4 INTRODUCTORY. 



once apparent, but every test and experiment made in 

 this way is going to help to build up a more complete 

 knowledge of the mechanical properties of all the known 

 materials. 



There is another branch of testing that comprises within 

 its limits both those already mentioned, namely, the 

 testing carried on for purely educational purposes. Most 

 of the colleges or departments of colleges devoted to the 

 scientific education of engineering students possess some 

 kind of a testing laboratory. Here, in these laboratories, 

 the students are taught by personal instruction and actual 

 experience to make tests of various materials, and in this 

 way they are not only enabled to learn the details of the 

 appliances used, and the methods and systems employed, 

 but their faculties of observation are called into play, and 

 the properties of the materials they are dealing with are 

 brought home to them in a manner not possible by mere 

 description and the study of books. The number and 

 completeness of the engineering laboratories at technical 

 schools and colleges is increasing year by year, and this is 

 as it should be, for no branch of the scientific educa- 

 tion of a young engineer is of greater help to hiua in after 

 life than the time spent in laboratory work. 



In the following chapters it will be the aim of the 

 luthor not only to describe the various testing appliances 

 ind methods as used in purely commercial work, but, at 

 the same time; to make these descriptions applicable to the 

 work of an engineering student. 



It has been stated that testing can, according to the 

 apparatus and rne'tbods employed, be divided into com- 

 mercial and scientific testing. These two are not 

 necessarily quite distinct and apart ; in many cases they 

 overlap, but, generally speaking, the methods of 

 commercial testing are more crude, and the measuring 

 appliances used not of so refined and delicate a character as 

 many of those used in purely research testing, which 

 partakes more of the nature of physical laboratory work. 

 In commercial testing, certain standards are usually fixed 

 by purchasers of materials and by certain competent 

 authorities, such as the Board of Trade and Lloyd's, and in 

 the tests to which they are subjected the specimens are 

 expected to exhibit such properties as are required in order 

 to comply with the standards and regulations laid down. 

 In making a commercial test, therefore, it is necessary to 

 know what properties must be specially observed, so that 



