their supporting columns in the building at Shaft 21 and shall place any other concrete that may be needed and is ordered in connection with making the buildings serviceable for the purpose intended. This section shall not be interpreted as including concrete that may be convenient in temporary works of the Contractor.

SECT. 9.2 Concrete shall consist of Portland cement, sand Proportions. and gravel or broken stone in proportions of 105 pounds of cement to 2 cubic feet of sand to 4 cubic feet of stone, or such other proportions of sand and stone as shall total 6 cubic feet and shall, in the opinion of the Engineer, give the densest practical mixture.

SECT. 9.3 All cement shall be true Portland cement of Cement. well-known acceptable brands and undamaged by moisture. Unless arrangements are made to get cement which can be shown to have been satisfactorily tested by The City or others, cement shall be delivered sufficiently in advance to permit the results of 7-day tests before its use. Cement, to be acceptable, shall satisfy the Standard Specifications of the American Society for Testing Materials.

stone.

SECT. 9.4 Sand shall be clean and shall contain both fine Sand and and coarse particles in acceptable proportions. Stone shall be clean gravel or fragments of hard insoluble stone. The sizes shall be suitable for the class of work, being not larger than 1-inch for reinforced concrete.

mixing and

SECT. 9.5 Forms shall be true to shape, unyielding and Forms; tight. Concrete shall be very thoroughly mixed. Concrete placing. around reinforcement shall be creamy, insuring proper covering of steel. The top surface where to be finished shall be moderately dry. Lampblack shall be used, if ordered, to match color of existing concrete floors. Concrete work shall be done in freezing weather only when approved precautions are taken.

Finish and protection.

Measurement

and payment.

SECT. 9.6 All unevennesses of concrete surfaces which are to be exposed shall be trowelled off immediately on removing forms. Tops of mezzanine platforms shall be finished equal to good side-walk work by artisans skilled in this class of work. Concrete shall be protected from too rapid drying and from freezing for a satisfactory length of time.

SECT. 9.7 The quantity of concrete masonry to be paid for under Item 9 shall be the theoretical number of cubic yards in the concrete actually deposited in place in accordance with the drawings and specifications and the requirements of the Engineer, except that no deductions shall be made for any spaces having a gross cross-sectional area less than 1 square foot, left void or occupied by pipes, or other metal-work. The price stipulated in Item 9 shall include all expenses incidental to providing and removing all forms, molds and centers, and all labor and materials necessary to accomplish the completed work, including all finishing of surfaces, except reinforcement and other metal-work, which are to be paid for under other items.