ANALYTICAL EDITION
36
and hence interferes with the reaction. In the case of hard sized papers, the boiling time is increased in order to get the proper disintegration. DRYIKGOF SLIDE. The slide may be either dried or blotted. However, the author’s reason for preferring drying is solely to eliminate one more possibility of contaminationthe blotting medium. METHODOF STAINING. There may also be some question as to whether it is better to immerse the slide in the staining solution or to drop the solution upon the slide. Either method of staining is satisfactory. However, if the dropping method is used, sufficient stain should be dropped on the slide from a pipet to cover all fibers a t once, since the most
Vol. 5 , No. 1
important part of the staining procedure is to remove the excess stain instantly. No mixing of the stain with the fibers is necessary. In fact it is detrimental, as this stain permeates the fibers instantly on contact. There may also be some question as to the economy of immersing the slide, instead of dropping the stain upon the slide. For analyses which make only one or two slides necessary, only a portion of the specified amount is made up. C. P. brazilin, made by the MacAndrews & Forbes Co., 200 Fifth Ave., New York, N. Y., at 50 cents per gram, is used. The oil immersion is not absolutely essential, but sharper differentiation can be obtained with oil than with water, R E C E I V July ~ D 7, 1932.
Equipment for Laboratory Fumigations with Hydrocyanic Acid With Controlled Temperature and Humidity H. L. CUPPLES,Bureau of Chemistry and Soils, Department of Agriculture, Whittier, Calif.
H
YDROCYANIC acid is used extensively for field fumigations of citrus trees, particularly in the control of the red scale, Chrysomphalus aurantii. I n field work it is very difficult to duplicate exactly any given treatment, owing primarily to the lack of control over meteorological conditions. I n order to pursue various research problems relating to the toxicity of hydrocyanic acid to red scale, it is of great advantage to be able to make fumigations in the laboratory under closely controlled conditions. This paper describes an assembly which has been found satisfactory for such experiments. Provision is made for the control of hydrocyanic acid concentration, relative humidity, time, and temperature of treatment.
FUMIQATION CHAMBER Laboratory toxicity tests may be made by fumigating lemons which are moderately heavily infested with red scale. The lemons are cut with stems about 4 inches (10 cm.) long.
MINUTES
FIGURE 1
They may be kept in good condition for a sufficient length of time after a fumigation to provide for satisfactory mortality counts. The fumigation chamber, which will conveniently accommodate four lemons, is adapted from a glass desiccator, 200 mm. inside diameter, with ground-on cover tubulated to accommodate a rubber stopper. Inlet and out-
let tubes for the air-hydrocyanic acid mixture enter through the rubber stopper, the inlet tube opening a t a point near the bottom of the desiccator and the outlet tube opening near the extreme top. Tests with fumes of ammonium chloride, using a gas flow of 6 liters per minute, have shown that sufficient turbulence is produced within the desiccator to insure a uniform distribution of the hydrocyanic acid. A support is provided within the desiccator to which the lemons are tied, and when the lemons are in place the desiccator may be covered and entirely immersed in a water thermostat. The bottom portion of the desiccator contains enough metallic lead to sink the desiccator to the bottom of the thermostat. The inlet and outlet tubes for the gas mixture are long enough to protrude above the surface of the water, and they are connected to the other units with short rubber connectors. I n the fumigation of red scale with hydrocyanic acid it is desirable, for maximum effectiveness, that the concentration be increased to its maximum value within a short period of time (2,s). Although this requirement would not seem to be 60 vital for the performance of comparative laboratory tests, nevertheless it has seemed desirable to obtain a comparatively rapid increase of concentration. This has been attained by using a fumigation chamber having the relatively small volume of 4 liters, and by supplying the air-hydrocyanic acid mixture a t the rate of 6 liters per minute. Experiments have been made to determine the rate of increase of concentration a t the start of a fumigation, and the rate of decrease of concentration a t the close, a t which time the fumigation chamber is usually swept out with air. The gas samples for these analyses were taken from the outlet tube leading from the top of the chamber, and thus represent a somewhat less favorable situation than a t a point centrally located within the fumigation chamber. These results are represented graphically in Figure 1.
