152 PROCEEDINGS OP SECTION B. 



about 1 lb. per acre and the nitrogen as organic matter a similar quantity. 

 The total combined nitrogen in the annual rainfall at Rothamsted would 

 thus be about 4.5 lbs. per acre. 



(4) Six years' determinations of chlorine in monthly mixtures of rain 

 give an average of 1.99 per million of water, or 14.92 lbs. per acre equal to 

 24.59 lbs. of pure common salt. Tm o thirds of the chlorides fall in the 

 six winter months, October to March. The minimum quantity falls in 

 July ; the maximum in October and November. 



(5) Determinations of sulphuric acid in the rain of two years have given 

 a mean of 2 41 per million (reckoned as anhydride), or 18.5 lbs. per acre per 

 annum. The sulphuric acid occurs in nearly equal quantity in summer 

 and winter." 



Many analyses of interest are contained in the work of the 

 late Dr. Angus Smith " Air and Rain," but the results given 

 cannot be used for comparison with our own, in consequence of 

 their not representing the rainfall of definite periods. 



At the Royal Agricultural College, Cirencester, determinations 

 of chlorine have been made for sixteen years in the mixed half- 

 yearly rainfalls. The results are reported by Professor E. Kinch 

 in a paper read before the Chemical Society of London, and 

 published in the Journal of the Society for January, 1887. The 

 mean results of twelve years are stated as follows — 



Rainfall in Chlorine 5,'?,"'''''^" m*° 

 inches. permillion. sodic chloride, 

 ^ lbs. per acre. 



Mean of 12 summer periods to 1885 17.04 3.14 19.91 



Mean of 12 winter periods to 1885-86 17-65 3.58 23.56 



Yearly average for 12 years ... 34.69 3.36 43.47 



Comparing the mean results obtained at Lincoln with those 

 above we notice that the total nitrogen received in rain is less 

 than one half of that received at Rothamsted. The nitric acid is 

 approximately the same but the nitrogen existing as ammonia is 

 especially low, only about one fifth the quantity, while the organic 

 nitrogen amounts to one half. It should be mentioned here, 

 however, that the method adopted by Frankland in the estimation 

 of organic nitrogen was probably the combustion process, and as 

 it is an open question whether the whole of the nitrogen contained 

 in the organic matter of rain-water is evolved by the " ammonia 

 process " our re.sults might be, in this case, below the truth. 



The amount of sulphuric anhydride is also less, but the chlorine 

 is considerably above that of Rothamsted, and also of Cirencester. 

 If we take into consideration, however, the excess of sulphuric 

 anhydride above that corresponding to the chlorine, according to 

 the ratio in sea-water, we find the quantity at Lincoln to be only 

 about one-ninth that of Rothamsted. 



The deficiency of nitrogen and sulphuric anhydride in the 

 Lincoln rain-water is pi'obably due to the less populated nature 

 of the country, while the excess of chlorine is due to the position 

 of the district with regard to the sea. 



Nitrous acid has not been detected in any of the samples of 

 rain-water examined. 



