EXRICHINO SOIL— COMMERCIAL RESOURCES 105 



Again try the litmus paper. It will no lonper turn red. Try 

 Home nir-slaked lime in the same way. Make the aami' tost 

 with plaster of paris or gypsum, which is sulfate of lime. This 

 will not neutraliro the acid or swet-tin the milk or viiu'iirar. 

 Makf the same test with salt and supnr. A substance which 

 turns Mue litmus red is acid ; one which turns rci' litmus liluc 

 is alkaline. 



ICtvi. The experiment stations of most of the older states 

 issue bulletins of advice on the use of fertilizers, and these 

 should be studied. In many states there are laws designed to 

 protect the purchaser of fertilizers ; and fertilizer control sta- 

 tioDR are established to analyze the different brands and to 

 publish the results. The general subject of fertilizers is pre- 

 sented in Voorhees' book on "Fertilizers." Good advice will 

 also be found in Chapter .xii. of Roberts' " Fertility." 



IGoh. Kvery school should have bottles of the leading ferti- 

 lizer chfMiicais for e.xhibition ; as muriate and sulfate of potash, 

 kainif. gypsum or plaster, bone and rock phosphates, bone- 

 blnck, dried blood, nitrate of soda, sulfat«* of ammonia, air- 

 slaked lime, and quick- lime. Tnese can be obtained from 

 doulera in fertilizers. 



