TOTAL PHOSPHORIC ACID IN GUANOS 607 



few years, some very rich in plant food have been found. In 

 one instance the total percentage of nitrogen present was io.ii 

 per cent. In some cases the phosphoric acid is high, but rarely 

 in conjunction with a high content of nitrogen. In one instance 

 where the total phosphoric acid reached 14.53 P er cent., the con- 

 tent of nitrogen was 4.87 per cent. 



In respect of the process of analysis there are no especial 

 directions to be given. The phosphoric acid may be determined 

 as given below, and the potash by the usual methods. The total 

 phosphoric acid and potash are determined only after the destruc- 

 tion of the organic matter. 



In old cave deposits the processes of decay and nitrification 

 seem to have long been completed and very little power of in- 

 ducing nitrification in culture solutions seeded from these sam- 

 ples has been found. 



514. French Official Method for Total Phosphoric Acid in 

 Guanos. To determine the phosphoric acid in guanos, the meth- 

 od officially adopted by the French agricultural chemists may 

 be used. 82 



Two grams of the sample are rubbed up in a porcelain cruci- 

 ble with a decigram of slaked lime to prevent the possible reduc- 

 tion of the phosphoric acid by the organic matter. The mixture 

 is slightly moistened with a few drops of water, dried on a sand- 

 bath, and afterwards heated to redness, best in a muffle, until 

 organic matter is destroyed. The contents of the crucible are 

 detached and placed in a flask of 200 cubic centimeters capacity. 

 The crucible is well digested twice with some hydrochloric acid 

 to dissolve any adhering fragments, and finally washed with hot 

 water, the acid and water being added to the flask. The con- 

 tents of the flask are boiled for 15 minutes and then poured 

 into a flat-bottom dish, the flask well rinsed three or four times 

 with small quantities of water, and the liquor and washings evap- 

 orated to dryness to render the silica insoluble. The residue is 

 taken up by a mixture of 10 cubic centimeters each of hydro- 

 chloric acid and water, heated for a few minutes and filtered, 

 and the dish well washed with successive small portions of water, 

 82 Sidersky, Analyse des Engrais, 1901 : 61. 



