Acid cuprous chloride solution.-Dissolve 100 grams of c. p. cuprous chloride in 600 c. c. of concentrated c. p. hydrochloric acid. Oxygen is readily absorbed by this solution and oxidizes some of the cuprous chloride, hence it should be excluded as much as possible during the preparation. Even slight oxidation causes the solution to be dirty black or greenish black immediately after preparation or on standing. It can not be used in this condition but must be reduced until it is a clear straw yellow.

Reduction by copper.-To the above solution in a bottle add some copper turnings, strips of sheet copper, wire, or copper gauze. Several days may be required to reduce the solution to a straw-yellow color; but after reduction has been effected the remaining copper will keep it reduced, unless, of course, the bottle is not tightly closed.

Reduction with stannous chloride.-The reduction can be effected immediately if stannous chloride is used instead of metallic copper. Drop the stannous chloride in the solution piece by piece, preventing the entrance of air as much as possible, or add small portions of a solution made by dissolving 25 grams of stannous chloride in 100 c. c. of a solution of equal parts of c. p. concentrated hydrochloric acid and water. Insert the stopper after adding each portion and shake gently. Continue in this manner until the solution becomes straw color (not merely greenish), then add another portion of stannous chloride in excess. This solution is ready for immediate use. If a large quantity has been made, it should be stored in accordance with the instructions given for alkaline pyrogallate.

Acid cuprous chloride is poisonous and fairly corrosive to the hands, clothing, shoes, metal, etc.

Cuprous sulphate beta naphthol.—Under the method for determining carbon monoxide the use of cuprous sulphate beta naphthol instead of cuprous chloride is discussed. Also, it is stated that the solution is rather difficult to prepare, hence no method is given here. Persons interested in preparing it, however, may consult the references given.12

CONFINING LIQUID FOR BURETTE AND COMBUSTION PIPETTE

The water used in the burette and combustion pipette should be kept slightly acidic with sulphuric acid. Also, it is desirable to color it red with an indicator such as methyl orange,13 because the color not only facilitates reading the meniscus but it also changes to a rather pale yellow if the confining liquid becomes alkaline, thus giving a warning to add more acid.

The acid solution is made by adding a few drops of concentrated sulphuric acid to the leveling bulb or burette reservoir and then

12 Methods of the Chemists of the U. S. Steel Corporation for the Sampling and Analysis of Gases, 3d ed., 1927, 187 pp. Prepared by a Committee of Chemists. Same method in Gas Chemists' Handbook, Am. Gas Assoc., 1928.

Methyl orange is a water-soluble organic compound which is red in acid solution and yellow in alkaline solution. It is commonly used in chemical analysis and may be obtained from any chemical-supply house.

adding a few drops of the methyl-orange indicator, or a stock of 10 per cent sulphuric acid solution containing the indicator may be prepared and small portions added as need arises. Any clear drinking water may be used to prepare the confining liquid.

LIFE OF SOLUTIONS

As the solutions absorbing carbon dioxide, oxygen, and carbon monoxide from gas samples will also absorb carbon dioxide or oxygen from the air, their life depends on (1) the effectiveness of protection from air when in the pipette or the storage bottle and (2) the amount of gas they absorb in the analysis of successive samples. Preservation during preparation and storage is referred to under "Preparation of solutions," and in the pipettes they are protected by rubber bags which preserve the solutions from deterioration when not in use. However, one can not always be sure that the bags will not leak air, and the solutions should be changed if they have stood two months or more, even though the apparatus has not been used. However, if an emergency arises and new solutions are not available, the old ones may be used, but more attention should be given to insuring complete absorption by checking each absorption as described in the analytical procedure for the various gases. Cuprous chloride deteriorates faster than any of the others and is more liable to be inefficient after prolonged standing. If it has turned quite. dark, it is worthless.

The approximate life of solutions during use depends on the manner of preparation of the original solution and how well it was preserved. The following facts are approximately true for average solutions and may be used as a guide to changing them, although toward the latter part of their life the speed of absorption and completeness should be observed occasionally, and if slow or inefficient the solution should be changed, even though its estimated life has not expired.

Sodium or potassium hydroxide.-Either of these solutions is capable of absorbing large amounts of carbon dioxide, and as many as 100 or 200 mine-fire samples can be analyzed before they are "worn out"; in fact, the solutions are generally changed due to other reasons, such as turbidity, sediment, or solid matter in the stems, etc.

Alkaline pyrogallate.-After alkaline pyrogallate has absorbed about 10 times its volume of oxygen its action becomes slower, and 9 to 12 passes into the solution may be required in making the determination. When the solution has absorbed 15 to 20 times its volume of oxygen it should be discarded. One filling of the pipette may be used satisfactorily for approximately 75 to 100 samples of mine-fire gases. This, however, depends upon the original preparation and how well it was preserved.

Cuprous chloride solution.-Cuprous chloride is a rather unsatisfactory absorbent, because it never completely absorbs all of the carbon monoxide from a gas mixture. The amount that it absorbs depends upon the amount that it has previously absorbed and the amount in the particular sample. For example, a new solution will absorb nearly all of the carbon monoxide from the first few samples and then leave more and more in the gas of succeeding samples. If it has already absorbed a considerable amount of gas from previous samples it may even give up small amounts of carbon monoxide to samples that contain only traces or none of that constituent. In types (not shown in figs. 10, 11, and 12) of gas apparatus used for analyzing samples containing large amounts of CO, such as water gas, producer gas, blast-furnace gas, etc., two cuprous chloride absorption pipettes are used in series, the gas being passed into the first to remove the major part of the gas and later into a comparatively fresh one to remove most of the remaining gas. The solutions are changed alternately; that is, as soon as the first one is worn out it is replaced by fresh solution and becomes the pipette to be used for the second absorption. The portable apparatus shown in Figures 10, 11, and 12 has only one cuprous chloride pipette, c. This, however, will give satisfactory results for mine-fire gases, afterdamp, etc., which contain relatively small amounts of CO, provided, of course, that the solution is changed frequently. The solution should be changed after every 8 to 10 analyses (not samples) if the samples contain 1.5 to 3 per cent of CO. With 0.5 to 1.5 per cent the solution should be changed every 15 to 20 analyses and with lower amounts of CO (0.5 per cent or less) the same solution may be used for 25 to 35 analyses if not previously darkened from oxidation by atmospheric oxygen.

