spiral creates obvious sources of ignition and can be considered similar in effect to open lights or flames. If the pressure test on the burette reveals a decrease in volume greater than 0.2, a significant leak has occurred. The test (raising f with all stopcocks closed) should then be repeated, using the same sample of gas and noting if there is additional decrease in volume. If the original loss was only slightly greater than 0.2, the burette may have been read erroneously, and this may be apparent after the second test. If the second reading shows a further decrease in volume, the apparatus apparently is leaking either at the rubber-tubing connections on the manifold or around the stopcocks. If the leak is at the pipette cocks, it may be caused by circular channeling in the grease, and the liquid in the stem of the faulty cock will drop below the mark. Should this occur, the particular cock or cocks should be regreased, after which the liquid should be drawn back to the marks as before. If no evidence of a leak is apparent through the falling of the liquid in the stems of a, b, c, and d, cock p should be regreased; if this does not remedy the condition, the rubber connections on the manifold should be replaced. There should be no difficulty in making tight joints at these connections if pure gum tubing of the proper internal diameter is used and the glass tubes are clean. Length of the pieces of pure gum tubing should be 12 to 134 inches. Leaks at these connections may be corrected in some instances by wrapping the rubber tubing at about 1/4 inch from the ends with two or three turns of soft copper wire, several turns of rubber band or string, drawing it tight, and twisting or tying the ends. If no leaks occur in the pressure test, but the results of analyzing the sample of air fail to agree closely enough with those for normal air, one of three things may be the cause: (1) Leaks in the rubber tubing on the pipette stems, (2) poor or wornout solution if the error is in the oxygen value, or (3) wrong technique or procedure. In making this test analysis, the percentage of each constituent should be calculated immediately after each successive step in the procedure, in which case the occurrence or error is noted at once, and certain tests can be made to ascertain the cause. Make sure the liquid has been brought exactly to the mark on the pipette stem and check the burette reading. If no error has been made in measurement, the following methods should be tried to ascertain the cause: 1. If the percentage is too low, as with oxygen, the sample should be passed again into the solution, as the error may be due to incomplete absorption, and more passes of the sample into the solution should be made or the solution should be renewed. 2. If the percentage is too high or continues to increase or decrease with successive passes into the same reagent, the cause is leakage. In most cases the leak is in the connection to that particular pipette, or there is a leaky stopcock, but leakage is sometimes due to unusual causes, such as the sliding down of one of the tubes inside the pipette into the opening below and when gas is forced rapidly into the pipette some of it being driven down this tube and traveling around the U-connection into the reservior in the back. The apparent presence of carbon monoxide in the sample of normal air indicates incomplete removal of oxygen, and an increase in the volume of the sample after it is passed into the acid cuprous chloride pipette may be due to the presence of the acid vapor, which may be removed by passing the sample into the caustic pipette, a, several times. Leaks in the combustion pipette may be due to faulty connections or to cracks in the tubes that support the platinum wire, if these tubes are of the type that has an incased copper-wire lead. These leaks, usually but not always, will be disclosed by water entering the inside of the glass tube that incases the leads. CONNECTING SAMPLE CONTAINER TO APPARATUS OPENING SAMPLE CONTAINERS If double-end sample containers are used, fill the capillary or the rubber hose of one end of the sample container with water to expel the air and, with this end of the container down, place it in a vessel of displacing water. (See fig. 24.) The displacing vessel should be Small-diameter rubber hose, capillary glass tubing, or copper tubing connected to gas analysis apparatus Screw For vacuum tubes and ordinary bottles For sample containers For sample containers considerably larger in diameter than the container and at least twothirds as deep. An ordinary water bucket, crock, or other such container is suitable. If the container tends to float horizontally, fasten it in a vertical position with string or wire. The temperature of the water should be about the same as that of the room or slightly higher, otherwise the gas will be cooled suddenly and will contract in volume, which might cause inward leaks of air. Connect