According to the serial number, which was allocated July 25, 1916, it's a Singer 115. The 115 is the rotary-hook version of the much more common model 15, which has an oscillating hook. It was Singer's top-of-the-line machine. To confirm that it's the rotary (rather than the oscillating) hook, turn the handwheel toward you while observing the action in the bobbin area. If it moves in a continuous clockwise direction, it's a rotary hook; if it reverses direction (back-and-forth), it's an oscillating hook. Parts are a cinch to find. It takes a standard 15x1 needle and the nice, roomy class 15 bobbin. A quick look on the internet for "115 bobbin case" came up with many from reliable sources for under $10.
The ornamentation is commonly called "Tiffany" decals, which I believe is not a Singer designation but rather a later, invented term. Beautiful. Start cleaning by using sewing machine oil and cotton balls. Go slowly and carefully. Decals this old can be fragile, and once you've ruined them they're gone. (I learned this the hard way.) If that's masking tape on the bed of the machine, sewing machine oil can remove that too. You'll probably have to let it sit for a day or two to soften. Go slowly. (It bears repeating.)
If you treadle, or have wanted to learn to, this would be the machine for it.
At $25, if this is a model 15, you got a very good deal. If it's a 115, you got a prize. Congratulations on a really nice find.
Last edited by Manalto; 08-29-2015 at 10:06 PM.