156 W. H. WARREN AND S. H. BARRACLOUGH. 



7. Compressive Tests. — These consisted of the determination of 

 the elastic limit and coefficient of elasticity as in the tensile tests, 

 the compressions being observed with the Marten's mirror extenso- 

 meter, the length of the specimens was ten inches, and diameter 

 one inch; one set of readings was taken on a specimen two inches 

 long. The compressive strength was determined by using cylinders 

 one inch in diameter, and one and two inches long respectively. 

 The compressive strength was taken as the yield point of the 

 test piece. See Tables VI. to IX. and summary of results 

 Table XII. 



8. Torsion Tests. — These consisted of the determination of the 

 value ofyin the equation — 



J 0-196 d 3 

 and the measurement of the total angle of twist in degrees. See 

 Table XIII. 



9. Shearing Tests. — These consisted of the determination of the 

 load necessary to shear the specimen on two planes, i.e. in double 

 shear ; the results are summarized in Table XIV. 



10. 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 1 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 deviation from the straight line much 

 earlier than could be seen in any autographic diagram. Careful 



l One part by weight of strong sulphuric acid to one hundred parts of 

 water. 



