Original sentence: Some western Historians believe that gunpowder was not discovered in China, as travellers like Marco Polo or Giovanni di Plano Carpini mentioned seeing gunpowder in China; But the Arabs referred to potassium nitrate as snow from China, so there is still some sort of controversy on the invention of gunpowder
Edited sentence: Some western Historians believe that gunpowder was not discovered in China, as travellers like Marco Polo or Giovanni di Plano Carpini mentioned seeing gunpowder in China; But the Arabs always mentioned in their manuscripts about about learning to make gunpowder from the Chinese, so there is still some sort of controversy on the invention of gunpowder