Thanks, all. I did a quick check with a couple of household lamps, and it appears the focal length of this magnifying glass is actually too long - it's about 18 inches (460 cm). The Speed Graphic doesn't go out that far Oh well, it was only $1. Next time I'm near the store I'll have to check to see if they have any others.
edit: It's been pointed out using a lamp may not be an accurate measurement, and I should use the sun. Unfortunately it's heavily cloudy here today. I tried it 2 ways inside the house:
a) with the magnifying glass held between my hand and and a ceiling light and measuring the distance between my hand and the magnifying glass when the fixture was in focus on my hand, and
b) using the magnifying glass to "project" the image of an incandescent bulb on the opposite wall, and measuring the distance between the bulb and the glass when the filament was in focus on the wall. Both come out to 18 inches, +/- an inch or 2 due to my own imprecise measuring.
In any event, it doesn't work, so I'll have to try another one.