Chemistry

How is milk powder made?

Who doesn’t love the taste of milk powder, whether dry or dissolved in milk. Do you know that as powder, milk can be preserved for years together? Let’s have a look into how it is made.

Drying Milk

The Italian explorer Marco Polo reported that the soldiers of Kublai Khan (the Emperor of the Mongols in the 13th century) knew how to make milk powder. They would leave milk to dry in the hot sun of the Gobi desert till it became quite thick. When they needed milk, they would put some of the dry paste in water and dissolve it. Easy wasn’t it?
Nowadays, milk is dried quickly in factories. There are two ways. One is called ‘spray drying’. Milk is sprayed into a huge chamber, and heated air is blown from the other end. The droplets of the milk dry up very quickly in the hot air, and fall down. The powder can then be scraped off and packed into jars or sachets.
Another way is ‘drum drying’. In this, milk is sprayed onto huge drums, which are heated by electric current. The heat makes the water in the milk evaporate, and the powder stays behind on the drum. Drum-dried milk is often flaky and sticky, while spray dried milk is powdery and non-stick.

Buy a few sachets of milk powder of different brands. Ask your friends to join you in feeling and tasting the powder. Which brand was spray-dried and which was drum-dried?

Why dry milk (and anything)

All living things need water to survive. This is because water is the solvent in which most chemicals dissolve – like vitamins, amino acids, carbohydrates and minerals. The enzymes that convert the food we eat into energy work only in a wet environment. This is true for every living organism, including bacteria.
If you go to a village, you will see chillies, papads, fish, grapes (to make raisins) and other things left out to dry in the sun. In a dry environment, bacteria cannot grow and multiply. If you remove moisture from food and store it in water-tight and air-tight containers, it will last almost forever.

The Colombo Plan

In the 1950s, there were food shortages in many countries, including India. A group of 8 countries had a meeting in Colombo, Sri Lanka. Here they created a plan by which countries like Australia, New Zealand and Canada would supply milk and other food to countries which were short of them. Under this plan, a large amount of milk powder was shipped from New Zealand to India. The powder would be dissolved in water to make milk, which was then distributed to homes. This continued till the White Revolution, when India was able to overcome its shortages.

Why is sulfuric acid called the king of chemicals?

What’s common to petrol, fertilizers, cars and soaps? They, like a lot of other things, require sulfuric acid to be made. That’s why sulfuric acid is called the king of chemicals.

The uses of sulfuric acid

Sulfuric acid is involved, in some way or the other, in the manufacture of practically everything. Indeed, the production of sulfuric acid is sometimes used as a measure of how industrially advanced a country is. India produces about 48 lakh tonnes of this acid a year.

60% of all sulfuric acid produced is mixed with crushed phosphate rock to make phosphoric acid. Phosphoric acid has two uses – to make phosphate fertilizers, and to make sodium triphosphate, which is a detergent. 

Lots of sulfuric acid is used to clean up rust from steel rolls. These cleaned up rolls are used to make cars, trucks, as well as household appliances. Sulfuric acid is used in petroleum refining to make high-octane petrol, which burns efficiently. It is put in the lead-acid batteries of your car battery. It is used to make aluminium sulfate, which is needed for making paper. It is used to make ammonium sulfate, a common fertilizer. It is used to make… well, it is used to make practically everything!

On earth, sulfuric acid does not exist in a natural form. But on the planet Venus, there’s plenty of it. There are lakes of the acid, which evaporate to form clouds, which then rain sulfuric acid upon the Venerean surface. The USSR’s Venera-3 spacecraft landed on Venus on March 1, 1966 and was digested in minutes!

Handling sulfuric acid

Never handle sulfuric acid yourself. If you spill a drop on your hand, it will react with the tissue, burning it instantly. It also causes dehydration. Fumes of sulfuric acid can cause blindness, and damage the lungs if inhaled. In case you accidentally spill acid on yourself, wash it under a tap for fifteen minutes at least, so that even the tiniest drop is washed away.

Even dilute sulfuric acid is dangerous. When handling sulfuric acid, always wear thick gloves and a lab coat or apron. Never handle it on an open bench, but use it in a fume hood. Never pour it from the bottle, but always use a thick glass pipette with a rubber bulb. The best is to let your teacher handle it, while you stand aside and watch.

Sulfuric acid is often stored in concentrated form. When diluting it, never pour water into the acid. That will make the whole thing explode. Instead keep crushed ice (made from pure water) in a large beaker, and pour the acid onto it, drop by drop. The ice absorbs the heat of the reaction, so it won’t explode. When the ice melts, you get dilute sulfuric acid.

Are tins really made of tin?

Ever waited impatiently, for mum or dad to open a tin of pineapples or rosogollas, floating in sugar syrup? Did you know the tin can isn’t actually made of tin?

