Moreover, the amount of water vapor given off during the combustion of gas is greater than in the case of the other illuminants.  Water vapor having a great power of absorbing radiant heat from the burning gas becomes heated, and diffusing itself about the room, causes great feeling of oppression; the air also being highly charged with moisture, is unable to take up so rapidly the water vapor which is always evaporating from the surface of our skin, whereby the functions of the body receive a slight check, resulting in a feeling of malaise.

Added to these, however, is a far more serious factor which has, up to the present, been overlooked, and that is that an ordinary gas flame, in burning, yields distinct quantities of carbon monoxide and acetylene, the prolonged breathing of which in the smallest traces produces headache and general physical discomfort, while its effect upon plant life is equally marked.

AMOUNT OF OXYGEN REMOVED FROM THE AIR, AND CARBON DIOXIDE AND WATER VAPOR GENERATED TO GIVE AN ILLUMINATION EQUAL TO 32 CANDLE POWER.

(The amount of light required in a room 16’ X 12’ x 10’.)

|Quantity of |          | Products of Combustion|      |
|  Materials | Oxygen   |           |  Carbon   |      |
Illuminant    |    Used    | Removed  |Water Vapor|  Dioxide  |Adults|
--------------+------------+----------+-----------+---------

--+------+
Sperm Candles |3,840 grains|19.27 c.f.|13.12 c.f. |13.12 c.f. | 21.8 |
Paraffin Oil  |1,984   "   |12.48 c.f.| 7.04 c.f. | 8.96 c.f. | 14.9 |
Gas (London)--|            |          |           |           |      |
Burners:      |            |          |           |           |      |
Batswing    |  11  c.f.  |13.06 c.f.|14.72 c.f. | 5.76 c.f. |  9.6 |
Argand      |   9.7 c.f. |11.52 c.f.|12.80 c.f. | 5.12 c.f. |  8.5 |
Regenerative|   3.2 c.f. | 3.68 c.f.| 4.16 c.f. | 1.60 c.f. |  2.6 |

Ever since the structure of flame has been noted and discussed, it has been accepted as a fact beyond dispute that the outer almost invisible zone which is interposed between the air and the luminous zone of the flame is the area of complete combustion, and that here the unburnt remnants of the flame gases, meeting the air, freely take up oxygen and are converted into the comparatively harmless products of combustion, carbon dioxide and water vapor, which only need partial removal by any haphazard process of ventilation to keep the air of the room fit to support animal life.  I have, however, long doubted this fact, and at length, by a delicate process of analysis have been able to confirm my suspicions.  The outer zone of a luminous flame is not the zone of complete combustion; it is a zone in which luminosity is destroyed in exactly the same way that it is destroyed in the Bunsen burner; that is the air penetrating the flame so dilutes and cools down the outer layer of incandescent gas that it is rendered non-luminous, while some of the gas sinks below the point at which it is capable of burning, with the result that considerable quantities of the products of incomplete combustion carbon monoxide and acetylene escape into the air, and render it actively injurious.