15 Hewitt: Large Scale Sand Culture Methods 



purified nutrient solution until all adsorbed acid is removed. 



Sand purified once in this manner is suitable for the produc- 

 tion of manganese and boron deficiencies. Satisfactory results for 

 iron deficiency and promising results with molybdenum deficiency 

 have been obtained with batches of sand that have been treated 

 twice, and the batches give uniform results. 



Sand used for experiments with major nutrient elements is 

 not treated as above but leached with water or cold 2% hydro- 

 chloric acid if required for more precise work, and particularly for 

 the study of calcium deficiency. 



Water Supply:— An adequate supply of sufficiently pure 

 water is essential to the technique and presents special problems 

 for large scale work. Rain water is used for most experiments 

 involving major element studies and is sufficiently pure for such 

 work when collected from a clean glass roof and stored in well- 

 weathered, galvanized tanks heavily painted with the pure bitu- 

 men solution. Rain water so stored may be purified by use of Per- 

 mutit ion-exchange resins to obtain some thousands of gallons of a 

 relatively pure water. The arrangement in use is shown in the il- 

 lustration (Figure 1). The supply to the small glass vessels (of 

 50 gallons total capacity) is automatically controlled, so that flow 

 ceases when they are full but continues slowly after water is with- 

 drawn as rapidly as required for use. Rain water so purified com- 

 pares favourably with distilled water from carefully managed 

 heavily tinned copper stills. It contains less than 0.002 p.p.m. 

 of iron and manganese. The boron content is about 0.004 p.p.m. 

 and copper and zinc do not often exceed 0.006 p.p.m. This 

 water is satisfactory for production of severe deficiency effects of 

 iron, manganese and boron as shown in the illustrations. So far, 

 for molybdenum deficiency work, water obtained by the redis- 

 tillation from pyrex glass of water from tinned copper stills has 

 been used. The glass stills are of the continuous action pattern. 



Nutrient Reagents:— Nutrient reagents used for work with 

 the major elements are not purified further and normally a re- 

 crystallised grade is used. When trace element deficiences are 

 studied salts of analytical reagent grade are chosen and further 

 purified by various means according to the element omitted from 

 the treatment. 



Those required for iron and manganese deficiencies are pre- 



