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.
I shall here describe very 'briefly Ae 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 -duced to sulphurets, we find it the only ethod by which any thing like an accurate estimate of the inorganic constituents can be .btained, inasmuch as many of these bodies cur in the form of chemical compounds vith organic matter, and are thus prevented rom forming precipitates with the ordinary re :ents : iron is particularly liable to be thus ffeeted. When practicable, tve should usually
nake an analysis of the solution for the Mor i pude acids before evaporation and afterwards p. second examination of the gxed residue after The inorganic materials for which we shall have in general to search are comparatively few in number; among the acids, hydro chloric, sulphuric, 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, lime, 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 should 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 nitrate of silver is dropped in slight excess ; a bluish white flocculent precipitate shews the presence of chlorides.