CHEMICAL COMPOSITION OF RAIN. I /I 



subject of Meteorological Chemistry at the International Con- 

 gress of Applied Chemistry which was held in Washington, 

 U.S.A., during 1912, and in this connection an attempt was made, 

 a few years earlier, to organise a systematic examination of rain 

 in various parts of the globe. There had been numerous previous 

 analyses of rain water, but many of these results were of little 

 practical value, because they had been made without any refer- 

 ence to the magnitude of the rainfall. Obviously, if the az'crage 

 composition of the rain during any particular month (or year) 

 has to be determined, either the ■:^'liolc of the rain falling on some 

 definite area right through that month (or year) has to be 

 analysed, or a iixcd proportion of that whole. Hence, in addition 

 to noting the amount of rain that falls on such an area, it is most 

 essential to include in each monthly sample the whole of each 

 day's rain. 



In connection with the scheme of world-wide examination 

 an invitation from Dr. Miller to co-operate therein reached me a 

 few weeks prior to the inauguration of the Union of South 

 Africa, and, although greatly hampered by the unsettled condi- 

 tion of afifairs just then, I undertook to aid in the investigation as 

 far as circumstances would permit. Those circumstances, as 

 subsequent events proved, could scarcely have been less pro- 

 pitious towards the organisation of a connected series of in- 

 vestigations. 



As already stated, one of the ultimate objects of studying 

 the chemical composition of rain, with reference to the propor- 

 tions of ammonia, nitrates, chlorides and sulphates present 

 therein, in different parts of the world, was that of comparing 

 the rain of temperate with that of tropical countries. A sub- 

 sidiary idea was to ascertain what differences, if any, were due 

 to land and sea winds. The only series of analyses of rain pre- 

 viously made in Africa was that performed by Mr. Ingle. Chemist 

 to the Transvaal Department of Agriculture, and published in 

 the Annual Report of that Department for the year 1903- 1904. 

 In these the relations of ammonia to nitric nitrogen were excep- 

 tionally high, and so, probably, for some unexplained reason, not 

 properly representative, as results subsequently detained by Mr. 

 Watt, Mr. Ingle's successor, were much lower. Mr. Watt shortly 

 afterwards left the country, and so the investigation was dropped, 

 and had not been restmied in 1910, when the general investiga- 

 tion above referred to was initiated. 



At the outset I sought and obtained the advice and practical 

 help of Mr. R. T. A. Innes, Director of the Transvaal Observa- 

 tory (now Union Astronomer), and of Mr. C. Stewart, Secretary 

 of the Cape Meteorological Commission (now Chief Meteorolo- 

 gist of the Union) ; but there, too, difficulties confronted one, for 

 meteorological work throughout the newly-formed Union was 

 linewise in a state of fluidity. 



My first idea was to collect and examine the rain only at 

 Cape Town and Grahamstown, as typical of the two sections of 



