802 



ORGANIC ANALYSIS. 



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 (B) 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 oj 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 magnesia 

 in solution falls as carbonate. 



q. Oxide *' iron is detected instantly by 

 adding a drop of solution of ferrocyanide ofpo- 

 tassiit/tilo 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 we may occasionally have 

 to look, the reader is referred to the following 

 directions for the quantitative estimation of the 

 different compounds. 



Quantitative estimation- 

 For the convenience of analysis our saline 

 matter may be divided into two portions, one 

 of which is employed for determining the acids, 

 the other for the bases. The first portion will 

 enable us to ascertain the quantity of carbonic 

 and phosphoric acids, of chlorine, and of sul- 

 phuric acid. From the second portion we 

 obtain the potash, soda, lime, magnesia, iron, 

 and alumina, if, as rarely occurs, the latter be 

 present. 



Other ingredients will usually be matter of 

 special examination ; the details of the methods 

 to be pursued are subjoined. 



We begin by treating the salts to be exa- 

 mined with water (solution A). Nothing but 

 carbonates and phosphates of the earths will 

 thus remain undissolved (residue B). 



(A.) Carbonic acid. The aqueous solution is 

 treated with lime-water, or with a mixture of 

 ammonia and nitrate of lime, as long as any 

 precipitate is produced. If no phosphates be 

 present, this consists of carbonate of lime, 

 the solution is boiled filtered, the precipitate 

 ignited, and after adding a few drops of strong 

 solution of carbonate of ammonia heated below 

 redness and weighed, 100 grs. of carbonate of 

 lime indicate 44 of carbonic acid When phos- 

 phates are present, we proceed as follows : 



Phosphoric acid. The precipitate obtained 

 by lime-water, as thus directed, contains all the 

 phosphoric acid that may be present. If there- 

 fore phosphates existed in our solution, the pre- 

 cipitate, after its weight has been carefully 

 ascertained, must be dissolved in nitric acid, 

 and caustic ammonia (free from carbonic acid) 

 added in slight excess. The phosphoric acid 

 separates as a gelatinous precipitate of phos- 

 phate of lime. It must be ignited and the 

 weight deducted from that of the mixed pre- 

 cipitate previously obtained ; the difference in- 

 dicates the quantity of carbonate of lime. The 

 precipitated phosphate of lime contains 49*1 

 per 100 of phosphoric acid. Phosphate of lime 

 dissolves in nitric, hydrochloric, or acetic acid 

 without effervescence, and is thrown down by 

 ammonia in a gelatinous form. The phos- 

 phates and carbonates being thus separated, 

 the filtered solution is treated for, 



Hydrochloric acid. The quantity of this 

 acid or of the chlorine it contains may easily 

 be determined by .precipitating the solution 

 pretty strongly acidulated with nitric acid by 

 means of nitrate of silver. The chloride of 

 silver thus obtained is completely soluble in 

 ammonia, but resists the action of strong nitric 

 acid even when boiling. The precipitate must 

 be ignited; it should undergo fusion into a 

 horny mass at a heat a little below redness. 

 It is now weighed; 100 parts indicate 25 of 

 chlorine. 



