166 



THE NATIONAL GEOGRAPHIC MAGAZINE 



slightest pressure on the bar — even the 

 weight of a visiting card or a pin — 

 causes these circles to expand outward, 

 forming, as it were, a series of ripples 

 like those made when a stone is dropped 

 into the center of a still pond. The pres- 

 sure of one finger on the bar causes the 

 formation of five or six new circles, 

 showing that the bar has been bent about 

 I /20,000th of an inch, as each new circle 

 means a movement of 1/ 100,000th of an 

 inch. 



At first sight the testing of sugar would 

 seem, to the lay mind at least, to belong 

 to the department of chemistry rather 

 than optics ; but it has been found that 

 the most perfect test of sugar is an opti- 

 cal one. The amount of impurity is 

 found by watching the twist of a light 

 wave passing through a sugar solution of 

 a certain strength. This is effected in 

 an instrument known as a saccharimeter, 

 and on these tests the import duty is 

 based. Samples of sugar are sent daily 

 by the customs service at the various 

 ports of entry for check analysis, and in 

 this way uniformity of analysis at the 

 custom-houses all over the country is 

 secured. 



In the division of chemistry nearly 

 9,000 tests are made in a year and almost 

 all of them for the government. Com- 

 missions are only accepted from private 

 bodies when such work cannot be done 

 anywhere else, for the Bureau declines 

 to enter into competition with private 

 laboratories ; under exceptional circum- 

 stances, however, umpire testing or analy- 

 sis is undertaken. 



TiSSTS THAT INSURE; TUt SAFETY OF SKY- 

 SCRAPERS 



In the engineering division the most 

 impressive feature to the layman is the 

 huge Emery testing machines ; the larger 

 one has a 2,300,000 pounds compressive 

 power and a pulling power of 1,150,000 

 (see page 164), while the smaller one 

 has a tension and compression strength 

 of 230,000 pounds. 



These great machines are of wonder- 

 ful delicacy and power ; for, after exert- 

 ing and accurately registering a pressure 

 sufficient to break a huge steel girder, an 



egg-shell can be crushed and the force 

 exerted recorded with equal accuracy. 



In the branch of the Bureau at Pitts- 

 burgh a still more powerful machine has 

 been installed — the great lo-million- 

 pound Olsen testing machine (see page 

 167). These machines are used in a 

 series of investigations conducted jointly 

 by the Bureau and the American Society 

 of Civil Engineers to check and correct 

 the formulas for computing column 

 strength, the formulas upon which the 

 efficiency and safety of building con- 

 struction depend. 



Another very interesting series of re- 

 searches is in progress, which may have 

 the effect of saving many valuable human 

 lives. Railroad companies send to the 

 Bureau rails that have failed, and ef- 

 forts are being made to discover a new 

 method of testing them. At present when 

 a rail (or any other piece of iron or steel) 

 is tested it is destroyed in the process and 

 becomes useless. Often a rail is full of 

 flaws, like that shown on page 163, but at 

 present there are no means of discover- 

 ing this until the rail fails beneath the 

 pressure of the express that thunders 

 over it. 



For the last six years the experts of 

 the Bureau have been seeking for a 

 method of testing the rails that will ac- 

 tually be used, and have conducted a 

 series of mechanical and magnetic tests 

 to discover some mechanical properties 

 which can be proved always to accom- 

 pany certain magnetic properties. 



The results of the work are so hopeful 

 that those engaged upon these researches 

 are justified in believing that further 

 studies along these lines will eventually 

 lead to success. 



W^HAT IS THE vSTRENGTH OE RED TAPE? 



In another division are tested a bewil- 

 dering variety of commodities used by 

 the government — ink, paper, rubber, clay, 

 bricks, oils, ropes, leather, cloth, silk, 

 sealing wax, mucilage, paint, and a hun- 

 dred and one other things. Everything 

 handled by the Federal government is 

 tested here, from the steel for the locks 

 on the Panama Canal down to the brushes 

 used to sweep out departmental offices. 



