He discovered sodium sulfate, which is commonly known today as Glauber's salt.
His discovery of sodium sulfate in 1625 led to the compound being named after him: "Glauber's salt".
Miescher devised different salt solutions eventually producing one with sodium sulfate.
This makes a solution of ammonium nitrate and sodium sulfate.
Solutions exposed to air are eventually oxidized to sodium sulfate.
So I'd guess that the solid remaining is sodium sulfate.
Demand for soda ash increased and supply of sodium sulfate had to increase in line.
The resulting sodium sulfate from these processes are known as salt cake.
The glass industry provides another significant application for sodium sulfate, as second largest application in Europe.
Although sodium sulfate is generally regarded as non-toxic, it should be handled with care.