5. In case any persons, having formed themselves into a company under this Act, have subscribed stock to an amount adequate in their judgment to the construction of the intended work, they shall sign a memorandum in duplicate according to form 1, and the company or one of its members, or the directors named in the said memorandum, shall then pay to the treasurer of the company six per cent upon the amount of the capital stock of the company mentioned in the said memorandum.