RECENT WORK IX AGRICULTURAL SCIENCE. 



CHEMISTRY. 



The colorimetric estimation of phosphates, second method, O. Schreixer 

 and B. E. Brown {Jour. Amer. Ch&m. Soc, 26 {1904), No. 11, pp. 1463-1468).— The 

 method proposed is as follows: 



"Measure out a convenient volume of the solution to be estimated, usually 50 cc, 

 into an evaporating dish, add 1 drop of ammonia water, and 2 or 3 drops of the ammo- 

 nium oxalate solution; evaporate to dryness on a water bath. To the cooled dish 

 add 1 cc. of the magnesia reagent, work up the residue well with a glass rod and 

 then allow to stand about 2 hours. The precipitated magnesium ammonium phos- 

 phate is then washed as follows: Add about 5 cc. of the ammonium hydroxid wash 

 liquid to the dish, washing down the sides, and then pour the liquid through a small 

 filter. 



"Repeat this operation five times, then wash down the filter and funnel until the 

 filtrate measures approximately 50 cc. ; then rinse the dish once with about 5 cc. 

 of cold water, and pour through the filter in such a way as to wash the filter; reject 

 the washings and put a clean salt mouth bottle or other receptacle under the funnel. 

 Add 5 cc. of nitric acid to the dish, working this about with the glass rod and pour 

 through the funnel in such a manner as to wet all the inside of the funnel ; then wash 

 the dish five times with hot water (about 5 cc. each), and continue washing the filter 

 until about 45 cc. of the filtrate have been obtained. To the cooled liquid add 4 cc. 

 of the ammonium molybdate solution and, after 20 minutes, read against the standard 

 colorimetric phosphate solution." 



The following reagents are required: 



" (1) Ammonium molybdate solution. — Fifty grams of the pure salt in 1 liter of solu- 

 tion. 



" (2) Nitric acid. — Specific gravity 1.07. 



"(3) Standard phosphate solution. — 0.5045 gm. of pure freshly crystallized sodium 

 phosphate, Na 2 HP0 4 .12H 2 0, is dissolved in water, 100 cc. of nitric acid (sp. gr. 1.07) 

 added, and the whole diluted to 1 liter. The nitric acid is added to lessen the con- 

 tamination with silica from the glass. One cubic centimeter = 0.0001 gm. P 2 5 . 



"(4) Standard colorimetric solution. — This is prepared by diluting 10 cc. of the 

 standard phosphate solution to about 80 cc. and then adding 9 cc. of nitric acid, 8 cc. 

 of ammonium molybdate solution, and making up to 100 cc. After standing 20 

 minutes it is ready for use. Each cubic centimeter of this colorimetric solution is 

 equal to 0.00001 gm. P 2 5 . 



"(5) Ammonium hydroxid. — Reagent. 



"(6) Ammonium hydroxid wash liquid. — One part of strong ammonia water (sp. gr. 

 0.9) and 9 parts of water. This liquid should be practically free from silica, and for 

 this reason is best prepared from redistilled ammonia water. 



"(7) Ammonium oxalate. — Saturated solution. 



533 



