364 On the best Kind of Steel and Form 
Experiment 7. 
Hardened with a bright red-heat, and then softened 
by a red-heat from the middle toward the ends, 
the extremities for about an incb remaining hard. 
Paralleloprand) oss fk oe A ee 
Small shombus dea Qe hig. legen 
Large rhombus weliilesdifttot vite er ead 
Fierebed shombuss au ilow 4. lode: tee | GBS 
Experiment 8. 
Softened at a red-heat between two plates of steel, the 
whole being allowed to cool gradually, and then the 
extremities of the needles hardened at a red-heat. 
Rargllelogpain ) sericea sia a saber eatits afte 
Small rhombus dhe) Carls deipyibanyls yee 
Large rhombus ve {oe apiiismid tei ele, OE 
Riercedshombuss 5.95 pirwisove desis: Hew te 
As it appeared from the above experiments that the needles 
had suffered a gradual deterioration, I imagined that this might 
have occurred in consequence of their having been exposed to the 
heat of a coal fire, by which some portion of the carbon of the 
steel might have been destroyed: I therefore re-carbonised the 
needles, by surrounding them with shreds of leather, and ex- 
posing them for several hours, in a close vessel, to a consider- 
able heat. After they had gradually cooled, the ends were hard- 
ened at ared heat. 
Directive 
force. 
Directive 
force. 
Experiment 9. 
‘ Needles soft, and then the ends hardened at a Directive 
red heat. force. 
Small rhombus dap letel, pie, Polk h, coer 
iargeshombus:<* 64 <p .ee)t? GOR) eae 
Pierced rhombus.«, . 66: aso.) Hh oa 
Here we may remark, that though the needles were apparently 
in the same state, except being re-carbonised, as in the last ex- 
periment, they had suffered considerable deterioration. 
The needles were now covered with a mixture, well known to 
workmen, to prevent decarbonisation: this had been before 
neglected, but was used ia all the subsequent experiments. They 
were hardened at a bright red heat, and afterwards tempered — 
throughout, rather beyond a blue colour. ‘The large rhombus 
and the parallelogram were accidentally broken. 
Experiment \0. \ 
Hardened at a bright red, and then tempered Directive 
beyond:a blue. force. 
Small rhombus Co. bai aNp atin i tts oe 
Perced THOMmDUS. . ss) ap bial dines AE 
From these last experiments | believe littie can be gathered, 
except 