FLOW DIAGRAMAND DESCRIPTION OF APPARATUS A flow diagram of the assembly is shown in Figure 2. Air enters through the flowmeters, A and B, and is finally exhausted to the atmosphere outside the building by a motordriven exhaust pump. The major portion of the air, about 6 liters per minute, enters through flowmeter A and is brought
January 15, 1933
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
to a desired temperature and humidity in the absence of hydrocyanic acid. A much smaller flow of air, about 200 cc. per minute, enters through flowmeter B. This portion picks up hydrocyanic acid in two “saturators” and is then mixed with the main current of conditioned air. The mixed gases pam through the fumigation chamber and are then exhausted to the atmosphere, The rate of flow of the mixed gases is controlled primarily by needle valve 1, but a portion of the gas flow, controlled by needle valve 2, passes through the gas analysis apparatus. This apparatus, of the flowmeter type, is similar to one described elsewhere (1). For the
F
FIGURE 2. FLOW DIAGRAM
control of temperature, certain units are immersed in a water thermostat. The parts so immersed include the fumigation chamber, the humidifying towers, the hydrocyanic acid saturators, and two copper coils which serve to bring the gas stream to the temperature of the water bath. The main flow of gas, entering through flowmeter A , is brought approximately to the temperature of the water bath by passage through a copper coil which is immersed in the bath. The humidity may be adjusted by properly setting valves 6 and 7, thus causing any desired part of the air t o pass through the humidifying towers, which are simple, glasspacked columns kept moistened with water. While the humidity is being adjusted, the air current is passed through a hygrometer of the wet- and dry-bulb type, illustrated in Figure 3. After adjustment of the humidity, valve 4 is opened and valve 5 is closed, thus by-passing the air stream around the hygrometer. This avoids any increase of humidity due to evaporation from the wick of the wet bulb. The hygrometer has been designed to obtain a rapid flow of air past the wet bulb, and tests have shown that it functions in a satisfactory manner. Valves 4, 5, 6, and 7 are screw clamps on short rubber connections. Valves 1, 2, and 3 are needle valves which permit close control of the rates of flow. The smaller current of air, entering through flowmeter B, is controlled by needle valve 3. I n passing through two saturators in series, this air picks up sufficient hydrocyanic acid to produce the desired concentration in the final mixture. It may be noted that this current of air will be substantially saturated with water vapor a t the temperature of the saturating bottles, and that the relative humidity of the final gas mixture will be influenced to some extent by the water vapor contained therein. This may be compensated for by suitably adjusting the humidity of the larger air stream which passes through the hygrometer. The combined gases flow through a second copper coil and into the fumigation chamber.
METHODOF SUPPLYING HYDROCYANIC ACID Each saturator is a one-gallon bottle containing 2 liters of aqueous hydrocyanic acid. Initially the concentration of hydrocyanic acid is the same in both bottles, but as an experiment progresses the concentration in the first bottle fPlls below that in the second. The aiv is slowly bubbled through the solution and reaches approxims,tc eqiiilibriurrt with it.
37
The concentration of hydrocyanic acid in this air will depend, therefore, upon the concentration of the solution and its temperature. The concentration of the final gas mixture will depend upon the same factors and, in addition, the fraction of the total air which passes through the saturators. The hydrocyanic acid solution may conveniently be prepared by dissolving in water the required amount of sodium cyanide, and then acidifying with an excess of dilute sulfuric acid. An excess of sulfuric acid, because of its low volatility, will not contaminate the air-hydrocyanic acid mixture. With a solution originally containing 18 grams of sodium cyanide per liter, maintained a t 23’ C., the described apparatus conveniently produces final gas concentrations ranging from 0.25 to 2.00 mg. of hydrocyanic acid per liter. The range may, of course, be changed by slight alterations in the apparatus. One of the objectives in mind when designing this apparatus was to be able to maintain a substantially constant concentration of hydrocyanic acid for a desired period of time. The question naturally arises as to the rate of decrease of concentration which may be expected due to loss of hydrocyanic acid from the saturators. It would be possible, of course, to employ some form of saturating device which would be fed by a constant stream of fresh solution. The present arrangement, however, is simple in construction and in
m
R
FIGURE 3. HYGROMETER
operation, and it has been designed to minimize such concentration changes. For this purpose the following features have been incorporated: 1. A relatively large volume of hydrocyanic acid solution is
used.
2. The “dilution factor” is comparatively high. That is, the air which passes through the saturating bottles is diluted many times to produce the final desired concentration. This enables the use of higher concentrations of hydrocyanic acid in the saturating bottles, and thereby reduces the percentage change of concentration therein. 3. Two saturating bottles, in series, are used. This greatly reduces the concentration change in the second bottle. If still greater constancy is desired, a third bottle may be added.
Calculations have been made to determine just what performance might be expected from the present apparatus in respect to such concentration changes. Assuming average operating conditions, it has been calculated that a continuous 5-hour run would cause a reduction in the gas concentration of less than 0.6 per cent. This in itself represents a fair degree of constancy, and it is evident that the variation during shorter
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ANALYTICAL EDITION
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periods of t,ime will ordinarily be negligible. Moreover, it is possible to readjust the concentration a t any time by slightly varying the rate of flow through the saturating bottles.
Entomology, for the loan of several pieces of laboratory equipment.
represented in Figure 1, and t o C . I. Bliss, of the Bureau of
R~~~~~~~~~~~~t3, 1932.
LITERATURE CITED
A Simplified Karns Technic for the Micro-Estimation of Iodine HARRY VON KOLNITZ AND ROE E. REMINGTON South Carolina Food Research Commission and Department of Nutrition, Medical College of the State of South Carolina, Charleston, S. C.
