Three hundred and ninety-five pounds of saltpeter are ground in a Coggswell mill. Where a number of different lots of saltpeter are to be used, it is desirable to sample and make a blend of the several lots, in order to insure uniformity. Ground sand is screened through a mechanical sifter with a 30-mesh screen and dried on a steam table; the steam table being of simple design. Thirty-two pounds of sifted sand are mixed with 395 pounds of saltpeter, and set aside to be introduced into the mixing kettle later. Two hundred and forty pounds of Barrett-specification pitch are melted in a steam-jacketed kettle and introduced into a steam-heated composition mixer, shown in figure 207.
Fig. 207. - Composition-mixing machine.
After the pitch has been introduced into the mixer, the previously blended saltpeter and sand are introduced, having been screened a second time. Thirty-five pounds of flour of sulphur, 33 pounds of powdered chalk, or powdered calcium carbonate, and 88 pounds of powdered borax are first screened through a 30-mesh sieve and added, along with the sand, to the melted pitch. The mixing machine is then operated for 30 minutes in order to knead the composition and thoroughly incorporate into the pitch the various constituents above mentioned.
Ref erring to figure 207, it will be noted that the container is in a tilted position. In this position it is easy to pour the melted composition into portable containers from which it may be transferred to the loading machines. The mixing machine has a steam-jacket container equipped with two shafts on which specially formed blades are keyed. These blades sweep close to the bottom of the container during each revolution of the shaft and prevent the sticking and balling of the magma. These shafts may be revolved in either direction and are so designed that when the container is tilted the shafts may still be in motion.
The melted composition is taken from the mixing machine by means of a small two-wheel bogie holding a container, such a truck as is used for transporting molten slag. The molten composition is now introduced into a steam-jacketed hydraulic press. This is a simple hydraulic press with an orifice in the bottom into which is set a nozzle, having a diameter of three inches. The ram exerts a pressure of approximately 3,000 pounds per square inch, which causes the composition to flow in a plastic form through the 3-inch orifice at the bottom of the press and into the cylinders which are set directly below the orifice. Three and one-half pounds of composition are by this means loaded into these cylinders. As each case is filled, it is trimmed off flush with the top, and a round depression is made in the center of the composition with a knife. The depression is 2 inches in diameter and 1/2 inch deep. This cavity is for the purpose of containing the first-fire composition.
Figure 208 shows the case filled with composition, in the center of which a depression has been made for the first fire.
The object of the first-fire composition is to ignite the smoke composition. This first-fire composition is a quick-burning mixture, consisting of -
Sulphur (flour)--------------- ....................
This composition is made by screening 18 pounds of saltpeter through a 30-mesh screen. To this are added 3 pounds of black antimony, 4 1/2 pounds of flour of sulphur, and 3 pounds of meal powder. These constituents are thoroughly kneaded by hand and then screened through a 30-mesh screen, before introducing the first-fire composition into the depression cut in the smoke composition. The first-fire composition is poured into the depression while the composition is still in a plastic condition.
Fig. 208. - Case loaded with composition showing depression for first-fire composition.
The match or fuse used in the smoke torch is similar to that used in various other pyrotechnic units, and consists of cotton cord of various strands thoroughly impregnated with a match composition. The formula for this composition is as follows -
Starch water is added, sufficient to make a paste of the combined ingredients.
This composition is made up in batches of 14 pounds, having 9 pounds of saltpeter, 2 pounds of sulphur, and 3 pounds of charcoal. It is. first separately screened through a 30-mesh screen and thoroughly mixed together by hand. The mixture is then twice screened through a 30-mesh screen. A mixture of starch and water is made up, in the proportion of about 1/2 pound of starch to 2 gallons of hot water. The starch is added to the water in sufficient quantity to form a plastic paste.
Figure 108 shows the apparatus used for the manufacture of this match. It will be noted that the cotton cord is furnished in spools, which are placed on spindles in such manner that two or more strands of the cord can be combined to form a match of the desired ply. The match used in the smoke torch is what is called "the two-ply," in which two strands from two separate spools are combined, and are passed through the wet composition in the tub. It will also be noted that, after the cotton strands have passed through the composition in the bottom of the tub, they are passed through a small hole, which acts as a wiper to remove the surplus composition. The composition must be sufficiently dampened, so that the cord will be thoroughly impregnated. The match is drawn through the composition and wiper, and reeled upon drying racks, as shown in figure 104. This rack is mounted in front of the mixing tub in such a manner as to move upon its shaft so that the operation of reeling can be done rapidly by one man, and so that the strands are separated from each other.
To make this match a quick-match, meal-powder dust is sprinkled on it while it is still in a damp condition. After the racks have been filled they are set aside to dry. A slow drying at room temperature is preferable to rapid drying, in order to prevent the match from becoming excessively brittle. Open-air drying is to be preferred to drying in drying rooms. After the match is thoroughly dry, requiring approximately twenty-four hours, it is removed from the rack and is then ready for cutting into the required lengths.
The match is cut into lengths about two inches long, and two of these are crossed and imbedded in the first-fire composition.