\begin{table}%t4
\caption{\label{clouds}Abundances in molecular clouds.  References: L1689N: SO, SO$_{2}$ and
H$_{2}$S from this work, SiO from \citet{2000AetA...357L...9C} and~H$_{2}$CO from \citet{2001AetA...372..998C}; L134N:
SO and SO$_2$ abundances from \citet{1989ApJ...345..828S}, H$_{2}$S
from \citet{1989ApJ...345L..63M}, SiO from
\citet{1989ApJ...343..201Z}, $\rm H_{2}CO$ from
\citet{1992IAUS..150..171O}; TCM-1: SO~abundances from
\citet{1995PASJ...47..845H} and \citet{1997ApJ...486..862P}, SO$_2$
from \citet{1983AetA...127L..10I}, H$_{2}$S from
\citet{1989ApJ...345L..63M}, SiO from \citet{1989ApJ...343..201Z},
$\rm H_{2}CO$ from \citet{1998cpmg.conf..205O}.}
%\centering
\par
\begin{tabular}{c|ccccc}
\hline \hline 
Cloud   & $x$(SO) & $x$(SO$_2$) & $x$(H$_2$S) & $x$(SiO) & $x$($\rm
H_{2}CO$) \\
& ($10^{-9}$) & ($10^{-9}$) & ($10^{-9}$) & ($10^{-12}$)
& ($10^{-8}$) \\
\hline
L1689N & 6--16 & 0.4 & 0.3 & 4 & 0.04 \\
L134N & 0.6--10 & 0.3$-$2.5 & 3 &$\leq$3.6 & 2 \\
TMC-1 & 0.3--4 & 2$-$6 & 0.7 & $\leq$2.4 & 7 \\
\hline
\end{tabular}
\end{table}