27 
With regard to the nature of the dissolved, organic matter, Pitter 
refers to some analyses of Natterer, who isolated from 200 litres of seawater a 
substance whose melting point indicated that it was palmitic or stearic acid. 
Further, on vapourizing the remaining substance in a vacuum a product was 
distilled which was diagnosed as glycerine. It seems possible also that humus 
compounds must be present, as they play a great part in many freshwaters. 
As result of the above, we may conclude that 3 groups of organic sub- 
stances occur in saltwater, namely, plankton organisms, detritus and dis- 
solved organic material. 
2. Methods. The apparatus and methods used in the study of the organic 
materials occurring in seawater are the following: 
1. Centrifugal apparatus (Gårtner's); in this there is room for 7 tubes 
of the ordinary kind, conical at the one end. Each tuhe could contain ca. 15 ccm. 
water, so that 105 ccm. of water could be centrifuged at one time. The apparatus 
was worked by means of a leather belt and was kept in movement for 10 minutes 
(cf. Lohmann). After this a fine siphon was used to draw off all the water with 
exception of !/,—1 ccm.; the precipitates in the tubes were stirred up in the water 
remaining and the contents of all the tubes thrown together into one tube, which 
was centrifuged again. In this way a single tube came to contain the plankton 
and detritus of ca. 100 ccm. water. . 
Lohmann has made a thorough critical investigation of the usefulness of 
the method, and reference may be made to his work. 
2. Detritus-collectors. All the organic and inorganic material floating 
in the sea, whether detritus or living organisms, will in the end, if not dissolved 
beforehand, sink to the bottom, the organisms however only after death. Thus 
there is a constant process going on of material falling to the bottom of the sea. 
To take up this material and thence to determine the quantity which in any unit 
of time falls to the bottom, Petersen has worked out an apparatus which we 
call a »detritus-collector«. It consists of an iron cylinder, closed below with a 
wooden bottom. Its diameter is 30 cm., its height the same. To prevent the iron 
rusting, which would cause the precipitated plankton to be mixed with rust, the 
iron cylinder is covered on the surface with a layer of cement. The quantity 
precipitated in such a detritus-collector is an expression for the quantity of plank- 
ton + detritus which in the time chosen sinks down through a plane in the 
water with an extent of ”/,, m? and lying "30 cm. above the bottom. As the 
water in such a collector, owing to its small diameter, is always at rest, the 
material which is once deposited will remain where it is. 
3. Oxidation by means of potassium permanganate. To deter- 
mine the quantity of both the dissolved and deposited organic matter (detritus- 
plankton organisms) I have used oxidation with potassium permanganate in the 
form indicated by Schulze. In the case of seawater the determinations must 
always be made on alkaline solutions, as the chlorine set free by the sulphuric 
acid in acid solutions has a reducing action on the potassium permanganate. 
Water-samples of 500 ccm. taken with the water-bottle were used for the 
analyses. The water-samples were preserved by the addition of 10 ccm. sublimate 
solution and kept in bottles with glass stoppers. For the analysis 2 samples, each 
