A building, the main or principal design or use of which is to be a place for producing articles as products of labor; not merely a place where something may be made by hand or machinery, but what in common understanding is known as a “factory.” Halpin v. Insurance Co., 120 N. Y. 73, 23 N. E. 989, 8 L. R. A. 79; Schott v. Harvey, 105 Pa. 227, 51 Am. Rep. 201; Franklin F. Ins. Co. v. Brock, 57 Pa. 82.