The Wire.lib In Arduino is a stupid 7 bit interface! Not 8!
Lets say you want the arduino to be a I2C slave with Wire lib address 1
Wire.begin(1);
To access this with another I2C device:

• The write address would be (1<<1)
• The read address would be (1<<1)|1

In other words: A Wire address of 1 seems to result in write address of  2, and a read address of 3
So if you use the Arduino Code examples..
Wire.begin(2);

Write:

(2<<1)=4

0010 <<1 = 0100

Read:

(2<<1)|1= 5

0010<<1 =0100

0100 | 1 = 0101

so much annoyance!