To adjust from a neutral flame to a carbonizing flame, one should _________ acetylene and ________________ oxygen.

To adjust from a neutral flame to a carbonizing flame, one needs to increase the flow of acetylene while decreasing the flow of oxygen.

In brazing, the neutral flame is characterized by a balanced ratio of acetylene and oxygen, producing a clear inner cone that is neither oxidizing nor carburizing. By increasing acetylene, you are introducing more fuel into the flame, which will lead to excess carbon in the combustion reaction. Simultaneously, by decreasing the oxygen, you reduce the combustion effectiveness, allowing for carbon to be deposited in the flame's envelope. This shift results in a carbonizing flame, which is suitable for certain applications where a bit of excess carbon is beneficial, such as when welding or brazing softer metals that may be susceptible to oxidation. This understanding is crucial for achieving the desired metallurgical properties in the workpiece.