The taxes paid into the state treasury under this article shall be deposited in a special fund to be used only by the Commission and by the Department of Taxation as provided in § 58.1-2664, for the purpose of making appraisals, assessments and collections against public service companies, and for the further purposes of the Commission in investigating and inspecting the properties or the service or services of such public service companies, and for the supervision and administration of all laws relative to such public service companies, whenever the same shall be deemed necessary by the Commission.