14 USE OF FELDSPATHIC ROCKS AS FERTILIZERS. 



plant foods, such as lime, magnesia, iron, and manganese. This 

 author published a philosophical work entitled '' Das Leben," which 

 treated in part of the use of rock fertilizers. Hensel thought that the 

 use of excreta, offal, and other decaying and waste material as manure 

 was harmful, if not to plants, at least to animals and men who sub- 

 sisted upon them. Like many enthusiasts, Hensel appears to have 

 been completely carried away by his ideas, which were not always 

 justified by known facts. Hensel obtained, nevertheless, a consider- 

 able following*^ and factories were established to prepare stone meal. 

 The subject evoked much discussion in Germany for many years. 

 Whether rightly or wrongly, HenseFs ideas provoked the antagonism 

 of nearly all the leading exponents of agricultural science in Ger- 

 many. A great many experiments were undertaken and in many 

 cases the stone meal as prepared by the factories was shown to be very 

 low in plant foods and nearly worthless as a fertilizer. 



Among the prominent agricultural chemists who waged war on 

 HenseFs stone meal Avere Wagner,'' B()ttcher,'' Steglich,'^ Hentschel,« 

 Pfeiffer and Hansen,^ and Morgen." , 



In some respects Hensel's arguments were not without weight, and 

 he was keenly aware of the necessity for very fine grinding before the 

 mineral constituents of rocks could be considered as practically avail- 

 able. The following quotation '' from a translation of Hensel's work 

 stands for itself : 



The practical point to settle is how far fertilizing with stone meal pays, what 

 yields it will afford ; thus, whether it will be profitable for the farmer to use it. 

 * * * It must here be premised that the fineness of the stamping or grinding 

 and the most complete intermixture of the constituent parts are of the greatest 

 importance for securing the greatest benefit of stone-meal fertilizing. A manu- 

 factured article of this kind has recently been submitted to me which showed 

 in a sieA-e of modern fineness three-fourths of the weight in coarse residuum. 

 But as the solubility of the stone meal, and thus its efficiency, increases in pro- 

 portion to its fineness, the greatest possible circumspection is required in grind- 

 ing it. The finer the stone dust the more energetically can the dissolving 

 moisture of the soil and the oxygen and nitrogen of the air act upon it. A grain 

 of stone dust of moderate fineness may be reduced in a mortar of agate perhaps 

 into twenty little particles, and then every little particle may be rendered acces- 

 sible to the water and the air, and can, therefore, be used as plant food. Thence 

 it follows that one single load of the very finest stone meal will do as nuich as 

 twenty loads of a coarser product, so that by reducing to the finest dust, the 



aPomol. Monatshefte, No. 1 (1892) ; also Wegweiser zur Gesundheit, Septem- 

 ber 15, 1891. 



fiZeit. Landw. Yereiue liessen, 1894, VA, 14. 



c Centbl. Agr. Chem., 1895, 24, .363. 



d Ibid., 1895, 24, 423. 



f Ibid.. 1890, 25, 1.36. 



f Ibid., 1890, 25, 802. 



a Ibid., 1898, 27, 743. 



h A. J. Tafel, Bread from Stones. 1894, p. 53. 



104 



