208 RILEY 



combustion, although he did not compare the two methods with duplicate 

 samples. 



Williams 14 described a method for destruction of the organic matter by 

 strong UV radiation and subsequent analysis of C0 2 evolution. Comparison with 

 persulfate oxidations showed that the latter were about 90% of the values 

 obtained by UV oxidation. 



Currently, several methods are under development for dry combustion, 

 involving evaporation or freeze drying of the sample or direct injection of a small 

 sample of water into the combustion chamber. Sharp 1 5 has developed the latter 

 to a point where it yields results of usable precision, although it is not an easy 

 method to use. The main difficulty is that the water sample injected into the 

 combustion chamber must be small, and C0 2 evolution is near the limit of 

 sensitivity of present detectors. Nevertheless, his observations provide the best 

 data available on intercomparison of methods. 



In a fairly large series of analyses of North Atlantic water, the general range 

 was 0.76 to 1.74 mg C/liter, with a mean of 1.2. The mean for shallow samples 

 (0 to 100 m) was 1.36; in deeper water (100 to 5000 m) the mean was 1.11. In 

 48 shallow-water samples, Sharp's method gave values averaging 0.186 mg C/liter 

 higher than measurements obtained by wet oxidation of aliquot samples. In 54 

 deep-water samples, the difference was 0.262 mg. This is about twice as large as 

 the difference between UV destruction and wet oxidation, 14 suggesting that dry 

 combustion is more effective than either of the other methods. 



Sharp fractionated a series of samples by passing them through filters of 

 various pore sizes. The largest pore size was 0.8 n, so that the organic matter 

 retained was the fraction ordinarily regarded as particulate organic matter. 

 Additional fractionation was obtained with a fine filter of 0.025 M and a Diaflo 

 membrane with an exclusion factor of 50,000 molecular weight, roughly 

 equivalent to 0.003 ju. Results are shown in Table 1. 



Comparison of dry combustion and persulfate oxidation showed no 

 significant differences in the fraction that passed through the Diaflo membrane. 

 The main difference was in the intermediate fraction. The meaning and 

 significance of these results are by no means clear. 



Indeed, very little is known as yet about the character and composition of 

 filter-passing materials. At one time it was supposed that they were largely 

 humic matter, such as one finds in freshwater as well as terrestrial situations. 

 However, wet oxidation methods 1 1 show that ratios of carbon to nitrogen were 

 remarkably low, of the order of 4 : 1 or less on the average, as contrasted with 

 ratios of 10 : 1 or more which are commonly found in humates. In the case of 

 the particulate matter, 85% of the organic nitrogen is in the amino form, 8 but 

 this may not be equally so in the dissolved fraction. Certainly free amino acids 

 are a small fraction of the total. 16 Urea is present, 17 and there are suggestions 

 that urea condensates might be important constituents. All this awaits further 

 study. Most of the attention has been centered on analyses of particular 

 substances that are potentially significant biologically. The list is fairly long, 1 8 



