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different gravestone, melted and analysed. The soot-fall amounted to about half-a-ton a day on the smoke-infected area of the city. Here is a photograph of the samples of melted snow.
The four bottles shown in the photograph contain specimens of the melted snow in the order in which the samples were taken. The first was very dirty, but the last was absolutely opaque.
Soot is not pure carbon; but it contains about 15 per cent. of a thick oil by virtue of which it adheres tenaciously to everything, so that much of it cannot be removed by rain. It is, in fact, a kind of varnish. In order to ascertain the effects of this sticky material in the soot, I stationed, during the winter and spring of ’93 and ’94, three glass plates, a foot square, one in a garden at Pool (9 miles from the centre of Leeds), one on the roof of the Yorkshire College (one-and-a-half miles from the centre of Leeds), and one on the roof of the Philosophical Hall (near the centre of the city). They were all removed from the immediate neighbourhood of chimneys. The deposit on these plates, after an exposure of a few weeks (loose matter having been washed away by rinsing the plates with water), was analysed and weighed. Fresh plates were then put in the places of those removed, and the process repeated from month to month.
The deposit consisted of 50 per cent. of carbon, or, roughly, three-quarters of it was soot, and the proportion was as follows:—For one part deposited at Pool, there were ten times that quantity at the Yorkshire College,
