I have read the Chemistry Code so many times that I am now offically confused. Could you please tell me if the letter sign is used for Chemical symbols or do I use Nemeth rules in the following equations and text (O is for Oxygen):
1.500 OX2 = 3 O atoms 1.000 AlX2 = 2 Al atoms
Therefore, this compound contains two Al atoms for every three O atoms.
My understanding is that I use Nemeth rules and therefore apply the letter sign when the symbols are comprised of single letters that are not in touch with math symbols.
When following the rules of the Braille Code for Chemical Notation 1997, chemical SYMBOLS do not use an English Letter Indicator, even if they are single letters or letter combinations that are the same as a short-form word. The Chem.Code uses the all-caps word SYMBOL be clear when discussing the elements. See Section 3.5 of the Chemistry Code. Look at Example 4.1.5-1 on page 22 to see that Cd--the SYMBOL for Cadmium--does not use an English Letter Indicator (ELI) in the narrative, even though "Cd" is a short-form word. You need to know what you are reading -- if C is the SYMBOL for carbon, you do not use an ELI. But if C is the abbreviation for Celsius, you do use an ELI following rules for abbreviations.
In your example, do not use ELIs with O (SYMBOL for oxygen) or with Al (SYMBOL for aluminum).