GREEN VITRIOL 603 



The moisture is determined by drying two grams of the well- 

 mixed and finely powdered sample to constant weight at 100. 

 The chlorin is obtained by precipitation of an aliquot part of a 

 solution of the salt by set silver nitrate, using potassium chro- 

 mate as indicator. 



In the determination of insoluble matter it should not be for- 

 gotten that a little gypsum may be present, and this should be 

 dissolved by rubbing to a finer powder and by repeated digestion 

 in water. The magnesia and lime are separated and determined 

 in the usual manner. If the quantity of gypsum present be suf- 

 ficient to warrant it, the sulfuric acid may be separated and 

 weighed in the manner already described. Common salt, when 

 present in the soil in proportions greater than o.i per cent., is 

 injurious to vegetation. The presence of salt in any greater 

 quantities in a soil renders it barren. In Texas the irrigation of 

 rice fields with slightly brakish water has had the effect of ren- 

 dering the fields unfit for rice growing. Salt is often used to kill 

 weeds, and it is extremely doubtful if its use as a fertilizer is 

 ever really indicated. 



509. Green Vitriol. When iron is used as a fertilizer it is 

 sometimes applied as ferrous sulfate. The value of iron in a 

 soil is incontestable, and by reason of the fact that fertile soils 

 are always well aerated, the iron present in the arable layer is 

 found in the ferric state. When green vitriol is applied to the soil 

 it undergoes gradual oxidation and appears finally in a more 

 highly oxidized form as ferric hydrate. Iron acts directly on the 

 plant in promoting the development of the chlorophyll cells, and 

 is also found in almost all parts of the vegetable organism. A too 

 great quantity of ferrous sulfate is destructive of plant growth, 

 in which respect it resembles common salt. It should, therefore, 

 be applied with due regard to the dangers which might arise 

 from an excessive quantity. It is not likely, however, that when 

 applied in a finely powdered state at the rate of from one to 

 two hundred pounds per acre it would ever prove poisonous to 

 vegetation. 



In the analysis of a sample of green vitriol it will be sufficient 

 to determine the moisture, water of crystallization, iron, and 



