The expense of maintaining the said work farm, factory or shop, over and above the receipts for labor of persons confined therein and for crops produced thereon, and for the support of those whose support shall not be chargeable to the county, shall be audited and paid from time to time by the board of auditors or the board of supervisors of the county in counties not having boards of auditors, and shall be raised, levied and collected as part of the general expense of said county.