PROPERTIES AND USES OF NICKEL STEEL. 693 
tests, and 121-3 lbs. for transverse tests. These tests 
are only preliminary, and are still in progress, but Tables 
XVII. and XVIII. give some of the results obtained. 
Torsion Tests.—These consisted of the determination of 
the value of f in the equation— 
Lr 
1= 9196 a? 
and the measurement of the total angle of twist in degrees. 
See Table XIII. 
Shearing T ests.—These consisted of the determination of 
th load necessary to shear the specimen on two planes, 7.¢., 
in double shear; the results are summarized in Table XIV. 
Corrosion Tests.—To obtain an indication of the relative 
values of the nickel steels as regards their resistance to 
corrosion, specimen discs of various irons and steels were 
prepared, as shown in the accompanying table. These were 
first weighed and placed in a large beaker containing about 
a gallon of a weak* solution of sulphuric acid, which was 
maintained at a temperature of from 170°--180° F. for 
twenty-four hours. The discs were then removed, thoroughly 
cleaned, and re-weighed. 
It is necessary to draw attention to the elastic limits 
obtained both in tension and compression, as the results 
may appear low when compared with similar results obtained 
from autographic apparatus. The large multiplication 
obtained by the Marten’s mirror apparatus shows a devia- 
tion from the straight line much earlier than could be seen 
in any autographic diagram. Careful tests of Vicker’s axle- 
steel made with Kennedy’s extensometer gave an elastic 
limit of 16 tons per square inch, whereas the Marten’s 
apparatus gave 14-5 tons per square inch. Untilastandard 
method for determining this point is agreed upon, it will 
always be difficult to compare the results obtained by experi- 
menters using different extensometers. 
* One part by weight of strong sulphuric acid to one hun- 
dred parts of water. 
