THE LOGANBURN SMOKE CASE. I 7 



bings — to mention only some of the more important factors. 

 The solution of the problem presented many difficulties, and 

 a very thorough and complete chemical investigation, extending 

 over several years, had to be undertaken. This chemical 

 investigation was carried out for the pursuer by Professor 

 Dewar, of Cambridge, and the late Professor Dittmar, of 

 Glasgow. To give some idea of the difficulties encountered, 

 it may be noted that the bings were not burning continuously, 

 so that there were enormous variations in the amounts of 

 smoke and fumes present in the air, making the selection of 

 suitable methods of chemical analysis exceedingly difficult; 

 that the different plantations were variously situated with regard 

 to the bings, making it necessary to carry out many perfectly 

 distinct series of observations. Finally, the difficulties of getting 

 a reliable method of analysing the air, capable of being worked 

 for months at a time, under what we may term "field con- 

 ditions," proved so great that direct analysis of the air was 

 given up. Instead of this, analysis of the rain-water collected 

 at different points in the plantations was adopted, with very 

 satisfactory results. The sulphurous vapours already referred 

 to dissolve in water, so that rain falling through the smoke 

 would take up a certain amount of the vapours — the percentage 

 of the vapours actually taken up depending on whether the rain 

 was heavy or light, whether there was much wind, and various 

 other causes. It is further evident that the sulphurous fumes 

 could only be captured if rain happened to be falling; the 

 rain-water might, and generally would, contain less sulphuric 

 acid than there was present in the air; it could not possibly 

 contain more, and so there was no possibility by this method 

 of exaggerating the amount of sulphurous vapours which 

 actually reached the woods. The rain-water collected in the 

 bottles employed was analysed at the end of each month, and 

 showed, as was to be expected, considerable variation, not only 

 in the amount of sulphuric acid present, but also in the amounts 

 collected at the different stations. The average results showed 

 an amount of sulphuric acid five times as much as that 

 commonly present in the air of inland places in Scotland, and 

 at some of the collecting stations the amount was many times 

 greater than this. Pure air contains no sulphuric acid at all, 

 but there is always a certain amount present where coal fires 

 are burned. 



VOL. XXII. PART I. B 



