This is a sample of tetraammine copper nitrate, which was prepared by dissolving a slight excess of CuO in 50% HNO₃ and then adding a large excess of 25% NH₃. This produces a dark blue precipitate. The NH₃ was allowed to soak the precipitate for a few days and then it was allowed to dry in contact with air. Final drying was done by blowing hot air over the mix. The sample shown here has a weight of approximately 1.5 grams.

The color of this compound resembles that of copper tetraammine sulfate. The compound looks lighter, because it is finely divided, while the sulfate consists of large crystals.

The name of this compound is abbreviated as TACN. Under this name it is known as an explosive, although it is not easy to make it detonate.