Retrieved 2011-11-28. now known precisely but, as with many other commodities, the Mongol campaigns served as one conduit. The Arabs learned of saltpetre around the end of the thirteenth century when they were introduced to it as 'Chinese snow' and began to use rockets they called 'Chinese arrows'. ↑ Original from the University of Michigan Thomas Francis Carter (1955). The invention of printing in China and its spread westward (2 ed.).