Nick Maclaren wrote:
In article ,
"Rupert \(W.Yorkshire\)" writes:

Oh, come off it! That is precisely what soaps ARE, and most common
detergents are fairly similar. And the reason has nothing to do with
surplus fat that people don't want to eat.

Similar in the sense that they combine a longish carbon chain molecule
with a hydrophobic group at one end that wants to be in oil and a
hydrophyllic group at the other that prefers to be in water. The net
effect is to emulsify any free fat or grease in the water.

| What's this thing about nitrogen and sulphur being a well know warning flag?

Check it out - it is. The point is that sulphur-containing proteins are
often/usually very bioactive, and a hydrocarbon that contains nitrogen
is very like a protein.

That is a pretty weird viewpoint and potentially very wrong. It all
depends on how the sulphur and nitrogen is bonded into the molecule.
For instance:

Sodium lauryl sulphate is mildly hazardous and irritating in pure
reagent form
http://physchem.ox.ac.uk/MSDS/SO/sod...l_sulfate.html

whereas the Ammonium salt, Ammonium lauryl sulphate is virtually
harmless.
http://physchem.ox.ac.uk/MSDS/AM/amm...l_sulfate.html

| Come to think of it where is the Nitrogen in Sodium lauryl sulphate? It does
| not contain any does it? Perhaps dissolved Nitrogen in the tap water:-)

Wikipedia said that it did, and I said that I was using that as a
reference. You may know better.

In that case Wikipedia is incorrect. Are you sure it didn't give the
formula as

CH3(CH2)nOSO3Na

Where n=11 for classic lauryl/dodecyl sulphate (and related compounds
exist for other n).

Any surfactant will suffocate aphids, but the more aggressive ones may
also remove the waxy protective coating off plant leaves as well. I
once defoliated a bay tree by spraying it with a wetting agent to treat
a bad infestation of scale insect.

Classic soft soap formulations are about as good as you can get for
killing insect pests without inflicting too much collateral damage on
the plant.

Regards,
Martin Brown