e. The solution (d) is filtered from the chlo ride of silver, is boiled for a few minutes, then saturated exactly with ammonia. If phosphoric acid be present, a yellow precipitate of phos phate of silver, very soluble in excess of ammo nia, is produced.
j: A little of the aqueous solution is evapo rated to dryness, and a drop of nitric acid added to the residue : effervescence indicates carbonic acid, due in all probability to the decomposition of some organic acid by ignition.
We have next to test for the bases in solution.
g. The liquid is rendered slightly alkaline by ammonia free frorn carbonate.* A white precipitate shews phosphate of lime or magnesia, or both.
h. The filtered liquid is tested by oxalate of ammonia; if lime be still in solution, a white cloud falls.
The oxalate of lime is separated by filtra tion and phosphate of soda or ammonia added ; brisk stirring with a glass rod causes a white crystalline precipitate if any magnesia were still contained in the liquid.
k. A portion of the original liquid (b) is acidulated with a drop or two of hydrochloric acid; if sulphuric or phosphoric acid have been detected (by c and e), chloride of barium in slight excess is added, the solution filtered, heated, and precipitated by a mixture of caustic and car bonate of ammonia ; it is again filtered, the liquid evaporated to dryness and ignited, the residue dissolved in alcohol, and sufficient alco holic solution of bichloride of platinum added to produce a yellow liquid : a yellow precipitate indicates potash. If no sulphuric or phosphoric acid be present, the use of the chloride of ba rium and ammonia will become unnecessary.
/. Decant the yellow solution just obtained ( k) from the precipitate, if there be any, and allow it to evaporate spontaneously or at a very gentle heat. If soda be present, long prismatic yellow needles of the double chloride of pla tinum and sodium form. This is the best test of the presence of soda. The yellow tint which its salts communicate to the exterior flame of the blowpipe, when heated on a platinum wire, has been proposed, but this is by no means an unequivocal appearance. Almost all the animal fluids contain soda in the form of common salt.
B m. The insoluble fixed residue (13) may contain phosphates and carbonates of lime and magnesia, as well as phosphate and oxide of iron, and traces of silica. The residue is treated with nitric acid, by which every thing but the silica is dissolved. Carbonic acid, if present, is manifested by effervescence.
n. The solution is diluted and filtered; to one portion ammonia free from carbonic acid is added ; if phosphoric acid be present, a preci pitate occurs whilst the liquid still remains acid ; under these circumstances ammonia is added as long as the precipitate at first formed re-dissolves in the solution, still acid. If a solu tion of acetate of lead, carefully dropped in, cause a white precipitate, soluble in nitric acid, and which if collected and dried fuses before the blowpipe into a semi-transparent bead, which assumes a crystalline structure on cool ing, phosphoric acid is indicated by the phos phate of lead thus obtained.
o. Another portion of the acid liquid is neu tralized by ammonia, and the precipitate, if any occur, re-dissolved by acetic acid. Oxalate of ammonia shews lime by the formation of a white precipitate.
p. To the liquid filtered from the oxalate of lime carbonate of ammonia is added in slight excess ; if the previous examination. have shewn phosphoric acid to exist, a crystalline precipitate indicates the double phosphate of ammonia and magnesia. If no precipitate be thus obtained, boil the liquid, and the ma,gnesia in solution falls as carbonate.
g. Oxide gf iron is detected instantly by adding a drop of solution of ferroryanide of po tassium to the acid solution: an immediate Prus sian blue precipitate shews iron, if present. The precipitates obtained in the previous experi ments for lime and magnesia will, instead of being white have a more or less decided rusty brown tint, especially when dry, if iron form any considerable part of the matter examined.
For the detection of iodine, lead, and the other bodies enumerated in the list of inorganic substances for which WC may occasionally have to look, the reader is referred to the following directions for the quantitative estimation of the different compounds.