Cooling exhibited by Glass and by Steel. 441 



cedure is excessively laborious, for it calls for a detailed construc- 

 tion of the relation of the density and the position of the points 

 along any given radius of the rod and subsequent examination 

 of the properties which the divers diagrams have in common. 

 We have gathered many data, but the work is as yet incomplete, 

 and the reader desiring further information will have to be re- 

 ferred to the Bulletin, where the whole subject is discussed. 

 Experiment on the fourth of the above topics we have now in 

 progress and shall publish later. This narrows the purposes of 

 this paper to the consideration of the first and most important 

 of the above points, viz: in what degree the density of a hard 

 steel rod at different points, even when measured with all attain- 

 able accuracy, is sufficiently sensitive to represent the character, 

 relations and intensity of the temper-strain. 



Density and Resistance (Strain) of Tempered Steel. 



Experimental residts. — The discussion may be appropriately 

 commenced by an examination of the variation of density of 

 steel successively annealed from hard to soft. Our experi- 

 ments on this subject, made in some number, are detailed in 

 Bulletin No. 27, now in press, and for this we select the follow- 

 ing digest. The table (I) contains data for length, diameter 

 and temper ; temper being expressed by the temperature and 

 time at which the divers glass-hard rods were annealed. The 

 table furthermore contains the specific resistance, (s ), at 0° C, 

 in microhms, referred to the centimeter cube ; the density (z/ ) and 

 the volume (j7 ) per unit of mass (g) for the same temperature, 

 0°. In the cases of rods Nos. I and II, density was measured in 

 the ordinary way. The other values of J are derived from 

 very painstaking pycnometric measurements, all of which 

 were made at least in duplicate and are warranted to two or 

 three units of the third decimal. Values for resistance which 

 could not be obtained by direct measurement were supplied by 

 interpolation from our earlier researches. All such data are 

 put in parentheses. Parentheses also enclose certain values for 

 the temperature of the annealing furnace to show that they are 

 derived by interpolation from the known power of the furnace 

 under given circumstances. The other temperatures are meas- 

 ured in a way to be indicated elsewhere. The greatest care 

 was taken to so anneal the rods as to exclude all errors due to 

 superficial oxidation or carhuration. 



Am. Joor. Sci.— Third Series, Vol. XXXI, No. 186.— June, 1886. 

 28 



