34 REPORT — 1875. 



The above results show that neither method is at all satisfactory ; and Sir, 

 John Hughes* has made experiments leading to the same conclusion. 



Another correspondent writes, " There is no reliable process known for the 

 estimation of ' reduced phosphates ' under all circumstances. Even the 

 citrate-of-ammonium method (which seems to be the one generally preferred) 

 utterly fails to distinguish between 'reduced phosphate' and the native 

 phosphate of aluminium known as 'Redonda phosphate,' the latter being 

 largely soluble in the citrate-of-ammonium solution ; so that the latter, which is 

 a comparatively cheap material, if introduced into a superphosphate, would, 

 according to the results obtained by the methods usually employed for esti- 

 mating reduced phosphates, be quoted as the latter." 



Mr. T. L. Patterson has criticised the citrate-of-ammonium method in a 

 paper contributed to the ' Chemical News' f. 



Mr. W. Galbraith makes the following remarks on the estimation of 

 " reduced phosphate " : — 



" It seems to me that an arbitrary method of determining these phosphates 

 would serve every purpose — that is, provided there is a necessity for deter- 

 mining them (from a commercial point of view), which I am inclined to 

 dispute ; because any other phosphate in as fine a state of division as these 

 'reduced phosphates ' is of equal value ; and if (as some chemists maintain) 

 these ' reduced phosphates ' consist principally of phosphates of iron and 

 aluminium, they cannot and should not be reported as, or assumed to be, 

 phosphate of calcium. 



" It is well known that the presence of oxide of iron and aluminium is 

 the cause of the manure ' going back.' Superphosphates containing no iron 

 and aluminium do not ' go back ; ' so that the manufacturer has the remedy 

 in his own hands — to avoid using mineral phosphate containing iron and 

 aluminium. 



" At present a manufacturer who makes his manure from a phosphate 

 containing iron and aluminium, and who sells it immediately after maniifac- 

 ture, has a decided advantage over another manufacturer who has made his 

 manure from a phosphate containing no iron and aluminium, because a 

 mineral phosphate containing iron and aluminium is much cheaper than 

 one free from those substances. Besides, the iron and aluminium are 

 almost invariably stated in the analysis of a mineral phosphate, while 

 those substances are seldom if ever mentioned in the analysis of a super- 

 phosphate. 



" I do not think it advisable (even if possible) to determine the actunl 

 amount of ' reduced phosphates ; ' but an arbitrary method, or a method of 

 determining phosphates of a given fineness, which would include ' precipi- 

 tated phosphates,' would, I think, be very serviceable ; and such a process 

 could be easily devised." 



Statement of the Commercial and Afirieultural Value of Manures. 



"Without exception, all the chemists who reply to this question are of 

 opinion that it is highly undesirable that analysts should express any opinion 

 on the commercial value of a manure. Many of them believe that tricalcic 

 phosphate (for instance) has a very different value according to its origin 

 and state of division, and that any valuation of a manure not taking this 

 and similar facts into account must be worse than useless. Most of the 

 chemists who have replied consider that phosphates of iron and aluminium 



» Ohem. News, June 4, 18G9, p. 26G. i" May 31 and June 7, 1872, 



