what has happened to portrait of Mme de Sorquinville by Perroneau? I
was able to bring it up on my screen 2 weeks ago simply by typing in
her name. Now I get something called "megasets" which is no help at
all.

Hello ted3129-ga,

You can still get to it by going to the Louvre web site at
http://www.louvre.fr/louvrea.htm  Select "Collections" and then
"Paintings" and then "Selected works" and then "France: 18th century"
(phew!)  The lady is second from the left in the second row, and you
can click on her to get a larger version.  Alternatively, you can get
to her directly by using the URL:
http://www.louvre.fr/img/photos/collec/peint/moyen/rf1937.jpg

As to what happened, I can only assume that before you were picking up
the Louvre web site on you search and now this no longer happens,
because (a) the Louvre web site structure has been changed and the
page which shows a caption to the picture, which includes her name,
has not yet been crawled;  or (b) the new site structure specifically
excludes that page from being crawled;  and maybe also (c) the name
was present in the file name of the picture and this has now been
renamed.

Search strategy: I confirmed that entering Sorquinville into Google
simply brings a link to a collection of art slides, which presumably
includes one of the painting.  However, the notes under the link to
Megasets did tell me that the painting is in the Louvre.  I searched
on "Louvre" to find the Louvre web site and once at that site explored
the "Collections" pages to find the picture.