(a) Purpose. For reasons of unavailability or for purpose of discovery, the testimony of any witness may be taken by deposition.

(b) Form. Depositions may be taken before any person having the power to administer oaths. Each witness testifying upon deposition shall be sworn, and the parties not calling him shall have the right to cross-examine him. Questions propounded and answers thereto, together with all objections made, shall be reduced to writing, read to or by the witness, subscribed by him, and certified by the officer before whom the deposition is taken. The officer shall send copies by registered mail to the Chief Administrative Law Judge or the presiding administrative law judge.