The nitrate content of sea water

With 1 Figure in the Text.THE estimation of chemically bound nitrogen compounds in sea-water has, in the past, been a matter of considerable difficulty because of the small quantities of these substances involved.They are present in the form of free and saline ammonia, nitrites, nitrates and organically bound nitrogen.The ammonia has usually been estimated by distilling it off in alkaline solution and determining colorimetrically in the slightly acid distillate by means of Nessler's reagent.The nitrites and nitrates are first of all reduced to ammonia, which is then distilled off in alkaline solution and estimated as before.The organic nitrogen compounds are first converted to ammonia by the Kjeldahl method or a modification thereof which is estimated as before.Even when comparatively large quantities of sea-water are used, the error of these methods is considerable, as is admitted by the investigators themselves.In making a series of analyses of the nitrogen compounds in sea-water by these methods I found the chief difficulty to be in the use of the Nessler reagent.In such dilute solutions of ammonia the addition of even a slight excess of Nessler reagent produced a greenish tint which interfered with the matching of the colours.In addition the process is long and requires considerable quantities of sea-water.Recently Gad-Andresen (5) has described a method for the estimation of nitrogen compounds in sea-water which, as it is volumetrio, is a great advance on previous methods.The process consists of a preliminary cop.version of nitrites, nitrates, and organic nitrogen to ammonia and subsequent decomposition of this with alkaline hypobromite in Barcroft's differential manometer.The nitrogen gas liberated is measured by the difference of pressure, and, the constants of the apparatus being known, the ammonia, and thus the other compounds, can be estimated.The free and saline ammonia are estimated by distilling off in alkaline solution after concentration of the sample, and measuring the liberated nitrogen as before.A series of test analyses were made, using this method, and it was