Page:Various Forces of Matter.djvu/83

Rh kind of condition as regards heat that I did the water and the ether [putting a few grains of iodine into a hot glass globe, which immediately became filled with the violet vapour], and you see the same kind of change produced. Moreover, it gives us the opportunity of observing how beautiful is the violet-coloured vapour from this black substance, or rather the mixture of the vapour with air (for I would not wish you to understand that this globe is entirely filled with the vapour of iodine).

If I had taken mercury and converted it into vapour (as I could easily do), I should have a perfectly colourless vapour, for you must understand this about vapours, that bodies in what we call the vaporous, or the gaseous state, are always perfectly transparent, never cloudy or smoky; they are, however, often coloured, and we can frequently have coloured vapours or gases produced by colourless particles themselves mixing together, as in this case [the Lecturer here inverted a glass cylinder full of binoxide of nitrogen over a cylinder of oxygen, when the dark red vapour of hyponitrous acid was produced]. Here also you see a very excellent illustration of the effect of a power of nature