For example, for the Gases under pressure hazard class, the hazard categories are Compressed gas, Liquefied gas, Refrigerated liquefied gas and Dissolved gas. These classes relate to the physical state of the gas when packaged and do not describe the degree of hazard.
1 In 1596, a flush toilet was invented and built for Queen Elizabeth I by her Godson, Sir John Harrington. 2  The first patent for the flushing toilet was issued to Alexander Cummings in 1775. 3  During the 1800s, people realized that poor sanitary conditions caused diseases.
The first public flushing toilet opens in London. Before the 1850s most people had to use an earth closet, which was a toilet outside the house with just soil in it and no water. Henry Bessemer found a way to convert iron into steel, which was both stronger and lighter than iron. This made it possible to build huge structures such as bridges and ships.