April 1908 



339 



Scientific Agriculture, 



95° (it was a damp cool day with an air 

 temperature of 13° C), and the wetted 

 heap ran up to this point more quickly 

 than the unsprinkled heap. This was 

 because 1 cwt. of superphosphate does 

 not contain water enough to slake all 

 the lime in h cwt. of cyanamide, so that 

 the mixture did not react as strongly as 

 one poorer in cyanamide would have 

 done. Further, with such a small pro- 

 portion of superphosphate there was not 

 enough acid in it to neutralise all the 

 ammonia produced, consequently a little 

 ammonia could be detected escaping 

 from the steaming heaps both by the 

 nose and by litmus paper. 



These latter trials are quoted here to 

 show that sprinkling with water can be 

 used with advantage while making up a 

 mixture of superphosphate and cyana- 

 mide, as it keeps down the dust and res- 

 tricts the rise of temperature without 

 adding any difficulties to the mixing 

 process or causing the final product to 

 cake or set in any way. In the above 

 experiments the material was friable 

 and in a good working condition on the 

 following day. 



As will be seen from the weights the 

 heat generated caused the evaporation 

 of a good deal of water, so that the 

 heaps had lost weight considerably when 

 they come to be bagged. There was no 

 tendency to cake shown during the 

 mixing, and on the folio whig day, when 

 the heaps had cooled down, the mixture 

 was still perfectly loose and friable, 

 neither has it caked at all after lying up 

 in bag for two months and a half. The 

 various mixtures are all light friable 

 powders, rather drier than the original 

 superphosphate and in perfect condition 

 for sowing by hand or drill. 





Mixture 

 in lb. 



Tempera- 

 ture, C. 



Loss of 

 Weight, lb. 



Experiment 



Cyanamide. 



Super- 

 phosphate, 



ab 

 a 



c3 



Maximum 

 in heap. 



After Mix- 

 ing. 



it 

 o 



02 <„• 

 s-i SO 



o a 

 < 



No. 1 



„ 2 

 „ 3 



;, 4 



„ 5 



11 



22 

 41 

 56 

 56 



224 

 224 

 224 

 112 

 112* 



16-5 



18 



18 



13 



13 



53 

 87f 

 llOJ 

 95§ 

 93|| 



5 

 5 

 28 

 3 

 5 



12 

 ]2 



29 



Samples were taken from the first 

 three mixtures and analysed with the 

 following results, in which comparison 

 is made between the figures obtained by 



* Also 20 lb. water, f After 6 hours. J After 

 11 hours. $ After 2£ hours. || After 1 hour. 



analysis and the figures calculated on 

 the assumption that no loss of fertilising 

 material bad taken ' place, after due 

 allowance had been made for the shrink- 

 age in weight due to the loss of water 

 on mixing. 



Cyanamide 

 Superphosphate 

 Mixture I .. 



II .. 

 HI 



Nitrogen. 



0- 864 



1- 510 

 3-080 



3 



3 



17-24 



0-852 

 1'630 

 3-054 



Phosphoric Acid. 



11-48 

 6-66 

 1-65 



Citric 

 Acid Soluble. 



12-35 

 12-14 

 11-88 



a 



3 



12-68 

 11-65 

 11-22 

 10-57 



Allowing for the errors introduced by 

 mixing and sampling, these results are 

 quite consistent and lead to the follow- 

 ing conclusions : — 



(1) There is no loss of nitrogen ; any 

 ammonia that is generated on the slak- 

 ing of the lime is at once fixed by the 

 superphosphate. This conclusion is con- 

 firmed by the observation that not the 

 least smell of ammonia could be detected 

 during mixing or arising from the heap 

 after mixture, except in mixtures 4 and 5 

 where an excess of cyanamide was used. 



(2) The water soluble phosphoric acid 

 in the superphosphate is rendered in- 

 soluble in proportion to the amount of 

 cyanamide introduced. .4s would be 

 expected, the free lime of the cyanamide 

 combines with the soluble calcium phos- 

 phate in the superphosphate to form a 

 calcium phosphate insoluble in water. 

 A mixture of one part cyanamide to ten 

 parts superphosphate precipitates most 

 of the soluble phosphate, when the 

 mixture is raised to 1 to 5 all the soluble 

 phosphate has been converted into di- 

 calcium phosphate. 



(3) The amount of citric acid soluble 

 phosphate (determined by the official 

 method of shaking for half an hour with 

 2 per cent, citric acid solution* under- 



* The citric acid solution is used to discrimi- 

 nate between phosphates which are readily 

 soluble in soil water, such phosphates as are 

 found in basic slag or basic superphosphate or 

 are produced in the soii by the application of 

 superphosphate, and on the other hand, the 

 unchanged phosphate of lime which is practi- 

 cally insoluble in the citric acid. 



