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.
Soluble chromate(VI) salts give yellow solutions, but lead(II) ions give a yellow ppt. of lead(II) chromate(VI) and silver ions a dark red ppt. of silver chromate(VI). A few drops of silver chromate is used as an indicator when titrating chloride solutions with silver nitrate solution in neutral solution.he chemistry of chromium (principal oxidation states +3 and +6) is described with particular emphasis on chromium(III) complex ions with ligands such as water, ammonia and chloride ion, and the chromium(VI) oxyanions i.e. chromate(VI) and dichromate(VI) including the latter's redox reactions.