ancient Roman cities commonly had vessels on the streets for collecting urine that would later be delivered to a fullonica.
Historically, urine had other applications as well. It was a key ingredient in the making of indigo, a much sought-after dye. Indigo comes from a plant of the same name, but no part of the plant is blue. The plant does, however, contain a compound called indican that is the dye’s precursor. This colourless compound is water soluble so it can be extracted by steeping the indigo leaves in water. Adding soda ash makes the solution alkaline and transforms indican into two molecules of indoxyl. When the solution is now whisked to introduce air, indoxyl reacts with oxygen to form indigotin, the blue pigment. But this pigment is insoluble and settles to the bottom of the container. To use it as a dye it has to be made soluble. This is where urine comes in. The action of ammonia in urine converts indigotin into soluble ‘white indigo,’ which is actually greenish-yellow. It is at this stage that wool or cotton is immersed in the indigo vat and the molecules of the white indigo attach themselves to the fabric. When the cloth is removed from the vat, the white indigo reacts with oxygen to form insoluble indigotin that is now attached to the fibres. The importance of this process faded when Adolph von Baeyer developed a process for making synthetic indigo and Haber and Bosch came up with a method of making synthetic ammonia from nitrogen and hydrogen.
This process was practiced until synthetic ammonia became available in the early 20th century. This in itself was a pivotal moment in chemistry. The discovery by Friedrich Wöhler in 1828 that urea can be produced from inorganic starting materials was also an important conceptual milestone. It showed for the first time that a substance previously known only as a byproduct of life could be synthesized in the laboratory without any biological starting materials. This contradicted the widely held doctrine of vitalism, which claimed that chemicals made by living organisms could never be made in the laboratory. So, now ‘urine’ the know!