There is a variety of formulas used in the preparation of the red signal composition, the basis of these being the use of from 7 1/2 to 11 3/10 per cent. of powdered orange shellac, which requires a certain oxygen-liberating salt to support its combustion, either potassium chlorate or strontium nitrate, Where strontium nitrate is used in place of strontium carbonate, the potassium chlorate is correspondingly reduced. Three formulas in use are shown as follows -
A. Strontium nitrate.....................
Potassium chlorate .....................
B. Strontium carbonate .....................
Potassium chlorate ....................
C. Strontium carbonate....................
Potassium chlorate ............................
When found necessary these compositions may be dampened slightly with a binder similar to that described previously.
The carton is of the same size as that described under the green light and the assembly, with the exception of the first fire, which is omitted, is identical with that described under the white light.
The various parts of the smoke signal are as follows:
2. First-fire composition.
3. Smoke composition.
6. Match band.
8. Tie string.
The case consists of a paper carton, similar to that used in the assembly of the signal lights and is made of strawboard or Bird's rocket hardware paper. When rolled from straw-board it is customary to use a sheet cut 9 by 22 inches from 100-pound stock, the rolling being done on a mandrel, after the surface of the sheet has been given a coat of paste. This produces a cylinder which when cut into three parts makes a carton 3 inches in length by 1 1/4 inches inside diameter, which is the size desired. If the carton is rolled by using Bird's rocket hardware paper, a strip 3 by 25 inches is used, also rolled on a mandrel, giving a carton 3 inches long by 1 1/4 inches inside diameter. These cases are set aside to dry after being rolled.
There are two methods of heading up the cartons. One is with the use of molding clay, a plug of which is put in under rather high pressure; the other by the use of a cardboard disk. Where the carton is rolled, from 100-pound straw-board, it is customary to use a clay heading. Sufficient clay is introduced into the carton which on being driven home occupies a space approximately 5/8 inch in thickness, forming the bottom heading. Where Bird's rocket hardware is used to roll the carton, the heading consists of a disk of 30-pound strawboard, cut 1 1/4 inches in diameter. A stripe of glue is wiped around the inner surface of the carton close to the bottom of the disk and the disk is then forced into place flush with the bottom, adhering firmly to the sides of the carton.
A first-fire composition is used in loading the carton which has a clay heading and consists of a mixture of 50 per cent. of the same composition as is used in charging the rocket body, and 50 per cent. of the smoke composition, to be described later. The carton which is made with the pasteboard disk substituted in place of the clay heading does not have a first-fire charge. The reason for this difference will be shown later under the heading "Vents."
A small charge of this first-fire composition, occupying a full 1/4 inch in thickness, is spread on top of the clay heading, and is rammed into place later on when the smoke-producing composition is pressed into shape.
Two different formulas are used for the smoke composition, varying only slightly in their component parts.
Formula A consists of -
Red arsenic (realgar)................
Formula B consists of -
Sulphur (flour) .....................
Red arsenic (realgar)..........................
It will be noted that these compositions are very similar to those used in the smoke tracer. In mixing the composition the customary method of hand mixing in an open trough and screening through a sieve is adhered to. It should be noted that the red arsenic often occasions discomfort to the operator who is mixing this composition by hand. A discussion of the use of red arsenic, its poisonous character, and the possible substitution of a less poisonous material is given in the chapter on Arsenic, in the volume on Chemicals.
In loading the smoke composition in the carton two rows of five cartons in a frame constitute one-half of the charge of the press, which is operated in much the same manner as the loading of the rocket-body case. This mixture when rammed home occupies a space of 1 1/8 inches in thickness and is capped with a clay heading in one instance and with a disk of strawboard when strawboard has been substituted in place of clay.
It must be noted here that in the burning of the smoke signal the composition does not burn away the carton as in the case of the white, red, or green lights, but merely generates a copious volume of smoke without burning through the walls of the carton. Consequently, openings are drilled into the walls of the case for the purpose of allowing the smoke to be forcibly expelled. There are two positions for the vents. In the case of the carton that is loaded with clay for a heading and with a first lire for an igniting charge there are four vents which are perforations 1/8 inch in diameter spaced equidistant on the same plane, which plane passes through the center of the first-fire ignition. In the second case there are three vents 1/8 inch in diameter equidistant, and in the same plane located at the center of the smoke-composition charge.
The match which ignites the charge occupies the position shown in drawing, figure 56.
Here two lengths of three-ply fuse cut 4 1/2 inches long are crossed and the ends of the fuse, so clipped as to give them a beveled edge, are bent and forced through the vents. In attaching the match to the carton having three vents a six-ply match 11 1/2 inches long is looped in three loops, the apex of each loop being forced into one of the vents. The remaining length of the fuse is carried across the bottom of the case and held in place by means of a band.
Fig. 56. - Smoke signal showing position of the match.
The match band consists of a strip of stout paper 1 1/8 inches in width, pasted around the case holding the match in place. This may be of 30-pound Kraft paper or 20-pound rope manila. The Kraft paper is cut to 6 1/4 inches, the manila to 6 1/8 inches. The match which crosses the bottom of the signal takes its ignition from the expelling charge in the rocket body.
The knot socket is similar to that previously described and is a strip of muslin 3 by 10 inches, pasted around the carton in such a manner as to allow an overlap into which may be inserted the knot tied to the end of the parachute cord.
The knot socket is crimped around the parachute cord with the knot firmly held in the crimping and a tie string of jute cord 8 inches long holds the crimping in place by means of two half hitches. After the tie string has been attached a stout pull by the operator insures a satisfactory connection.