ENRICHING SOIL COMMERCIAL RESOURCES 105 



again try the litmus paper. It will no longer turn red. Try 

 some air-slaked lime in the same way. Make the same test 

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

 will not neutralize the acid or sweeten the milk or vinegar. 

 Make the same test with salt and sugar. A substance which 

 turns blue litmus red is acid ; one which turns red litmus blue 

 is alkaline. 



166. 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- 

 tions 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." 



1666. Every school should have bottles of the leading ferti- 

 lizer chemicals for exhibition ; as muriate and sulfate of potash, 

 kainit, gypsum or plaster, bone and rock phosphates, bone- 

 black, dried blood, nitrate of soda, sulfate of ammonia, air- 

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

 dealers in fertilizers. 



