184 TRANHACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



classes of material — dust, fume, and gases. The deleterious 

 substances present were sulphur dioxide, sulphur trioxide, 

 compounds of lead and arsenic, and flue dust. 



As the result of methods for purifying the smoke before 

 allowing it to escape into the air, and also of alterations in the 

 metallurgical methods employed in the works, the escape of 

 visible smoke or fumes into the air was ultimately entirely 

 prevented. These improvements had been carried out partly 

 by the Company themselves and partly at the request of the 

 Commission. The inquiry was therefore narrowed down to 

 determining the amount of sulphur dioxide in the air in the 

 neighbourhood of the works under varying atmospheric con- 

 ditions, and to discovering how much of this gas must be 

 present in the air in order to cause definite damage to vegeta- 

 tion. 



First of all, the factors causing the distribution of the sulphur 

 dioxide in the atmosphere had to be studied. This meant a 

 careful investigation of the directions of the wind throughout 

 the year, and measurements of the time the wind was blowing 

 in each particular direction. 



Next, methods had to be invented for the rapid determination 

 of the sulphur dioxide in the air ; certain fixed stations for this 

 purpose were set up and a large number of analyses made. It 

 was sometimes essential to make simultaneous determinations 

 at two places at considerable distances apart to test the effect 

 of the wind on the distribution of the sulphur dioxide. For this 

 purpose a moveable laboratory was fitted up on a motor car, 

 much after the plan of the motor laboratories and operating cars 

 used in the war. This enabled determinations of the amount of 

 sulphur dioxide in the air to be made at many places, in 

 addition to the analyses made at the fixed stations. During 

 the six months of active field work no less than 4862 analyses 

 were made, 3629 at the fixed stations, and 1233 ^^ a great many 

 points by means of the motor laboratory. In this way a large 

 amount of valuable data was obtained regarding not only the 

 amount of contamination in the zone affected by the smoke, but 

 also as to the amount of sulphur dioxide usually present in the 

 air where there is no special industrial pollution. 



During the time the above work was in progress, other 

 members of the staff carried out a very complete series of 

 observations on the effects of different amounts of sulphur 



