SPECIFICA TIONS. 295 



together, and combining the special knowledge which each has, 

 that a really valuable specification can be made. 



" (8) A complete workable specification should contain the 

 information needed by all those who must necessarily use it, in 

 obtaining the material desired. On railroads this may involve 

 the purchasing agent, the manufacturer, the inspector, the engineer 

 of tests, the chemist, and those who use the material. A general 

 specification may be limited to describing the properties of the 

 material, the method of sampling, the amount covered by one 

 sample, and such descriptions of the tests as will prevent doubt 

 or ambiguity. 



" (9) Where methods of testing or analysis or inspection are 

 well known and understood it is sufficient if the specification 

 simply refers to them. Where new or unusual tests are required, 

 or where different well-known methods give different results, 

 it is essential to embody in the specification sufficient description 

 to prevent doubt or ambiguity. 



" (10) The sample for test representing a shipment of material 

 should always be taken at random by a representative of the 

 consumer. 



" (n) The amount of material represented by one sample can 

 best be decided by the nature of the material, its importance, 

 and its probable uniformity, as affected by its method of manu- 

 facture. No universal rule can be given. 



" (12) The purchaser has a right to assume that every bit of 

 the material making up a shipment meets the requirements of 

 the specification, since that is what he contracted for and expects 

 to pay for. It should make very little difference, therefore, what 

 part of the shipment the sample comes from or how it is taken. 

 Average samples, made up of a number of sub-samples, are only 

 excusable when the limits of the specification are so narrow that 

 they do not cover the ordinary irregularities of good practice 

 in manufacture. 



" (13) Retests of material that has once failed should only 



