ON THE ESTIMATION OF POTASH AND PHOSPHORIC ACID. 35 



have an exceedingly limited raanurial value. The relative maiiurial values 

 attributed to phosphoric acid existent in various states is very differently 

 regarded ; and as many of the opinions expressed appear to be based on very 

 insuiScient evidence, the Committee thinks it unnecessary to quote the 

 diflferent replies received. 



Mode of occurrence of the Constituents of Manufactured Manures, and 

 statement of the Hesults of Analysis. 



On this subject the Committee has received a large amount of valuable but 

 somewhat discordant evidence. 



Very strong opinions are expressed to the effect that the quantity of iron 

 and aluminium present in a manufactured manure (superphosphate) should 

 always be stated. Such a plan would enable the manufacturer or purchaser 

 to judge of the probability of a newly made manure " going back " on 

 keeping, and would enable a more accurate opinion to be formed of its true 

 value than is possible while the presence of iron and aluminium is ignored. 

 At the same time the estimation of the " reduced phosphates " would often 

 be rendered superfluous. 



With respect to the mode of occurrence of the constituents of manufac- 

 tured manures, the Committee considers the evidence before it too vague and 

 conflicting to justify any expression of opinion at present. 



Potash Salts. 

 Estimation of Potash. 



The Committee has received comparatively few replies on the estimation of 

 potash in commercial salts containing it, on account of the limited number 

 of chemists having special experience in its detennination. The answers 

 received are, however, from chemists of the first rank as authorities on the 

 subject, and appear to be almost exhaustive of the question. 



The method of estimation by piatinic chloride is employed by all the chemisfa 

 who have communicated their processes to the Committee, the only differences 

 being in the manipulation and details of the method. 



Some chemists recommend the removal of any sulphates by addition of a 

 sHght excess of chloride of barium, and some also remove any calcium or mag- 

 nesium which may be present. 



The Committee is in possession of some correspondence respecting a sami)lo 

 of " muriate " which was analyzed independently by Professor Fresenius and 

 Mr. R. E. Tatlock ; and as it throws much light on the origin of the discrepancies 

 often observed in the estimation of potassium, the Committee quotes it almost 

 in extenso, together with a descriijtion of the methods employed by the two 

 authorities above i-eferred to. 



Messrs. Wallace, Tatlock, and Clark write : — 



" We employ the platinic-chloride method as described by Fresenius in the 

 sixth edition of his ' Quantitative Analysis,' with a slight modification which 

 renders it more applicable to all the numerous varieties as well as strengths 

 of commercial potash salts. After pounding and mixing in the usual way, 

 a quantity of the salt (500 grains) is weighed out, dissolved in hot water 

 and filtered. The filtrate and washings being cooled to normal temperature 

 are mixed well, made up with cold water to a fixed bulk (5000 grains) and 

 again mixed ; a portion of this solution (100 grains), equal to 10 grains of the 



d2 



