Early wheels were simple wooden disks with a hole for the axle. In the early Roman empire, most horse-carts used a design featuring two chords across the wheel. The spoked wheel was invented much more recently, and allowed the construction of lighter and swifter vehicles.
Chromium(III) sulfide. Chromium(III) Sulfide is the inorganic compound with the formula Cr2S3. It is a brown-black solid. Chromium sulfides are usually nonstoichiometric compounds, with formulas ranging from CrS to Cr0.67S (corresponding to Cr2S3). Preparation.
Aluminium sulfide or aluminium sulphide is a chemical compound with the formula Al2 S3. This colorless species has an interesting structural chemistry, existing in several forms.The material is sensitive to moisture, hydrolyzing to hydrated aluminium oxides/hydroxides.t higher temperature, the Al(III) centers become randomized to give a defect wurtzite  structure. And at still higher temperatures stabilize the Î³-Al 2 S 3 forms, with a structure akin to Î³-Al 2 O 3. Molecular derivatives of Al 2 S 3 are not known. Mixed Al-S-Cl compounds are however known.