EXPERIMENTS ON POTATOES WITH DIFFERENT MANURES. 291 



In accordance with calculations based on these analyses, the 

 manures were carefully weighed, so that all the plots should 

 have equal weights of phosphoric add, whether in the soluble 

 or insoluble condition, as also of ammonia and of potash, no 

 matter in what form it was employed. The mixtures having 

 been made in the laboratory, they were placed in bags, and the 

 bags on their respective plots, so that no mistake should occur 

 in their application ; the manures were then sown personally by 

 myself, aided by two skilled assistants, in as even a manner as 

 it was possible.* 



When the time arrived that the crops should be lifted, the 

 samples for determination of the composition of the potatoes as 

 affected by the manures, were chosen from those plots which 

 ■stretched in a band across the field, viz., plots 2, 7, 12 ; 3, 8, 13 ; 

 18, 23, 28 ; 33, 38, 43 ; and 24 (see Table I., these plots are en- 

 closed in black lines). Some of the tubers were reserved for 

 the estimation of the specific .i^a-avity, which is generally con- 

 sidered as an indication of the amount of starch present, others 

 were employed for the direct estimation of the starch, nitrogen, 

 fibre, moisture, and ash. The amount of starch was estimated 

 by Sicgert's process, as this, when done in du})licate, was found 

 to give the most accurate results, as, for example, No. 33, accord- 

 ing to two analyses of the dried sample, was found to contain 

 76-9 and 7G'G per cent, of starch.-f- 



* This does not apply to y)lots A. and B. 



t Siuwert's process (Landw. Vers, .s'/^f/., xxiv. 427), in which the potato meal is 

 heated in sealed tubes with tjirtaric acid to 115" C, was tried, but the ri\sult.s 

 were so discordiint that it was abandoned in favour of the al)ove-mentioned 

 method, in which sulnhuric acid is eniploycd at 95" C. for ei<;ht hours, and then 

 after filtration, the solution lu-in^ first diluted, is again licatcd with more acid ; 

 the resulting glucosp wnsestimated by ravy'samnioniacal FchJ'ng's copper solution. 



