28 
of 100 ccm. water, were used, the one being centrifuged, the other not. The 
amount of organic matter found in the centrifuged sample gives the quantity of 
dissolved organic matter in 100 ccm. water. The difference between the quantity 
of organic mater found in the uncentrifuged and the centrifuged sample gives 
the quantity of suspended organic material (plankton + detritus). 
The analyses were carried out in the following manner. To 100 ccm. of 
water 20 ccm. of a ca. ; potassium permanganate solution were added (in 1 liter 
water ca. 0.33 gm. potassium permanganate is dissolved) plus !/, ccm. of a sodium 
hydrate solution (1 part of caustic soda in 2 parts water). The mixture was 
boiled for 10 minutes, then cooled to 50—60?, and 5 ccm. of dilute sulphuric 
acid were added (1 part concentrated sulphuric acid to 3 parts water). Further 
20 ccm. my oxalic acid were added. This will give an excess of oxalic acid in 
the liquid, and the amount of this excess is determined by titration with potassium 
permanganate solution. So much of the latter solution is added until a perma- 
nent, very faintly rose tone appears. We have now determined, how many cem. 
of potassium permanganate solution are required to oxidize the organic materials 
in the water + 20 ccm. 7% oxalic acid solution. We now add, whilst the liquid 
is still maintained at the same temperature of 50—609, a further 20 ccm. mn 
oxalic acid solution and determine by titration, how many ccm. of potassium 
permanganate solution are required to oxidize 20 ccm. — oxalie acid solution 
alone. The difference between the quantities of potassium permanganate solution 
used gives how many ccm. of this solution are required to oxidize the organic 
matter in the analysed sample, and at the same time we obtain the strength of 
the potassium permanganate solution accurately determined in relation to the 
mm oxalie acid solution. 1 ccm. 7 potassium permanganate solution means 0.08 
mgr. oxygen. 
Ån example will illustrate this. For the first titration (oxidation of 20 ccm. 
oxalic acid + the organic materials in 100 ccm. water) 26 ccm. of potassium 
permanganate solution were used. For the second titration (oxidation of 20 ccm. 
of the oxalic acid solution) 19 ccm. of the potassium permanganate solution were 
used. The difference between the two titrations, 7 ccm., thus gives the number 
of ccm. of potassium permanganate solution, which is used to oxidize the organic 
matter in 100 ccm. At the same time we know (through the second titration) 
that the potassium permanganate solution is of such a strength, that 9.5 ccm. of 
potassium permanganate solution are used for 10 ccm. 7, oxalie acid solution. 
Thus 7 ccm. corresponds to ieres == ccm 0 oxalic acid solution; in other 
words, to oxidize the organic material in 100 ccm. water we required in the case 
chosen 7.4 ccm. mm potassium permanganate solution. 
3. Quantitative determinations of dissolved and suspended organic matter. 
I may now briefly discuss the results obtained by meaus of the above methods; 
beginning with the determinations made by the potassium permanganate method 
(cf. the accompanying tables). 
The following remarks may he added to these tables. The number of 
analyses is, as will be séen, fairly small and the water-samples chosen somewhat 
accidental. In this direction the investigations have not been carried out suffi- 
