The term "net profits," as employed in this chapter, means the amount of money received from the mining of said metals or minerals from said mine or mining claim, after the deduction of the actual expenditure of money and labor in and about extracting the metals and minerals from the mine or mining claim, and transporting the same to the mill, concentrator or reduction works, and the reduction thereof, and the conversion of the same into money, or its equivalent, and also the deduction of all moneys expended for necessary labor, machinery and supplies needed and used in the mining operations, for the improvements necessary in and about the mine or mining claim, for reducing ores, for the construction of the mills and reduction works used and operated in connection with the mine or mining claim, for transporting the ore, and for extracting the metals and minerals therefrom; but the money invested in the mine, or improvements made during any year except the year immediately preceding such statement, must not be included therein. Such expenditures do not include the salaries, or any portion thereof, of any person or officers not actually engaged in the working of the mine, or personally superintending the management thereof.