xii. CROPS 261 



In the high-farming districts of Scotland, a six- course rotation is 

 often followed : 



1. Turnips or swedes, with farm -yard manure and artificials. 



2. Barley, wheat, or oats, unmanured. 



3. Seeds for hay, often with artificials. 



4. Oats, often top dressed with 1 cwt. of nitrate. 



5. Potatoes with farm-yard manure and artificials. 



6. Wheat, unmanured. 



Where high-class malting barley is grown, as on the east coast of 

 England, wheat often follows roots, in order to diminish the supplies of 

 nitrogen left in the soil, before barley is sown. The Norfolk rotation 

 then becomes a five -course one. 



Note on the Analysis of Crops. 



A few remarks about the usual method of analysing crops and 

 other foodstuffs may be given here. Almost all analyses of foods, which 

 have been published until quite recently, were made by a method 

 introduced by Henneberg in 1864, generally known as the "Weende" 

 method. According to this plan, the constituents are reported as 



Water. 



Proteids or nitrogenous matters. 



Fat or ether extract. 



"Nitrogen-free extract" or "soluble carbohydrates". 



Crude fibre. 



Ash. 



The water and ash are determined by general methods, the nitrogen- 

 ous matter by a determination of the total nitrogen and multiplying 

 this by 6'25, and the "fat" by ether extraction. The "crude fibre" 

 is then determined by treating a portion of the sample, from which 

 the fat has been extracted, with boiling dilute sulphuric acid (contain- 

 ing 1*25 per cent real acid) for half an hour, washing the residue until 

 free from acid, and again boiling for half an hour with a solution 

 containing T25 per cent of sodium hydrate. The whole is then filtered 

 and the residue thoroughly washed, dried at 110, and weighed. The 

 residue is next completely incinerated, when the loss of weight gives 

 the "fibre". 



The method used in the determination of the remaining item, "the 

 nitrogen-free extract," in these analyses, is least satisfactory of all 

 being simply to take the difference between the sum of the percentages 

 of the other constituents and 100. 



In the form just described, thousands of analyses have been 

 published, and, though the results are of considerable value, they can- 

 not be considered satisfactory. 



Water. The assumption that only water is expelled by heating a 

 food to a temperature of about 100 is certainly not warranted, as many 

 organic compounds undergo change below this temperature ; moreover, 

 many fats and oils absorb oxygen and consequently increase in weight 

 when exposed to air. The latter objection can be overcome by drying 

 in a current of hydrogen. 



