How to calibrate a temperature sensor

I am using an LM35 temperature sensor, which produces an output of 10.0 mV/°C. My circuit will handle temperatures up to around 90C

What can I do to check the LM35 output, and maybe fine tune it for accuracy? Are there any non hazardous easy to obtain chemicals that boil below 100C?

Or if I am forced to change the circuit to handle temperatures up to 100C would sticking the suitably waterproofed sensor in a pan of boiling water be sufficient to calibrate it?

Note

I am not looking for 0.1C accuracy, 0.5 will do.

Update

All interesting answers, thanks, but the simplest solution seems to be changing the circuit to allow 100C as a close enough calibration point

Answer

Physicist's answer ahead:

Prepare a bowl of (melting) ice water on a day where the barometer is near 1013 mbar of pressure. Stick your sensor in it. The reading you get at equilibrium is your 0C reading.

Prepare a pan of slowly boiling water, also on a day where the barometer is near 1013 mbar of pressure. Stick your sensor in it. The reading you get at equilibrium is your 100C reading.

Divide the intervening range into 100 equal parts.

The beauty of this method is that you are not tied to errors made while calibrating the sensor you are using to calibrate with, or errors made when calibrating the sensor they used to calibrate the sensor you are using to calibrate with, or ... (etc).