Abstract: A histological tissue freezing process is provided. The process includes an aerosol can with an adjustable flow rate spray unit for spraying a chemical, monochlorodifluoromethane, onto a portion of a histological tissue specimen before sectioning thereof. The use of monochlorodifluoromethane has the dual advantage reducing ozone depletion and producing a colder spray. The spray means has a horizontal hinged spray bar with a passage with a spray outlet and has a horizontal hinged actuator plate with a trigger for slightly turning the actuator plate unit and spray bar. A tube has a passage connecting to the spray bar passage. The tube has an upper end coupled to the spray bar and an intermediate end extending through a can upper wall and a lower end disposed inside the can. The tube lower end has an adjustable orifice opening. The tube also has a latching unit, a compression spring, and seal ring.