90 BULLETIN 1216, U. S. DEPARTMENT OP AGRICULTURE. 
with the form and size of the piece to be used. Thus, if I or T sec- 
tions are to be used, the specimens shall be of I or T section. 
In the case of flat springs or plate glass, they shall be flat ; in 
the case of timber, rectangular ; etc. 
Note. — It is well known that the modulus of rupture varies with 
the shape of the section, being very much greater in the case of round 
than in I sections. Hence the modulus of rupture suitable for use 
for one would be entirely unsuitable for the other. In rolled sec- 
tions, the smaller ones are subjected to a more thorough working in 
the process of rolling than the larger. 
2. In the case of the " arbitration bar " adopted for cast iron, 
the span has been fixed at 12 inches, but may be extended as above 
stated. The bar will serve for cast and brittle materials. 
In the case of ductile materials, when tbe modulus of rupture 
is desired, the span shall generally be less than 12 or 15 times 
the depth. Exceptions, however, occur, as in flat springs and in 
some cases in full-sized pieces, when the spans and methods of 
supporting the ends, etc., shall conform to the conditions of 
service. 
3. In the case of cast and brittle metals, the speed of testing 
shall not exceed 0.2 inch per minute. For other specimens the 
speed shall be correspondingly low. 
Preparation 4. The preparation of the specimen shall be such that it truly 
of specimens, represents the material itself. The introduction of extraneous 
influences should be avoided as far as the knowledge of the ma- 
terial will permit. Thus, in cast metals no coupons shall be used ; 
cast materials for tests shall go into dry molds standing vertical. 
No specimen shall be machined before testing, except when 
information is specifically desired regarding the strength of such 
machined specimens. 
5. The transverse yield point for ductile materials shall be 
noted approximately by the drop of the scalebeam. 
6. If the transverse elastic limit is to be determined for com- 
parison with that obtained in the tensile test, the successive in- 
crements of load in the neighborhood of the transverse elastic 
limit shall be comparatively small, and after each load has been 
applied and the corresponding deflection measured by means of 
the deflectometer, the load shall be removed and the deflection 
measured again, to determine the permanent set. 
In those cases where the arbitration bar is used for such cast 
materials as have an elastic limit, the increment of load used near 
the transverse elastic limit shall be 250 pounds. 
Note. — It is well known that when the transverse elastic limit is 
determined of course by means of a transverse test, the extreme fiber 
stress at this transverse elastic limit is not the same as that at the 
tensile elastic limit of the material ; and, moreover, that it varies 
with both the section and the span ; hence the desirability of compar- 
ing the transverse elastic limit with the tensile elastic limit. 
7. In the case of ductile materials the arrangement of the sup- 
ports shall be such that longitudinal tension in the specimen due 
to the rigidity of the supports is avoided. 
8. In the case of ductile materials special care shall be used 
when determining the ultimate load. For this purpose it will be 
necessary when approaching the ultimate (that is, the maximum) 
load to make the speed of testing slow enough to enable the 
observer to note the maximum load. 
In many cases, as in I and T beams, the maximum load can be 
easily ascertained, while in others, such as round or flat sections 
with short spans, it may not be possible to determine it exactly, 
but it will almost always be possible to determine it with sufficient 
accuracy for all practical purposes. 
IV. METHODS FOR BRINELL HARDNESS TESTS OF METALS. 
Chemical Composition and Heat Treatment of Balls. 
1. The chemical composition, as far as carbon and chromium 
are concerned, should be from 1 to 1.2 per cent of carbon and 
from 1 to 1.5 per cent of chromium. 
