A definite formula should not be laid down for the oxy-acetylene flame as used. This for the reason that the products of combustion vary with different proportions of the gases and in different parts of the flame. Lewes4 gives the probable maximum of the flame as lying between 3100 deg. Cent, and 4000 deg. Cent. This forbids the formula of Davy,

2C2H2+502 = 2H20+4C02, because water is dissociated at only 780 deg. Cent. Beltzer makes it

C2H2+02 = 2CO +H2, while Beaupre allows less than one part monoxid in 100,000 of the residual gas.1 Presuming that none of the carbon forms monoxid, Beaupre states that oxids of nitrogen are formed in small quantity and ozone in very appreciable amount. Le Chatelier2 gives hydrogen, carbon dioxid, and monoxid as the principal gases from burning 7.74-17.37 parts acetylene in 100 parts air. It is quite likely that the layer of hydrogen on the outer surface of the flame is partly burned to water, and partly dissipated.

1 Bulletin Technologique, Sept., 1907.

2 Medium-pressure torch used.

3 Low-pressure torch used.

4 "Acetylene," Vivian Lewes, 1900, 0. 120.

Theoretically, the acetylene requires about 2.5 parts of oxygen. But practice proves that this gives an oxidizing flame. So the proportion of 1 part acetylene to 1.50 oxygen is recommended. Recently M. Bournonville's experiments have shown that, with his torch in working order and the flame the proper color and shape, the proportion fell as low as 1 of acetylene to 1.28 oxygen.3 Repeated trials confirmed these figures. However, this seems a small matter. The flame should be decidedly reducing, but should not be so charged with excess acetylene that it will deposit carbon.

The temperature commonly ascribed to the oxy-acetylene flame is 3500 deg. Cent. Acetylene is composed of 92.3 parts carbon and 7. 7 hydrogen, according to its symbol. Its temperature of dissociation is 780 deg. Cent., according to Lewes;4 on burning, its heat value is 310,500 cal., according to Thomsen.5 This great heat need not all be attributed to the burning of nascent carbon, for the gas is endothermic, requiring 47,700 cal. for its formation.6

1 Comptes rendu., 1906, 142, 165-6.

2 Comptes renin., 121, 1144.

3 Special information.

4 "Acetylene," Vivian Lewes, 1900.

5 Thermochem. Unters., 4, 74.

6 Roscoe and Schorlemmer, Vol. I, p. 770. "Treatise on Chemistry."

Le Chatelier1 gives formulas of reaction and temperatures for three different mixtures of acetylene with air, and shows that a minimum of air produces carbon dioxid and water; and an excess of air, carbon monoxid and hydrogen. In any case, the flame if properly handled is reducing beyond the blue cone, which should never be allowed to more than touch the work in hand. Such hydrogen as remains unburned in the flame is claimed to form a protecting envelope.

Testing

It is natural to expect that a unit cross-section of an oxy-acetylene welding will not be of equal strength with the metal before welding. The metal has been melted, perhaps oxidized or carbonized slightly, and has cooled quickly. If the weld is not pounded or worked while cooling, the chances are that the metal has crystallized and is brittle. The average oxy-acetylene weld is more brittle than the metal itself, and has from 60 to 95 per cent, of the tensile strength. To make a weld as strong as the unwelded metal, an upset or extra thickness of metal must be added to the weld. Some writers make the ridiculous statement that the weld is even stronger than the original metal. This is only possible when a large joint is made. And in any event the elasticity is much reduced even when the joint has been hammered or pressed.

But for its purpose, when carefully made, the acetylene weld is strong enough and compares favorably with welds made by other processes. Tubing, automobile frames, boiler patches, and miscellaneous joints which have successfully withstood the excessive shocks, stresses, or pressures demanded of them, all attest to the ability of the acetylene welder to do good work.