32 



THE LABORATORY. 



The testing laboratory is the basement story of the gymnasium building of Washington Uni- 

 versity. Its dimensions are 71 by 46 feet, with one corner partitioned off, as shown on the floor 

 plan, Plate i. The net area used for laboratory purposes is 2,500 square feet. All the apparatus 

 suspended from the ceiling, as shafting, steam pipes, exhaust tan, etc., is shown in dotted lines. 



The apparatus pertinent to the timber tests consists of a 1,000,000-pound columu-testing 

 machine; one 100,000-pound beam-testing machine, one 1()(»,00(> pound universal testing machine, 

 of Riehle's "Harvard" pattern; one small portable beam machine, one 6-horse power Brayton coal- 

 oil engine, one 4-horse power steam engine, one planer and one lathe, for ironwork; one planer, 

 one band saw, and one cutting-off saw, for shaping and dressing wood specimens; suitable scales, 

 drying ovens, etc., for the moisture and specific gravity tests; the drying box with its steam coils 

 and exhaust fan, and all the necessary appliances, benches, tools, desks, etc., including a Thatcher's 

 slide rule for making the computations. The timber is stored in various parts of the room not 

 otherwise utilized. Ultimately a warehouse will have to be obtained for storing the broken speci- 

 mens. 



The cross-hn'filiufj texts. 



Large /x'rtwi.s.— The large beams are tested on the large beam-testing mac^hine shown on Plate ii. 

 The base of this machine consists of two long-leaf ])ine sticks {Pinm p<(hintris), 6 inches by 18 

 inches by 24 feet long, with a steel plate three-fourths of an inch Ity is indios by 20 feet long, all 

 bolted up as one beam. The power is applied by hydraulic pressure upon a plunger below, to the 

 crosshead of which are attached the two side screws, on which the u])])er crosshead is moved by 

 sleeve mits and spur gearing. The beam to be tested rests on pivots at the ends, placed on top 

 of the base beam, and the upper crosshead is moved down liy means of the gearing until the central 

 pivot attached to it comes in contact with the beam, or rather witli the distribution blocks placed 

 on the beam at this point. The test then begins, the power originating in a d.mble-plnnger pump, 

 operated by hand or by steam power in another part of the rt)om. 



To prevent the pivots or "knife-edges " from crushing into the timber, it is necessary to make 

 the contact at both ends and center, first upon a cast-iron plate, then through longer Avooden 

 blocks to the timber. The center block is curved somewhat on the lower side, to allow for a con- 

 siderable deflection in the beam when nearing its maxinuim load. 



In the tests of all beams, both large and small, the load is put on at the same uniform rate, so as 

 to eliminate the time effect, which is very great in timlier tests. The load on the small beams is 

 increased at such a rate as to produce an increase in the deflection of one-eighth inch per minute 

 without any pause until rupture occurs. This causes rupture in from ten to fifteen minutes time. 

 The load is rend off wh(ni it reaches certain even amounts, and an observer notes the corresponding 

 deflection without stopping the test. The time required for the large lieam tests is about the same, 

 the deflection rate being greater when the total deflection is expected to be greater, as is the case 

 with 4 by 8 inch sticks 12 feet long. The deflections of the large beams are observed upon a paper 

 scale, graduated to inches and tenths, glued to a i)iece of mirror, which is tacked to one side of the 

 stick at the center. A fine tliread is stretched, by means of a rubber band, over nails driven into 

 the side of the stick above the end supports on the line of the neutral axis. This string or thread 

 is moved about an inch away from the surface of the timlier, and all parallax, or error of reading 

 from an oblique position of the eye, is avoided l)y keei)ing the eye where the thread and its image 

 in the mirror coincide and form one and the same Une. The readings are taken to inches and 

 hnndredths by estimating the tenths of the graduation spaces on the scale. 



The loads are weighed on the large universal testing machine in another part of the room. 

 This is done by having both machines connected up to the same pump, blocking the weighing 

 machine so that the load on its plunger is transmitted to the scales and weighing beam, and then 

 pumping into both machines. The plungers are of exactly the same diameter; they have similar 

 leather cu]) i>a(kiiig, and hence the error -of this method is simply the difl'erence in the friction of 

 the two plungers in their packing rings. To test the accuracy of this method, and to (h'termine 

 the error, if any, at any time, a nest of calibrating springs, sliown on Plate ii, was made and tested 

 first on the limery machine at the United States Arsenal, at Watertown, Mass. The loads were 



