[mir]

From my physical organic chemistry book:

"Kropo and co-workars have reported that the addition of HC1 to 1-octene can be effected m CHCl3 solution under surface-mediated conditions involving the generation ofHCl in situ in the presence ofsilica gel or alumina. The surface-mediated reaction appears to involve a longer-lived carbocation intermediate, since 3chlorobutane is isolated along with 2-chlorobutane, and both (.E)- and (Z)-2octene can also be recovered from the reaction mixture "

How do this surface-mediated insitu generated HCl method work, technical speaking?

[movies]

Chloroform decomposes to HCl and dichlorocarbene (CCl₂).  The carbene is pretty reactive, so it probably reacts with the silica gel.