TOWN SMOKE AND PLANT GROWTH. 



465 



cleansing of the surface with a dry cloth was found to nearly double 

 their assimilatory power, although this still remained far below that of 

 the leaves grown in the purer atmosphere of Station 9. 



Having investigated in this way some of the effects of the solid 

 impurities of smoke upon vegetation, attention was also directed to the 

 soluble impurities, which may be brought down by rain or in particles 

 of soot upon the leaves of plants, but which will mostly find their way 

 to the soil. Of these the influence of free acid was selected for special 

 investigation. 



Influence of Acid" Waters upon Growth of Grass. 



For the pm^poses of the experiment a number of boxes, each one foot 

 square, were filled with well-mixed soil from the same field and sown 

 with tim^othy grass. The boxes were placed under glass to shield them 

 from rain, and were watered periodically at rates corresponding to an 

 annual rainfall of 25 inches, some with rain-water collected in Leeds 

 (acidity usually 1-2 parts per 100,000), others with rain-water collected 

 on the farm (situated in a rather polluted area), a third series with rain- 

 water collected on the farm but with its free aeidity neutralized before 

 applying to the boxes, whilst six other series of boxes were watered 

 with specially prepared waters containing respectively 1, 2, 4, 8, 16, 

 and 32 parts of sulphuric acid per 100,000. 



In the case of the Leeds rain, and of those waters containing the 

 higher degrees of acidity, germinatioipL was distinctly checked, and the 

 young shoots quickly acquired a yellowish tinge. The grass that 

 received the strongest dose of acid (32 parts per 100,000) was killed off 

 in little more than six months, and not a trace of vegetation of any kind 

 was visible in the following spring. The watering with water contain- 

 ing 16 parts of acid per 100,000 proved fatal in little over a year, whilst 

 the effects of the Leeds rain and of all waters containing more than 

 1 part of acid per 100,000 were very marked by the end of the third 

 season. The weight and character of the grass grown in the three 

 seasons is indicated in the 'following Table : — 



Table V. 



Description of Water Used 



Total Dry Matter 



Nitrogen in Dry 

 Matter 



Crude fibre in Dry 

 Matter 







1908 



1909 



1910 



1908 



1909 



1910 



1908 



1909 



1910 



Garforth rain, 





grams 



grams 



grams 



% 



96 



0/0 



% 



0/0 



% 



neutralized . 



28-0 



24-9 



14-7 



2-47 



2-22 



1-68 



24-3 



21-9 



23-7 





ordinary 



24-8 



18-5 



110 



201 



1-75 



1-54 



25-9 



25-3 



26-0 



Leeds rain . 



23-8 



17-5 



6-6 



1-96 



1-42 



1-23 



26-4 



26-3 



27-2 



i 1 part H2SO, 



per 100,000 . 



30-5 



18-2 



12-0 



1-89 



1-61 



1-40 



25-5 



27-3 



26-2 



2 parts „ 



28-7 



17-8 



8-0 



1-84 



1-06 



109 



26-3 



28-8 



28-7 







28-8 



10-0 



3-9 



1-74 



0-95 



0-86 



27-4 



28-9 



28-9 



!i6 ;; ;; 





24-8 



8-2 



3-7 



1-77 



0-89 



0-82 



28-2 



33-4 



30-3 







23-8 



1-8 



nil 



1-62 



0-87 





30-8 



36-2 





i " " 





14-1 



nil 



nil 



0-93 







31-6 







VOL. XXXVIII. 



H H 



