A positive result of Hoesch Test is shown in the image. This test allows to confirm or rule out an acute attack of Porphyria. It is a simple, fast and cheap method that produces the immediate color of the urine in contact with Ehrlich reactive. This reactive can be easily prepared in the laboratory adding 42 ml of acetic acid (100%) and 8 ml of percloric acid (60%) to 1 grame of 4-dimetilamine-benzaldehyde. Hoesch test is done by addition of 2-3 drops of the urine to 1 ml of reactive in suspected cases of acute Porphyria.

Figure 1. Multiple kidney stones composed of calcite from a 64-year-old man subjected to lithotripsy. The structure is described as granuloporous, concentric in the nucleus and the trigonal system crystallization. Its composition is 90% calcite, 10% calcium oxalate monohydrate. In the lower, the infrared spectrum of the stone is shown, and at right, the effervescence when it reacts with 0.2M HCl, generating bubbles of CO2 can be observed.