ANALYZING AND TESTING SOILS 567 



acids with the liberation of carbonic acid, which breaks down into 

 water and gas, carbon dioxid. Consequently the carbonates, such 

 as calcium carbonate and magnesium carbonate, serve as mild 

 alkalis, in the presence of which soil acidity cannot exist. 



Carbonates. To test for carbonates in the soil, make a shallow 

 cup of a ball of soil and pour in a few drops of concentrated hy- 

 drochloric acid. If carbonates are present, a reaction occurs with 

 the liberation of carbon dioxid which appears as gas bubbles, 

 producing foaming, or effervescence : 



CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 . 



With much carbonate present the action is rapid and abundant, 

 but with mere traces of carbonate in the soil only few bubbles will 

 appear. 



The same test may be applied to limestone, marl, etc., to ascer- 

 tain -if carbonates are contained in the material. Most limestones 

 and marls will show some effervescence with cold concentrated 

 acid, but some nearly pure dolomitic limestones require the appli- 

 cation of heat to properly develop the reaction. 



Five cents' worth of concentrated hydrochloric acid in a small 

 glass-stoppered bottle is sufficient for many tests for carbonates. 

 Of course, care must be taken not to get the acid on the clothing or 

 skin. In case the acid gets on the fingers, it should be washed off, 

 or rubbed off with soil, as soon as possible. It is not especially 

 dangerous to handle, but will soon "eat" or "burn" through the 

 skin if not removed or neutralized, which could be easily done by 

 rubbing with soil containing carbonates. 



As in the case of acidity, it is especially important to test the 

 subsoil for carbonates; for an abundance of carbonates only i to 

 3 feet beneath the surface serves as a store and protection, especially 

 in critical periods in the growth of such plants as clover and alfalfa, 

 which may die during a few weeks of summer drouth if the rising 

 capillary moisture carries acidity, but would be kept alive if this 

 moisture brought traces of calcium bicarbonate. 



If the landowner has no other source of information concerning 

 the composition of his soil, it is altogether advisable to collect a 

 composite sample of the plowed soil (made by mixing together 



