Gas made by the " water-gas process is more poisonous than that made by the distillation of coal, owing to the presence of so much carbon monoxide in water-gas; otherwise the gases are much alike. The quantity of manufactured gas used in the United States is about 100,000 millions of cu. ft. annually. Chicago, alone, used more than 17,000 millions of cu. ft. of it in 1911.

300. Pintsch and Producer Gases.

Pintsch gas is an illuminating gas made by cracking," or decomposing, petroleum through contact with bricks at 1000° C. (cf. § 298). It must be burned with a special burner, as must acetylene, but it has great illuminating power. It is stored in steel cylinders, under pressure, and is used in lighting railway

cars.

Producer gas is a fuel gas made by passing air through white hot coke or coal. It usually has about 30% of carbon monoxide, the remainder being the nitrogen of the air, and carbon dioxide formed by oxidation of some of the carbon monoxide.

301. Exercises.

1. How many grams of carbon are needed to reduce 15 grams cupric oxide, CuO, if the carbon is oxidized to carbon dioxide? How many grams of carbon dioxide are formed?

2. What volume of carbon dioxide at 30° C. and 730 mm. can be produced from 840 grams magnesium carbonate, MgCO3? 3. How many grams of sodium bicarbonate are needed to give, when heated, 36 liters of carbon dioxide? (Cf. § 284.)

4. If 50 1. of water-gas (§ 299) were burned, how many grams of water and carbon dioxide would result? Use standard conditions, and consider "hydrocarbons" to be ethane.

5. How many liters of carbon dioxide are formed, under standard conditions, by the combustion of 250 grams carbon monoxide?

6. Calculate the percentage composition of calcium carbonate, carbon dioxide, oxalic acid.

7. How would you distinguish between sodium carbonate, sulphite, sulphide, and formate, chemically?

8. How would you distinguish between the gases carbon dioxide, carbon monoxide, oxygen, hydrogen, and ammonia?

9. Calculate the volume, in liters under standard conditions, of 10 g. of each of the following: methane, ethane, ethylene, and acetylene.

Calculate also the volume of oxygen needed, and the volumes of steam and carbon dioxide produced, in the combustion of 10 g. of each of these gases. Use standard conditions.

CHAPTER XXIII.

FLAMES, LIGHT, AND HEAT.

302. Luminosity of Flames. As stated in Chapter II, § 28, a flame is a burning gaseous body. The amount of light given off by a flame depends upon the nature of the burning substance and upon its density.

As an illustration of the influence of density, we may take the case of hydrogen. This substance ordinarily burns in air and in oxygen with an almost invisible flame; if, however, the hydrogen and the oxygen are very much compressed before ignition, the flame produced by their union is a very brilliant

one.

The illuminating power of all ordinary flames is due to the presence of incandescent solid particles. This may be illustrated by introducing any fine dust into a flame of hydrogen or into the colorless Bunsen flame; the flame at once becomes luminous.

In the combustion of substances containing carbon, — such substances as candles, illuminating gas, paper, petroleum, wood, coal, etc., the luminosity of the flame is due to the glowing of particles of carbon in the flame. A cold object inserted into the flame produced by one of these substances becomes covered with soot; and too little

air, or too much gas, causes the flame to smoke, owing to the escape of unburned particles of carbon.

303. Structure of Flames. A burning candle shows practically the same phenomena as the other compounds of carbon just named, and may be taken as representative of them.

The burning of a small portion of the wick of the candle furnishes heat enough to melt some of the wax. The wick then draws the melted wax, by capillary action, into the flame, where it is vaporized and ignited.

If the candle flame be examined, it will be found to consist of several regions, cr zones, of combustion, surrounding a central cone-shaped region of unburned gases. These parts are shown in vertical section in Fig. 69.

FIG. 69.

A

-B

X is the region of unburned gases.

B is the luminous zone. It contains solid particles of carbon in a state of combustion.

A is the outer mantle of the flame. Being nonluminous it is obscured by the light of B, except -C at the bottom, where it forms a blue, cup-shaped I region.

A

In addition to the parts just named, an important region (C) is believed to exist about the region X. Being non-luminous, the region C is obscured by the light of B.

Whether a flame is to be luminous or nonluminous depends upon the condition of affairs in the region C.

NON-LUMINOUS FLAMES.

283

What takes place in a candle flame is probably as follows:

The vaporized paraffin (wax) of the region X (Fig. 69) burns in part in the zone C, producing enough heat to decompose some of the paraffin vapor into hydrogen, certain hydrocarbons (especially acetylene), and solid carbon. These substances burn further in the region B, the carbon burning, as usual, with a bright glow, and thus causing the luminosity of this region. In A the gases and the carbon escaping unburned through B are more or less completely burned.

304. Non-Luminous Flames. The decomposition of the combustible material of region X (Fig. 69) into acetylene, carbon, etc., in the region C requires a definite degree of temperature; hence, if the temperature of C is sufficiently lowered, the flame becomes non-luminous.

This is what takes place in a Bunsen burner (Fig. 70). When the holes are closed, the flame is luminous, and has the same regions as a candle flame. When the holes are opened, the gas rushing past the holes draws in air, the region C is cooled, and the flame becomes non-luminous. If carbon dioxide, nitrogen, etc., are introduced, instead of air, the result is the same.