MKTHODS FOR TKSTINC, II A K I>N KSS.
It should be finished all one way, so as not to leave small, irregular siTutrhes, and should be as smooth and bright as possible-. As a rule, an experienced workman should not take more than halt' an hour in preparing such a specimen, although oeeasionally a hard material will take longer. If the surface tested be rough, the results are erroneous, being generally higher than with a good surface. It can, however, be told at once on inspection whether a surface is suitable for the purpose. If any doubt should exist, another smooth face must be prepared and the experiment continued until uniform results are obtained.
The following Table prepared by Professor Turner clearly presents the utility of his device and illustrates the thorough manner in which he completed his work. It has been thought by some inexperienced founders that there is no limit to silicon softening* iron, but this is strongly refuted by the following Table 87 and sustains the author in statements made in other writings to the effect that silicon can harden as well as soften iron:
'I'.MM.l-' 87.......-IM''I.fK\<'K ()K SILICON ON 'I'! IK IIARDNKSS AND TK.NAt'ITY
ol' ('AST IRON.
Silicon per cent.
m. i.\ tons,
1 i. . .» jl •ju
1 1 ,aH r;
10. If, .V
\VOKKI\J; «.»t ,\i,n IMS.
Vi-iy haj«J imlwcl.
Very hatd, though not MO hard an No. i,
Hard, though soflrr than N«>, j.
("pood, Mitnxi, ordinary, sof't-ciiltiiiK iron, of excellent quality.
Rather harder than No. .\,
Like No. .».
Like No u, hut rather harder.
Kulhet harder than No. y, though not unuHtmlly hard.
Still harder, rutting vei'y like No, 10,
Hand etitttng iron, though slill sul'ter than No. t.2 grammes on the diamond. Three estra weights, I, are used when necessary. Tlniy are each of the same weight as II. Uc-nee, with one weight, scale division m eorre:,ponds to m y^rammes on the diamond, with two weights i«> corresponds to '/o grammes,with thr<*e weights to -\n ^nimmes, and \«-ith tour weights to ,|o grammes, the other scale division:, in Volume XXIII. of the .*