THE LAW OF THE MINIMUM IN THE SEA 199 



acidified with acetic acid, and the nitrous acid was distilled off 

 and estimated by the metaphenylene-diamine sulphuric acid 

 reaction. Then magnesium oxide was added to the residue, 

 and the ammonia set free was distilled off and estimated by 

 Nessler's reagent. To the residue in the distilling flask mag- 

 nesium ribbon was added to precipitate the mercury, and the 

 nitric acid was reduced by means of sodium amalgam and 

 distilled off and estimated as ammonia. 

 Raben's results were : 



One litre of sea-water from the Baltic contained in 1904 : 



Now the above results show that the average amount of 

 nitrogen compounds in Baltic and North Sea water may be 

 taken as about 0*2 mgr. in a litre, or o - 2 parts in one million. 

 It is also of importance to note that the amount is at a minimum 

 in August — that is, in the hottest month in the year. 



Nitrogen compounds are thus less abundant in the warm 

 seas of the Mediterranean area than in the much colder seas 

 of Northern Europe, and they are also less abundant in the 

 latter seas during the month when the temperature is highest. 

 Obviously there is some kind of relationship between the tem- 

 perature of sea-water and the amount of nitrogen compounds 

 it contains. 



So much for these compounds, but we have also to consider 



the phosphoric and silicic acids. The occurrence of both has 



been investigated by Schmidt, 1 who examined the water of both 



warm and cold seas. The average amount of calcium phosphate 



found in the Arctic and Norwegian Seas was 1 3'8 parts in 



one million of sea-water. For the Indian and Chinese Seas 



the amount was 3*5 parts in one million. The temperature of 



1 See Brandt, " Stoffwechsel im Meeres," Wiss. Meeresunters. Kiel. Komm. 

 Bd. 6, 1902. 



