Section 8. The department may by its members or duly authorized employees investigate and examine the books, accounts, contracts, records and memoranda of any partnership, express trust, voluntary association or corporation which is under the same ownership, control or management as a railroad, street railway, electric railroad or elevated railway corporation, gas, electric or water company, or company engaged in the common carriage of passengers by motor vehicle, in respect of the relations and of any contracts and dealings between such railroad, street railway, electric railroad or elevated railway corporation, gas, electric or water company, or company engaged in the common carriage of passengers by motor vehicle and such partnership, express trust, voluntary association or corporation, and in relation thereto may require from such partnership, express trust, voluntary association or corporation such reports and information as the department shall from time to time direct.