440 Cast SteeL 
than such cutting tools as are formed of a more unifbnri 
Substance. 
This experimental enquiry directed my attention to a 
method of ascertaining the uniformity of texture in iron 
or steel, which perhaps may have been noticed by others* 
but is certainly unknown in most manufactories, though 
I have found it of great utility. If a weak acid, for ex- 
ample the nitrous, which I have usually taken in a very 
diluted state, be applied to the face of iron or steel pre - 
viously cleaned with the file, or with emery paper, the 
parts which contain the greatest portion of carburet of 
iron (or plumbago) immediately shew themselves by their 
dark colour. It very frequently happens that articles of 
considerable value, intended to be fabricated in iron or 
steel, are not known to be defective until much expence 
has been laid out in manufacturing them. A piece of 
iron, which has a vein of steel running through it, as is 
too often the case, will require at least three times the 
labour and care to turn it in the lathe, which would have 
been demanded by a piece of greater uniformity. Steel 
which abounds with spots, or veins, or specks called pins* 
may be fashioned completely, and will not shew its de- 
fects, until the final operation when an attempt is made 
to polish it. Other articles, such as measuring screws* 
blades of sheers, fine circular cutters, &x. either bend in 
the hardening, from the difference of expansion, or re- 
sist the tool when wrought in the tempered state, or ex- 
hibit other incurable defects when they come to be tried ; 
which the test by nitrous acid would have indicated be- 
fore any expense had been incurred. In these, and in 
numberless other instances, it would have been incom- 
parably more advantageous to have rejected the material 
upon the first trial, rather than have proceeded to the 
very expensive process of manufacturing the article and 
then finding it of no value. By this simple expedient l 
