Column 7 of Table II. gives the expenses of putting down apparatus and mains for candle power per hour, calculated on the following grounds: -

In Belgium the cost of establishing a public burner may be estimated at 125. (for private illumination, stations, rooms, etc, where more elegant appliances are used, the cost may rise to 20s. or 27s. 9c*. per burner), and main-5 tenance and interest may be taken at 10 per cent, of this amount, say 5l. 18s. 9d. per annum. This cost must be spread over the entire consumption, depending on the number of hours during which it is in use.

Assuming a minimum of 700 hours per annum, and a consumption of 250 litres per hour, it will be found that at 1 1/2d. per cub. metre, interest and maintenance must be valued at about 6 per cent, of the value of the gas.

The corresponding expenses for a regenerative Siemens or Wen ham lamp, which costs at least 47s. 6d. for a consumption of 250 litres per hour, may be calculated in the following manner, a saving of 50% of gas being supposed: -

I

8.

d.

2 ordinary burners . value

2

5

2 secondary tubes. „

3

2

Piping and main tube (23s. 9d. less 5s. 7d.) „

18

2

23

9

II

One complete regenerative burner, giving the same light as the two burners above..

47

6

Piping and principal tube..

18

2

Secondary pipes..

1

7

67

3

The expense of maintenance and interest is found to be 17 %.

Table II. - Illuminating Gas

Type of Burner.

Angle with

Horizon.

Candle Power.

Gas per Hour in

Cub. Metres.

Consumption of Gas per

Candle Power per Hour in

Litres.

Value at l 1/2d.

per Cub.

Metre,

Working Expenses.

Total Cost per

Candle Power per Hour.

d.

d.

d.

Split burner..

0

16.9

0.251

14.81

•021232

•001273

•022505

45

17.2

0.256

14.9

Argand burner..

0

21.9

0.239

10.91

•01767

•001054

•018724

45

19.4

0.241

12.4

New Clamond burner..

45

21.1

0.190

9

.01282

•00123

•01406

Aver or de Pintsch burner..

0

14.4

1.0951

6.60

•014079

•001406

•01548

45

10.5

0.1037

9.88

Cardinal or de Brauer burner..

45

21.9

0.219

10

•0142

•000902

•0151

Siemens regenator..

0

653

0.460

7.05

• •

• •

• •

No. 3 ......

45

46.9

0.456

9.75

•013889

•002356

•01624

Wenham,No2..

0

28.4

0.249

8.77

•008208

•001396

•099604

45

44.5

0.257

5.77.

90

45.8

0.256

5.58

Wenham ,No4..

0

99.0

0.285

6.92.

•005671

•000959

•009196

25

152.0

0.686

4.51

45

170.0

0.677

3.98

65

200.0

0.685

3.42

90

2020

0.671

3.33

We have, therefore, calculated at this rate the expenses tabulated in column 7, Table II., for the illumination given by Siemens or Wenham lamps.

For Clara on d and Aver burners we have adopted 10 % of the gas consumed as representing the corresponding expenses. The rate of 6% remains for ordinary burners, the cost of which does not exceed 4s.

It must be borne in mind that the numbers should vary inversely with the number of hours during which the burners are employed, since the sources of expense remain almost constant whatever be the consumption of gas.

Before passing to the examination of some other modes of illumination, a word may be said on the subjects of recuperation and intense burners.

Table III. - Water Gas. Photometric Tests Of Some's Burner

Consumption per Hour.

Pressure at the Burner.

Candle Power.

Candle Power per Cub. Ft.

cub. ft.

litres.

in.

mm.

9.66

272.4

2.25

57.15

12.85

1.33

831

234.3

2.37

60.19

10.88

1.31

7.90

222.7

2.50

63.50

12.24

1.55

6.70

188.9

1.75

44.45

8.48

1.26

6.70

188.9

1.00

25.40

8.41

1.25

5.58

157.3

3.25

82.55

9.94

1.78

5.10

143.8

4.50

38.10

6.85

1.34

3.96

111. 6

2.00

50.80

5.47

1.38

53.91

1519.9

75.14

Consumption per candle power per hour.... 20.20 litres,

Price of gas at Frankfort per cub. metre.... .712d.

Cost per candle power per hour...... • 0142d.

Working expenses, 10 per cent....... .00142d.

Total cost per candle power per hour..... .01567d.

Table IV. - Magnesium Lamps

Illuminating Power.

Without Reflector.

No. of Ribbons.

With Reflector.

Without Reflector.

Candle

Power per

Ribbon.

Consumption per Hour par Ribbon.

gnu.

Consumption per Hour per Candle.

grm.

Total Cost per Candle. Magnesium at 14s. 6(2. per lb.

