Well ... this isn't really a glossary definition, but is still very much related to safety (which, if you've just been dropped into this page by a search engine, is what this glossary is all about). A note regarding spellings. When searching for chemicals, it is important to recall that the spelling of chemical names may differ from country to country, even within the same language. In English the most frequently-encountered differences are between {sulphur, sulphate, sulphite, ...} and {sulfur, sulfate, sulfite, ...} and between {aluminium} and {aluminum}. The former spellings are common in the UK, the latter are standard in the US. Although the spellings sulfur, sulfate etc are becoming more common in the UK, and will eventually replace the -ph- spellings, aluminium seems destined to remain in use throughout the UK. When checking for data on a chemical, it is also important to remember that many chemical many several alternative names. For example, propanone and acetone, or copper (II) sulfate (sulphate!) and cupric sulfate.