Section 25. If the capital stock fixed in the agreement of association is found to be insufficient for the construction and equipment of the railroad, the corporation at a meeting called therefor may, subject to section forty-seven, increase the same, from time to time, to the amount necessary for those purposes. It may, at a meeting called therefor, reduce the amount of the capital stock, but not below the limit prescribed in section fourteen. It may, also, in like manner, change the gauge to the other authorized gauge; but a corporation organized to construct its railroad on a gauge of three feet shall not change such gauge to four feet eight and one half inches without complying with all provisions of law relative to the capital stock of railroads of the broad gauge; and the fact that such provisions have been complied with shall be shown to the satisfaction of the department, and endorsed by its clerk upon the certificate of such change of gauge before it is filed in the office of the state secretary. A certificate of the increase or reduction of capital or change of gauge shall, within thirty days thereafter, be filed in the office of the state secretary.