396 PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 



In this case, the quantity of insoluble phosphates was much 

 higher than I had anticipated. My instructions to the manu- 

 facturer of the manure were, to send me a superphosphate in 

 which all the phosphates were soluble ; and though I did not 

 expect that this could be done, it was hoped that not more than 

 2 to 4 per cent, would have been found insoluble. Had time per- 

 mitted, an endeavour would have been made to procure another 

 sample, but, unfortunately, this was not possible, and it was 

 necessary to use the manure as it reached me. 



The sulphate of ammonia was a good sample, containing 

 2072 per cent, of nitrogen, equal to 25-16 per cent, of ammonia, 

 or 97"58 of the pure sulphate. The glue used was good carpen- 

 ters' glue. Reducing this substance to a state of powder proved 

 a task of some difficulty. Previous experience had shown me 

 that the only chance of succeeding was to kiln-dry it carefully, 

 and then grind it under edge-stones, which Messrs. Poynter & 

 Son, of Glasgow, undertook to do. After kiln-drying for some 

 days, the attempt was made to grind it, but without success, and 

 it was necessary to return it into the kiln and continue the dry- 

 ing process, until at length, by grinding and sifting, it was got 

 in the form of a powder of about the fineness of coarse sand. 

 In this state it contained 1421 per cent, of nitrogen. 



It was intended that the manures should have been dis- 

 patched to the experimenters in time for sowing in the last 

 week of May, or first week- of June, but owing to the unexpect- 

 ed delay occasioned by the difficulty of grinding the glue, they 

 could not be sent out till the end of the first week of June, 

 which is later than could have been desired in an ordinary sea- 

 son, but, as the event proved, was no disadvantage during the 

 past year. 



In the arrangement of the manures, it will be understood that 

 each kind of superphosphate was used alone, at such a rate as to 

 supply 112 lbs. soluble phosphoric acid;* again, mixed with sul- 

 phate of ammonia in quantity sufficient to supply 56 lbs. nitro- 

 gen ; and a third time with glue, supplying the same amount of 

 that element. Every plot was in duplicate, and the general 

 arrangement was that shown in the instructions issued to the 

 experimenters (see page 390), but they were not absolutely tied 

 to this, as it was manifest that the nature of the piece of land 

 selected for the experiments must to a considerable extent 

 govern the arrangement. 



* The substance here called phosphoric acid is that known in the accurate 

 nomenclature of modern chemistry as phosphoric anhydride, and I mention this 

 particularly hei e so as to avoid misapprehension. I have preferred to use the term 

 phosphoric acid, because, though less accurate, it is better known to non-chemical 

 readers. 



