ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMy. 449 



of cultures of plankton diatoms ; so an attempt was made to analyse 

 the various samples of water both before and after treatment as 

 culture media. The method adopted was a modification of that used 

 by Tornoe and Dittmar. Solutions of NaOH and H.2SO4 of strength 

 N/50, ^y intention, were made up and stored in 5-litre " aspirator " 

 bottles. Two accurately graduated burettes standing side by side 

 were connected to these by tubes, so that they could be readily filled 

 by gravity. All air inlets to burettes and stock bottles were fitted 

 with tubes of soda lime. A standard solution of NaoCO^ of exactly 

 known alkalinity, approximately that of average sea-water (40'00 

 mgrm. OH 7,,), was prepared by diluting down from a N/j,, solution, 

 all operations being performed by weighing. These standards were 

 stored in stoppered bottles of the fairly insoluble dark green glass, 

 but those that had been kept for any length of time were not trusted, 

 fresh standards being prepared. On analysis these standards agreed 

 with one another to well within '1 mgrm. OH °/^^. The water used 

 for diluting the standards was distilled water from the laboratory 

 still, redistilled in all-glass apparatus with potassium bichromate and 

 sulphuric acid. 



When carrying out an analysis, equal volumes (about 100 cc.) of 

 sample and standard were measured out into Jena glass Erlenmeyer 

 flasks with a Knudsen automatic pipette. The specific gravity of each 

 was determined by weighing in a 25 cc. pyknometer. Sample and 

 standard were then titrated by running in acid from the burette and 

 back titrating with alkali, using a 1 % alcoholic solution of aurine as an 

 indicator and keeping the liquid boiling. The acid to alkali equiva- 

 lent was determined by titrating a pipetteful of double-distilled water 

 in the same manner. The mean of at least four readings was always 

 used. Let N and n be number of burette divisions of alkali equivalent 

 to standard and sample respectively, and D and d their density at the 

 time of pipetting out. Then if A is the alkalinity of the standard and 

 X the required alkalinity of sample : — 



x=a5l; 



Since all operations were carried out at the same room temperature, 

 no corrections for temperature are necessary. 



In spite of the greatest care consistent results could not be obtained 

 by this method of analysis. A sample analysed against the same 

 standard would sometimes give results varying as much as 0*5 mgrm. 

 and occasionally I'O mgrm. OH %^. The work on indicators by Salm 

 (42) and its application to this question has only recently come to our 

 notice, and it is our intention to experiment on this in future research. 



