The board of chosen freeholders of any county may cause to be employed within the county, prisoners in any county workhouse or penitentiary under sentence, or committed for nonpayment of fine and costs or committed in default of bond for nonsupport of family, and the product of their labor may be disposed of to the county or to any public institution of the county.

Nothing herein contained shall permit the employment of prisoners to take the place of free labor locked out or on strike, nor shall any prison labor be employed on any public improvement when free labor sufficient to carry on the work makes application for employment thereon.