Two cases may present themselves: the materials to be examined possess either an alkaline (or neutral) or an acid reaction. As the methods to be pursued in either of these cases differ somewhat, they will be treated separately.
THE SUBSTANCE POSSESSES AN ACID REACTION.
The materials are mixed with water, placed in a retort provided with a delivery-tube which dips in a solution of nitrate of silver, and heated over a water-bath: if a cyanide be present, hydrocyanic acid will be disengaged, and a white precipitate of cyanide of silver formed: this is examined as previously directed (vide p. [50]).
In case a precipitate is not produced by the above treatment, more water is added to the retort, and the mixture boiled for about an hour, care being taken to collect the evolved vapors in a well-cooled receiver. The portion remaining in the retort is thrown on a filter and the filtrate obtained united with the distillate. The residue remaining on the filter is next washed with boiling absolute alcohol, the washings being added to the aqueous solution. In this way, the suspected substances are divided into soluble and insoluble portions, which are examined separately, as directed below.
a. LIQUID PORTION.
If the addition of alcohol caused a precipitation of animal matters, these are separated by filtering the solution. The filtrate is then placed under a bell-jar over concentrated sulphuric acid until its volume is considerably reduced. The solution may contain organic and inorganic bases and acids. In order to detect all bodies that are present, the following course is pursued:
(1). A current of sulphuretted hydrogen is conducted through the solution: the precipitation of some metals, usually thrown down by this gas, may fail to take place in this instance, owing to the presence of organic substances; however, some metals are precipitated, even in presence of organic compounds, and organic acids are but seldom present. In case a precipitate is formed, it is mixed with pure silica, collected on a filter, and treated with nitric acid. If the precipitate fails to dissolve, it is treated with aqua regia. In either case, the solution obtained is examined for metals by the ordinary methods.
(2). The solution in which sulphuretted hydrogen failed to produce a precipitate, or the filtrate separated from the precipitate formed, is divided into two parts: one portion is treated with ether and a solution of potassa; the other with ether and a solution of soda. Both mixtures are then well agitated, and notice taken if the ether dissolves any thing: if so, the operation is repeated several times until all soluble substances are removed. The ethereal solutions are next decanted and united, and then submitted to the examination for alkaloids as directed pp. [65]-[84].
(3). If—the above treatment giving either positive or negative results—a precipitate insoluble in ether is formed by the addition of potassa or soda, it is collected on a filter, washed, and dissolved in an acid. The solution is then tested for mineral bases.
(4). In case no definite result has been obtained by the preceding operations, one of the portions (for instance, the one to which potassa was added) is tested for the acids possibly present in the state of salts. The solution is divided into two parts (A and B) which are examined separately: