28 REPORT — 1875. 



" Mr. Alfred H. Allen. " J"'^^ ^^' ^^^^- 



" Dear Sir, — "We are in receijDt of your favour relating to the examination of 

 phosphates and potash salts; but we must decline to give you the information 

 required, as we do not think ourselves called upon to publiah our methods of 

 analysis, which we have perfected after long aud careful investigation, for 

 the benefit of those who have not taken this trouble. 



" We arc, dear Sir, 



" Yours obediently, &c." 



A French chemist of very high standing says he belongs to that class of 

 chemists who cannot afford to work " pour la gloire," but must keep their 

 methods, their only capital, secret. 



It is evident that the interests of science would materially suffer if a 

 similar system were adopted by many chemists ; but happily the above 

 answers stand in striking contrast to the generous and elaborate replies that 

 have in very many instances been sent to the Committee. 



The answers received to the various specific questions put have shown in 

 a very striking manner how very various and even irreconcilable are the 

 opinions held by chemists on many of the points submitted for their con- 

 sideration. On this account the Committee refrains for the present from 

 expressing any definite opinions on the points in question ; but feeling that 

 the communications received contain much information which should be at 

 once in the possession of those interested, it begs here to submit to the 

 Association the following digest of the replies received up to the present 

 time. 



The Committee has avoided as far as possible any specific mention of the 

 sources of the various items of information, but has departed from this rule 

 in cases in which the value of the information would have been seriously 

 diminished if the authority on which it was quoted had not been given. 



Phosphoeic Acid. 



Solution of tJie Manure and separation of Silica, 



In the case of soluble phosphates treatment with cold water, with (in 

 some cases) subsequent washing with hot water, seems universal. Most 

 chemists prefer to lake a considerable quantity of the manure, and grind it 

 with small successive quantities of cold water in a mortar. An aliquot part 

 of the filtered solution is taken for analysis. 



With but one or two exceptions, h3rdrochloric acid is universally employed 

 for effecting the solution of insoluble phosphates *. 



In the great majority of cases they then recommend evaporation to com- 

 plete dryness. Some operators omit this step as a rule, but classify it among 

 the precautions necessary when great accuracy is required. The effect of 

 evaporation to dryness is considered to bo twofold ; silica is rendered 

 insoluble and fluorides are decomposed with volatilization of hydrofluoric 

 acid or of fluoride of silicon. The residue is next treated with hydrochloric 

 acid in the ordinary manner, and the insoluble silica filtered offf. 



* It is evident that the addition of a few drops of nitric acid is desirable here to insure 

 the complete peroxidation of any ferrous compounds which may be present. 



t It is evident that iu presence of fluorides the silica here found will not strictly 

 represent the quantity originally present in the sample. 



