For the purposes of this chapter and unless otherwise required by the context:
(1) The term "department" without other designation means the department of revenue of the state of Washington.
(2) The term "private car company" or "company" shall mean and include any person, copartnership, association, company or corporation owning, controlling, operating or managing stock cars, furniture cars, refrigerator cars, fruit cars, poultry cars, tank cars or any other kind of cars, used for transportation of property, by or upon railroad lines running in, into or through the state of Washington when such railroad lines are not owned or leased by such person, copartnership, association, company or corporation; or owning, controlling, operating or managing sleeping cars, parlor cars, buffet cars, tourist cars or any other kind of cars, used for transportation of persons by or upon railroads on lines running in, into or through the state of Washington, when such railroad lines are not owned or leased by such person, copartnership, association, company or corporation and upon which an extra charge in addition to the railroad transportation fare is made.
(3) The term "operating property" shall mean and include all rolling stock and car equipment owned by any private car company, or held by it as occupant, lessee or otherwise, including its franchises used and reasonably necessary in carrying on the business of such company; and in the case of rolling stock and car equipment used partly within and partly without the state, shall mean and include a proportion of such rolling stock and car equipment to be determined as in this chapter provided; and all such property shall, for the purposes of this chapter be deemed personal property.