II. The combination of hydrogen and chlorine under the influence of light

Abstract

In the year 1801, William Cruickshank noticed the gradual combination of a mixture of hydrogen and chlorine in diffuse daylight. Gay Lussac and Thenard observed that the mixture of these two gases exploded on exposure to direct sunlight. In the same year, 1809, Dalton made several experiments with direct sunlight, and with diffuse daylight, as causes of the combination. He states, “upon repeating the experiment with sundry variations it was confirmed that light is the cause of this rapid combustion of hydrogen and oxymuriatic gas; that the more powerful is the light, the more rapid is the diminution of the mixture; and that if the eudiometer be covered by an opake body, the mixture will scarcely be affected with any diminution for a day, and will not completely disappear in two or three weeks. Moreover when the diminution is going on with speed, if the hand, or any other opake body, is interposed to cut off the solar light, the diminution is instantly suspended.” Dalton also, as well as Cruickshank, noticed that the diminution did not begin at once under the influence of sunlight. This was the first notice of the “period of induction” of Bunsen and Roscoe. Dalton, in his analysis of the oxymuriatic gas, mixes hydrogen and chlorine in an eudiometer over mercury and water, and exposes the mixture to the sunlight, “when after remaining two or three minutes without any change, the water, and afterwards the mercury ascend the tube with increasing and afterwards diminishing velocity, till they nearly reach the top.” Seebeck discovered the effect of difference in the colour of the light used, observing that in a clear glass vessel explosion occurred with sunlight, in a dark blue vessel combination occurred quickly without explosion, whilst in a dark red glass vessel the action was very slow.