Bricks and...how to clean them?

[aafm]

Hi all!

 

[aafm]

Took some bricks like this of a demolition.
They belong to a cold storage plant bilt in 1912 by an english company; Swift.

 

[aafm]

This is another interesting brick i took from another place of the same company.
Also digg and found some buckets that donatet to a museum (and of course b. too).
Unfortunatly they are strongly stuck with cement. Could somebody tell me how to remove it without demage the bricks?
Thanks