XVI. W. H. WARREN. 
does not apply, and the useful length should be 4.” Plate 1, figs. 
lto6. Test pieces cut from plates should be taken from the 
longitudinal and transverse sides, and when uncut plates are used 
at least 1” in width should be cut away to waste. The skin left 
by the rolls in plates should not be removed, and with rails the 
bars detached should have square sections, and contain the exterior 
fibres of the rail. The foregoing rules for the sizes and proportions 
of test pieces are almost exactly the same as those adopted by the 
various Conventions which have considered the subject, the slight 
alterations made being necessary in consequence of the reductions 
from the metric system used in Europe, these are represented 
more fully in Plate 1, figs. 1 to 6. 
In regard to the accuracy of the machines and the errors per- 
missable, the Conventions state that they will accept an error of 
one-tenth of a kilogramme per square millimeter corresponding to 
the elastic limit and to that of rupture, which is 1422-32 pounds 
or 0°635 of a ton per square inch, This necessitates accurate 
testing machines and skilful handling. 
All authorities agree that the test piece should be accurately 
placed in the axis of the machine; this can generally be more 
easily accomplished with round than with rectangular specimens, 
and in all cases the rectangular specimens held by a pin passing 
through a hole in the heads of the test piece is preferable to the 
ordinary serrated wedge holders. Again the threaded ends Plate 
1, figs. 4 and 5, are not so good as the standard form for round 
pieces shown in fig. 3. 
In regard to the rate pf testing, the Conventions while admit- 
ting its importance, recommend further study before establishing 
rules. The American Society consider that the duration of the 
test should be in a certain measure, a function of the volume of 
the test piece, and recommend that the time should be from one 
to six minutes. 
The use of autographic apparatus for drawing a diagram of tests 
is generally recommended, and the Conventions require that their 
