234 
NATURE 
[Yan. 19, 1871 

the metal will be fluid enough to run from the furnace 
into ingot-moulds. The economy of the process consists 
in the saving of the labour of eight workmen making 
steel, and two workmen making wrought-iron ; and in the 
superior quality of the result as compared with puddling 
the refined metal. The time occupied by the conversion 
of the refined metab into steel or wrought-iron by the 
process without puddling is about the same as that 
usually taken in puddling pig-iron. 
Ordinary coke pig-iron, smelted near Pittsburgh from a 
mixture of hematite ore and mill cinder, has been treated 
by this process. The refined metal was afterwards puddled 
and rolled into “muck” bars, and once heated and rolled 
into merchant bar-iron. The pig, refined cast, and 
wrought-iron, have been analysed by an analytical chemist 
in this city. These analyses are annexed, also analyses 
of refined cast-iron by the English finery and German 
reverberatory furnace process, and of the highest standard 
qualities of English, French, Swedish, and Russian 
wrought-iron, are given for comparison, taken from 
Percy’s “ Iron Metallurgy” and Ure’s Dictionary : 
Pittsburgh Coke Patent Refined 
Pig-iron. Cast-iron. Bar-iron. 
Carbon (combined) 02040 0°3613 not deter. 
do (graphite)  2°7685 2°5066 —_ 
Silicon 2°3096 none none 
Slags (silicates) 073623 0°2983 not deter. 
Phosphorus 0°4196 01029 0'0087 
Sulphur 0°1298 0°1269 0°0438 
Analyses of Foreign Iron. 
English Finery Process. German Reverberatory Furnace Process. 
Refined Cast-iron. Pig-iron. Refined Cast iron. 
Carbon 3°07 — = 
Silicon 0°63 4°66 0°62 
Phosphorus 0°73 0°56 0°50 
Sulphur 0'16 0'04 0°03 
Silica, iE «=. 
Alumina \F 9°44, 
English Wrought-iron, French. Swedish, Russian. 
Low Moor Stamp. Petin, Gaudet, & Co. Hoop L. CCND 
Carbon o'016 O'143 0'087 0'272 
Silicon O°122 — Ovrr5 0062 
Sulphur O'104 0'058 0'220 0'234 
Phosphorus 0°106 0'030 0'034 - 
of the refined cast-iron of the 
patent process with those of the English and German 
processes, it will be seen that while the refined iron of 
the new process contains wo sz/icon, that of the English 
and German processes contains 0°63 and o’62 per cent. 
respectively ; and compared as regards phosphorus, the 
German process reduces it from 0°56 to o'50 per cent., or 
about o'06 per cent., and the new process reduces it 0°32 
per cent., or over five times as much phosphorus is re- 
moved by the new process as by the other processes. 
The slags or silicates are o°15 per cent. less than in the 
refined iron of the English finery process. The analysis 
of the patent refined cast-iron, compared with that of the 
above English wrought-iron, shows that whilst the wrought- 
iron contains o°122 per cent. of silicon, the refined metal 
contains none, and compared as regards phosphorus they 
are about the same. 
The analysis of the puddled wrought-iron, made from 
the refined cast-iron by once heating and rolling the 
puddled or “muck” bar, shows a purer quality of iron 
than the most celebrated makers of Europe produced 
from the purest ores with charcoal. 
The economy of using the refined metal in saving cost 
of labour, fuel, &c., for the puddling process, has been 
fully demonstrated by numerous trials. When all the 
advantages of the process are realised, about one-half of 
the cost of converting cast-iron into wrought-iron can be 
saved ; and there is an improvement in the quality equal 
to the difference between ordinary forge pig-iron and 
charcoal iron, 
These advantages are :— 
On comparing the analysis 

1. Better quality, which is due to the purity of the 
refined metal; as good qualities of wrought-iron are 
produced from it as from pig-iron made from the best 
ores smelted with charcoal. 
2. The refined metal being as pure as wrought-iron, 
with respect to silicon and phosphorus, requires merely 
decarbonising, with less skill to work it, and greater 
certainty of the quality of the product. 
3. Large saving in cost of production, owing to the 
shortening of the time of puddling, which is caused by 
the removal of a large part of the impurities by the re- 
fining process. White refined iron is decarbonised in 
twelve to fifteen minutes, and a “heat” or charge of five 
hundred pounds is puddled in fifty-five minutes, including 
time of charging, melting the iron, and stirring or 
puddling or “ balling” and removing it from the furnace ; 
grey forge iron requires sixty-five minutes, and foundry 
iron about seventy minutes. Seven “ heats” or charges to 
a “turn” or a day’s labour, are of easier accomplishment 
than five charges are from the pig-iron from which it was 
produced ; the five charges now require ten hours to con- 
vert pig-iron into wrought-iron. It is possible to obtain, 
with the patent refined metal, by employing three sets of 
workmen in twenty-four hours, instead of two sets as is 
now customary, twenty-one charges in twenty-four hours 
instead of ten charges ; and allowing sufficient time for 
repurs, the production of any ironwork may be doubled, 
without additional investment of capital and without 
additional cost of repairs. 
4. Saving of fuel per ton of iron produced, amounting 
to one-half, caused by increased production. 
5. Reduction of general business expenses per ton of 
iron, amounting to one-half, caused by increased pro- 
duction. 
6. Reduction of wages, by reason of the diminished 
labour, of 40 per cent. per ton of iron, 
7. The puddling furnace cinders of the refined metal 
contain but about one-fourth of the phosphorus, as com- 
pared with the cinders resulting from the use of pig-iron ; 
and when smelted produce better qualities of pig-iron. 
The cost of refining in the pig-moulds is very little. 
Fluorspar is a cheapmaterial, and but about seventy pounds 
are required to refine a ton of iron. The cost is nearly 
compensated by the saving of the fuel and lime which 
would be required to reduce the puddle cinders of the 
refined cast-iron to pig-iron, as they contain but small 
portions of silica, and will require less fuel and limestone. 
The residue of the fluorspar and oxide is agglutinated, 
and remains in the pig moulds, and is pure lime and de- 
oxidised iron ore, and is available as so much lime and 
ore in the blast furnace. JAMES HENDERSON 

SOME EXPERIMENTS ON COLOUR 
“THE theory of colour perception, although in England it has 
not yet made its way into the text-books, still Jess into the 
popular works on science, is fully established with regard to 
many important points. It is known that our perception of 
colour is threefold, that is, that any colour may be regarded as 
madeup of definite quantities of three primary colours, the exact 
nature of which is, however, still uncertain. More strictly stated, 
the fundamental fact in the doctrine of colour is that, between 
any four colours whatever given, as well in quantity as in quality, 
there exists what mathematicians call a linear relation, that is, 
that either a mixture of two of them (in proper proportions) 
can be found identical, so far as the eye is able to judge, with a 
mixture of the other two, or else that one of them can be 
matched by a mixture of the other three, There are yarious 
optical contrivances by which the mixture spoken of may be 
effected. Inthe year 1857, Mr. Maxwell published an account 
of some experiments with the colour top undertaken to test the 
theory, From six coloured papers, black, white, red, green, 
yellow, and blue, discs of two sizes were prepared, which were 
then slit along a radius so as to admit of being slipped one over 
the other, Any five out of the six being taken, a match or colour 
