of the different effect of ignition on the solubility 

 of phosphates in minerals and in soils, if such a dif- 

 ferent effect was definitely shown to exist. Accordingly 

 five different soils were selected, each sifted through 

 a 0.5 mm. sieve and prepared for analysis for phos- 

 phoric acid. The soils were as follows: 



No. i. A very rich, black, fine silty loam, rich in 

 phosphoric acid and humus, from Arroyo Grande, 

 San Luis Obispo County, California. 



No. 2. A fine sandy soil with a good supply of phos- 

 phoric acid, but poor in humus, from Escondido, 

 San Diego County, California. 



No. 3. A very heavy black, clay adobe soil with 

 sufficient phosphoric acid for fair crop production, 

 from West Berkeley, Alameda County, California. 



No. 4. A sandy loam with a fairly good humus and 

 phosphoric acid content from South San Francisco, 

 California. 



No. 5. A light sandy loam, of fairly good humus con- 

 tent and phosphoric acid, from Anaheim, Orange 

 County, California. 



The analysis was carried out as follows: Four 

 grams of soil were placed in a porcelain cup and di- 

 gested with concentrated nitric acid for two days 

 on the steam bath. Two samples of each soil were 

 ignited for twenty minutes at a low red heat in a plat- 

 inum dish and two others of each soil were placed in 

 the cups without ignition. The greatest caution 

 was exercised to prevent loss by dusting in the process 

 of ignition and in the transfer from platinum to di- 

 gestion cup. After the period of digestion, the soil 

 cups were placed on the sand bath and evaporated 

 to dryness to dehydrate the silica, after which more acid 

 and a little distilled water were added and the cups 

 were replaced on the steam bath for four hours. 

 The solutions were then carefully filtered and the soil 

 residue washed on the filter. The filtrate was warmed 

 to a temperature of 65 to 70 C. and the phosphoric 

 acid precipitated with ammonium molybdate. The 

 precipitate and solution were allowed to stand at 

 65 to 70 C. for about four hours, then filtered and 

 the precipitate washed with a solution of ammonium 

 nitrate. After this it was dissolved out with ammonia, 

 and precipitated with magnesia mixture, then al- 

 lowed to stand over night, filtered the next morning 

 and washed with distilled water containing a little 

 ammonia. The precipitate and filter were then dried, 

 ignited, weighed and the phosphoric acid determined 



(2) 



