34 MANUAL OF GENEEAL AGEICULTUEE. 



the crucible until there remains a light, gray colored ash. 

 These ashes show the part of the plan that is derived 

 from the soil. How does it compare with the part derived 

 from the water and air (the part that has burned away) ? 

 Save the plant ash for Exercise 33. 



The average plant derives about 9.0% of its weight 

 from the air, 89.5% from the water and 1.5% from the 

 soil. The air always supplies its portion to the plant 

 without assistance of the farmer ; our California soils are 

 generally quite fertile and with proper cultivation will 

 usually yield their portion of the food ; but to supply the 

 large amount of water that the plant soil requires, offers 

 a problem that is becoming very serious, and one to which 

 we are prone not to give proper consideration. 



33. COMPOSITION OF PLANT ASH. 



Materials: Evaporating dish, funnel, niters, test 

 tubes, three inches of platinum wire (fine iron wire may 

 be used), cobalt blue glass (or a blue glass bottle), glass 

 stirring rod, concentrated hydrochloric acid, concentrated 

 nitric acid, distilled water, solutions of potassium sulpho- 

 cyanate, sodium phosphate, silver nitrate, barium chlorid, 

 ammonium molybdate, and ammonia. 



Place in an evaporating dish about y 2 gram of the 

 plant ash left from the previous exercise. Add to it 5 c.c. 

 each of distilled water and concentrated hydrochloric acid 

 and a few drops of concentrated nitric acid. A rapid froth- 

 ing, or effervescence, when the acid is added, proves that 

 carbon is a constituent of the ash. Heat the mixture to boil- 

 ing and evaporate it nearly to dryness. Add 10 c.c. distilled 

 water and stir well with a glass rod. The small amount 

 of white insoluble matter contains the silicon of the ash. 

 Filter and wash the residue on the filter with a little dis- 

 tilled water and add the washings to the filtrate. To this 

 add ammonia with constant stirring till the solution smells 

 strongly of ammonia, and heat to boiling. Filter and 

 wash the residue as above and save the filtrate and wash- 



