210 



of steam and air at a higher temperature upon the residue from 

 the first stage of the operation. 



Such a process would probably work best under suction. The 

 recovery of nitrogen as ammonium sulphate would also be an 

 essential feature of the process. 



xx. 



Chalking, Marling and Liming. Gypsum as a corrective of 

 soils. Other soil-correctives. 



C. A. STEWART. The Definition of Marl. (Econ. Geol., 4, 1909, 

 No. 5, Pp. 485-489). E. S. JR., Febr. 1910. Washington. 



The various uses which have been made of the term marl are 

 given and the author concludes that in his opinion the term " should 

 be employed in its original sense as any rock that is valuable as 

 a natural fertilizer (with the exception of the phosphate rocks and 

 such well-defined minerals as gypsum which seem to be separated 

 in general usage)." 



, 



J. HUGHES. Value of Chalk as a Dressing for Light Soils. | 



The Journal of Board Agriculture. July 1910, vol. XVII, N 4, 

 p. 306. 



Observation on the agricultural value of chalk, with special re- 

 ference to particular kinds of soil requiring lime in a mild form, 

 have recently been made by Mr. John Hughes, Agricultural Analyst 

 for Herefordshire. Chalk is but slightly soluble in cold distilled 

 water very much less so than caustic lime. It was found that 

 while i part of caustic lime dissolves in 833 parts of water, i part 

 of chalk only dissolves in 22 222 parts of water the relative so- 

 lubility being, therefore, about as i to 27. Under soil conditions, 

 however, the solvent is not pure water, but "soil water," which 

 contains various vegetable acids exerting a considerable solvent 

 action on plant foods. It is usual, therefore, to make comparisons 

 by the use in chemical practice of a 2 per cent solution of citric 