the other end (keeping it closed) to o (fig. 18) by a short piece of rubber tubing (inside diameter approximately 316 inch). If available, 2 mm. capillary glass tubing is better, as it holds a smaller volume of dead air. If the latter is used, make connections to the sample container by means of a short length of pure gum tubing. If the samples have been collected in ordinary bottles or vacuumtype containers, it is necessary to insert a tube or hose into the neck of the container while it is in an inverted position with the neck under water. A U-tube made from 1-inch inside diameter copper tubing or 2 mm, capillary glass tubing, one arm of which is a little shorter than the depth of water in the bucket or vessel, is more convenient than a rubber hose. The longer arm of the U-tube is connected to outlet o of stopcock p with a short length of pure-gum tubing. Although preliminary connections to sample containers may be made, no containers should be opened to expose the gases to the displacing water (which will absorb carbon dioxide) until everything is in readiness to draw a sample into the burette. All containers should be opened under water, and care should be taken to avoid contamination by air. Open vacuum containers by carefully making a file scratch on the shell tubing neck about midway between the point where the capillary tip is attached and the body of the container. Avoid excessive pressure on the stem lest it be crushed or break prematurely at the file scratch. Then, while holding the container in a vertical position, tip down and end under water, break the neck at the scratch in a manner similar to the breaking of the tip in filling. To avoid cutting the fingers, a cloth may be used to grip the neck. If the vessel containing the displacing water is not large enough to admit the hand to grasp the tip for breaking, the neck of the sample container may be broken by carefully striking it (beyond the point where the file scratch was made) against the side of the vessel or against an iron rod or other object placed therein, taking care to keep the open end under water after the neck has been broken. If the sample container is an ordinary bottle closed with a cork or spring fastener, these also must be opened under water to avoid contamination of the sample with air. After the sample container (vacuum-type or ordinary bottle) is opened, the U-tube connection (as shown in fig. 24) is inserted into the opening with both the open end of the sample container and the tip of the U-tube under water to exclude air from the sample. When the arm of the U-tube has been inserted, allow the container to sink as far as it will and then fasten it in a vertical position. If this is not done, and the displacing water vessel is wide, the container will tend to float horizontally, and the water seal may be broken. The container should not be fastened so tightly as to be unable to sink farther into the water when gas is removed. In using ordinary bottles or vacuum-type_containers, a means of closing the connecting tube where it is attached to o should be provided as a safeguard, so that the sample container may be closed after the first sample is withdrawn and the remainder of the sample preserved for a duplicate analysis. A screw clamp may be applied to the rubber connection between the U-tube and stopcock p. The end of the connection between the sample container and o should always be closed either by a screw clamp or by previously connecting to o, with p closed before inserting the U-tube into the sample, otherwise the sample may be contaminated with air. ANALYTICAL PROCEDURE PREPARATION Before starting an analysis, complete all preliminary steps such as greasing stopcocks, purging the dead space of air or residuals from the previous analysis, and adjusting the filament current and obtaining a supply of oxygen for combustion (if oxygen is needed). Bring the solutions in pipettes a, b, c, and d exactly to the marks on the capillary stems and close the cocks. These operations have been described previously in detail. OBTAINING SAMPLE Connect the sample container to o by any suitable means, as shown in figure 24, and have the stopcock p closed between o and the sample. With p open to n, raise f until the water just reaches h, turn p to connect with o, lower f, open all connections to the sample container, and allow gas to flow from the sample container through o into the burette. When about 20 cc. of gas has been drawn into the burette, turn p to connect the burette with the exterior through n, raise ƒ, and discard the gas through n. As soon as the water reaches h, close p. This procedure fills the sampling system, from container to burette, with a representative sample. Avoid waste of gas in flushing connections or purging the apparatus. With the ordinary 250 cc. sample it is necessary to use the gas sparingly, otherwise there will not be enough for duplicate analyses. Next, turn p to