AGRICULTURAL CHEMISTRY — AGROTECHNY. 511 



acid is added in the same manner until no more precipitate is formed. From 

 tlie amount of molybdic acid used the pliosphoric acid content can be calculated. 



The reagents employed are a molybdic acid solution, wliicli is prepared by 

 adding a concentrated solution of molybdic acid in ammonium hydrate to nitric 

 acid until the precipitate obtained does not redissolve, and adding ammonia. 

 The solution is then titrated with potassium diphosphate solution and each 

 cubic centimeter made to corres[)ond to 0.002.5 gm. phosphoric acid. The nitric 

 acid-ammonium nitrate solution is composed of 200 gm. ammonium nitrate and 

 2G.5 cc. nitric acid and made up to 1 liter. The glue solution is made by soalv- 

 ing the glue overnight in cold water, pouring off the water, and boiling the 

 residue in water and nitric acid. After cooling, the mixture is made alkaline 

 with ammonium hydrate, and magnesia mixture added in order to precipitate 

 any phosphoric acid which may be present in the glue. Ammonium carbonate 

 is then added and the glue solution filtered off wlien required. 



Estimation of sulphur in alkali polysulphids, G. Dussekre and V. Vuilleu- 

 MiER (Chrm. Zig., 33 (1909), No. 127, p. 1129; Analust, 3.'f (1909), No. J,05, 

 p. 5.'i5). — As other forms of sulphur exist in these insecticides besides the 

 active polysulphid, the authors suggest estimating the latter as follows: Dis- 

 solve 10 gm. of the substance in 500 cc. of water and filter. Place 5 cc. of 

 the filtrate in a flask with 30 to 40 cc. of strong ammonia, and dilute with 

 an equal volume of water. Heat the mixture gradually to the boiling point' 

 and titrate with decinormal silver nitrate solution, adding the same drop by 

 drop until a black precipitate suddenly forms and leaves a colorless super- 

 natant liquid. Each cubic centimeter of silver nitrate used equals O.OOIG gm. 

 of sulphur in the polysulphid form. 



Volumetric estimation of calcium, oxid in presence of dissolved silica, K. 

 Baltiiasar {Chcm. Ztg., 33 {1909), No. 11, pp. 6J,G, 6Ji1 ; aU. in Jour. Clicm. 

 Soe. London, 96 {1909), No. 56.',, II, p. 831).— The metliod is carried out as 

 follows: Seven-tenths gm. of the substance (cement, etc.) is treated with 

 strong hydrochloric acid, using heat if necessary. The mixtui-e is then trans- 

 ferred to a 350 cc. flask, rinsed with water until about 100 cc. is obtained and 

 boiled a few minutes to expel carbon dloxid. After this 50 cc. of ammonium 

 mixture (25 gm. ammonium chlorid, 100 cc. acetic acid and ammonium hydroxid 

 to malce 1000 cc.) is added, boiled, and then while boiling 50 cc. of seminormal 

 oxalic acid is added, cooled, and filled to the 350 cc. mark with water. The 

 solution is then filtered and in 50 cc. of the filtrate the excess of oxalic acid 

 is determined by decinormal permanganate in the presence of 5 cc. of sulphuric 

 acid and a few cubic centimeters of manganous sulphate solution. From this 

 data the percentage of calcium oxid is calculated. 



Estimation of calcium carbonate in soils, F. S. Marr {Jour. Agr. ScL, 3 

 {1909), No. 2, pp. 153-160).— The author draws attention to the fact that the 

 boiling strong acid employed in the analysis of soils decomposes some of the 

 organic matter and results in the production of carbon dioxid. Soils which 

 contain less than 1 per cent of calcium carbonate, particularly acid soils, there- 

 fore yield incorrect results on ajialysis. Recommendations are made to 

 eliminate this source of error, such as the reduction of the strength of the 

 acid, etc. 



A modification of the Kjeldahl method for foods, R. Corradi (Bol. Ghim. 

 Farm.., J,6 {1907), pp. 861-86J,; ab.<^. in Ztschr. Untersuch. Nahr. u. Gcnu.<i.<imt1., 

 18 {1909), No. 11, p. 671). — The modification consists of the use of sodium 

 hypobromite and thereby discarding the usual distillation process. 



The method is as follows: To 2.5 gm. of a foodstuff which contains more than 

 3 per cent of nitrogen, or 5 gm. of a foodstuff which contains less than 3 per 



