Three tests are used: (1) Resistance to tensile force. (2) Specific gravity. (3) Water test. The first is by making a specimen briquette in a mould with a transverse section of 2.25 square inches, the specimen being held vertically in clips, which is placed under the short arm of a steel-balance, and broken. A test of 500 lbs. has been used on an area of 2.25 square inches after 7 days' immersion in water. The second method is by finding the weight in pounds of the struck bushel. The water test is useful when the others can not be applied. It consists of gauging a small quantity of the dry powder with water, and immediately immersing it in water. If the sharper edges crack or break away after a short time, the cement is too hot or fresh, or is inferior in quality. The weight of good Portland cement ranges from 100 lbs. to 130 lbs. per bushel, equal to from 80 lbs. to 102 lbs. per cubic foot. The lighter kinds set more rapidly than the heavier, but are weaker. The specific gravity should he of 110 lbs. to a bushel.