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.
Tin(IV) sulfide is a compound with the formula SnS 2. The compound crystallizes in the cadmium iodide motif, with the Sn(IV) situated in octahedral holes' defined by six sulfide centers. It occurs naturally as the rare mineral berndtite. It is useful as semiconductor material with band gap 2.2 eV. Reactions. The compound precipitates as a brown solid upon the addition of H 2 S to solutions of tin(IV) species.