If the results of analysis of several successive samples taken from the same place, as the same seal of a mine fire, show a continual trend toward decrease in carbon monoxide content, the cuprous chloride solutions should always be changed to ascertain whether the trend is due to actual decrease in the carbon monoxide content or due to the solution becoming worn out and leaving more and more of the carbon monoxide in the gas.

OPENING SAMPLE CONTAINERS

Although preliminary connections to sample containers may be made, no containers should be opened and the gases exposed 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 taken to avoid contamination by air.

Open vacuum tubes by carefully making a file scratch on the shell tubing stem about midway between the point where the capillary

tip is attached and the body of the tube. Avoid excessive pressure on the stem lest it be crushed or break prematurely at the file scratch. Then, while holding the tube 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 the possibility of cutting the fingers, a handkerchief or rag may be used to grip the neck. If the vessel containing the confining water for displacing samples is not large enough to get the hand in, to grasp the tip for breaking, the tube may be broken by carefully striking the neck beyond the point where the file scratch has been made against the side of the vessel or against an iron rod or other object placed therein. In either event, take care to keep the open end under water, thus sealing it against contamination by air.

SUPPLY OF OXYGEN FOR COMBUSTION

If the ordinary compressed oxygen made from air or electrolytic oxygen contains less than 0.1 per cent of combustible gases, it is suitable for making combustion analyses. A convenient way to use oxygen is to fill a double-end sample container from the cylinder of compressed gas, place the container in water, and when oxygen is desired make a connection to n (fig. 10) similar to that described for connecting sample containers. The oxygen reservoir is connected to n only when it is desired to draw portions into the burette, and it should therefore be equipped with a screw clamp or pinch clamp for closing when not in use.

The sample container used as an oxygen reservoir may be filled with oxygen by just cracking the valve of a cylinder of compressed gas and inserting a 1-hole stopper in (or holding it against) the valve outlet. A short piece of glass tubing is inserted in the stopper for making the connection to the tube or reservoir. The exit end of the reservoir must be open when the compressed oxygen enters, and the containers must not be subjected to high pressures, as they will break and possibly endanger the operator. The filling may be done by air or water displacement; that is, by first filling the container with water and then displacing it with oxygen or by allowing the oxygen to flow through the container until all of the air has been removed.

PREPARING APPARATUS FOR USE

GREASING STOPCOCKS

When occasion arises to use the apparatus after it has been in storage for some time (refer to Care and Storage, p. 85) remove the stopcocks, being careful not to interchange them, and carefully clean out the paper strip if this has been used to keep the stopcocks from sticking. Do not scratch with iron or steel implements but use a copper wire

or wood splinter. If small particles of paper remain, soak them with water and remove the last traces of them by wetting the plug, inserting it in the barrel, and turning it a few times.

Heavy-grade vaseline may be 'used; in fact, it is recommended where solutions or water come in contact with the grease. However, if precautions are taken to prevent this contact with water, a rubberbeeswax-vaseline preparation1 will give a better seal and will need to be renewed less frequently than vaseline.

In greasing a stopcock remove the plug and wipe it and the barrel free from all water or grease. Then, by using a piece of copper wire bent at right angles or the end of an ordinary pipe cleaner remove particles of grease or dirt from the bore in the plug and from the outlets of the barrel. Wipe the barrel and plug again. Apply a thin uniform film of grease to the plug, remove any grease that may have entered the bore, insert the plug in the barrel, and turn it a few times, after which a transparent film should be formed throughout the barrel. If streaks occur, traces of either water or dirt were present or insufficient grease was applied. Remove the plug, wipe it clean of grease, regrease, and proceed as described.

Whenever streaks appear in the film when in use the stopcocks should be regreased before the next analysis is attempted. Also, in some instances grease will collect in the bore during use and form a plug that will cause a stoppage in the gas flow. In most cases the particular analysis can be finished by forcing the flow, but the cock should always be removed and regreased before the next analysis is attempted. When vaseline is used the cocks may become tight; this indicates that the film is too thin, and the cocks should be regreased even though the film appears clear.

Properly greased stopcocks are important in avoiding leaks and consequent errors in analysis.

FILLING THE BURETTE AND COMBUSTION PIPETTE

The water jacket and leveling bottles should be filled with clear water. Any water suitable for drinking purposes may be used. The leveling bottles ƒ and g (fig. 10) should be nearly filled with water and enough of the colored 10 per cent sulphuric acid solution added to give the solution a distinctly sour taste and red color. (See Preparation of Solutions, p. 42.) The acid is desirable, although not entirely essential if the water is not normally alkaline or if none of the caustic solution or alkaline pyrogallate gets into the burette. If the displacing water is alkaline, it will absorb some of the carbon dioxide from the sample before the determination for that constituent is made, in which case less than the correct amount will be found.

14 For formula and method of preparation, see Burrell, G. A., and Seibert, F. M., Sampling and Examination of Mine Gases and Natural Gas: Bull. 197, Bureau of Mines, revised by G. W. Jones, 1926, p. 30,