Section 169. A railroad corporation using any vacuum brake shall provide and use on every locomotive equipped therewith a muffler or other appliance, approved in writing by the department, for deadening the noise incident to the operation of such brake; but any other appliance may be used upon any locomotive for the purpose of experiment only, for not more than thirty days, but not upon more than two locomotives of the same corporation at any one time. Every application to the department for approval of such appliances shall be in writing; and such approval may be revoked by the department by written notice to the corporation.