At the outset it is needful to test the sulphuric acid and zinc to demonstrate that they yield hydrogen free from phosphuretted hydrogen. For this purpose allow the gas to evolve until air is displaced from the appa

ratus, then close c until the acid has been forced into f, then close d, open c, and lastly open d, cautiously inflaming the gas at the jet and properly regulating its issue. If the flame, when examined in a rather dark place, is colorless, exhibits no trace of a green cone in its interior and no emerald-green tinge when a porcelain dish is depressed into it, the hydrogen is pure. After verifying this result by a second trial, the precipitate to be examined is rinsed into f, care being taken that it passes completely into a, and the flame is again observed as before. In case but a minimum of phosphide of silver be present the green inner cone and

emerald-green coloration of the flame will be perceptible.

b. The SOLUTION filtered from the silver precipitate, is freed from excess of silver by hydrochloric acid, filtered through a well purified filter, strongly concentrated in a porcelain capsule, and finally tested for phosphoric acid by means of molybdate of ammonia or magnesia mixture.

In this manner we have most plainly detected the phosphorus of a common match mixed with a large quantity of putrefied blood, and in presence of those substances which prevent luminosity in the method of Mitscherlich.

V. When enough phosphorus is present to weigh, its estimation is practicable by adopting Scherer's modification of the process of Mitscherlich. The mass, acidified with sulphuric acid, is distilled in an atmosphere of carbonic acid gas. For this purpose it is best to fit into the cork of the flask in which the mixture is distilled, a second tube through which pure carbonic acid may be transmitted into the distilling apparatus, until it is completely filled, when the stream of gas may be cut off and the process continued as usual. The receiver may consist of a flask with a doubly perforated cork, the opening of which passes over the end of the condensing tube, the other carrying a bent glass tube which is connected with a U tube containing solution of nitrate of silver.

When the distillation is finished, globules of phosphorus are found in the receiver, which, after again establishing a gentle stream of carbonic acid, are united by gently heating and then are washed and weighed as described (III. a.). The solution poured off from the globules is luminous in the dark, when shaken, though not to the same degree as in Mitscherlich's process. The phosphorus in this liquid may be determined, after oxidation, by nitric acid or chlorine, as

phosphoric acid; though, only, when the operator is certain that none of the contents of the distilling flask, which usually contain phosphoric acid, have spirted into the condenser. The entire quantity of phosphorus is obtained by adding to that, thus determined, what exists in the U tube. Its contents are treated with nitric acid, the silver thrown down by hydrochloric acid, filtered through a washed filter, concentrated, precipitated as phosphate of ammonia-magnesia, and weighed as phosphate of magnesia.

B. Detection of Phosphorous Acid.

VI. In case free phosphorus itself has not been detected by the above methods, it is needful to look for the first product of its oxidation, viz., phosphorous acid. To this end the residue of the distillation (II. a.), or (V.), or also the residue of (IV.) is brought into the apparatus, Fig. 44, and tested as described (IV. a.) as to any green coloration of the evolved hydrogen. If the phosphorous reaction appears, it is sufficient; otherwise organic matters may have hindered its production. If, therefore, the flame is not colored, the clamp is closed, and a U tube containing neutral solution of nitrate of silver is affixed to the apparatus and the gas is allowed to stream slowly through the silver solution for many hours. In presence of phosphorous acid, phosphide of silver is formed, which is filtered off and examined as directed in (IV. a.).

130. SILICATES.*

A few silicates are directly attacked by acids, while others cannot be decomposed by acids, except by the addition of a base, as, for example, lime.

* Methods of Sainte-Claire Deville, as given by Messrs. Grandeau and Troost.

By modifying the composition of a silicate, it may always be rendered decomposable by an acid. For example, a silicate containing the following elements:

Silica,

Alumina,
Iron,

Manganese,

Lime,
Magnesia,

Potassa,

Soda.

This combination occurs in porphyry, gneiss, and granite.

In the first place it is necessary to observe the action of heat upon the silicate, and if there is a loss in weight, to determine its nature, whether it consists of water or fluorine.

In most cases, the water contained in a silicate evaporates at a red heat, and it is only necessary to

heat it over a lamp fed by bellows. The water from talcose minerals is only driven off at a white heat.

This temperature may be obtained by using the lamp represented in Fig. 43. The apparatus is composed of three principal pieces: a bottle A communicating with the tube E with the reservoir I of spirits of turpentine or the lamp proper, which communicates by the double tube & with an apparatus for the distribution of air forced by the bellows K, which feeds at the same time the tube H.*

Generally when minerals lose their volatile matter, only at the temperature attained by the large lamp, it is those containing fluorine, and it is then necessary first to examine the nature of the volatile matter.

The calcination is carried on until neither water nor fluorine remains.

It should be noticed whether any material is lost in

*Fig. 46 shows the interior construction of the lamp. The annular space O O is closed on all parts, above and at the side by

a thick plate; below by a copper plate raised externally in such a manner as to form a little cup around the lamp in which water is poured.

For the management of this lamp we refer to the article by M. H. Deville, Annales de Chimie et de Physique, 3d series, vol.