In a later patent(1748817), Zerk helpfully provides a list of his earlier patents....
1,475,980, 1,619,455, 1,632,985, 1,632,986,
1,632,987, 1,645,888, 1,645,889, 1,645,890,
1,655,213, 1,676,626, 1,679,887, 1,679,888,
1,684,080, 1,692,320, 1,696,217, 1,700,527,
1,703,285, 1,703,286, 1,708,040, 1,708,041,
1,710,719, 1,710,959, 1,711,870, 1,711,871,
1,714,254, 1,720,871, 1,720,872, 1,720,873,
1,720,874.
Oscar was a very busy fellow - P