the gas by raising f. This washes or sweeps the original gas from the manifold. Now lower f and draw in about 50 c. c. of air, close cock p, and by raising ƒ and opening the cock to b pass the gas into b and absorb the oxygen and traces of carbon dioxide. The nitrogen is then passed once into each pipette, and the liquids in turn are carefully brought to the marks on the stems. Discard the gas through n until the water in e just reaches h. Immediately lower f and draw in 95 to 100 c. c. of normal air, allow the burette to drain one minute, and read the volume accurately. Now raise the leveling bulb as high as possible and hold it there for two or three minutes. Return the bulb to its position near the 100 c. c. mark, allow it to drain one minute, and again read the volume. If the reading is the same as the previous one, plus or minus 0.2, the apparatus may be considered free from leaks in the burette connections and stopcocks. The sample of air is then subjected to a complete analysis by passing it into the various pipettes (including the combustion pipette) according to the regular procedure. If the results obtained are within 0.2 per cent of the composition of normal air-that is, carbon dioxide, 0.03; oxygen, 20.93; carbon monoxide, 0.00; and nitrogen, 79.04 per cent-the apparatus with but few exceptions can be considered in good working condition. The operator should remember that if this air test is conducted in a mine where the sample is taken from a room or in a return air course where the air may contain some black damp, the results obtained will vary from those for normal air. No tests involving combustion analyses should be conducted underground or in other places where there may be combustible gases or vapors; also the battery equipment for combustion analyses should not be taken underground. The use of the electrically heated platinum spiral presents obvious sources of ignition and can be considered similar in effect to open lights or flames. If, however, 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. However, if the second reading shows a further decrease in volume, the apparatus is apparently leaking either at the burette connection or around the stopcocks. If it is leaking at the pipette cocks, it is usually due to 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; and if this does not remedy the condition, the rubber connection to the burette and to c, if it is of the bubbling type, should be replaced. The proper size of pure-gum tubing usually fits tightly if the glass tubes are clean, and there should be no difficulty in making a tight joint if the lap over each end of the capillary stems is approximately 1% to 1%1⁄2 inches. However, if the leak appears to be at the connection, the tubing should be examined for holes, especially at the seams. If none are found, the hose should be replaced or ferrules made at about the mid-point of each end by wrapping them with either 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 at the pipette connection, (2) poor or worn-out 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 of error is noted at once, and certain tests can be made to ascertain the cause. The first thing to do is to see if the liquid has been brought exactly to the mark on the pipette stem and to check the burette reading. If no apparent 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 or carbon dioxide, the sample should be passed again into the solution, as the error might be due to incomplete absorption, and more passes should be employed or the solution changed. (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 one of the tubes inside the pipette sliding down into the opening below and when gas is rapidly forced into the pipette some of it being driven down this tube and traveling around the U connection into the reservoir in the back. The presence of carbon monoxide indicates incomplete removal of oxygen and an increase in the volume of the gas after it passes into the acid cuprous chloride pipette may be due to incomplete removal of the acid vapor. Leaks in the combustion pipette may be due to faulty connections or to cracks in the tubes which support the platinum wire if the type which has an incased copper wire lead is used. These leaks can usually but not always be discerned by water entering the inside of the glass tube which incases the leads. CONNECTING SAMPLE CONTAINER TO APPARATUS OPENING SAMPLE CONTAINERS If double-end tubes are used for containers, fill the capillary or the rubber hose of one end of the sample container with water to expel the air and place it in a vessel of displacing water. (See fig. 15.) The displacing vessel should be larger in diameter than the container and at least two-thirds as deep. An ordinary water bucket, crock, etc., is suitable. If the tube tends to float horizontally, fasten it in a vertical position by tying it 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 augments conditions for inward leaks of air. Connect the other end (keeping it closed) to o (fig. 10) by a short piece of small small-diameter rubber nose, capillary glass tubing,or copper tubing For vacuum tubes and ordinary bottles Screw clamp For sample containers FIGURE 15.