The flame which issues from the converter during this period is usually characterised by a green colour, caused apparently by the formation of iron-silicate slag.

When this stage is completed and the slag poured off, the white metal is blown up to blister copper—this constituting the second main stage of the process. The chief reactions are those of sulphur elimination and the production of metallic copper, caused by the action of some of the copper oxide first produced, upon the copper sulphide still present.

The flame during this period is small, thin, and fairly non-luminous, usually of a red-purple to bronze purple colour.[16]

The progress of the blowing from copper matte to white metal and thence to blister copper is usually indicated and controlled at the smelter by the appearance of the flame which issues from the nose of the converter during the first periods, and by the character of emitted shots during the later stages. This is particularly the case with mattes of moderate purity worked in the silica-lined converter. The successive changes in these indications are gradual, but are easily followed by the experienced skimmer, who is thus able to judge readily as to the manner in which the blow is progressing, and also as to the temperature, composition, and nature of the metal in the converter.

TABLE XII.—Changes in Composition during Bessemerising.

Time.Composition.
Hrs Mins Cu.Au.Ag.
%Oz.Oz.
11.52 amCharged No. 1 blast matte, .... 46·08 0·15 31·50
11.54 amBlow commenced.
12.04 pmSample No. 1 blowing,..1046·020·1731·80
12.14 pmSample No. 2 blowing,..2051·460·1835·80
12.18 pmPunched 3 minutes.
12.24 pmSample No. 3 blowing,..3053·270·2037·80
12.25 pmPunched 7 minutes.
12.34 pmSample No. 4 blowing,..4056·290·2140·80
12.40 pmPunched 2 minutes.
12.44 pmSample No. 5 blowing,..5059·900·2243·70
12.45 pmPunched 2 minutes.
12.54 pmSample No. 6 blowing,10062·670·2344·90
12.55 pmPunched 6 minutes.
1.04 pmSample No. 7 blowing,11067·890·2549·20
1.07 pmPunched 3 minutes.
1.12 pmBlow stopped.
1.13 pmSkimmed.
1.14 pmBlow resumed.
1.14 pmSample No. 8 blowing,12073·970·2754·90
1.17 pmPunched 2 minutes.
1.21 pmBlow stopped.
1.22 pmSkimmed.
1.25 pmBlow resumed.
1.25 pmSample No. 9 blowing,13077·820·2857·30
1.34 pmSample No. 10 blowing,14074·160·2654·30
1.44 pmSample No. 11 blowing,15081·720·1557·60
1.54 pmSample No. 12 blowing,20098·500·78107·70
2.02 pmPunched 1 minute.
2.04 pmSample No. 13 blowing,21098.570·4081.60
2.05 pmPunched 2 minutes.
2.08 pmBlow stopped, test for Cu.
2.09 pmBlow resumed.
2.10 pmBlow finished.
Converted copper,21699.080·3883·80
Total time punching,..28......
Total time of blow,216......
Actual time of blow,209......
Time.Composition.
Hrs Mins Insoluble Fe.S.As.
%%%.%.
11.52 amCharged No. 1 blast matte, ....0·15 24·30 24·700·22
11.54 amBlow commenced.
12.04 pmSample No. 1 blowing,..101·3023·7022·950·07
12.14 pmSample No. 2 blowing,..200·3020·5023·100·06
12.18 pmPunched 3 minutes.
12.24 pmSample No. 3 blowing,..301·1018·7022·150·06
12.25 pmPunched 7 minutes.
12.34 pmSample No. 4 blowing,..401·3016·2021·850·06
12.40 pmPunched 2 minutes.
12.44 pmSample No. 5 blowing,..500·9013·7021·950·06
12.45 pmPunched 2 minutes.
12.54 pmSample No. 6 blowing,1001·3011·4021·350·06
12.55 pmPunched 6 minutes.
1.04 pmSample No. 7 blowing,1100·65 7·60
1.07 pmPunched 3 minutes.
1.12 pmBlow stopped.
1.13 pmSkimmed.
1.14 pmBlow resumed.
1.14 pmSample No. 8 blowing,1200·25 3·4020·100·05
1.17 pmPunched 2 minutes.
1.21 pmBlow stopped.
1.22 pmSkimmed.
1.25 pmBlow resumed.
1.25 pmSample No. 9 blowing,1300·15 0·9019·600·04
1.34 pmSample No. 10 blowing,1403·30 2·6016·600·04
1.44 pmSample No. 11 blowing,1500·25 0·2015·350·04
1.54 pmSample No. 12 blowing,200 0·017trace0·780·050
2.02 pmPunched 1 minute.
2.04 pmSample No. 13 blowing,210 0·052 0·010·780·033
2.05 pmPunched 2 minutes.
2.08 pmBlow stopped, test for Cu.
2.09 pmBlow resumed.
2.10 pmBlow finished.
Converted copper,216 0·017 trace 0·010·033
Total time punching,..28........
Total time of blow,216........
Actual time of blow,209........
Samples taken each 10 minutes from beginning of blow until finished.

In general character, this colour sequence, during the bessemerising of the ordinary class of copper mattes—i.e., those consisting largely of iron, copper, and sulphur, with but moderate quantities of impurity—does not vary very markedly, but the body and luminosity of the flame depend to a great extent on the nature of the charge and on the working conditions. The colours are intensified by very hot metal, large charges, heavy blast, and rapid working, and particularly by the presence of secondary constituents, such as zinc, lead, or arsenic, which liberate dense white fumes, and so increase the luminosity of the flame.

There are generally four main variations in the appearance of the flame from the acid-lined converter:—