The use of a larger pan containing water, into which the smaller one containing the sulfur is placed, is an effective aid in preventing fire and accidents. In houses having dirt floors, pits may be dug therein and the sulfur burned as in the pans. Sulfur should not be burned on concrete floors, as the heat is likely to cause the concrete to crack and buckle, thus throwing the burning sulfur about and setting fire to the house. Keeent experiments have shown that it is very unusual to get complete combustion by any method of burning sulfur within the houses, and that the time required for bui-ning averages about 3 hours.
In burning sulfur vrithin the houses a uniform concentration is rarely if ever obtained, as the hot sulfur dioxide gas from the pans rises to the top of the house. By the time the gas has cooled sufficiently to settle to the floor the total concentration of sulfur dioxide gas vdthin the house has reached a point too low to be of much value. There is also considerable hazard of fire and danger to human beings in btirning sulfur within the houses by the methods now commonly used. It produces a highly concentrated gas in the house with less than one-third of the quantity of sulfur required by the pan method, burns the sul- fur completely vdthin about 30 minutes, reduces the fire hazard, and gives completely uniform distribution of the gas within the house.
The details of construction are shown in figure 2. At each end is a cone IS inches long, terminating in an open pipe, the intake pipe being 5 inches and the outlet pipe 6 inches in diameter.
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TTithin the box. The door at the side is secured by bolts and wing nuts. To prevent the gas from escaping, a gasket of asbestos cloth is placed between the door and the body of the burner. All seams and connections are strongly crimped or riveted, as the heat of the burning sulfur will quickly melt any solder work. In preliminary tests it was found that the sulfur in the middle tray burned faster than that in the top and bottom trays, owing to uneven distribution of air.
This condition was corrected by using baffles in the intake funnel. The ends of the strap iron are pierced with holes and project into the intake pipe, being held in place by bolts, the nuts of which are outside on top of the intake pipe j fig. The bases of the baffles rest on the tray supports. The spacing of the baffles must be determined by testing, or by the use of an anemometer, so that each pan receives air at the same rate. The fan used is of the centrifugal type in a steel housing, connected directly to a 1 20 horsepower electric motor running at 1.
This fan delivers cubic feet of air per minute. In use, the fan is connected to the intake, and stovepipe is led from the delivery pipe into the house through an asbestos-lined opening in a false door made Figure 2. It is advisable to extend the outlet, by means of sev- eral extra lengths of stove-pipe, so that the delivery of gas will be along the floor in the central alleyway.
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The fumes from the sulfur did not cause appreciable corrosion of the galvanized metal, of which the greater part of the burner is composed, during the 3 years that it was in use. The iron frame has corroded to a slight extent, but the burner will probably last for a long time under ordinary conditions. The burner was designed to burn 32 pounds of flowers of sulfur, this being the maximum dosage allowable in a standard mushroom house of 16, cubic feet when at peak heat.
With this dosage, flame has at times been blown into the house through 10 feet or more of pipe. When using the maximum dosage it has therefore been thought best to cut down the speed of the fan by attaching one or two electric- light bulbs to the line or by using a rheostat. By increasing the length of lead-in pipe to 20 or 30 feet the same result might be ob- tained, together with a cooling of the fumes. In empty houses ex- cellent fumigations have been obtained with as little as 20 pounds of flowers of sulfur.
The source of the heat may be steam, or it may be electricity if the current is very cheap. The room should be as dry as possible during this heating period. A small quantity of manure in a large cool place will not heat up so well as a greater quantity, nor will it raise the temperature of the surrounding space greatly.
If the filling occupies too much time, considerable heat is wasted. For this reason the house should be filled as quickly as pos- sible, the aisles swept out and cleaned of all loose manure, and the doors closed tightly. Some growers fill a part of the house and wait several days before filling the remainder.
If manure is scarce, it is better to form storage heaps until a sufficient quantity is obtained to fill the house in one operation. Since ground beds are very difficult to heat properly, the insect and mite pests contained therein cannot be driven to the surface or killed by heat, and, since the fumigants in use at present do not penetrate the compost more than an inch or so, the pests present in such loca- tions will survive and reinfest the house.
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Consequently, if the ground beds cannot be raised 4 or 6 inches from the floor to allow circulation of heated air beneath, it is better to abandon them entirely. If the weather is very cool at the time of filling, or, as is frequently the case in amateur mushroom culture, the quantity of manure is too small and the insulation insufficient to allow the temperature to rise, the house may be heated artificially.
Where steam or hot-water heat is not available, kerosene or oil burners have been used with success, but the use of oil heaters should usually be avoided, as oil fumes some- times have a harmful effect on mushroom growth. Care must be taken that the beds do not dry out too much while this is being done. Because the lower beds are filled first and lose much of their latent heat, and also because the warm air naturally rises to the top of the house, the tops beds heat faster and attain a higher temperature than the bottom ones.
A more even distribution of heat may be obtained by the use of some method of forced air circulation. Where electric current is available the best method is to place two or three inch electric fans in the central alleyway. Better results, however, have been obtained by placing the fans on supports resting on the top beds, with the air current directed straight down. By this means the heated air in the top of the house is driven to the floor and is forced to circulate over the bottom beds before again rising to the top of the house. To keep a check on the conditions during the heating process, ac- curate thermometers should be inserted into the top and bottom beds and hung in the central alleyway at the top and bottom of the house.
