52 



allude to immediately ; so that for the present I can only give the 

 following rough average of a certain number of analysis of the ash of 

 the ripe cane with its leaves. It will serve us to form at least a very 

 approximate notion of the relative proportions of each substance taken 

 from the soil during the life of the cane : — 



Ash of full-grown Cane and Leaves. 



Silica ... ... 43.0 



Phosphoric acid ... ... 6.0 



Sulphuric acid . . ... 8.0 



Chi rine ... ... 4.5 



Lime ... ... 10.0 



Magnesia .... .... 6 5 



Potash ... ... 18.0 



Soda ... ... 2.0 



Oxide of iron, manganese, and loss in analysis 2.0 



100.0 



The largest figures are those of silica, potash, lime, and phosphoric 

 acid ; but sulphuric acid and magnesia appear to have their importance 

 also, whilst chlorine and soda, though represented by comparatively 

 small figures, are usually present as chloride of potassium and chloride 

 of sodium to the extent of 4 or 5 per cent. The principal substances re- 

 quired in an available state in a cane soil are, therefore, nitrogen, potash, 

 silica, phosphoric acid, sulphuric acid, lime, and magnesia. We may 

 state at once that oxide of iron and oxide of manganese are, perhaps, 

 also essential, for in a long series of interesting experiments made in 

 1849 by the Duke of Salem-Horstmar, a chemist of much ex- 

 perience, the conclusion was drawn that a graminaceous plant (the 

 oat) absolutely required for its complete development all the mineral 

 substances we have just mentioned. 



As to the relative importance of each substance in particular, it is a 

 difficult problem to solve. We know by experience that the composi- 

 tion of the ash of any plant varies very considerably with the period of 

 the year at which the plant is cut, and the parts of the plant that are 

 burnt for analysis ; so that it is by no means an easy task to state with 

 scientific accuracy what substances any plant takes in largest quantities 

 from the soil. 



It is, however, a fact of the greatest interest that for a given plant 

 the mineral ingredients derived from the soil are constantly found in the 

 same relative proportions, and the same law holds good for the various 

 portions of a plant, provided that we consider them in a state of 

 maturity — i. e., when each portion has done all the work that is allotted 

 to it by Nature. 



I was requested some time ago to draw up a report upon a number of 

 •jnulyses of sugar-cane executed by chemists whose results could be 

 thoroughly relied upon, and to explain, if possible, why they differed so 

 widely with regard to the relative amounts of potash, phosphoric acid, 

 silica, &c, found by each of them, and occasionally by the same chemist. 

 After submitting the matter to a careful investigation it was found, not 



