CULTURE OF PLANKTON DIATOM THALASSIOSIRA GRAVIDA CLEVE. 423 



The following details of the preparation of the molecular solutions 

 may be of assistance to future workers : — 



Msol, NaCl. Kahlbaum's " Sodium chloride for Analysis." 58-5 

 grams dissolved in double-distilled water, and brought 

 to 1000 c.c. at 15°C. 



Msol. KCl. Kahlbaum's " Potassium chloride." 74-5 grams dis- 



solved in double - distilled water and brought to 

 1000 c.c. at 15°C. 



3Isol. CaClg. Kahlbaum's " Calcium chloride cryst. for Analysis." 

 About 300 grams were dissolved in about 1 litre 

 of double distilled water. On titration with silver 

 nitrate solution 2 c.c. of the above CaCla solution 

 required 30-3 c.c. of AgNOg. 2 c.c. of Msol. KCi 

 required 8-34 c.c. AgNOg, so that 2 c.c. of Msol. KgC 2 

 would require 16-68 c.c. AgXOg. The CaClg solution 

 is therefore too strong in the proportion j^g= 1-8166. 

 In order to get the Msol. CaClg 1000 c.c. of the strong 

 solution prepared must be diluted to 1816-6 c.c. This 

 was done and the final solution again titrated against 

 the Msol. KCl. 



Msol. MgCIg. Kahlbaum's " Magnesium Chloride for Analysis." As in 

 the case of CaClg a strong solution was first prepared, 

 titrated with AgNOg and diluted with double-distilled 

 water to the required extent, Msol. KCi being used 

 as standard. 



Msol. MgS04. Kahlbaum's " Magnesium Sulphate for Analysis." 

 Crystalhzed magnesium sulphate has the formula 

 MgS04 7H2O, the molecular weight of which is 

 246-4. To make the molecular solution 246 4 grams 

 of the salt were dissolved in double-distilled water 

 and brought to 1000 c.c. at 15'C. 



Msol. XaHCOg. Kahlbaum's " Sodium Bicarbonate for Analysis." 84 

 grams dissolved in double-distilled water and brought 

 to 1000 c.c. 



In order to prevent the growth of moulds in the stock solutions these 

 were all brought to the boil and kept in sterihzed glass-stoppered bottles, 

 the stoppers being tied down with a cap of parchment paper which was 

 taken directly out of boiUng water. When any of the solution was used. 



