In 1841 the British government supported an expedition to the River Niger. This venture aimed to spread Christianity and encourage the abolition of slavery in the region, but the high mortality rates due to tropical disease presented a threat to the undertaking. To resolve this problem, the three expedition steamships were built as giant ventilating systems, under the direction of chemist David Boswell Reid. Grounded on miasmic notions of disease, it was hoped that these vessels would purify the air for the expedition’s crew and protect them from the ravages of malaria and yellow fever. This article examines how contemporaries evaluated the performance of this ventilation scheme. It argues that the credibility of Reid’s apparatus was highly political and engendered differing imperial agendas. In Victorian Britain, the potential for ventilation technology to assist colonial expansion was debated through differing accounts of the Niger Expedition as either a success or failure.