is computed. The briquet molds are of the 5- and 3-gang type and are made of brass (Pl. II, A). Compression test pieces are 2-inch cubes, the molds being of the 3-gang type. The mortar cubes are tested in the 40,000-pound hydraulic hand-operated compression machine shown in Pl. III, A, in which a is a ball-and-socket bearing and b and c are handles that give fast and slow motions, respectively. A cube is shown in the machine just above a. The stronger neat cubes are tested in the 200,000-pound testing machine. Transverse test pieces are 1 inch square in cross section and 13 inches in length; they are tested on a span of 12 inches. The transverse molds are of the individual type. The transverse specimens are usually tested on the machine shown at the left of the center in Pl. II, A, but can be tested in the briquet machine by means of the apparatus illustrated in Pl. III, C. The test pieces are stored in the moist closet for twenty-four hours, and are then placed under water, in the immersion tanks, until tested. The water in the immersion tanks is kept constantly running and heated when necessary in order to maintain a constant temperature of about 70° F. The order of testing is regulated by a filing system with cards 6 by 4 inches in size which have blanks for data, as shown in Form A. When a sample of neat cement, for example, is molded into test pieces, a card is made out for each group of three, and the date upon which the group will be tested is placed at the top of the card. The cards are then filed in the order of the dates. Calendar guide cards are used, dividing the months into three parts. Each morning the cards bearing the date of that day are removed from the front of the file, and the test pieces indicated on them are tested that day. In this way the cards are kept moving toward the front of the file and reach the front on the day when the test pieces whose register numbers they bear are to be tested. The results of these physical determinations are entered upon Form B for filing at the laboratory, and are subsequently copied into tables for publication. a Forms B to R, inclusive, are condensed in the pages of this bulletin, in connection with the subject-matter to which they severally relate, for the purpose of showing in detail how the results of the various tests are recorded. In practice, each form is printed on a sheet of paper 8 by 10 inches in size. Water used: Neat. .....per cent; 1: 3......per cent. Kind of sand used in 1:3.. [Tension-water.... ° F.; air.....° F. Compression-water..... ° F.; air.... ° F. Temper-Neat Flexure-water.....° F.; air.. ° F. Pats-water..... ° F.; air.... ° F. mixing. 1:3..Tension-water.....° F.; air.....° F. Compression-water.....° F.; air...............° F. Flexure-water.....° F.; air.....° F. ature at SAND, STONE, GRAVEL, and OTHER AGGREGATES. PHYSICAL TESTS MADE. Samples of sand, stone, gravel, cinders, etc., are collected by a geologist who makes a complete report on the location, extent, and geological formation of the source of the supply, the methods of preparing the material for the market, the market supplied, the output, etc. In the case of broken stone and gravel he collects samples of crusher or pit-run screenings below one-fourth inch, and pieces of stone about 1 cubic foot in size. The physical tests made upon this material are as follows: Percentage of voids; percentage of moisture; weight per cubic foot; percentage of absorption; specific gravity; percentage of silt; granulometric analysis; strength and density tests of mortar; strength, modulus of elasticity in compression, and density tests of concrete. PERCENTAGE OF VOIDS. Apparatus.-The apparatus shown in Pl. V, A, consists of a heavy galvanized-iron cylinder 12 inches in diameter and 15 inches high, inside dimensions. The pipe a admits water through four 1-inch apertures in the bottom of the vessel, the inlets being fitted on the inside with perforated porcelain disks which prevent fine material |