Catalysis

La velocità spaziale is the term on this list that an English reader will translate perfectly and still misread. The Italian adjective spaziale behaves like « spatial » and like « space »: it belongs to la navetta spaziale, to la stazione spaziale, to geometry and to orbit. So the phrase reads as the speed of something moving through space, and the example sentence seems to agree, because una velocità spaziale alta lascia poco tempo alla reazione puts speed and time side by side exactly as a schoolroom formula would. The formula is not that one. The quantity divides a flow of gas by the volume of catalyst that gas passes through, so the litres cancel and what survives is one divided by an hour. It is a residence time turned upside down: how many vessel volumes go through in an hour, not how fast anything goes. The trap is not the translation but the transparency, because « space velocity » plays the same trick in English, and the « space » in it is the room inside the reactor, never a distance covered.