122 University Geological Survey of Kansas. 
considering the convenience to the manufacturer and dealer, 
and because it makes it unnecessary to run a somewhat cumber- 
some machine, the liquefied gas will be extensively used. Even 
large wholesale bottlers buy the gas in preference to making it. 
MATERIALS USED IN THE MANUFACTURE OF CARBON-DIOXID GAS. 
In order to make this gas, a carbonate—as sodium carbon- 
ate (Na,CO;), sodium bicarbonate (NaHCO,), or marble dust 
(CaCO,)—is used, together with an acid, as sulfuric (H.SO,), 
or hydrochloric (HCl). The cheapest carbonate and the cheap- 
est acid would be selected, other things being equal. The chem- 
ist represents the reaction by CaCO,--H,SO,=—CaSO,-+ H,O + 
CO,. Water and calcium sulfate are left in the generator after 
the chemical action is over. The carbon-dioxid gas might also 
be made by the simple combustion of charcoal or coke, but this 
gas is not very readily purified. Another method of making is 
by simply heating limestone; thus, CaCO,+heat—Ca0+CQ,. 
The calcium oxid left can be utilized as quicklime. 
Another and recent source of the gas is from the vats in which © 
beer is fermenting. By the process of malting some of the 
starch of the grain is changed into a kind of sugar and this fer- 
ments readily with yeast, the products being alcohol and car- 
bon-dioxid gas. The carbon-dioxid gas is pumped off and 
condensed to a liquid by pressure. The gas obtained in this 
way must be thoroughly washed and purified before being used. 
In fact, a process of washing is necessary to purify the gas in 
whatever way it is made. Sometimes washing with simple 
water is sufficient, and in other cases more thorough washing 
through chemical solutions is necessary. This gas finds many 
uses in the arts. In England it is used instead of yeast in the 
manufacture of ‘‘aerated bread.’’ 
PROPERTIES OF CARBON DIOXID. 
This gas is much heavier than air, will extinguish a fire, and 
is not poisonous. As stated above, it may be condensed to a 
liquid, and when some of this liquid is allowed to escape into 
the air it vaporizes so rapidly that it takes heat from the sur- 
rounding gas and converts it into a snow-white solid. This 
