118. Carbon Protoxide, called also carbon monoxide, carbonic oxide, etc., is a gas, having no color or taste, butpossessing a faint odor. It is very poisonous. Being the lesser oxide of C, it is formed when C is burned in a limited supply of O, whereas CO2 is always produced when O is abundant. The formation of each is well shown by tracing the combustion in a coal fire. Air enters at the bottom, and CO2 is first formed. C + 2O = CO2. As this gas passes up, the white-hot coal removes one atom of O, leaving CO. CO2 + C - 2CO. At the top, if the draft be open, a blue flame shows the combustion of CO. CO + O = CO2. The same reduction of CO2 takes place in the iron furnace, and whenever there is not enough oxygen to form CO2, the product is CO.
Great care should be taken that this gas does not escape into the room, as one per cent has proved fatal. Not all of it is burned at the top of the coal; and when the stove door is open, the upper drafts should be open also. It is the most poisonous of the gases from coal; hence the danger from sleeping in a room having a coal fire.
119. Water Gas.—CO is one of the constituents of "water gas," which, by reason of its cheapness, is supplanting gas made from coal, as an illuminator, in some cities. It is made by passing superheated steam over red-hot charcoal or coke. C unites with the O of H2O, forming CO, and sets H free, thus producing two inflammable gases. C + H2O —? As neither of these gives much light, naphtha is distilled and mixed with them in small quantities to furnish illuminating power See page 183.
CHAPTER XXV.
CARBON DIOXIDE.
120. Preparation.
Experiment 74.—Put into a t.t., or a bottle with a d.t. and a thistle-tube, 10 or 20 g. CaCO3, marble in lumps; add as many cubic centimeters of H2O, and half as much HCl, and collect the gas by downward displacement (Fig. 39). Add more acid as needed. CaCO3 + 2 HCl = CaCl2 + H2CO3. H2CO3 = H2O + CO2. H2CO3 is a very weak compound, and at once breaks up. By some, its existence as a compound is doubted.
121. Tests.
Experiment 75.—(1) Put a burning and a glowing stick into the t.t. or bottle. (2) Hold the end of the d.t. directly against the flame of a small burning stick. Does the gas support combustion? (3) Pour a receiver of the gas over a candle flame. What does this show of the weight of the gas? (4) Pass a little CO2 into some H2O (Fig. 32), and test it with litmus. Give the reaction for the solution of CO2 in H2O.
Experiment 76.—Put into a t.t. 51 cc. of clear Ca(OH)2 solution, i.e. lime water; insert in this the end of a d.t. from a CO2 generator (Fig. 32). Notice any ppt. formed. It is CaCO3. Let the action continue until the ppt. disappears and the liquid is clear. Then remove the d.t., boil the clear liquid for a minute, and notice whether the ppt. reappears.