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January 13 th marks the passing of Paul Niggli. Niggli was a Swiss mineralogist who was a pioneer of x-ray crystallography. He developed the mathematical system of space groups that defined 230 different atom arrangements based on x-ray diffraction patterns. X-ray crystallography works by shining x-ray radiation through a crystal structure and detecting the interference pattern generated by the gaps between individual atoms. This information can tell you the position of atoms in a crystal, the width of atomic bonds, and even the size of the atoms themselves. All this information can give detailed help in determining the structure of a molecule. All that is really needed is a pure sample that can be crystallized.

Litmus paper is a type of pH paper that is used to test the acidity of water-based liquids. David Gould, Getty Images

This animation illustrates the relationship between temperature and volume when mass and pressure are held constant, which is Charles's Law. NASA's Glenn Research Center

Boyle's Law describes the relationship between pressure and volume of a gas when mass and temperature are held constant. NASA's Glenn Research Center

This is a phase diagram, which includes the critical point and triple point. Booyabazooka, Wikipedia Commons

Many a lover has been seduced by a sincere and beautifully illustrated letter of affection. If the perfect words elude you at the moment, but your heart's in the right place, find help and inspiration below. How To Write a Love Letter Learning how to write a love letter isn't difficult. Once you gather your thoughts and follow these simple steps to express the way you feel in a love letter you'll know how to do it. Difficulty: Average Time Required: 1 hour Here's How: Clear your desk and your mind of distractions. If you love someone enough to craft this letter, he or she deserves your full attention. Place a picture of the one you love in front of you. Put on your favorite music. Take out your best letter writing stationery and pen. On another sheet of letter paper, make two lists: a) the unique qualities you love about him/her; b) your hopes for the future together. Personalize the love letter salutation. "Dear ___ ," or "To my darling __...

Love has a lot to do with chemistry, so if you're looking to connect Valentine's Day with chemistry, you've come to the right place. Take a look at these chemistry projects and topics that relate to Valentine's Day. Chemistry of Love Sweaty palms and a pounding heart don't just happen! It takes complex biochemistry to give you the symptoms of being in love. And lust. And security. Chemistry may even play a role in falling out-of-love. Get some of the details here, with links for further study.