-Suggestions for removing sample from container (inside diameter approximately three-sixteenths inch) rubber tubing. If available, 2 mm. capillary glass tubing is better, as it holds a smaller volume of dead air. In using the latter make slip connectors to the sample tube by using pure-gum tubing. If the samples have been collected in magnesium citrate bottles, ordinary bottles, or vacuum tubes, it is necessary to insert a tube or hose into the neck of the bottle while it is in an inverted position with the neck under water. AU 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. With one arm of the U tube connected to o in the manner described above and with as short a piece of hose as possible, hold the other end about 1 inch under water and insert it in the container opening by bringing the latter over the top of it but without breaking the water seal, as that would contaminate the sample with air. When the arm has been inserted allow the container to sink as far as it will and then fasten it in an approximately vertical position. If this is not done and the displacing water vessel is wide, the bottles will tend to float horizontally, and the water seal may become broken. The container should not, however, be fastened tightly enough to prevent its sinking farther in the water when gas is removed. In using ordinary bottles or vacuum tubes a means of closing the connecting tube where it is attached to o should be provided if the type of stopcock shown at p, Figure 10, is not employed, 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. The most convenient arrangement is permanently to attach a 1-way capillary stopcock to o by means of a short rubber connection. However, a screw clamp will suffice or the short arm of the U tube or hose may be removed from the neck of the container, although the latter is somewhat inconvenient and wastes the sample. As stated, this closing device is not needed if the type of cock shown in p (fig. 10) is used. 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 hose or U tube in the sample, otherwise the sample may be lost or become contaminated. ANALYTICAL PROCEDURE PREPARATION Before starting an analysis take care of all preliminary items such as greasing stopcocks, purging the dead space of air or residuals from the previous analysis, and adjusting the filament current and supply of oxygen for combustion (if oxygen is needed). These operations have previously been described in detail. OBTAINING SAMPLE Bring the solutions in pipettes a, b, c, and d exactly to the marks on the capillary stems and close the cocks. Connect the sample container to o by any suitable means, as shown in Figure 15, and have the stopcock p closed between o and the sample. With p open to n, raise ƒ until the water just reaches h, turn p to connect with o, lower f,15 open all connections to the tube, and allow gas to flow 13 In using vacuum tubes or bottles where a U tube (see p. 56, Connecting Sample Container to Apparatus) is required to withdraw the gas, the latter will be filled with water which would be drawn into the manifold ahead of the gas. This can be avoided by closing the hose to f with a screw clamp when the water is ath. Open the cock to d and lower g. Then open connections to the sample container and draw off water and a little gas into d. Close cock p to the sample container and turn p to connect through n to the exterior, raise g, and discard the gas. Bring the water to the mark and close the stopcock to d. Now turn p to again connect to o and proceed in obtaining a sample as given herein. from the sample container through o into the burette. When about 20 c. c. of gas has been drawn into the burette turn p to connect the manifold with the exterior through n, raise ƒ, and discard the gas through n. As soon as the water reaches h close p to n. This sweeps out the gas left in the manifold from the preceding analysis, which, if not removed, would probably give high results for oxygen. Avoid waste of gas in flushing connections or purging the apparatus. With the ordinary 250 c. c. sample it is necessary to use the gas sparingly, otherwise there will not be enough for duplicate analyses. Turn p to connect to the sample through o, lower ƒ 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 one minute for the water to drain from the sides of the burette, then read the volume according to the instructions given under Reading Gas Volume With the Burette, page 37. If the volume is 100 c. c. or less, record it and proceed with the next step in the analysis. If the volume is more than 100 c. c. (which falls below the lowest graduation mark and hence outside the range of measurement with the burette), raise f, at the same time observing the meniscus; and when the latter coincides with 100 c. c. 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 Since 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 that 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 three to five seconds in a for contact and then withdraw it by lowering ƒ until the solution in a is about onehalf inch below the stem. Immediately raise ƒ 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 will eventually allow contact of all of the gas with the reagent and avoid the danger of drawing or forcing liquid into the manifold. When five or six complete passes have been made withdraw the gas and bring the liquid exactly to the mark on the stem |