RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



Reasons for the variation in the citrate solubility of Thomas 

 slag meal, P. Wagner (Landw. Vers. Stat., 49 (1897), No. 3, pp. 

 227-230). — Bucking and Linck have found l in Thomas slags three dis- 

 tinct minerals, one with hexagonal crystals resembling apatite, another 

 with bluish monocliuic crystals of the formula 4Ca :i P 2 8 -f 3Ca 3 Si() 5 , 

 and a third with yellowish rhombic crystals with the approximate 

 formula Ca 4 P 2 9 . These contain 30.8, 31.2, and 38.8 per cent of P 2 0„ 

 respectively. The author has isolated these different minerals and 

 determined the citrate solubility of each. He finds that 85.42 per cent of 

 the P 2 Or, of the bluish crystals is soluble, 88.75 per cent of the yellow, 

 and about GO per cent of the apatite-like substance. He suggests that 

 these differences in solubility may partially explain the variations 

 noticed in the solubility of the phosphoric acid of different slags. — J. p. 



STREET. 



Volumetric method for the determination of combined sulphu- 

 ric acid, F. Mareoutin and M. Molinie | Bui. Soc. ('him. Paris, 3. ser., 

 17 {1897), No. 22, pp. 950-955).— This method, which is adapted to the 

 analysis of water, is as follows: Acidulate 100 cc. of the water with 

 hydrochloric acid and boil to drive off carbon dioxid. Add, drop by 

 drop, 30 cc. of barium chlorid, maintaining the temperature of the solu- 

 tion meanwhile near the boiling point, and afterwards keep in an oven 

 at about 40° until the precipitate has settled. Neutralize with a few 

 drops of ammonia and add 30 cc. of potassium chromate. Heat slightly, 

 and after cooling make the volume to 300 cc. To 100 cc. of the clear 

 liquid add 2 cc. of sulphuric acid (1:4) and 5cc. of arsenious acid solution, 

 heat gently, and stir until color disappears. Neutralize with potassium 

 carbonate and run in standard iodid solution until the blue coloration 

 appears on testing with starch. The following equation is given, in 

 which t=mg. of iodid in 1 cc. of the iodid solution; n=cc. of iodid solu- 

 tion required by each 100 cc. of distilled water; n'=cc. of iodid solution 

 required by 100 cc. of the water tested, and x=mg. of sulphuric anhy- 

 drid in a liter of water : 



in/ no. 3x4x127 



ff=10 (n-n<) 3t 4x8Q • 



If the iodid solution is exactly fiftieth normal (1 cc.=2.54 mg. of iodid) 

 then 



#=16 (n—n'). 



1 Ztschr. Stahl u. Eisen 1887, p. 245. 



617 



