370 E. J. ALLEN ANJJ E. W. NELSON. 



difference. Experiments also showed that the formula for 

 solution A could, without any appreciable detriment to 

 results, be further simplified to the one salt KNO.5 or NaNO^, 

 but not NHjNO.j. At first the amount of KNO.^ dissolved in 

 100 c.c. distilled water, used to make the modified solution 

 A, Avas the same as the sum of the weights of the nitrates in 

 Miquel's own formula, viz. 5 grm. But later experiments 

 showed that a considerably greater concentration of KNO3 

 than this gave more lasting cultures; the strength of solu- 

 tion and amount to be added to a litre of sea-water iu 

 order to obtain the best results being 2 c.c. 2 M KNO3. 



In the case of solution B no modification has been adopted, 

 but it has been found that small variations iu the amounts of 

 the ingredients used do not affect the results. A convenient 

 method for measuring the right amount of FeCl.5 is to warm 

 the salt until it just melts in its own water of crystallisation, 

 and to pipette out 2 c.c. with a previously warmed pipette. 

 No temperature corrections need be considered. Also 2 c.c. 

 of the ordinary pure concentrated hydrochloric acid at room- 

 temperature will suffice. 



Our own formula for preparing Miquel sea-water is now : 



Solution A.^ 



Potassium nitrate, 20*2 grm. 1 _ .^ ^r ij-fjf) 

 Distilled water, 100 ,, J 



Solution B.- 



Sodium phosphate (Xa.HP0^12H.O) 

 Calcium chloride (CaCL6H.O) . 

 Ferric chloride (melted) 

 Hydrochloric acid impure concentrated) 

 Distilled water .... 



' This strength has only lieeu used in the most recent experiments ; 

 and solution A in this paper, unless otherwise stated, means the 5 96 

 solution of KXO3. 



- For preparing this solution see p. 364. 



