Production of Colored Smokes
There are three possible ways of obtaining signal smokes.
- I. Mechanically dispersing solids.
- II. Chemical Reaction.
- III. Volatilization of colored materials.
I. The first method, while possible, can never be an efficient method of producing signals. Some success was met with in dispersing certain inorganic materials, as rouge, and ultramarine, in projectiles fired from a 3-inch mortar and exploded by a time fuse arrangement at the height of their flight. Various mixtures were also tried, such as antimony oxysulfide and aluminum powder (red), arsenic and antimony trichlorides with sodium thiosulfate (yellow), etc., but these compositions have the disadvantages of being liable to catch fire if dispersed by a black powder explosion.
II. While colored smokes may be produced by chemical reaction, such as the combination of hydrogen iodide (HI), chlorine and ammonia, the clouds are not satisfactory as signals. In this particular case, the purple cloud (to the operator in the aeroplane) appeared white to the observers on the ground.
High temperature combustion smokes have also been studied. These are used in the so-called smoke torches. The yellow arsenic sulfide smoke is the most widely used. Most formulas call for some sulfide of arsenic (usually the native realgar, known commercially as “Red Saxony Arsenic”), sulfur, potassium nitrate, and in some cases, a diluent like ground glass or sand. A typical mixture consists of:
| Red arsenic sulfide | 55% |
| Sulfur | 15% |
| Potassium nitrate | 30% |
A very similar smoke may be obtained from the following mixture:
| Sulfur | 28.6% |
| White arsenic | 32.0% |
| Potassium nitrate | 33.8% |
| Powdered glass | 6.6% |
These smokes are not as satisfactory in color as the smoke produced by a dye smoke mixture, especially when viewed from a distance, with the sky as a background. They fade out rather quickly to a very nearly white smoke.
A black smoke upon first thought might seem to be the easiest of all smokes to produce, but actually the production of a black smoke that would be satisfactory for signalling purposes was rather a difficult matter.
Starting with the standard smoke mixture, which gives a white or gray smoke, hexachloroethane, which is solid, was substituted for the carbon tetrachloride, in order to avoid a liquid constituent. Naphthalene was first used, until it was found that the mixture of naphthalene and hexachloroethane melted at temperatures below that of either of the constituents. Anthracene was then substituted. The principal reaction is between the magnesium and the chlorine-containing compound, whereby magnesium chloride and carbon are formed. The reaction is very violent, and a white smoke is produced. The anthracene slows down the reaction and at the same time colors the smoke black. The speed of the reaction may be controlled by varying the anthracene content.
In burning this type of smoke mixture in a cylinder, it is essential that free burning be allowed. It has been found that if combustion is at all smothered, and the smoke forced to escape through a comparatively small opening, it will be gray instead of dense black.
III. Various attempts have been made to utilize the heat evolved when the Berger type smoke mixture reacts to volatilize or mechanically disperse various colored inorganic substances, and especially iodine. These were unsuccessful. Modifications, such as
| Strontium nitrate | 1 part |
| Powdered iron | 2 parts |
| Iodine | 3 parts |
were also tried, but while such mixtures ignited easily, burned freely and evenly, and gave a continuous heavy purple cloud, they were very sensitive to moisture and capable of spontaneous ignition.
The most satisfactory and successful colored smokes are those produced by the volatilization of organic dye materials. This practice seems to have originated with the British, who produced such smokes by volatilizing or vaporizing special dyes by igniting mixtures of the dye, lactose and potassium chlorate and smothering the combustion.
In selecting dyestuffs for this purpose it was at once recognized that only those compounds can be used which are volatilized or vaporized without decomposition by the heat generated when the mixture is ignited and the combustion smothered. It was also found that the boiling point and melting or volatilization point of the colored compound must be close enough together so that there is never much liquid dye present. Since all colored organic compounds are destroyed if subjected to sufficient heat, the mixture must be so prepared and the ignition so arranged that the heat generated is not sufficient to cause this destruction.
The oxidizing agents used in the combustion mixture may be either potassium or sodium chlorate. The nitrate is not satisfactory. Lactose has proven the best combustible. Powdered orange shellac is fairly satisfactory but offers no advantage over lactose.
The following dyes have been found to give the best smokes:
| Red | “Paratoner” |
| Yellow | Chrysoidine + Auramine |
| Blue | Indigo |
| Purple | Indulin (?) |
| Green | Auramine Yellow + Indigo |
At the beginning of the war, the only colored smoke used by the United States Army was a yellow smoke. The smoke mixture used in all signals, excepting the smoke torch, was the old arsenic sulfide mixture. The following smoke signals were adopted during the World War:
| Signal Parachute Rocket | Yellow and Red |
| V. B. Parachute Cartridge | Yellow |
| 25 mm. Very Parachute Cartridge | Yellow |
| 35 mm. Signal Cartridge | Yellow |
| 35 mm. Signal Cartridge | Red |
| 35 mm. Signal Pistol | |
| 25 mm. Very Signal Pistol | |
| V. B. Rifle Discharger Cut |