THE AIR OF TOWNS. 361 



feet, which, we took as the smoke-infected area, the amount of carbonic 

 acid, would be about 1 per cent higher in twenty-four hours, or would 

 have to be renewed fifty times in twelve hours to keep down the aver- 

 age amount of carbonic acid to 0.04: per cent. 



Let us attack the problem iu another way. In Professor Roberts- 

 Austen's report on the London smoke-abatement exhibition a large 

 number of analyses are given, from which it is easy to calculate the 

 weight of smoke from coal burnt in house fires. These analyses refer 

 to different kinds of sinoke-i>reventing domestic fire grates burning 

 different kinds of coal. According to these results about 5 per cent of 

 the coal burnt gets into the air. Mr. Russell, of the Yorkshire Col- 

 lege, and myself experimented in the same direction and arrived inde- 

 pendently at the same conclusion, without having referred to the 

 results of Roberts- Austen's analyses. 



If we take 100,000 tons as the house consumption of coal in the year 

 for Leeds, this is equivalent to about 11 tons in twenty-four hours 

 throughout the year. If we allow an equal amount for factory chimneys, 

 this brings it to 22 tons in twenty-four hours. Or if we follow Scheurer- 

 Kestner and take one-half to three-fourths per cent as the amount of 

 coal given off as smoke from boiler furnaces, then if Leeds consumes 

 1,500,000 tons of coal a year, or 4,000 tons a day, one-half per cent upon 

 this is equivalent to 20 tons a day. So you see that whichever way 

 we work our calculation we can not get below 20 tons of smoke a day, 

 and I consider that this figure represents a minimum quantity rather 

 than the true average. 



And now as to the amount that falls. The winter before last snow 

 fell on January 7. A sample covering 1 square yard was carefully 

 removed from a gravestone in the parish churchyard a short time after 

 the fall ceased. The snow was melted and analyzed. Fresh samples 

 were taken and analyzed on the following three days. They contained 

 a variety of things in solution — ammonium sulphate, sulphate of lime, 

 and free sulphuric acid, all mainly derived from coal. We need not 

 trouble ourselves about these at present, although we can not mask the 

 injury which this corrosive acid produces upon vegetation and the stone 

 and brick work of our buildings. 



It is the solid matter which now concerns us. 



Here are some of the samples (fig. 16) : A was collected on the first 

 day, B on the second, C on the third, and D on the fourth. The accu- 

 mulation of soot is evident from the depth of color, 



The weight of solid matter carried down, as determined from the first 

 sample, was equivalent to 16 hundredweight on the square mile. The 

 additional weight of soot which accumulated each day was equivalent 

 to 4 hundredweight on the square mile ; or, if we take a smaller quantity 

 as an average over the 4 square miles of the city, we arrive at the daily 

 smoke fall of about one-half ton. 



It is impossible to say what proportion of the soot in the air, during 

 the snowfall, the 16 hundredweight represents, but it all points in one 



