Insecticides and other sprays

Hamish Sloan
Thu, 13 Feb 2003 10:50:13 PST
Pat asked about soft soap. This is a soap made from animal fats and 
potassium carbonate reaction - the soap is essentially potassium salts of 
fatty acids. It is a very soft gel which does not set. If your forebears in 
the US were pioneers, then this is what they had for their own home-made 
soap, the source of the potassium being woodashes (hence potash).

Ordinary hard soap is the similar reaction of sodium carbonate (washing 
soda) with animal fats. The better "quality" soaps contain larger amounts 
of the glycerin which is the other product of the alkali + fats reaction. 
Glycerin acts as a moisturizer and some cosmetic preparations contain it 
though it is probably not used as much as it used to be. The problem with 
high levels of glycerin is that the soap takes longer to set. The soap bars 
you use today still contain about 27% water, otherwise the sodium salt 
based soap would be too hard and difficult to lather (notice how the last 
fragment of the bar never lathers so well? - its too dry).

The only trade name for soft soap I know is Swarfega and this may be a UK 
name only. However, ask any mechanical engineering friend. If he/she 
forgets to use a barrier cream, he/she will probably use a soft soap to 
wash off the oily grime afterwards. The soft soap is acting as a spreader 
but also has some insecticidal properties of its own.

Definitely do not use a detergent.

Diana mentioned using baking soda with a spreader to combat mildew and 
black spot. Sodium bisulfite is more powerful. If any of your friends do 
any of their own brewing or fermenting, they will use sodium bisulfite to 
sterilize their bottles, etc., so this material is readily available from 
any home beer- or wine-making kit provider. I don't have the recipe ready 
to hand but I'll pass it on when I find it. Sodium bisulfite is much 
stronger than sodium bicarbonate (baking soda) so if you try your own 
experiments start at the dilute end! Essentially it works by producing low 
concentrations of sulfur dioxide. One of the noticeable effects over my 
gardening lifetime is the way in which the reduction in air pollution has 
allowed black spot to return and infect roses much more. Put it another way 
- when the air was polluted with sulfur dioxide, black spot on roses was 
very rare. Mildew was similarly affected.

Enough of your chemistry lesson for today.

Regards to all

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