424 E. J. ALLEX. 



the parchment cap was removed and placed in boiling water, the bottle 

 was carefully opened and the amount of solution required poured out, 

 the stopper being quickly replaced and tied down. These precautions are 

 important, as the growth of mould in the solutions may have an important 

 influence on the diatom cultures. 



It has generally been found most convenient to make up the sodium 

 chloride solution, of which, large quantities are required, as it is wanted, 

 and not to store it. 



In the last table above the relative amounts (c.cs. of M solutions) of 

 the different salts required to prepare the artificial sea-water are given. 

 There remains to consider the actual salinity of the water which we are 

 to employ, which is generally expressed as the weight in grams of the total 

 salts contained in 1000 grams of the water. The salinity of natural sea- 

 water in the western portion of the English Channel generally varies from 

 about 35-5 to 35-0 per thousand, the water being generally lower in saUnity 

 near the coast. In laboratory experiments the water in the flasks becomes 

 progressively more concentrated owing to evaporation, and a low salinity 

 has therefore been adopted for the artificial sea- water used, namely, 35-0 

 per thousand. 



The following table gives the composition of an artificial sea-water 

 having a salinity of 35 per thousand, and with the salts in the relative 

 proportions obtained above from Dittmar's analysis. The composition 

 is stated (1) as the number of cubic centimetres of gram molecular solution 

 contained in 1000 c.c. of the artificial water, and (2) as the number of 

 grams of each salt contained in 1000 c.c. 



To make up a litre of artificial sea-water the simplest procedure is 

 therefore to weigh out 28-13 grams of sodium chloride, dissolve it in about 

 half a litre of double-distilled water placed in a 1 litre flask, add the re- 



* 2-6 c.c. was the amount generally used, as the increased alkalinity is favourahle to 

 diatom »rowtli. See below. 



