Newer builds require the use of a device tree overlay to ensure the hardware you need is available, in older builds, you had to rebuild the kernel if what you wanted wasn't available. Although recent builds have had the dto support, I have found various issues here and there.
So i2c-1 is the enumeration linux gave one of the i2c buses and does not necessarily correspond to the i2c pins you are using. The BBB has two usable i2c devices , as follows:
- i2c0: Not exposed in the expansion headers
- i2c1: pins P9 17,18 (and 24,26)
- i2c2: pins P9 19,20 (and 21,22)
The i2c devices appear in the AM335x memory map  at the following locations:
- i2c0: 0x44E0_B000
- i2c1: 0x4802_A000
- i2c2: 0x4819_C000
Linux creates mappings in the /sys/bus/i2c/devices pseudo-filesystem that indicates the mappings from the i2c-* devices to the underlying hardware:
root@beaglebone:~# ls -l /sys/bus/i2c/devices/i2c-*
lrwxrwxrwx 1 root root 0 Jan 1 2000 /sys/bus/i2c/devices/i2c-0 -> ../../../devices/ocp.2/44e0b000.i2c/i2c-0
lrwxrwxrwx 1 root root 0 Jan 1 2000 /sys/bus/i2c/devices/i2c-1 -> ../../../devices/ocp.2/4819c000.i2c/i2c-1
So you can see here, that on my BBB, i2c0 is mapped to /dev/i2c-0 and i2c2 is mapped to /dev/i2c-1.
You can check your system, but I suspect that i2c-1 is actually i2c2 on pins P9_19,20.