6 



readings have been made at frequent intervals. The beam machine is greatly simplified by thus 

 dispensing with all attached weighing ai)paratus, which would be greatly in the way in the 

 handling of large beams sometimes weighing over 1,000 pounds. 



*S'W(«// beams. — The snuill beams, which are nominally -i inches square and GO inches hmg be- 

 tween supports, are tested on the small beam-testing machines (shown on Plate iii). This machine 

 was designed originally for testing east-iron beams, the load at one end or one-half the load at 

 the center being weighed on a pair of ordinary platform scales. The deflections are read off to 

 thousandths of an inch upon a micrometer screw held in the to|) iron crossbeam. By this means 

 a rigid connection is obtained, through parts not uiuler stress, from the eml supports to the center 

 bearings. The movement of the center with reference to the ends is therefore obtained, regardless 

 of the absolute movements of the parts. The load is put on by the hand wheel and power screw, 

 and the weighing beam kept in balance by putting on overweights and moving the poise. Thn-e 

 men are required to make this test. One moves tlic power screw, wliich has oue-forth inch pitch, 

 so as to make one revolution every two minutes, and he coutinues this uniform motion till rup- 

 ture occurs. Another keei)s the scales balanced and calls off the even hundreds of i>ounds. 

 Another kee]ps the nncronieter screw in contact with the head of the power screw, reads it tin- cer- 

 tain even hundred-pound loads called off, and records the time of ea<li such reading to the nearest 

 minute, the load, and the corresponding reading of the micrometer screw. Here also the en<l and 

 center ijeariugs are jirotected by iron plates large enough to prevent any appreciaWe distortion 

 from lateral compressi(»n.* 



After rupture occurs the stick is bored for samples from which to obtain the moisture tests 

 and the uninjured ends ai'e sawed olf and used for the remaining tests, as described below. 



The moisture testA 



The borings are taken from two holes, 20 inches from each end and at about one-third the 

 width of the stick from either side. These borings are first weighed on a delicate balance, then 

 idaced in a drying oven, at a temperature of 212° P., until they have icached a nearly constant 

 weight, when they are reweighed. The dry weight is taken as the basis on which to compute 

 the percentage of moisture. Thus, if the original weight is twice the final weight, then there 

 ■was as much water as woody fiber in the stick, or one-half or 50 ])er cent of the original weight 

 was water. But when comijuteit on the basis of the dry weiglit there would be 100 per cent of 

 water. The advantage of computing the i)ercentage on thj dry weight is that it furnishes a con- 

 stant basis of comparison, wliereas if computed on the actual or wet weight the basis on wliieli the 

 percentage would l)e computed Avould vary with every change in the amount of moisture. 



The specific yriirit;/. 



The specific gravity is found by taking one of the end i^ieces, usually i by 4 by 8 inches, 

 measuring carefully its lateral dimensions by calipering them at the middle points of the sides 

 at the central section, measuring the length in a similar manner, and taking the ]U-oduct of these 

 three dimensions as tlu' volume. From the total vohune and the actual total weight, the weight 

 per unit volume or per cubic foot is found, and from this the specific gravity, which is the weight 

 per cubic foot divided by the weight of a cubic foot of distilled water. It nmst be understood 

 that all the small (-t by 4 inch) beams are planed up true aiul rectangular before testing and 

 that all the crosscuts are made by power saw so adjusted as to cut truly at right angles to the 

 sides. The volume can therefore be very accurately comjiuted from the dimensions as above 

 described. 



* Since December 1, 1892, all tests made on this small machine are arranged witli two center hearings, 12 inches 

 apart, on sticks 72 inclies long. 



t Thi! percentage of moisture is imw found by sawiug oil a thiu scctuiu of thr entire stick and using it in phice 

 of the borings. 



