328 
PRESENT STATE OF THE CHEMISTRY OF GAS-LIGHTING. 
is easily accomplished, for carbonic acid is soluble at common temperatures, in its own 
volume of water, and alkalies absorb it very freely. Caustic lime, for example, will take 
up nearly its own weight of the gas; and, as I have already said, the purification should 
always be so managed that lime is the last agent through which the gas passes on its 
way to the holders. 
Another objectionable property of carbonic acid is its action on the animal system. 
Iu its concentrated state the gas is absolutely irrespirable, and it kills immediately by 
causing spasm of the glottis. Even when it is diluted with air to the extent of 1 in 10, 
it quickly produces insensibility, and an atmosphere containing only 4 per cent, of it is 
dangerous. This is the proportion found in the air expired from the lungs; and there¬ 
fore I have used it in the diagram just referred to as the proportion which renders air 
irrespirable. As little, indeed, as 2 per cent, of the gas in air will cause distress, as 
headache, and great depression of the vital powers; and no doubt the discomfort which 
arises from the too liberal use of gas in badly-ventilated rooms is in great part due to 
the carbonic acid produced by the burning gas. I have found by experiment that a 
small gas stove in one of Phillips’s baths, in my own bath-room, will charge the ai 
so oppressively with carbonic acid as to render it almost irrespirable. On one occasion 
I detected 3-5 per cent, of carbonic acid in the air of the room ; and I need not say that 
this is a dangerous quantity. It is therefore advisable that the products of the com¬ 
bustion of gas, when it is burned in large quantity, should be carried out of the room ; 
and this precaution is applicable to every illuminating agent which vitiates the atmo¬ 
sphere, as you will see from this diagram :— 
Relative Values of Illuminating Agents, 
In respect of their Heating and Vitiating Effects on the Atmosphere, when burning, so 
as to give the Light of 12 Standard Sperm Candles. 
Cannel gas 
Pounds of Water 
Heated 
1° Fahrenheit. 
Oxygen 
Consumed 
Cubic Feet. 
Carbonic Acid 
Produced 
Cubic Feet. 
Aii- 
Vitiated . 
Cubic Feet. 
. . 1950 
3-30 
2-01 
50-2 
Common do. . 
. . 278G 
5-45 
3-21 
80-2 
Sperm oil . . 
. . 2335 
4*75 
0,00 
o oo 
83-3 
Benzole . . 
. . 2326 
4-46 
3-54 
88-5 
Paraffin . . 
. . 3619 
6-81 
4-50 
112-5 
Camphine . . 
. . 3251 
6-65 
4-77 
119-2 
Sperm candles 
. . 3517 
7*57 
5-27 
131-7 
Wax candles . 
. . 3831 
8-41 
5-90 
149-5 
Stearic candles 
. . 3747 
8'82 
6-25 
156-2 
Tallow candles 
. . 5054 
12-06 
8-73 
218-3 
The mode of discovering the presence of carbonic acid in coal gas is very simple; for if 
the gas is passed through a little lime-water it will render it milky, or if shaken with a 
solution of potash the amount of absorption indicates the proportion present. 
(b) Oxygex (0).— This comes from the too active operation of the exhauster, and the 
drawing in of air through the retorts. The mischievous influence of this gas on the 
illuminating power of coal gas will be seen from this experiment, where I will pass about 
6 per cent, of air into the burning gas, and you will notice how seriously the light of the 
flame is destroyed. It has fallen, in fact, to about half its original power. The follow¬ 
ing are the proportions of light lost by different amounts of air in gas, supposing the 
light to be 100 : - 
Light. 
2 per cent, of air in gas 90 
5 » » 70 
7 ?? „ 52 
10 „ „ 34 
-0 „ „ .12 
40 >, „ .. . 1 
50 „ „ 0 
The test for the presence of oxygen in coal gas is a little pyrogallic acid; and in 
operating you will proceed thus : First, agitate a known volume of the gas with a strong 
solution of potash, and observe the loss of volume—that is, due to carbonic acid ; then 
