ON THE ESTIMATION OF POTASH AND PHOSPHORIC ACID. 33 



Other Methods. 



Besides the above-described processes, and trifling modifications of them, 

 descriptions have been received of no other method. The lead, bismuth, and 

 tin processes appear to have fallen into complete disuse. K^o chemist has 

 reported that he precipitates phosphoric acid as tricalcic phosphate by direct 

 addition of ammonia to the original solution. 



'^Reduced" Phosphates. 



Of all the chemists who have communicated with the Committee, only two 

 consider that the so-called "reduced" phosphates can be estimated even 

 approximately by any known method. 



One of these writes as follows : — 



" I employ a process based on the read)' decomposition of gelatinous phos- 

 phate of lime by oxalate of ammonia *, and the almost complete inaction on 

 the mineral phosphate by the same salt. Although not an exact process, it 

 gives good approximate results within g per cent. ; and seeing the urgent 

 need for some such means of estimation, more especially in the case of bone- 

 manures, in which a large proportion of decomposed phosphate may exist 

 imrecognizable by the ordinary soluble phosphate determination, I think it 

 better to employ even an imperfect process than to classify such decomposed 

 phosphate with undecomposed mineral phosphate." 



Professor A. H. Church, referring to the bicarbonate-of-sodium method 

 described in his 'Laboratory Guide 'f, writes, " It is the only method giving 

 approximate results." 



A series of highly instructive experiments on the estimation of " reduced " 

 phosphates has been contributed by Mr. M. J. Lansdell. 



With the oxalate-of-ammonium method of Mr. Alfred Sibson J, and with 

 the bicarbonate method (which was first described by Mr. Chesshire §), Mr. 

 Lansdell obtained the following results, the samples being all passed 

 through the same sieve and the proportions employed being the same as 

 those recommended by the authors. 



Dissolved 

 (equal to C&^ P.^ O^). 

 Sample contained By Sibsoii's By Chesshire'a 



(equal to Caj P^ O^). method. method. 



Cambridge coprolite .... 56-07 per cent. 8-32, 2-23 per cent. 



Bone-ash 76-87 



Navassa phosphate 65-62 



German phosphate 60-74 



Eedonda phosphate (dried) 87-42 



Eedonda phosphate (lump) 86-58 



10-68, 3-07 



7-48, 5-73 



8-04, 2-09 



19-72, 56-97 



19-10, 64-65 



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

 Eedonda phosphate gave equal to 84-3 of Ca3P2 0^ in solution. 



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

 cent, passed into solution. 



* See Chem, News, Sept. 10, IfifiO, p. 123. 



t 3rd Edition, p. 14(5. This process consists in boiling the insoluble poi'tion of 6 

 gvamraes of the sample for one hour with a solution of 10 grammes of sodium bicarbonate 

 in 300 cub. centims. of water ; filtering hot, acidifying, oonnentrating, precipitating with 

 magnesia, &c. 



X Chem. News, Sept. 10, 1809. § Ibid. Sept. 3, 1809, p. 111. 



] 87-">. D 



