\begin{table}%T3
      \caption{\label{Carbone-Silicates}Aliphatic hydrocarbons/silicates ratio.}
             %\centerline
{
         \begin{tabular}{lccc}
            \hline \hline
            {{\rm Source}}	&$\tau ({3.4}~\mu${m}) 		&$\tau$({silicates})    
	&{3.4}~$\mu${m}/{silicates} \\
            name&&& \\
\hline
NGC 1068		&$0.1\pm0.015$		&$0.9\pm0.1^{{a}}$    	&$0.11\pm0.05$ \\
NGC 7172		&$0.09\pm0.015$ 		&$>$0.3$^{{b}}$   	&$<$0.35	\\
IRAS 19254--7245	&$0.7\pm0.1$ 		&{\rm Saturated}    	&--	\\
NGC 5506		&$0.04\pm0.01$ 		&$0.9\pm0.2^{{c}}$     	&$0.05\pm0.2$ 	\\
\hline
         \end{tabular}}
\smallskip
\begin{list}{}{}
\item
 ${^{a}}$  Using the value derived by Tomono et~al. (\cite{2001ApJ...557..637T}) in the central~1$''$ of~NGC~1068;  ${^{b}}$  based on the color excess $E(B-V)$ as explained in Veilleux et~al. (\cite{1997ApJ...477..631V});
 ${^{c}}$  estimated using the Infrared Space Observatory Photometer PHT40 spectrum recorded on~\mbox{13-Aug.-1996}. 
\end{list}
   \end{table}