add tilveoilS^ c&)i»dii(iBH Hh W^o^AIwi y^l'jof course sub- 

 tracted, rj gqoiD OHfiO Vilv/ 39? lOfT ol) T - 



c. The liquor from which the phosphate of lead had been 

 separated (6), when freed from lead by sulpliuretted hydrogen, 

 and rendered alkaline by ammonia, was employed for the de- 

 termination of the lime and magnesia, by means of oxalate of 

 ammonia and phosphate of soda in the usual way. In the last 

 five cases the determination of the phosphoric acid was con- 

 trolled by the process lately recommended by Fresenius with 

 sulphate of magnesia. (See Liebig's Aii7talen, July 1845, and 

 Chemical Gazette for October 15.) 



IV. A fourth quantity of ashes (about 2-3 grammes) was 

 employed to determine the alkalies. It was digested with an 

 excess of barytes and a little water in a silver basin for about 

 two hours. The alkaline mass was acidified with muriatic 

 acid, and evaporated to dryness. It was then redissolved in 

 distilled water, and caustic barytes added to the solution, to 

 precipitate all the phosphoric acid, sulphuric acid, lime and 

 magnesia it contained. The filtered liquor was then freed 

 from barytes by means of carbonate of ammonia, and the clear 

 solution was evaporated to dryness and heated to redness till 

 nothing remained but the chlorides of the fixed alkalies. The 

 potash was separated from the soda by means of chloride of 

 platinum in the usual way. 



It is evident, from the results of the analyses contained in 

 the preceding tables, that the sugar-cane, to ensure its success- 

 ful cultivation, requires to be furnished with a very large 

 quantity of silicate of potash, and also with a considerable 

 amount of the phosphates. In fact, there are few of our cul- 

 tivated plants, except perhaps wheat, barley and the other 

 Cerealia, which require so large an amount of these substances. 

 It is not wonderful therefore that the cultivation of the sugar- 

 cane, from the inconsiderate way in which it has hitherto been 

 too often conducted, should have been found rapidly to dete- 

 riorate, and in the course of time to exhaust most ordinary 

 soils. I apprehend, however, that this exhaustion of the soil 

 by the cultivation of the sugar-cane is by no means an vm- 

 avoidable result, and that by means of suitable arrangements 

 successive crops of sugar might be raised without the soils 

 being materially injured. Wheat, or any other kind of grain, 

 necessarily causes the removal of a portion of the valuable inor- 

 ganic constituents of the soil, such as the alkalies, phosphates, 

 &c., which can only be returned to it indirectly ; but with 

 sugar the case is quite otherwise. Sugar is a purely organic 

 substance, consisting of carbon and the elements of water, all 

 of which can be derived from the atmosphere, and contains 

 neither alkalies nor phosphates; so that if the ashes of the 