Such temperatures on the floor of the house and just above the floor are difficult to maintain, consequently fumigation is necessary. During the heating of the compost in the beds much moisture is driven off. In basements of dwellings it is inadvisable to try to reach a high temperature unless the room can be sealed tightly enough to prevent the moisture and heat from warping the floor above. Fumigation When the temperature of the beds has reached its maximum the house should be fumigated with either sulfur or cyanide.
The amount used per 1, cubic feet, how- ever, should not exceed 2 pounds.
Within 5 or 6 hours after the sulfur has finished burning, the ventilators should be opened, the house allowed to air out, and then closed again to prevent too rapid cooling. Owing to the slow rate of burning and the rapid absorption of gas by the moisture in the house, it is doubtful whether an efficient fumigation is ever attained by burning sulfur in pans within the house at peak heat. The outside burner previously described p. Sulfur fumigation has a tendency to raise the acidity of the first one-half inch or so of the beds the limit of penetration of the gas , and a green mold often follows.
This soon disappears, however, and neither it nor the increased acidity of the surface of the beds seems to have any harmful effect upon subsequent mushroom growth. When a house to be fumigated is immediately adjacent to another in production, every precaution should be taken to keep the fumes from reaching and damaging the growing mushrooms. The ventilators of the house in bearing should be open, and the house in heat should be fumigated only when there is no wind, or when the wind is blowing away from the house in bearing.
In case of a double house, the other half of which is in bearing or spawned, it is better to use cyanide rather than to risk damage from sulfur fumes. Since the application of liquid hydrocyanic acid requires special equipment, as well as special training on the part of the operator, and since it gives little better results than sodium cyanide and acid, it may be left out of this discussion. The use of granular calcium cyanide at the rate of 1 pound per 1, cubic feet of air space is at present the most common method for fumigating mushroom houses at peak heat. As hydrocyanic acid gas is readily absorbed by moisture, the house, although damp, should not be wet, with puddles of water standing in the alleyways, or much of the gas will be lost before it is fairly liberated.
In view of the deadly nature and the rapid evolution of this gas, every precaution should be taken against accidents. No one should be permitted to open calcium cyanide or scatter it without wearing an approved gas mask equipped with a canister especially designed for that gas. In the case of a single house, the chemical should be scattered in the central alleyway as evenly and quickly as possible, beginning at the back of the house and working toward the door.
Special care should be taken to see that the alleyway is clear of obstructions before the fumigation is begun, as a stumble over some obstacle while walk- ing backward and scattering the cyanide might easily result fatally, even though the workers are wearing gas masks. In the case of a double house the material is scattered in the two main alleyways, the workers starting together at the far end and working toward the doors, timing themselves so as to reach the doors simultaneously. After the operators have left the house the doors should be closed and tightly sealed and left so for about 12 hours.
Small fertilizer spreaders such as are used for distributing com- mercial fertilizer on lawns, when properly set, will give a more even and rapid distribution of calcium cyanide, and a higher concentration of gas than can be obtaining by hand scattering. Caution: When entering a house after it has been fumigated, use a gas mask until the house has been thoroughly aired out. The same precautions are necessary as with sulfur to prevent fumes from reaching and damaging growing mushrooms, although this gas is not so harmful to them as sulfur fumes.
In the case of a double house, the other half of which is in bearing, the doors between them should be made gas-tight, all cracks and openings in the partition tightly sealed, and the doors and ventilators of the house in bearing opened. As a further precaution, it is desirable to fumigate when the wind is blowing away from the house in bearing.
The so-called pot method of fumigation, in which sodium cyanide and sulfuric acid are used, is almost as easy and convenient as that with calcium cyanide, and gives a more rapid liberation of gas and a much higher concentration. Three or four 3- gallon glazed crocks may be used for generators. The necessary quan- tity of water is measured out and divided among these.
They are then set at equal intervals in the central alleyway of the house. The acid is similarly measured out and the necessary quantity placed in a glass jar beside each generator. Having reached the back of the house, he then walks rapidly toward the door, dropping one of the bags of cyanide in each generator as he passes it. The doors should be closed and sealed at once. As an extra precaution, a house that has been fumigated should not be entered, even by a person wearing a gas mask, until it has been thoroughly ventilated.
Fumigation with hydrocyanic acid gas should be avoided during periods of cold weather, in order that the house, may be properly ventilated after the fumigation without possible in- jury to the crop because of a rapid drop in temperature during the ventilation.
As the floor is always the coolest part of a house that is heating or at peak heat, it is here that insects and mites are most likely to sur- vive the heat. Unless fans are kept running in the house at the time of fumigation, the gas.
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The best results have been obtained, by raising the fans to the level of the fourth or fifth beds, about 5 or 6 feet or more from the floor. In the pot method the air blast from the fans should be directed straight down over each generator. This causes the gas to blow along the floor and between the lower beds. After 20 or 25 minutes the concentration becomes nearly uniform throughout the house, but for the first 20 minutes most of the gas is along the floor, where it is most needed.
Unless fans are of the fully enclosed type, it is better to wait for about 10 minutes before turning them on. In experimental fumigation of commercial mushroom houses it was demonstrated, by using chemically equivalent dosages of calcium cyanide and sodium cyanide with acid il:! There are two or three types of generators using sodium cyanide and acid which, if properly used, are almost if not quite as effective as the pots, and have the additional advantage that the gas is gener- ated outside the building and forced in.