Canning

The idea of sealing food in a tight container goes back to 1809. Napoleon, the French Emperor was fighting wars all over Europe, and his army needed huge supplies of preserved food. He offered a prize of 12,000 francs (about Rs. 14 lakh in India today) to anyone who could find a method. The prize was won by Nicolas Appert, A French brewer.
He discovered that if you sealed food airtight immediately after cooking it, it would remain fresh as ever. That’s because bacteria and fungi cannot enter from the air, and all the ones in the cooked food would have died.
In the early days, food was put into a steel canister, and then a steel plate would be welded on top of it. Over time, the word ‘canister’ got shortened to ‘can’. While steel cans are easy to transport, the food reacts with the steel producing rust and other toxic stuff.

Tinning

The trick is to make the can out of steel and tin. A very thin sheet of tin is hammered onto a sheet of steel. This way, you make a material called tinplate steel. You can then roll this sheet into a cylinder, such that the tin comes on the inside. Then you cut a circle from the sheet and weld it to the can, with the tin facing inside. Now pour the food in, and seal off with another plate.
The steel on the outside helps keep the can firm. It won’t get any dents while the can is being transported. The tin on the inside prevents food reacting with the steel. Over time, the name tinplate can got shorted to tin!
Nowadays, a whole lot of cans are actually made of aluminium, because it’s cheap and can be recycled.

Malleability

Try this experiment in school. Take a few sheets of different metals, like steel, tin and aluminium. It’s best if they have the same thickness. Try to roll them into shapes. Which rolls easily? Malleability is the name scientists give to how easily you can roll or hammer metals into different shapes.
If there’s a workshop near your school, you can ask them to help you weld a tin can into shape. Ask them to make sure that there are no sharp edges. While it may not be good for food, you can keep flowers or pencils in your own handmade tin can!

How does thermal ink work?

Can you write without ink on a piece of paper? If you had some special fax paper, and an old refill, there’s a special trick you can use to write. That’s called thermal printing!

Fun with fax paper

Get hold of some fax paper and an old, empty refill that doesn’t write. Heat the end of the refill on a candle flame and then try and write your name on the paper. Does it seem to appear magically? But there was no ink!
That’s because the ink is being made on the fax paper even as you write with the hot refill. (You won’t see any writing once the refill has cooled.) Fax paper is made in a special way. It is coated with two materials – a leuco dye and a mild acid. They do not react with each other when cool. When the hot refill end scratches the paper, the heat causes the leuco dye to react with the acid. The dye changes colour (mostly to black) and gets deposited on the paper.
Here’s an interesting video that shows you how to make a picture using just heat and some fax paper:

How a fax machine prints

When you receive a fax from someone, the machine converts the electronic signals into words. These are passed to the printer head, that part of the fax which helps print out stuff. The head is made of thousands of tiny pins. Say the signal says to print the word ‘CHEMISTRY’. Some pins will stick out from the other pins in the shape of the word. These pins are quickly heated by an electric current. When the head stamps the paper, the pins will cause the dye to react right under them. So the word ‘CHEMISTRY’ gets formed on the paper. The areas that weren’t touched by the heated pins will stay white.

Thermal printing is much faster than ink-based printing. That’s why it’s used in places where quick printing is needed, like credit card bills, supermarket bills, etc.

Why does fax ink fade?

You might have noticed that faxes printed on fax paper fade after sometime. This is because many things cause the dye on the paper to go back to its colourless ‘leuco’ form. UV rays from bright sunshine cause ‘bleaching’ of the ink. If you touch the paper with oily or wet fingers, the ink will leach out of the paper.

What is dry ice?

Tried making ice-cream at home? All that ice and salt makes such a mess, doesn’t it? What if there was a dry kind of ice, that didn’t melt into a mess? Well, there is - it’s called dry ice.

The trouble with water ice

Ice is anything that is frozen, though we commonly use the word for frozen water. Dry ice is frozen carbon dioxide. Carbon dioxide goes from being a gas to a solid at −78.5°C. It’s a lot more useful than ice for freezing some kinds of foods.
Water ice can cause a few problems. When it melts, the water can make a sticky and dirty mess. It helps bacteria and fungi to grow, spoiling the food. It can also cause crystal formation, ruining the texture of some water-containing foods.

What’s good about dry ice?

Dry ice doesn’t melt, but becomes gas immediately (this is called sublimation). Also, it stays solid much longer, because a lot of heat is needed to sublime it completely. Therefore, there’s no mess being created, for the sublimed dry ice will simply waft into the air. And carbon dioxide acts as a preservative, killing bacteria and fungi. And it doesn’t help crystal formation.
So next time you make ice cream at home, try dry ice!

Artificial fog

Seen a horror or thriller film, in which there’s a lady in white walking on a lonely road, surrounded by cold fog? The fog is made of dry ice!
You keep big blocks of dry ice on the film sets. They slowly sublime into carbon dioxide. This is a dense gas, heavier than air. So it hangs low, looking like fog. There are other ways to make artificial fog, but using dry ice is safer. That’s because you need no chemical other than carbon dioxide.
So next time you see a thriller film, you can point out the secret of the fog to your friends!