ORGANIC ANALYSIS. 



801 



mains, as the phosphate of iron is insoluble in 

 acetic acid. The absence of iron must be 

 determined by dissolving the precipitate in 

 nitric acid, nearly neutralizing with ammonia 

 and adding hydrosulphuret of ammonia; the 

 iron, if present, would fall as a black sulphuret, 

 mixed with oxalate of lime. Oxalate of lime 

 dissolves in dilute nitric acid, and, on super- 

 saturating with ammonia, is thrown down un- 

 changed. By converting the oxalate of lime 

 into the carbonate or sulphate, as directed when 

 speaking of the estimation of lime, the quan- 

 tity of oxalic acid may be inferred 100 grs. 

 of the carbonate indicate of anhydrous oxalic 

 acid 72 grs., and 100 of the sulphate 51.94 of 

 (he acid. 



2. For the inorganic constituents. 

 To ascertain the nature and proportion of 

 the saline matters incineration is resorted to in 

 the manner already described. This process, 

 however, only tells us what the fixed ingre- 

 dients are, and their quantity, in the form of 

 oxides, chlorides, sulphates, phosphates, or 

 carbonates. All the ammoniacal salts are ne- 

 cessarily dissipated, frequently carrying off 

 portions of sulphuric acid and chlorine. The 

 organic acids that may have been combined 

 with the bases are entirely decomposed and 

 their place supplied by carbonic acid, which 

 renders it difficult to 'decide whether any car- 

 bonate actually existed as such in the com- 

 pound ; and moreover the metals, as iron, cal- 

 cium, and magnesium, with other bodies, as 

 sulphur and phosphorus, are for the most part 

 estimated, not (as is sometimes probable, and 

 at others certain, that they existed) in the me- 

 tallic or unoxidized form, but. as oxides or 

 acids. The information we derive from inci- 

 neration is therefore incomplete, and the mere 

 deduction of the weight of ashes from the 

 entire weight of the body burned by no means 

 furnishes us with a correct estimate of the pro- 

 portion of volatile ingredients ; generally speak- 

 ing, however, it is the nearest approximation 

 we can obtain. 



1 shall here describe very briefly the means 

 best adapted to the qualitative and quantitative 

 determination of the saline matters, referring 

 those requiring more ample instruction on this 

 subject to Rose's Manual of Analytical Che- 

 mistry, and the various systematic treatises on 

 the science. 



Although during incineration portions of 

 saline matter, and especially of chlorine, are 

 carried off, and the sulphates are sometimes 

 reduced to sulphurets, we find it the only 

 method by which any thing like an accurate 

 estimate of the inorganic constituents can be 

 obtained, inasmuch as many of these bodies 

 occur in the form of chemical compounds 

 with organic matter, and are thus prevented 

 from forming precipitates with the ordinary re- 

 agents : iron is particularly liable to be thus 

 affected. When practicable, we should usually 

 make an analysis of the solution for the inor- 

 ganic acids before evaporation, and afterwards 

 a second examination of the fixed residue after 

 ignition. 



The inorganic materials for which we shall 



VOL. III. 



have in general to search are comparatively 

 few in number; among the acids, hydro- 

 chloric, sulphuric 1 , phosphoric, and carbonic, 

 with traces of silica, will be those of most fre- 

 quent occurrence. Occasionally we may have 

 to seek for iodine, fluorine, and unoxidized 

 sulphur. Potash, soda, ammonia, lirne, mag- 

 nesia, and oxide of iron, are the bases that will 

 be most frequently the objects of experiment, 

 and now and then we may have to look for 

 copper, lead, and some other metals. 

 Qualitative examination. 



a. The saline residuum, after ignition, is 

 boiled with a little water (solution A) and fil- 

 tered from the insoluble residue (B). 



A. b. The solution, except in special cases, 

 will only contain sulphates of potash, soda, lime, 

 and magnesia, as well as chlorides of the same 

 bases, and phosphates and carbonates of potash 

 and soda. When the alkaline carbonates are 

 present, lime and magnesia need not be looked 

 for; nor need we search for either of these 

 bases if the solution contain phosphates, unless 

 the liquid reddens litmus paper. The liquid 

 is, therefore, in the first place tested with blue 

 and with reddened litmus paper, by which 

 acidity, alkalinity, or neutrality is rendered 

 evident; we then proceed to determine what 

 acids are present. The absence of a precipitate 

 sliould not be too hastily decided on. As a 

 general rule the tests should be allowed to 

 stand twelve hours before a negative result is 

 recorded. 



c. A portion of the liquid is acidulated with 

 nitric acid, and to a small quantity of it a drop 

 or two of solution of chloride of barium added ; 

 a white cloud indicates sulphuric acid. 



d. Into another portion of the acidulated 

 fluid nit rate of silver is dropped in slight excess; 

 a bluish white flocculent precipitate shews the 

 presence of chlorides. 



e. The solution (d) is filtered from the chlo- 

 ride of silver, is boiled for a few minutes, then 

 saturated exactly withammonia. If phosphoric 

 acid be present, a yellow precipitate of phos- 

 phate of silver, very soluble in excess of ammo- 

 nia, is produced. 



f. 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 from carbonate.* A white 

 precipitate shews phosphate of lime or magnesia, 

 or both. 



A. The filtered liquid is tested by oxalate of 

 ammonia; if lime be still in solution, a white 

 cloud falls. 



i. 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 



* The absence of carbonic acid is easily ascer- 

 tained by adding some lime-water to the solution 

 of ammonia ; it ousrht to remain perfectly transpa- 

 rent ; opalescence indicates the existence of carbo- 

 nic acid. 



3 F 



