John wrote:
"Do not use washing liquid in washing machines, it creates a greasy
film that makes the machine pong."


Surely another reason is that it would create too much lather.



Not sure that Liquid Soaps contain Fat - Bar soaps do. I use liquid soaps
only as they don't give a scum or leave spots on the shower screen.


soaps and detergents are olefins IIRC with a bit chopped off the end an
an OH group added by dint of being hit with alkalis. The OH bit is
water soluble and the organic bit dissolves with greases.


For soap you start with long chain fats, for detergent with oils,
possibly vegetable, more likely petroleum.

Most washing up liquid is treated with things that*

- make it bubble.
- make it thick
- give it a nice pong
- give it a suitable color.
- take out any calcium ions to prevent scum in hard water areas.

Only the last has anything to do with its abilities to wash dishes.

Frankly, you could load a dishwasher with sodium hydroxide, and it would
probably work better than most detergents.

We don't hand wash with it because it turns your hands into soap...

*My chemistry master spent 5 years at Unilever...