connect to the sample through o, lower f until the water falls approximately to the lowest division on the burette, pinch off the leveling-bottle hose (between e and f) with the thumb and finger, and quickly close stopcock p. Release the hose, and with ƒ on the table or at approximately the height of the bottom of e, allow 1 minute for the water to drain from the sides of the burette, then read the volume according to the instructions given under "Reading Gas Volumes With the Burette," page 58. If the volume is 100 cc. or less, record it and proceed with the next step in the analysis. If the volume is more than 100 cc. (below the lowest graduation mark and hence outside the range of measurement with the burette), raise f, at the same time observing the meniscus; when the latter coincides with 100 cc., again pinch off the hose. Now turn p to open the manifold momentarily to the exterior through n and allow the excess gas to escape. Close p and read the volume, which should be recorded as "original volume of sample." The sample is now ready for absorbing the first constituent, namely, carbon dioxide. DETERMINATION OF CARBON DIOXIDE As mine atmospheres always contain carbon dioxide, the procedure for determining that constituent must be followed, even though the results may not be desired. Raise the level of the water in ƒ a little higher than in e to insure against drawing solution over from the pipette, open the cock to the sodium or potassium hydroxide pipette a, and pass the gas into a by raising f until the level of the liquid is near but not above h. Allow the gas to remain 3 to 5 seconds in a for contact and then withdraw it by lowering f until the solution in a is about one-half inch below the stem. Immediately raise f again and pass the gas back into a. Repeat this procedure five or six times. It is not necessary, each time a pass is made, to bring all of the gas out of the pipette or to raise the level of the water in e exactly to h, as five or six passes eventually will cause contact of all of the gas with the reagent, and the danger of drawing or forcing liquid into the manifold is avoided. When five or six complete passes have been made, withdraw the gas and bring the liquid exactly to the mark on the stem of a, being careful not to draw the liquid into the stopcock of the manifold. (See p. 69, Procedure for Withdrawing Gas from Pipettes.) Close the cock, allow the burette to drain one minute, and read the volume. Beginners should now repeat the entire procedure for absorbing carbon dioxide to ascertain if complete absorption has been effected. (If any carbon dioxide escapes absorption at this time, it will be removed during the determination of oxygen by the alkaline pyrogallate, and the apparent percentage of carbon dioxide will be too low, and the percentage of oxygen will be erroneously increased.) The volume after absorbing the carbon dioxide subtracted from the original volume of sample equals the volume of carbon dioxide in the sample. Percent of carbon dioxide= volume of carbon dioxide x 100. For example, if the original sample volume was 98.0 cc. and the volume of sample after absorbing the carbon dioxide 94.5, the calculation is as follows: Volume of carbon dioxide-98.0-94.5-3.5 cc. Actually, the calculated percentage is 3.57, but as the error of the portable Örsat method is approximately 0.2 for this determination, it is meaningless to report figures beyond the nearest tenth of a percent; in fact, it is misleading to report results in the second decimal place. DETERMINATION OF OXYGEN If complete analysis of the sample is desired, determination of oxygen is the next step in the procedure. Again raise ƒ a little above the level of the liquid in e, open the stopcock to b, and pass the gas into the alkaline pyrogallate solution in the manner described for carbon dioxide. Alkaline pyrogallate solution does not remove oxygen from a gas mixture as rapidly as the sodium or potassium hydroxide solution removes carbon dioxide, consequently more contact must be allowed between the solution and the sample. Eight or nine passes usually are enough. An experienced analyst can ascertain from the color of the solution as it drains down the pipette whether or not a sample contains oxygen and when it is nearly all absorbed. If the thin film of solution left on the walls of the pipette as the solution recedes is a deep brownish red, it indicates the reaction with oxygen; but if it is greenish, little or no oxygen is present. Hence, if oxygen is present in the sample, the film first will be reddish and later turn to the green when nearly all the oxygen has been absorbed. After the greenish color appears, two or three more passes usually are enough to complete the absorption. Upon completing the absorption, draw the solution to the mark on the pipette stem, close the cock, allow the burette to drain one minute, and read the volume. Beginners should repeat the procedure to |