6O2 AGRICULTURAL ANALYSIS 



Per cent. 



CaSO 4 .2H,O 88.15 



CaCOj 3 50 



Fe 2 Os and A1 2 O 3 1.50 



Insoluble 2.80 



Organic matter 0.50 



Water and undetermined 3.55 



Fine ground gypsum in the arid regions of the United States, 

 especially when transported during the hot months, loses one 

 molecule of its crystal water, and this often leads to disagree- 

 ments respecting weight. 78 



Hilgard also calls attention to the fact that soils naturally 

 impregnated with gypsum are not productive. It is, however, 

 very useful as a dressing to soils containing "black alkali" (car- 

 bonate of soda), converting the carbonate of soda into sulfate, 

 a far less injurious ingredient. After solution in water it pene- 

 trates the soil and effects changes in its zeolithic constituents, 

 setting potash free and thus increasing the stores of plant food. 79 



508. Common Salt. Common salt is highly esteemed in many 

 quarters as a top dressing for lawns and meadows, and also for 

 cultivated crops. Its action is chiefly of a mechanical and cata- 

 lytic nature, since it does not form a notable percentage of the 

 mineral food of plants. On account of its affinity for moisture it 

 is also said to have some value as a condenser and carrier of water 

 in times of drouth. On account of its great cheapness, selling 

 often for less than $10 a ton, its use in moderate quantity en- 

 tails no great expense. Its ability, however, to pay for its own 

 use in the increased harvest is of a doubtful character when it 

 is applied at a cost of more than a few dollars per acre. In the 

 chemical examination of a sample of common salt which is to be 

 used as a fertilizer, a complete analysis is rarely necessary. 

 When desired it can be conducted according to the usual methods 

 of mineral analysis. For practical purposes the moisture, insol- 

 uble matter, magnesia and chlorin should be determined and the 

 quantity of sodium chlorid calculated from the latter number. 

 Traces of iodin or bromin which may be present are of no con- 

 sequence. 



18 Hilgard, Letter to Author, 1907. 

 " Soils, 1906 : 43. 



