ANALYSIS. 



of the sulphate of lime obtained per- 

 mits us to calculate that of the lime 

 which formed part of the precipitate 

 thrown down by the ammonia in tbe 

 first instance. 100 of sulphate of lime 

 are equivalent to 41-5 of pure lime. 



The alcoholic liquor is concentra- 

 ted in order to expel the spirit ; as it 

 is acid, it is saturated with ammonia 

 until a slight precipitate begins to be 

 formed, which is not redissolved upon 

 shaking the mixture. A few drops 

 of the hydrosulphate of ammonia are 

 then added, upon which the iron and 

 the manganese fall in the state of sul- 

 ])luirets. As a part of the metals has 

 been precipitated in the state of ox- 

 ide by the ammonia added in the hy- 

 drosulphate, it is well to digest for 

 eight or ten hours, because the hy- 

 drosulphate of ammonia always ends 

 by changing the metals present into 

 sulphurets, which being washed, 

 dried, and reduced to the state of 

 oxides by calcination in a platinum 

 capsule, are weighed. 



If the first ammoniacal precipitate 

 did not contain phosphoric acid, its 

 w-eight ought to be reproduced by 

 addmg that of the lime to that of the 

 metallic oxides proceeding from the 

 calcination of the sulphurets. Any 

 loss which is noted after this, is due, 

 if the process has been well conduct- 

 ed, to phosphoric acid, which had not 

 been collected, but which has remain- 

 ed in the state of phosphate of ammo- 

 nia in the liquid treated by the hydro- 

 sulphate. To determine with pre- 

 cision the presence of phosphoric 

 acid, the liquid in question must be 

 evaporated to dryness, and the resi- 

 due heated strongly in a platinum 

 capside. After the dissipation and 

 decomposition of the ammoniacal 

 salts, there remams watery phos- 

 phoric acid, distinguishable by its 

 powerful acid reaction, its sirupy con- 

 sistence, and its fixity. 



By way of example, I shall give the 

 results obtained in an analysis of this 

 kind : 



From the acid liquor, ammonia threw down 

 of: grs- troy. 



Phosphates and metallic oxides . • tj'012 



rhese gave of sulphate of lime . . &"68 

 Equivalent to lime .... 3'612 



Hydros\iIphate of ammonia caused a pre- 

 cipitate, which, calcined, gave of me- 

 tallic oxides 1620 



Lime and metallic oxides together . 5-233 

 Uiffereuce due to phosphoric acid . 2'789 



The analysis for phosphoric acid 

 may be simplified by employing a pro- 

 cess conceived by M. I3erthier, and 

 which is founded upon the strong af- 

 finity of this acid for the peroxide of 

 iron, and the insolubility of the phos- 

 phate of the peroxide of iron in dilute 

 acetic acid. If to a fluid containing at 

 once phosphoric acid, lime, peroxide 

 of iron, alumina, and magnesia in so- 

 lution, ammonia be added, the precipi- 

 tate will contain the whole of the phos- 

 phoric acid. The acid will be in great 

 part combined in the state of phos- 

 phate of iron, if the peroxide of iron 

 be in quantity more than sufficient to 

 neutralize it : a condition which must 

 be frequently expected in an arable 

 soil ; however, to make sure of this 

 point, it is well to add a certain quan- 

 tity of the peroxide of iron to the soil 

 which is to be analyzed. Besides the 

 phosphate of iron, the precipitate may 

 contain phosphate of lime, phosphate 

 of alumina, and certainly ammoniacal 

 magnesian phosphate. Finally, with 

 these phosphates will be found asso- 

 ciated alumina and oxide of iron, the 

 latter especially, if it has been intro- 

 duced in excess. The precipitate, col- 

 lected upon a filter and washed, must 

 then be treated with dilute acetic acid, 

 which will dissolve the lime, the mag- 

 nesia, and the excess of the oxides of 

 iron and alumina ; and there will re- 

 main phosphate of iron or phosphate 

 of alumina, because the latter salt is 

 as insoluble as the former in acetic 

 acid. Whenever the precipitate in 

 question, therefore, leaves a residue 

 which is insoluble in vinegar, the 

 presence of phosphoric acid may be 

 inferred ; this residue may consist of 

 basic phosphates of iron or alumina, 

 or of a mixture of the two salts, and 

 no great error will be committed if 

 one hundred parts of this residue, cal- 

 cined, be assumed as representing 

 fifty of phosphoric acid. 



The presence of silica in the pre- 

 cipitate insoluble in acetic acid may, 



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