52 WATER-CULTUEE. [CH. Ill 



attention to the following precautions. The cylinders 

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

 in an experiment and should therefore be of at least 

 700 c.c. capacity. 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. 



The culture solution should be boiled rapidly for at 

 least half-an-hour, the water which evaporates off being 

 replaced from time to time with pure distilled water, and 

 transferred to the cylinder as soon as it has cooled. 



Two holes should be cut in the cork, one for the plant 



^ Sachs recommends the following : 



Potassium nitrate 1 "0 gram 

 Sodium chloride 0-5 



Calcium sulphate 0'5 

 Magnesium sulphate 0*5 

 Calcic phosphate 0-5 

 Water 1000 c.c. 



Pfeffer, Physiologie, 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 formnlse. 



