FERTILIZERS. 625 



If it sliiill prove that it is comparatively easy to transfonn a difli- 

 cnltly soluble slag into an easily soluble one simply by increasing tlie 

 silica content, it will then be important to study what effect this opera- 

 tion has on the fertilizing- A^alue of the resulting product. 



The chemical constitution of Thomas slag and the determina- 

 tion of its relative effectiveness, P. Wagner {Chon. Zt<j., 18 (1894), 

 Ko. 98, pp. 1933-1935, Jig. 1). — The results of analyses and experiments 

 are reported in support of the statement previously made' that the 

 richer a slag is in combined silica the more soluble it is in citrate solu- 

 tion and the more active it is in the soil. 



Contrary to tlie opiition of Hoyermann, the analyses show that the 

 solubility in citrate solution does not always increase with the decrease 

 of free lime. They indicate, further, that the silicate and phosphate of 

 lime of the slag are united to form easily decomposable silico-phos- 

 pliates. Analyses of Khenish slags of good (juality and of the trans- 

 parent blue crystals found in the cavities of slag show them to contain 

 phosphoric acid and silicic acid in the proportion corresponding to 

 these silico-phosphates (about 42 parts of silicic acid to 100 parts of 

 phosphoric acid). It is to the readily decomposable character of these 

 silico-phosphates and not to the saturation of the free lime by silicic 

 acid, as claimed by Hoyermann, that the solubility of siliceous slags in 

 citrate solution is due. 



Vegetation experiments on white mustard gave the following results: 

 Without phosphoric acid. 24.1 gm. of crop; with 0.5 gm. of phosphoric 

 acid in form of superphosphate, 84 gm.; with 0.5 gm. of phosphoric 

 acid in form of Hoyermann's Thomas slag, poor in silicic acid (62 per 

 cent soluble in citrate solution), G2.1 gm.; and 0.5 gm. of phosphoric 

 acid in form of Hoyermann's slag, rich in silicic acid (98 per cent 

 soluble in citrate solution), 84 gm. These results furnish a strong con- 

 firmation of the statement that not only the citrate solubility, but also 

 the effectiveness as a fertilizer, of slag increases with an increase of its 

 silicic acid content. 



The following is the author's latest revised method for determining 

 citrate- soluble phosphoric acid in Thomas slag and untreated phos- 

 l^hates: Five grams of the slag (as it appears on the market, unground 

 and unsifted) is placed in a 500 cc. flask, 200 cc. of water and 200 cc. 

 of citrate solution (containing 150 gm. of citric acid and 23 gm. of 

 nitrogen, equal to 27.93 gm. ISTH:,) are added, the flask filled to the mark, 

 and shaken for 30 minutes in a shaking machine making 30 to 40 revo- 

 lutions per minute. The mixture is filtered at once, and 50 cc. of the 

 filtrate is measured into a beaker, 100 cc. of molybdic solution added, 

 heated to about 80^ 0. in the w^ater bath, cooled, and filtered. The 

 precipitate is carefully washed with 1 per cent nitric acid and dissolved 



'Chem. Ztg., 18 (1894), No. 79, pp. 1511, 1512 (E. S. E., 6, p. 624;. 



