\begin{table}%t1
\par
\caption{\label{tbl-1}Summary of derived column densities and abundances.}
\small%\centering
\par
\begin{tabular}{cccccc}
\hline
\hline
\noalign{\smallskip}
$V_{\rm LSR}$ & $N$(HF) & $N$(H$_2$O)  & $N$(H)\tablefootmark{a} & $N$(H$_2$)\tablefootmark{b} &HF/H$_2$ \\
(km~s$^{-1}$) & $\rm 10^{12}~cm^{-2}$ & $\rm 10^{12}~cm^{-2}$ & $\rm 10^{20}~cm^{-2}$ & $\rm 10^{20}~cm^{-2}$ & \\
 \hline
\multicolumn{5}{l}{Results for W51} \\
0--10  & 14.5~$\pm$~1.1 & 6.2~$\pm$~0.5 &  13.9 & 10.5& $1.4\times 10^{-8}$  \\
10--20 & 1.8~$\pm$~0.3 & 0.4~$\pm$~0.1 & 6.4& 1.4 & $1.3 \times 10^{-8}$\\
20--30 & 0.8~$\pm$~0.1 & $<$0.2 & 11.1 & $<$0.7 & $>$$1.2\times 10^{-8}$\\ 
42--47  & 8.0~$\pm$~1.0 & 5.4~$\pm$~0.7 & ... &  5.0 &   $1.6\times 10^{-8}$ \\
 50--75 &  $>$130 &  $>$113 & 22.1 &  ... &  ... \\[3mm]
\multicolumn{5}{l}{Results for W49N} \\
30--50 & 55~$\pm$~10 & 22~$\pm$~8 & 69.5 & 37 & $1.5\times 10^{-8}$\\
50--78 & 69~$\pm$~10 & 34~$\pm$~9 & 72.3 & 66& $1.1\times 10^{-8}$\\
67--71 & 5.6~$\pm$~1.0 &  1.5~$\pm$~0.3& ... & 4.4& $1.3\times 10^{-8}$ \\
\hline 
\end{tabular}
\tablefoot{\tablefoottext{a}{from Koo \cite{Koo1997} (W51) and Godard et~al.\ \cite{Godard2010} (W49N), for an assumed 21~cm spin temperature of 100~K.}\\
\tablefoottext{b}{Derived from CH observations (Gerin et~al.\ \cite{Gerin2010}), assuming $N$(CH$)= 3.5\times10^{-8}$ $N$(H$_2$) (Sheffer et~al. \cite{Sheffer2008}). The relationship shows a scatter of 0.21 dex, corresponding to a factor of 1.6.}}
%\vspace*{2mm} 
\end{table}