No such stock insurance company shall be licensed to do business in the state unless it shall possess a paid-up capital of $800,000, invested in securities readily convertible into cash,
1/2 at least of which are not loans secured by real estate; nor unless it shall possess, in addition to such capital, assets equal in amount to all its outstanding liabilities, estimating 50 percent of premiums received on unexpired fire risks running one year or less from date of policy, and a pro rata amount of all premiums received on unexpired risks running more than one year from date of policy, and on marine risks 50 percent of the amount of premiums written on policies upon yearly risks, and upon risks covering more than one passage not terminated, and the full amount of premiums written on policies of all other marine risks not terminated as a liability.