Like many people who use LaTeX, I like using the mhchem package to type chemical equations, but there was a problem I met when I was typing numbers with decimal in mhchem package, e.g. if an equation is written as follows,

\ce{3.043 Fe2O3}

mhchem would gives the result 3·043 Fe₂O₃ instead of the expected 3.043 Fe₂O₃. The dot here is actually for the center dot in chemistry equations. But we need the mathematical decimal dot (period).

because mhchem normally does not render the dot as decimal. I tried several methods to make the decimal dot does not display at the middle, e.g. a possible method can be

\ce{\text{3.043} Fe2O3}

though it is not so handy and looks a bit weird (numbers display as plain texts). Finally, I found the following trick works:

\ce{$3.043$ Fe2O3}

just use maths-escape mode, using $$ to embrace the number. There should not be any white spaces between $ and the number otherwise the compiling would go wrongly, though this is not the case in normal equations.

中文：在LaTeX mhchem包中输入带小数点数字的化学公式时，用美元符号$$将小数点数字包括起来，就可以正常显示小数点而不是在中间位置的点，$与数字之间不得有空格。