Metallic arsenic forms alloys with many metals, some of which are produced by pulver izing and intimately mixing the constituents, and subjecting them to a pressure of 6,000 or 7,000 atmospheres. If much arsenic be present the alloys are usually brittle. Arsenic is an undesirable impurity in iron, in general, but it is sometimes added to iron and steel for the manufacture of small chains and ornaments, because it makes the metal susceptible of a very brilliant polish. When alloyed with copper, arsenic gives a brittle gray metal, having a brilliant, silvery appearance, which is used to some extent in making buttons The chief use of metallic arsenic, however, is in the manu facture of small shot. Pure melted lead, when dropped from a height, tends to form tailed drops; but if arsenic be added in small quanti ties this tendency disappears and the drops are nearly spherical. Another important use of metallic arsenic is in the manufacture of special alloys for bearings. With hydrogen, arsenic forms a very important gaseous compound known as arseniuretted hydrogen, or arsine, and having the formula MIL. This compound is best obtained by the action of sulphuric acid upon an alloy of arsenic and zinc. It is color less, and so poisonous that Gehlen, its discov erer, was killed by inhaling a single bubble of it. Arseniuretted hydrogen burns with a bluish flame, and metallic arsenic is deposited upon a cold body that is held in the flame. Marsh's test for arsenic depends upon this fact. In executing this test, zinc and sulphuric acid are added to the solution to be tested, and the hydrogen evolved is allowed to issue from a small jet, where it is lighted. A piece of cold white porcelain is then held in the flame, and if arsenic be present, the characteristic dark, metallic, mirror-like deposit will be produced, owing to the arseniuretted hydrogen that is evolved, simultaneously with the hydrogen. Antimony gives the same kind of a deposit, so i that it is important to examine the deposit (or *arsenical mirror,* as it is technically called), to make sure that it is not composed of anti mony. Marsh's test is extremely delicate, and
will demonstrate the presence of incredibly small traces of arsenic, if proper precautions are taken to ensure absolute purity in the zinc and sulphuric acid that are used. Scheele's green (known chemically as *arsenite of cop per))) is a compound of copper arsenic, oxygen and hydrogen of a light green color. It was formerly much used in calico printing and for wall paper. Schweinfurth green is a different compound of the same elements, and is used for similar purposes. A great diversity of opinion has prevailed among chemists as to the danger of using arsenical colors, especially in connection with wall papers. Some maintain that *there is no possibility of any arsenical ex halation arising from the walls, as has been al leged*; while others claim that certain micro scopic fungi and other low forms of vegetable life act upon these coloring matters and cause the production of arseniuretted hydrogen, which can actually be detected in the air of rooms hung with arsenical papers. Schwein furth green is better known in the United States by the name *Paris green,* and is much used for preventing the destruction of crops by insects.
The most familiar compound of arsenic (with the possible exception of Paris green) is undoubtedly arsenious oxide, As.O. (often written As,O,), or ((white arsenic,) known to the general public simply as •arsemc.) This is used in the arts, in the manufacture of indigo blue and aniline; in glass-making, to remove the color due to the lower oxides of iron; in fly and rat poisons; in taxidermy; in making fireworks; and for several other pur poses. Paris green and London purple are used in large quantities as insecticides. Arsenic is used in medicine in the treatment of anaemia and asthma. Not all persons, however, can take it. In homoeopathic treatment in minute quantities it is administered for several ail ments.