Litmus: chemistry all around you

You float in an empty dark space with atoms and molecules all around you. Turn to find what you need, tap it to pull it in, and build. Litmus has three chapters. In the Moleculator you build molecules atom by atom, across 100 levels. In the Reactor you run real reactions in a glass sphere across 60 levels, some as the molecules meet and some with a catalyst, heat, a spark, light or electricity. In the Carbon Chamber you make alkanes, alcohols, acids and esters across 40 levels. After each level a card shows what happened, in a science textbook's words.

How to play

Drag to look around: all the way round, up and down. Molecules float on every side and drift slowly round you, so what you need may be behind you.

• Build a molecule: in the Moleculator you start holding an atom. Tap another and it glides in and bonds. Each atom makes a fixed number of bonds, and a free bond grabs the first atom it touches on the way, so turn until the line is clear before you tap. Tap what you hold to let it go.
• Run a reaction: in the Reactor and the Carbon Chamber, tap a molecule to put it in the glass sphere, which holds four. Some react the moment they meet. Others need an agent: pick one of the four orbs at the bottom.
• Two chances: a wrong agent bounces off and costs one of your two chances. A wrong agent with no chances left pours the reaction away.
• Products: anything a goal at the top wants flies up into it. Anything else waits above the sphere: tap it to put it back in, or drag it away to keep it. Whatever still waits when the next reaction starts is lost.
• The daily molecule: one molecule a day, the same for everyone. Build it to keep your streak going.

Your progress is saved automatically, so you always pick up where you left off.

Real chemistry

Every reaction in Litmus is one that happens in a school lab or in industry, with the agent it really needs: iron for the Haber process, vanadium oxide for the Contact process, a few drops of concentrated sulphuric acid to make an ester, acidified potassium dichromate to turn an alcohol into its acid. The molecules a level floats are chosen so that whatever you put together does what it really does.

Tips

• Read the goal first, then work backwards: what has to meet to make it, and is one of those made by another reaction first?
• A catalyst comes back after the reaction. A spark, light or electricity is used up in the flash.
• Before you tap in the Moleculator, turn so that nothing sits on the line between you and the atom you want.

Frequently asked questions

Is Litmus free? Yes, completely free to play, with no account or download, in any modern browser on phone, tablet or desktop.

Does it work on mobile? Yes. Litmus is built for touch as well as mouse.

How do I win a level? Make every goal shown at the top of the screen.

Is every level solvable? Yes. Every level, and each daily molecule for the year ahead, is played and won through real taps on a phone and on a computer before it goes out.

Stuck? Read the Litmus strategy guide →

Enjoy a good thinking puzzle? Try Marble or Comb, or browse all Zamborin games.