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X. — On the Chemical Constituents of Crops. Bj Charles 

 Daubeny, M.D., F. R.S.J Professor of Rural Economy in the 

 University of Oxford. 



To the Editor. 



Sir, — I hasten to apprise your readers of an error which has been 

 kindly pointed out to me by a friend, as occurring in the Table of the 

 Constituents of Crops published in the last number of the Journal, and 

 affecting the whole of the column in which the proportion of azote be- 

 longing to the several vegetables is stated. Owing to the omission of a 

 cipher, the quantity of azote given by Boussingault for 10,000 lbs. is 

 represented as that existing in 100,000 lbs., and the error has of course 

 been the means of rendering the numbers in the antecedent column re- 

 lating to the amount of water and carbon likewise incorrect. 



It will be easy for your readers to correct both these errors, by add- 

 ing in every case a cipher to the nimibers quoted in my Table in the 

 column relating to azote, and by calculating the water and carbon from 

 the difference between the amount of the fixed ingredients and of the 

 azote added together, and that of the sum total supposed to have been 

 operated upon. 



Thus if in wheat the azote be .... 2,380 



And the fixed ingredients • . . . • 2,137 



Together . . 4,517 



Then its carbon and water ought to be . . . 95,483 



That being the sum necessary to make up . . 100,000 



But I ought not, perhaps, to forego the present opportunity of caution- 

 ing your readers against placing too implicit a reliance on the results of 

 the analyses therein given, whether as relating to the proportion of 

 nitrogen, or to that of the fixed ingredients of the crops. 



With regard to the former, Boussingault, who is my authority, has 

 published, in a later number of the " Annales de Chimie " than that 

 Avhich supplied me with the numbers quoted in my Table, a fresh 

 series of results concerning most, though not all, of the vegetables enu- 

 merated, which, being probably more accurate than the former ones, I 

 will by permission insert; and with regard to the fixed ingredients, I 

 believe many of our first chemists are of opinion, that the results ob- 

 tained by Sprengel require verification before they can obtain the full 

 confidence of the scientific public. 



When indeed we consider the labour, skill, and experience which 

 must be called into requisition for the execution of so difficult and ex- 

 tensive a series of analyses as that quoted in my Table, we cannot help 

 wishing that so great a work had been undertaken under the auspices of 

 a public body capable of furnishing the requisite funds, and by an 

 association of chemists, who could assist each other in their respective 

 labours, and be a check upon the errors into which they might severally 

 fall, rather than by a solitary and irresponsible individual, whatever may 

 be his meiits or respectability. 



