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.
Ammonium sulfide, also known as diammonium sulfide, is an unstable salt with the formula (NH 4) 2 S. Aqueous solutions purporting to contain this salt are commercially available.ith a p K a exceeding 15, the hydrosulfide ion cannot be deprotonated to an appreciable amount by ammonia. Thus, such solutions mainly consist of a mixture of ammonia and (NH4)SH. Ammonium sulfide solutions are used occasionally in photographic developing, to apply patina to bronze, and in textile manufacturing.