34 report — 1877. 



to the Committee by Mr. M. J. Lansdell j and as they appear to show con- 

 clusively the valueless character of either of the above processes for deter- 

 mining " Reduced " Phosphates, the results are given in full. The samples 

 were all passed through the same sieve, and the proportions employed were 



those recommended by the authors. 



Dissolved (equal to Ca 3 P 2 0„). 



Sample contained By Sibson's By ChesshiveV 



(equal to Ca 3 P 2 H ). method. method. 



Cambridge coprolite 56-07 per cent. 8-32 p. c. 2'23 p. c. 



Bone-ash 76-87 „ 10-58 3-07 



Navassa phosphate 65-62 „ 7*48 5-73 



German phosphate 60'74 „ 8-04 2-09 



Bedonda phosphate (dried) 87-42 „ 19-72 56-97 



Bedonda phosphate (lump) 86*58 „ 19*10 64-65 



By employing a solution of bicarbonate of twice the above strength, the 

 Bedonda phosphate gave equal to 84-3 of Ca 3 P 2 O a in solution. 



Using a smaller quantity of the sample in the oxalate method, 47'76 per 

 cent, passed into solution. 



It appears, therefore, that " reduced '' phosphates are indicated by each 

 process, even in natural phosphatic materials which have never been treated 

 with acid, and hence the methods of determination are useless*. 



The same objections apply to the citrate-of-ammonium method, especially 

 with respect to the phosphate of aluminium known as " Bedonda Phosphate." 



It follows, therefore, that the latter comparatively cheap material would 

 (if introduced into a superphosphate) be mistaken for and quoted as " re- 

 duced phosphate." 



From the above considerations it appears that the known methods of 

 determining the reduced phosphates are purely arbitrary. 



It is now generally admitted that the cause of the "going back" to the 

 condition of insoluble phosphate is the presence of iron or aluminium in the 

 manure; and many chemists are of opinion that the "reduced" phosphates 

 actually consist of the phosphates of iron and aluminium produced by some 

 such reaction as the following : — 



*B 



CaH 4 (P0 4 ) 2 + Al 2 (S0 4 ) 3 = 2 Al P0 4 + CaSQ , + 2H 2 S0 4 . 



At any rate it is a fact that only manures containing iron and aluminium 

 have a tendency to form reduced phosphates ; so that the manufacturer has 

 the remedy in his own hands, to avoid using mineral phosphate containing 

 iron or aluminium. 



In the analysis of mineral phosphates the proportion of oxide of iron and 

 alumina is usually stated, but these constituents rarely appear in the analyses 

 of " superphosphates " made therefrom. 



It is generally held that the phosphates of iron and aluminium have a 

 very limited manurial value, and this fact is a strong argument against the 

 reduced phosphates being calculated into and credited as phosphate of 

 calcium. The value of a manure so largely depends on the proportion of 

 oxide of iron and alumina present, that the Committee is very strongly of 

 opinion that the united percentage of these two bases in a manufactured 

 manure (superphosphate) should always be stated. By doing so the manu- 

 facturer or purchaser would be enabled to judge of the probability of a newly 

 made manure " going back " on keeping, and he would be in a better posi- 

 tion to form an opinion of the true value of the sample. At the same time 



* Mi-. John Hughes has made experiments leading to a similar conclusion. Chem. 

 News, vol. xix, p. 220 and vol. xx. p. 111. 



