What it shows
Three quick tests catch the commonest milk adulterants: a drop on a tilted plate flows slowly for pure milk but runs fast if watered, iodine turns blue if starch was added to thicken it, and shaking with water gives a thick lather if detergent was mixed in. The project compares packet, dairy and loose milk.
The science
Pure milk is a thick emulsion of fat and protein, so a drop clings to a tilted surface and leaves a white trail; adding water thins it so it runs faster and leaves little trail. Starch, sometimes added to make thin milk look rich, forms a blue black complex with iodine, while pure milk has no starch and stays brown. Detergent, added to make synthetic milk froth and look creamy, lowers surface tension and produces a dense, lasting lather on shaking, whereas pure milk gives only a thin foam that collapses.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three milk samples of 50 ml each from different sources
- A smooth steel plate or glass slide
- Tincture of iodine diluted ten times (adult prepares)
- A dropper
- Three small bottles with caps
- Cornflour and a drop of liquid detergent to make known adulterated controls
- Labels and a notebook
Safety
For this project: An adult must dilute the iodine, which stains and must not be swallowed. Do not drink any sample used in the tests, and especially not the controls.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Make two control samples from one milk: one with a pinch of cornflour stirred in, one with a drop of detergent.
Tilt the plate and put one drop of each sample at the top; time how long it takes to run 5 cm and note the trail.
Put a drop of diluted iodine into a spoon of each sample and record the colour.
Pour 5 ml of each sample into a bottle with 5 ml water, cap and shake ten times, then measure the foam height after one minute.
Compare each real sample with the controls for all three tests.
Record results in a table with a column for each test and a row for each sample.
Repeat the plate test three times per sample, because single drops vary.
Write a conclusion stating which samples passed every test, and note that passing does not prove the milk is free of every possible adulterant.
What you should see
The cornflour control turns blue with iodine and the detergent control gives a tall lasting foam, while clean samples stay brown and foam little; any real sample that runs fast, turns blue or foams heavily is flagged for the test it failed.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does a pure milk drop flow slowly?
It is thick with fat and protein, so it clings to the surface and leaves a trail.
2What does a blue colour with iodine mean?
Starch is present, which pure milk never contains.
3Why does detergent milk foam more?
Detergent lowers surface tension, so bubbles form easily and last longer.
4Can these tests prove milk is completely pure?
No, they only check three common adulterants; laboratory tests are needed for others.
Take it further
Measure the density of each sample with a lactometer or by weighing 50 ml, since watered milk is less dense.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Science Projects for Class 9 and 10
Models and experiments for high-school physics, chemistry and biology
Science projects
Safe Chemistry Projects for School
Experiments and models with kitchen materials and proper safety
Find out more about chemistry
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.