191 1.] Summary of Agricultural Experiments. 781 



Garforth results is the relatively high amounts of each of the impuri- 

 ties. The results bear unmistakable evidence of the fact that the 

 impurities have their origin largely in the combustion of coal, this 

 being the most obvious source of the acid which occurs in such appre- 

 ciable quantities in the rain. Very large areas of such smoke-infested 

 agricultural land are to be found in the north. 



The second part of the investigation was concerned with the effect 

 on plant growth and the soil of the state of the atmosphere thus 

 ascertained. The intensity of the daylight throughout the day was 

 measured at six stations in Leeds, and was found to vary regularly 

 in inverse ratio to the amount of suspended matter in the air, the 

 effect being so considerable that at a station in the industrial part of 

 the city the average intensity was 40 per cent, less than at a suburban 

 station. These suspended impurities also check vegetation by settling 

 on the leaves, and thus shutting out further light, and clogging the 

 stomatal openings. The assimilatory powers for carbon dioxide of 

 laurel leaves gathered in different parts of the city were measured, with 

 the result that if the rate of assimilation be represented by 100 in 

 leaves from the suburban station with the purest air, at the other 

 stations it varied down to only 11^. As regards the dissolved impuri- 

 ties brought down in rain, detrimental action is probably confined to 

 the free acid and the lower sulphur compounds (SO a , H 2 S, &c), as 

 there is no reason to believe that the nitrogenous impurities and per- 

 haps the chlorides and sulphates, will be other than beneficial. An 

 experiment with timothy grass showed the effect of the application 

 of acidulated water to the soil. Boxes of the grass, sown in 1908, 

 were watered at the rate of the average Garforth rainfall with water 

 containing from one to thirty-two parts per 100,000 of sulphuric acid, 

 and with Garforth rain water, neutralised Garforth rain, and Leeds 

 rain. The weights and composition of the material grown each year 

 were ascertained. In every case the yield steadily decreased with 

 increased acidity of the water, and by 19 10 the grass watered with the 

 water containing sixteen and thirty-two parts of acid was dead. 

 Analysis of the grass showed that the nitrogen content was reduced, 

 and the content of crude fibre increased by the acid. This inferiority 

 in nutritive value was quite evident even in the case of the grass 

 watered with water containing only one part of acid per 100,000. a 

 proportion that is about the average in Garforth rain, and it becomes 

 of importance to ascertain to what extent such deterioration can be 

 traced on a large scale in the meadows of smoke-infested regions. 

 Chemical analysis of the soil, which had been used in these grass 

 experiments for three years, showed a distinct correlation between 

 the amount of acid applied and the constituents of the soil except in 

 respect to total nitrogen. Increasing acidity led, on the one hand, to 

 diminished content of nitrates and carbonates, and to diminished 

 absorptive power for oxygen, but on the other hand to increased 

 content of the easily soluble mineral ingredients and ammonia. The 

 bacterial flora of the soil was strikingly influenced by the acid, the 

 total number of bacteria diminishing rapidly with increasing acidity, 

 this being reflected also in diminished activity as regards ammonia 

 production, nitrogen fixation, and, above all, nitrification. The greater 

 check to the nitrifying than to the ammonia-producing organisms 



