FERTILIZERS. 081 



"The one ingredient of which a surplus is rarely found, esin'cially in the soluble 

 condition, is jjhosplioric acid ; and to supply it in an efficacious, easily soluble form 

 is usually the most probable remedy indicated, when deficiency of plant-food makes 

 itself felt in this State." 



The relative merits of different fertilizing materials are briefly 

 discassed. 

 On the composition and agricultural value of Thomas slag, G. 



I'ATUREL {Ann. Agron., 22 {18'JG)^ No. 11, pj). 497-515 ; But. Soc. Chim. 

 Paris, 17-18 {1897), iS^o. 5, pp. 319-321. — The author gives a compre- 

 hensive report on his own work and that of other investigators in this 

 line. The principal results are briefly summarized as follows: 



(1) The nse of slag is increasing in France and is attended with 

 great benefit to all kinds of crops on account of the phosphoric acid 

 and lime which it contains. 



(2) The chemical composition of slag has been much discussed 

 recently. In Germany Hilgenstock and Otto have arrived at the con- 

 clusion that it is composed of tetracalcium -phosphate and calcium sili- 

 cate with an excess of free lime. This has been denied by French 

 chemists, particularly Haneuse and Souris, who claim that it is trical- 

 cium phosphate and i^hosphate of iron. 



(3) Analyses by the author of 5 samples of slag commonly used in 

 France showed 14 to 19 per cent of phosphoric acid and 41 to 52 per 

 cent of lime. The proportions of phosphoric acid, silica, and lime, cal- 

 culated from these analyses (deducting the amount of lime which is in 

 the free state in the slag) confirm the hypothesis of the German chem- 

 ists as to the chemical constitution of slag. 



(4) The free lime in the Slag is difficultly soluble in chemical reagents 

 on account of the high temperature to which the slag has been submit- 

 ted. It is nevertheless jiossible to determine it by digestion of the 

 slag in ammonium chlorid, which dissolves the lime completely without 

 attacking either the silicate or phosphate. 



(5) The method proposed by Wagner for determining the agricultu- 

 ral value of slags did not give satisfactory results on account of the 

 free citric acid in the reagent. The quantity of phosphoric acid dis- 

 solved varied widely with the method of manipulation and with the 

 content of free lime. 



((>) By prolonged digestion of extremely finely powdered slag in 

 normal alkaline amonium citrate more than four-fifths of the phosphoric 

 acid was dissolved. This result is in accord with the well-known efiect 

 of slag as fertilizer and is an additional indication that it does not con- 

 tain tricalcium phosphate. Crude pliosphates treated in the same man- 

 ner did not give a trace of phosphoric acid. 



(7) Slags exert a very active influence upon nitrification of nitroge- 

 nous matter in acid soils. The ainoun t of nitrates formed increases with 

 the i:)roportiou of slag used. Since this action is due to the free lime 

 wliich the slag contains it follows that with an ecjual content of phos- 

 phoric acid that slag will be most effective in acid soils which contains 

 14786— No. S- 4 



