Observations on the Ammonia Content of Sea Water

Abstract

It has recently been suggested by H. Wattenberg 1 that it is advisable to pay more attention to the ammonia dissolved in the sea water as a source of nitrogen for the vegetable plankton, and to determine it as a nutrient of the same value as phosphate and nitrate. That this has been relatively seldom done has been due chiefly to the lack of a suitable method for the estimation of NH3 in the very diluted condition in which it is present in sea water. A suitable method for the estimation of NH3 in sea water which avoids distillation of the sample and also avoids, by the use of suitable reagents, the precipitation of the alkaline earths by the alkaline Nessler's reagent, has been described by \Vattenberg 1 and is here given in essential detail. A ioo cubic centimeter sample of sea water is treated with 5 cc. of 30 per cent solution of rochelle salt, and this mixture is then added slowly to a io cc. solution of 20 per cent sodium hydroxide. Then 2 CC. of Nessler's reagent (prepared according to Treadwell) are added, and, after i5 to 45 minutes, the color developed is compared with the color of a standard solution of NH3 treated in the same way. Standard solutions of NH3 are prepared in the following way: sea water of the same salinity as the water to be analyzed is made slightly alkaline and then diluted with distilled water to i.5 times its volume. The whole is then boiled down to the original volume, and the resulting turbidity is cleared up by the addition of as little HC1 (NH3 free) as possible. The water is then stored by stopping the mouth of the bottle with a U-tube filled with pumice stone and sulphuric acid. Standard NH3 solutions are made up to suitable concentration for comparison with the samples under examination. Because of the very small quantities of ammonia present in sea water, the reagents must be carefully freed of ammonia and then stored in bottles stoppered as above described. The sodium hydroxide solution was diluted with 50 per cent of its volume of distilled water and boiled down to the original quantity, and the rochelle salt solution, after being made slightly alkaline with NaOH, was treated in the same manner. Using the purest chemicals obtainable and treating the reagents in this manner, it was never