1

150

3,200

150

16.7

0.1114

2

237

5.880

118.7

16.7

0.1410

4

450

8,000

112.5

16.7

0.1480

•0418d

6

700

11,300

117

16.7

0.1415

8

950

17,000

117

16.7

0.1430

Table V. - Electric Light - Arc Lamps. (Heim.)

Circuit Lamp of Pieper.

Piette Erizich

(Schnckert)

Differential Lamp.

Siemens and

Halske

Differential Lamp.

Diameter of Carbons..

6.7 mm. 5.0

1.0 .

14 .

Length of Arc..

2 „ 2

4 .4

. 4.5

Angle with horizon .

0° . 45°

0° . 45°

0° . 45°

Candle power..

126 . 377

220 . 1,420

575 . 3,830

Electric work in volts amperes

160 . 153

414 . 410

918 . 912

Volts amperes per candle

Power..

1.27 .0.405

1.88 . 0.291

1.60 . 0.238

Candle power per horse power

433 . 1360

293 . 1,890

344 . 2,310

Table VI. - Incandescent Lamps. (After Heim.)

Types,

Candle Power.

Electric Work in

Volts Amperes.

Volts Amperes per Candle.

Candle per H.P.

Lamps per H.P.

Edison lamp, old model

16

72

4.50

122

7.6

„ new „

16

60

3.75

147

9.2

Swan lamp, old „

16

66

4.13

133

8.3

„ new „

16

56

3.50

157

9.8

Siemens and Halske

16

52

3.25

169

10.6

Bustien (Cannstadt)

16

56

3.50

157

9.8

Table VII. - Incandescent Lamps

Kind of Installation.

Price per

Candle Power per Hour.

Private installation for 200 lamps at least, with special motive power..

•0294d.

When a part of the labour is on hand and an excess of power can be utilised for the production of the light..

•0152d.

Special installation for private lighting...

•0446d.

(Chem. Trade Jl.)

The luminous intensity of a flame increases very rapidly with its temperature, and may be approximately represented by an expression of the form I = at, when I is the intensity of the flame, and t its temperature. The great increase of intensity obtained by superheating the air may thus be- conceived, when it becomes sufficient to sensibly increase the temperature of the flame and so produce a more efficacious combustion. In the Siemens and Wenham lamps the air may be heated to 400°-600°C.,but the apparatus soon wears out if the latter temperature be habitually employed.

To render the recuperation rational and efficacious it is essential that the apparatus be so arranged that the air is heated by the products of combustion, and not simply by the flame of the burner, for this can only give up part of its heat at the expense of its illuminating power.

It has not been found advantageous to strongly heat the gas itself; on the contrary, deposits are thus formed which rapidly block up the orifices by which it escapes from the burner.

For a given consumption of gas there is a definite supply of air which corresponds to a maximum of luminous intensity. The determination of this quantity is of special importance when ordinary burners with cold air are employed; but even when hot air is supplied it is still important to ascertain exactly the draught which corresponds to a maximum of illuminating power.

Everyone can convince himself of the effect of the draught or volume of air brought into contact with luminous flame on its illuminating power by simply placing a glass chimney on the top of the glass of an Argand burner, so that the height of the chimney is doubled. It will be observed that the flame immediately becomes lower and throws a less powerful light on surrounding objects, although it may itself become whiter. Inversely, the intensity of a flame, which is burning with an excess of air, may be increased by diminishing the supply of the latter. This increase continues until the flame becomes brown towards the top, after which further diminution of the air supply causes a rapid diminution in the brightness of the flame, the combustion then becoming incomplete.

This experiment justifies the conclusion that for burners with cold air the maximum of light corresponds to the minimum of air which permits of complete combustion, and that the yellow flame is more economical than a white flame obtained by means of an excess of cold air.

When the air arrives at the burner Seated to 500° C., the influence of the draught will, of course, not be so great, but it must be remembered that the temperature of the flame expressed in degrees is twice as great as this.

The economy effected by these intense flames, that is to say, flames produced by a large amount of gas, may be explained by the facts that, in the first place, the amount of air immediately surrounding the flame is smaller for an equal volume of flame than in the ordinary burner, and that the loss of heat is thus also rendered smaller; and that in the second place the surfaces and volumes of neighbouring parts of the apparatus so situated as to be capable of absorbing heat from the flame are also smaller in proportion to the gas consumed; finally,. a wide flame consists of an interior cone of gas, surrounded by a thicker incandescent layer (which must be traversed by the air) than is the case in a narrow flame burning the same volume of gas.

On account of these various circumstances the temperature of a large flame is appreciably higher than that of a small one, and hence arises its greater illuminating power. This luminous intensity therefore, results from a more effective combustion, which produces an increase in the light radiated from the flame.