APPENDIX B. 



559 



fairly definite conclusions may be drawn from the character of the 

 native vegetation ; regarding which, detailed information may be found in 

 Parts III and IV of this volume. But where, as in the arid region, this 

 criterion is not available, since the controlling factor there is the mois- 

 ture supply, a presumption may be gained by the application of a slip 

 of moistened red litmus paper to the wetted soil. Should the red 

 paper be turned blue within one or two minutes it would indicate the 

 presence of carbonate of soda (" black alkali ") as well as of lime car- 

 bonates : but if blued only after twenty minutes or more, it would indicate 

 the presence of the carbonates of lime and magnesia. If not changed 

 at all, the conclusion would be that either lime carbonate is in very 

 small supply, or that the soil is in an aci 1 condition. (See chapter 8, 

 p. 122). 



Saline and Alkali Soils. The presence of an unusual or injurious 

 amount of soluble salts, as in the case of seacoast and alkali soils, is 

 commonly easily ascertained in the field ; where, if the surface soil is 

 at all seriously contaminated with soluble salts of any kind, these may 

 be seen on the surface during a dry season, forming a whitish efflores- 

 cence, which in most cases is definitely crystalline. In doubtful cases 

 a tablespoonful of the surface soil may be leached with water, and the 

 first ten or fifteen drops caught in a clean, bright silver spoon and 

 evaporated. Or the soil may be stirred up with about twice its bulk of 

 water and the mixture be allowed to clear by settling, then evaporating. 

 A slight whitish film will almost always remain in the spoon ; but if the 

 amount be somewhat considerable, the presence of soluble salts is very 

 readily recognized by pouring a few drops of clear water on one side of 

 the spot, and then allowing it to flow gently over the spot to another 

 place, where it is again slowly evaporated. Any considerable amount of 

 salts present will be shown both in the diminution of the original spot, 

 and in the soluble residue accumulated where the water was List 

 evaporated. Should common salt be present to any considerable extent, 

 the residue in the silver spoon will, if the last drops be allowed to 

 evaporate slowly, show square or cubical crystals to the naked eye, and 

 certainly to a common pocket lens. The residue may also be tested 

 with red litmus paper for carbonate of soda, which would quickly turn 

 it blue. 



More detailed examination requires chemical reagents and experience, 

 but the above tests should be sufficient to prevent the mistaking of 

 mere white spots, whose humus has been destroyed by fermentation 

 caused by bad drainage, with true alkali caused by excess of soluble 

 salts ; a mistake not uncommon in both the arid and humid regions. 



