CH. Ill] WATER- CULTURE. 59 



used should not contain less than 500 c.c. of the solution 1 

 in an experiment and should therefore be of at least 

 700 c.c. capacity 2 . Every cylinder used should be carefully 

 cleaned just before setting up the experiment. For this 

 purpose the cylinders are thoroughly washed, and then 

 rinsed out with strong commercial nitric acid which is 

 removed by distilled water. They are then again rinsed 

 out with a strong aqueous solution of mercuric chloride, 

 and lastly with distilled water, which has been boiled for 

 some time immediately before use, till portions of the 

 wash-water give no trace of turbidity with a solution of 

 silver nitrate. 



1 Sachs recommends the following : 



Potassium nitrate I'O gram 

 Sodium chloride 0-5 

 Calcium sulphate 0'5 

 Magnesium sulphate 0-5 

 Calcium phosphate 0-5 

 Water 1000 c.c. 



Pfeffer, Physiologic, Vol. i. p. 253, quotes from Knop the following : 

 Calcium nitrate 4 parts by weight 



Potassium nitrate 1 ,, 



Magnesium sulphate (crystals) 1 ,, 

 Potassium phosphate 1 ,, 



One part of the mixture of salts is dissolved in 50 parts of water : for use 

 it is diluted to 2 or 3 per mille. A drop or two of iron chloride must be 

 added to it as in the case of all normal nutrient solutions. Schimper 

 (Flora, 1890, p. 220) gives a variety of useful formulas. 



2 Wortmann (Dot. Zeitung, 1892, p. 643) recommends the use of very 

 large vessels for water-culture. He states that in this way the respiration 

 of the roots is better provided for, and that culture fluid remains at a 

 lower and healthier temperature. According to Wortmann the plants 

 flourish far better than in the ordinary small vessels, and moreover 

 require practically no further attention when the culture has once been 

 set up. He uses glass cylinders containing 26 liters, which are supplied 

 at a cost of 5 marks each by Messrs Ehrhardt and Metzger of Darmstadt. 



