484 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1-9 3 8 



phuric acid may be purchased and diluted to 3 percent strength, but 

 the concentrated acid is dangerous to handle by inexperienced persons.) 

 This 3 percent acid may be further diluted witlTwater if a preliminary 

 test indicates that only small additions of acid are required to bring 

 about a desirable reaction. 



Test the degree of acidity of a measured sample of the water or 

 nutrient solution (a quart, for example) by noting the color of the 

 added indicator or test paper immersed in the solution. When 

 bromthymol blue indicator is used, a yellow color indicates an acid 

 reaction (with no further adjustment necessary), green a neutral 

 reaction, blue an alkaline reaction. 



If the original color is green or blue, add the dilute sulphuric acid 

 (3 percent or less in strength) slowly with stirring until the color just 

 changes to yellow (indicating approximately pH 6). Do not add more 

 beyond this point, since the yellow color will also persist when excessive 

 amounts of acid are added. Record the amount of acid required. 



Finally, add a proportionate amount of the acid to the water or 

 nutrient solution in the culture tank or vessel, having first determined 

 how much it holds. 



MODIFICATION OF NUTRIENT SOLUTION BASED ON ANALYSIS OF WATER 



A chemical analysis of the water to be employed in making the 

 nutrient solution is useful. Some waters may contain so much cal- 

 cium, and perhaps magnesium and sulphate, that further additions of 

 these nutrient elements are unnecessary, or even undesirable. The 

 objective should be to approximate the intended composition of 

 the nutrient solution, taking into account the salts already present 

 in the water. Since, however, considerable latitude is permissible in 

 the composition of nutrient solutions, analysis of the water is not 

 indispensable, unless the content of mineral matter is very high. 



SELECTION OF A NUTRIENT SOLUTION 



As stated before, there is no one nutrient solution which is always 

 superior to every other solution. Among many solutions which might 

 be employed, those described below have been foimd to give good 

 results with various species of plants in experiments conducted in 

 Berkeley, with a source of good water. Other solutions can also be 

 used with good results. 



The composition of the solutions is given in two forms: (A) by 

 rough measurements adapted to the amateur without special weighing 

 or measuring instruments, and (B) in more exact terms for those with 

 some knowledge of chemistry, who have proper facilities for more 

 accurate experimentation. 



