There are two main types of fire extinguishers: stored-pressure and cartridge-operated. In stored pressure units, the expellant is stored in the same chamber as the firefighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, nitrogen is typically used; water and foam extinguishers typically use air.
The Encyclopedia Britannica, which has been in continuous print since it was first published in Edinburgh in 1768, said today that it will continue with digital versions currently available online. The final set of the 32-volume printed edition remains available for sale on the company's website for Â£890 ($1,400). Scroll down for video
Who invented the dictionary? Dictionaries have been around since 2300 BC and the oldest dictionaries were discovered in Syria. Over the years Chinese, European, Arabic and English dictionaries were also written. Robert Cawdrey, an English school teacher published the first English alphabetical dictionary. However it was Samuel Johnson who compiled the first widely recognized and reliable dictionary in English in 1755. Samuel Johnson was a popular British author and published âA Dictionary of English Languageâ which took him nine years to complete.