Listener Question

Kaye asks

In the “How to clean saucepans” section you recommend using ‘washing soda’ can you please verify exactly what it is that you call ‘washing sode’.? The only thing I can think of is washing powder from the laundry but surely that isn’t what you mean.

I get asked this a lot. People just can’t find soda ash in supermarkets. The reason is that it’s at ankle height, and most people never look at the bottom shelf.

Go into the cleaning aisle, lower your sight to the bottom shelf, and look for this:

I have yet to find a supermarket that doesn’t have it.

So why does it work so well?

Two reasons – it hydrolises the fats (the same as caustic soda), and the adsorption to the metal substrate helps separate charred material.

All you need to do is bring it to the boil, let it cool, then tip it out – all the fat will be gone. Check out the Lectric website for more recipes



How Do I Know if Something is Microwave Safe?

Reader Paul asks:

I was zapping some pasta in the micro wave and one of the kids said you can’t put melamine in the microwave, it’s dangerous. I’ve never heard that before and wanted to check if that was actually the case. And if so, why?

There is a simple test you can do, but first let’s look at how microwaves work.

Essentially, they heat water. Water is a polar molecule, which means it has an uneven separation of charge. That is, the molecule has a positively and negatively charged end.

Microwaves, like other electromagnetic waves, introduce an oscillating electric field. This electric field switches the molecule backwards and forwards rapidly, and this generates mechanical heat, just as you can start a fire by spinning a tick rapidly against another one.

The heated water then disperses its heat through the rest of the material and so it heats up.

But you don’t want the microwaves heating the vessel itself, particularly if it’s a plastic, as it could potentially release carcinogenic chemicals into the food.

So the test is simple – heat the vessel by itself with nothing in it. If it gets hot, it’s not microwave safe.

And melamine is definately not microwave safe.


How to Avoid Soap Scum in the Shower

Reader Jenny says:

I have found my answer for the shower screen problem. Use liquid soap only in the shower. (Not my brilliance btw). It works really well!! The claim is that hard soap contains fat which causes scum.
Some general washing down still required of course for any mould buildup but no scrubbing, and now have clear screens. Whoopee!

This is an excellent idea!

I’ve discussed shower screens before. Essentially, soap scum is the calcium or magnesium salts of negatively charged surfactants.

As it happens there are four types of surfactants – anionic (negatively charged), cationic (positively charged), non-ionic (no charge) and amphoteric (both positive and negatively charged).

Each of these has its own particular applications, which is a story for another day, but the takeaway lesson for today is that by far the most common, and the cheapest, and the oldest, are the anionic surfactants (the ones that make soap scum).

Incidentally, when Jenny says they contain fat what she means is that they are made from fat ( and is easy to do at home – there is an idea for another post).

Liquid soaps on the other hand tend to be non-ionic in nature.  Therefore, none of the calcium or magnesium salts will form and no soap scum results.

Very clever!

If you want to use a hard soap, however, there is an option – Dove. I don’t know what’s in it, but I know it isn’t ordinary (anionic) soap, as it has a neutral pH (unlike anionic surfactants which are highly alkaline).

Dove is also available as an all over body wash, which is an excellent product which avoids those little unusable fragments of soap that you get in your soap holder when the bars get too small to use.

Rusty Biscuit Tins

Reader David asks:

Hi Dr Chemical,
Hope you can help? I am a collector of old biscuit tins. I have recently received one that is in poor condition and is showing signs of rusting all over. Is there anything that i can use to at least clean tin up, without damaging print on tin?

Yes, there sure is – Citric Acid.

Rust is ferric oxide, and like many metal oxides is very chemically stable. To break the oxide bond you either blast it apart with hot sulphuric acid, or you treat it with a chemical that forms an even stronger bond with the iron than the oxide.

Citric acid fits the bill perfectly. it’s a weak acid, so it won’t damage the paint or metalwork, but it forms a very strong complex with the iron and will therefore remove the rust very effectively,

Incidentally, this is why the traditional breakfast involves an iron fortified cereal with orange juice.  The citric acid in the orange juice binds with the iron in the breakfast cereal and makes it more bioavailable (that is, more readily absorbed into the body).

So I would use the citric acid with a wet sponge – dip the wet sponge into the citric acid power and use it as a type of powder cleaner as you rub the tin.

So where do you get citric acid from?  Unfortunately, it doesn’t appear to be readily available from hardware stores.  So I’d look in yellow pages under chemical suppliers.  It’s not a restricted or dangerous chemical, so there is no reason you can’t buy it over the counter.


Radio Show 9/5/12

Some good questions today:

1. How do you get dog slobber off the windows of your car?  Dip a wet sponge into some soda ash (washing soda, or sodium carbonate) and rub it on as you would a powder cleanser.  Rinse and wipe away.  If there are white streaks when it dries, they can be wiped away with a bit of vinegar on a sponge.

2. Bore stains.  Bore stains are ferric oxide (rust) caused by the oxidation of iron in the bore water by atmospheric oxygen.  The solution for removal is an acid.  And the best option is probably sulphamic acid, which you find in Easy Off BAM bathroom cleaner.  Spray it on, let it soak for a minute or two, and it should just wipe off.  Failing that, you could try powdered pool acid from Bunnings, or powdered citric acid (but I’m not sure where you can get that from).

3.  Demisting your windscreen.  I suggested a preventative approach – wiping the inside of your windscreen with dishwashing detergent.  But off air, a truckie called in and suggested hairspray.  That’s what I love about my radio show, clever ideas from listeners.  As it happens, if you do have a misty windscreen, hairspray would be an excellent way to demist it (with one caveat).

The reason it would work, is that hairspray is alcohol based.  We have seen that short chain alcohols possess the property to both mixed with oil and water to a degree.  In this case, the alcohol will break the surface tension of the little beads of water that are scattering the light as it passes through your windscreen, making it look opaque (misty).

Because the alcohol breaks the surface tension, it allows the drop to wet, or smear, across the surface so that it will not disrupt the passage of light, and therefore the mist disappears.

The only problem with hairspray, however, is that it does not contain just alcohol – it also contains the resins that stick your hair together.  And I’d suggest that spraying sticky stuff on the inside of your windscreen is not a particularly good idea, as it will suck up dust and cause the light to scatter badly, particularly if you are driving into the sun.

So the best thing is just to spray alcohol by itself. In other words, use Glen 20.  Glen 20 is just an alcohol spray – that’s all it is.  So you could spray as much of that onto your windscreen as you want and it would do a really nice job of demisting in a jiffy.

Tomorrow: Aluminium and Alzheimers