there. These compounds remain in part with the gas, causing it to burn with
a persistent smoky flame and with the deposit of objectionable tarry
substances. Where the gas is generated without undue rise of temperature
these difficulties are avoided.

_Purification of Acetylene._--Impurities in this gas are caused by
impurities in the calcium carbide from which it is made or by improper
methods and lack of care in generation. Impurities from the material will
be considered first.

Impurities in the carbide may be further divided into two classes: those
which exert no action on water and those which act with the water to throw
off other gaseous products which remain in the acetylene. Those impurities
which exert no action on the water consist of coke that has not been
changed in the furnace and sand and some other substances which are
harmless except that they increase the ash left after the acetylene has
been generated.

An analysis of the gas coming from a typical generator is as follows:

Per cent
Acetylene ................................ 99.36
Oxygen ................................... .08
Nitrogen ................................. .11
Hydrogen ................................. .06
Sulphuretted Hydrogen .................... .17
Phosphoretted Hydrogen ................... .04
Ammonia .................................. .10
Silicon Hydride .......................... .03
Carbon Monoxide .......................... .01