Alas, I tried it.
My Canon printer/scanner will only scan at 600 dpi,the highest it will allow, and when I tried that --using your suggestion for trying with multiple slides, they all came out too dark..and even when trying to go in an manipulate the images, I did not have success. (My scanner even allows for changing brightness and contrast iof the images before saving them as .jpegs, but that did not work satisfactorily.)
You may be right, a different scanner may do the trick..but since since this Canon Pixma 610 multi-function printer and scanner is new, I will probably just have photos printed out from these very old 35 mm slides. Then, if I want to scan the photos, I can still do that. One last thought...i might try a discussion forum at the Canon website....althoiugh I am partial to these great Apple support pages.
Thanks for your reply.