I
N T H E estimation of the minute quantities of iodine which normally occur in animal and vegetable matter, the step of greatest difficulty has been the destruction, without loss of iodine, of the organic matter present. Earlier workers used fusion with alkali, with or without nitrate, while in recent years combustion in a current of oxygen in a silica or Pyrex tube, i.gnition in a muffle a t a controlled low temperature, or digestion with hydrogen peroxide and sulfuric acid has been employed with varying success in different laboratories. Alkaline fusion is applicable only to small samples, and introduces large quantities of reagents, which in themselves constitute a danger of contamination. Low-temperature ignition in a m d e (450' C.) was proposed by Remington (6),and used on a, lar e number of samples of ve etables. The authors were able to &ow good recoveries when &ied thyroid gland was added to dried potatoes, but Reith (8) reported large losses when iodine compounds were added to cereal products or dried milk. Karns (a), on the other hand, found good recoveries of added potassium iodide, but that plant and animal tissues alone gave consistent1 lower values than by other methods. Di estion wit{ hydrogen peroxide and sulfuric acid, proposed by Pfeiffer (T),requires costly and fragile apparatus, and possessea objections which include the distillation of unoxidized fatty acids and other volatile substances, inability to handle large samples, and time required for the oxidation. The silica tube furnace devised by McClendon (4) and adopted with various modifications by Reith, von Fellenberg ( I ) , McHargue ( 6 ) , and others, insures, with proper operation, rapid and complete oxidation in a semi-enclosed system;all evolved gases being drawn through an absorption train. The capacity of the absorption s stem has to be large, so that while the actual combustion oPthe sample may take half an hour or less for 100 grams, the subsequent evaporation and manipulation of the large volume of absorption liquid and washin s will require several days. The intense heat developed in t i e McClendon furnace, in an atmosphere enriched with oxygen, creates conditions favorable to fixation of atmospheric nitrogen. Nitrite, thus formed, is hard to get rid of, and unless eliminated may oxidize and drive out of solution all the iodine present. ComFIete failures to recover any iodine by this method are annoyingly requent. Recently Karns (2) has proposed ignition in oxygen in a specially constructed flask or bulb, claiming that the oxidation could be made slower and could be more easily controlled, and that hence it is possible to work with a much smaller absorption train than with the tube furnace. Karns also introduced the idea of condensing the evolved iodine by freezing, instead of absorbing it in solutions. The method of Karns seemed to be a distinct advance, particularly for those laboratories where iodine assays must be made frequently, and the authors accordingly undertook to simplify the apparatus and manipulation. The essential
part of the simplified set-up is the torch (Figure 1) which contains combined in one piece of apparatus the feed device for the sample, jets for supplying oxygen, exit tube for products of combustion, and support for the flask or combustion chamber. It is made of brass, the cup being of such size as to accommodate and provide water seal for a 500CC. wide-mouth Erlenmeyer flask of Pyrex glass. The oxygen feed tubes are so set as to throw the jets of oxygen against the tip of the advancing candle, and are offset slightly so as to give the gaseous stream a whirling motion, For dry milk and some other substances two oxygen jets are sufficient, but for samples more difficult to burn cleanly torches with four jets have been constructed. Oxygen consumption approximates 1 to 1.5 liters per minute. The Erlenmeyer type of flask was chosen after many trials as giving the maximum efficiency with the least volume. An essential part of the operation is the manner of feeding the sample. This is packed into Visking sausage casing1 (0.94 inch, 2.35 cm.) to form a cartridge which fits very freely in the feed tube. The feed plate has two pins projecting from its upper surface, which engage the cartridge and cause it to rotate with the feed screw, thus enabling the oxygen jets to exert a cutting action as the cartridge advances. With this device it has not been found necessary to use carbon dioxide, but the feed tube is provided with a hole near the lower end, to permit a small amount of air to be drawn in and guard against the water seal being broken by sudden changes of pressure. The exit tube leading to the absorption train is of glass rather than metal, since the products of combustion are apt to be corrosive, and all brass surfaces exposed in the combustion chamber and water-seal cup are given a coating of nitrocellulose lacquer, it having been found that copper in the washings may interfere in the analysis. Samples of dry milk or dried vegetable matter weighing 25 to 50 grams can be burned readily in one operation. The combustion can be interrupted to introduce new cartridges of material, or to change the flask, should it become so coated with sublimed material as to make proper observation of the operation impossible. Good vision of the tip of the burn1 The Visking 8ausage casing may be objected to as a possible source of iodine, but we have used it continuously for several years when burning samples in the silica tube. Some of the diets employed to produce goiter in the r&t oontain so little iodine (16y per kilo) that a kilogram must be burned in one sample, and any appreciable amount of iodine in the sausage crteing would become evident.
