Patent 3899144 "Powder Contrail Generator" is for creating a visible trail on a towed target (a target towed behind another plane, and used for target practice). With self powered targets they use smoke created with heat from the engine to create a visible trail, but in the towed target there is no heat source.
The entire aim of the patent is to create the VISUAL of a contrail (and really more like the visual of a smoke trail), to help people see the target.
Here's what the "contrail" will be emerging from - a "towed target"
The difficulty in seeing a small towed target is a long-standing problem, as discussed in this patent for a different towed target:
Like all patents, the presence of a patent does not indicate the invention works, or that it is in use. It seems like they are more likely to use flares now, which also gives the benefit of simulating the engine heat source.
Spraying things from a plane is not rocket science. This is a very simple device used to simulate a smoke trail. But despite that, Alex Jones nonsensically used it as "evidence" of "weather manipulation".
The "Powder Contrail" has been confused with this image:
For example, in this image shared on Facebook:
However that shows an entirely different thing, a Cobham Refueling Pod