The globe is first thoroughly cleaned and dried and the stopcock lubricated, care being taken to keep the hole in the plug free from grease; the globe is then exhausted and weighed. After the globe is weighed it is filled with boiled water and suspended in a basin of water for 15 minutes at constant temperature. After the temperature has been observed and the stopcock closed the water is removed from the capillary tube above the tap and the bulb carefully dried and suspended from the balance for the second weighing. The authors use a 100-c. c. bulb.

For a rapid and approximate determination of the density of different kinds of natural gas, Bunsen's effusion method can be used, whereby a given quantity of the gas is allowed to flow through a small aperture. The time taken by a like quantity of air in passing is a measure of the density of the gas. The specific gravities of gases are inversely proportional to the squares of their rates of

effusion.

CALCULATION

The density of a natural gas may also be calculated from its chemical analysis. The different percentages of the constituents found are multiplied by their densities as compared to air, and the sum of these values divided by 100. The following table gives the values used at the Pittsburgh station of the Bureau of Mines for the calculation of the densities of natural gases. The values obtained by this method are on a dry gas basis. To correct for the moisture content present the percentage of moisture in the gas must be determined; then the percentages of gases found by analysis must be recalculated to include the water vapor present. The density is then calculated from the corrected gas analysis, as given before. The water-vapor content seldom' exceeds 2 per cent, and since the density of water does not differ much from that of the majority of natural gases, the dry gas analysis may ordinarily be used for calculating the density of a gas.

2.9266, observed. 2.2638, observed.. Jacquerod and Pintza, Mem.

• This table was adopted by the chemical section of the Pittsburgh experiment station of the Bureau of Mines in January, 1921.

• Weight of gases per liter at 0° C. and 760 mm. were obtained by the following formula: The calculated molecular weight of gas X1.4291

weight of gas per liter=molecular weight of oxygen=32

d Specific gravity of gas (air=1)=weight of gas per liter divided by 1.2928.

PROPERTIES OF THE MORE COMMON PARAFFIN HYDROCARBONS

Because of the increased interest taken in natural gas and in gasoline from the natural-gas industry, the authors have compiled from various sources the following table showing the properties of the more common paraffin hydrocarbons:

Properties of gaseous and some liquid paraffins

• Holleman, A. F., Organic chemistry. Edited by A. J. Walker, 1910, p. 41. Other authorities give -17° C.

Properties of the gaseous and some of the liquid paraffins

• Wright, L. T., Jour. Chem, Soc., vol. 47, 1885, p. 200. Landolt, H., and Börnstein, R., Physikalisch-chemische Tabellen. 1905, pp. 182-185 (by Dewar). Landolt, H., and Börnstein, R. Work cited, pp. 182-185 (by Olszewski). d Frankland, P., Jour. Chem. Soc., vol. 47, 1885, p. 235.

SUMMARY

The apparatus and methods described in this bulletin have proved suitable for the analysis of gas mixtures containing the constituents usually determined in gas analysis. The apparatus shown in Plate III is especially adapted for making a complete and accurate analysis of mixtures containing very small proportions of some constituents. The range of work possible with the apparatus is limited by the capacity of the stem of the burette, which is purposely made small so that successive graduations may mean very small differences in volume. Gas mixtures containing large percentages of such constituents as methane, hydrogen, and carbon monoxide are analyzed with the apparatus shown in Figure 10. For such mix

tures an apparatus as accurate as that shown in Plate III is seldom necessary. With these two types of apparatus the authors perform most of the eudiometric analyses in connection with their investigations for the Bureau of Mines, whose gas laboratory makes over 400 determinations a month.

The other apparatus illustrated in this bulletin are modifications of these two types and are designed for special work. Mining com⚫panies, for example, are chiefly interested in the methane content of mine air, or in the amount of methane and carbon dioxide therein. A particular ventilation study may frequently require a large number of analyses for carbon dioxide and oxygen.64

Laboratories at industrial plants not infrequently are content to sacrifice speed in the endeavor to make more accurate determinations of industrial gases than can be made with the ordinary technical forms of apparatus designed for use with water in the burette and combustion pipette. The apparatus shown in Figure 11 is adapted for such work, and is also suitable for a large variety of . experimental work. For analyses of natural gas, which constitute the gas analyses made in connection with some investigations, the apparatus shown in Figure 12 has been stripped of unnecessary pipettes, as shown in Figure 26. In designing apparatus for special work a reduction in the number of parts has been sought, because needless parts involve complications.

An attempt was made to assemble precise apparatus for exact work in experimental and other laboratories, as well as simpler apparatus for field work and for use by mining men who are not very familiar with apparatus for gas analysis. For instance, the authors have found that men entirely unfamiliar with such apparatus have done good work with the apparatus shown in Figures 7, 8, and 9 after a little instruction.

PUBLICATIONS ON ANALYSIS OF MINE GASES

Requests for publications available for free distribution should be addressed to the Director, Bureau of Mines.

The Bureau of Mines issues a list showing all its free publications that are available for distribution as well as those obtainable only from the Superintendent of Documents, Government Printing Office. Interested persons should apply to Director, Bureau of Mines, for a copy of the latest list.

PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION

TECHNICAL PAPER 357. A critical study of the Burrell indicator for combustible gases in air, by Lowell H. Milligan. 1924. 40 pp.

64 Burrell, G. A., and Seibert, F. M., Apparatus for gas-analysis laboratories at coal mines: Tech. Paper 14, Bureau of Mines, 1913, p. 7.

PUBLICATIONS ON ANALYSIS OF MINE GASES

105

TECHNICAL PAPER 373. The pyrotannic acid method for the quantitative determination of carbon monoxide in blood and in air, by R. R. Sayers and W. P. Yant. 1925. 18 pp., 2 pls., 1 fig.

PUBLICATIONS OBTAINABLE ONLY FROM THE SUPERINTENDENT OF DOCUMENTS

BULLETIN 42. The sampling and examination of mine gases and natural gas,
by G. A. Burrell and F. M. Seibert. 1913. 116 pp., 2 pls., 23 figs. 20 cents.
BULLETIN 105. Black damp in mines, by G. A. Burrell, I. W. Robertson, and
G. G. Oberfell. 1916. 88 pp. 10 cents.
TECHNICAL PAPER 11. The use of mice and birds for detecting carbon monoxide
after mine fires and explosions, by G. A. Burrell. 1912. 16 pp. 5 cents.
TECHNICAL PAPER 13. Gas analysis as an aid in fighting mine fires, by G. A.
Burrell and F. M. Seibert. 1912. 16 pp., 1 fig. 5 cents.

TECHNICAL PAPER 14. Apparatus for gas-analysis laboratories at coal mines, by G. A. Burrell and F. M. Seibert. 1913. 24 pp., 7 figs. 5 cents.

TECHNICAL PAPER 39. The inflammable gases in mine air, by G. A. Burrell and F. M. Seibert. 1913. 24 pp., 2 figs. 5 cents.

TECHNICAL PAPER 62.

Relative effects of carbon monoxide on small animals, by G. A. Burrell, F. M. Seibert, and I. W. Robertson. 1914. 23 pp. 5 cents. TECHNICAL PAPER 119. The limits of inflammability of mixtures of methane and air, by G. A. Burrell and G. G. Oberfell. 1915. 30 pp., 4 figs. 5 cents. TECHNICAL PAPER 121. Effects of temperature and pressure on the explosibility of methane-air mixtures, by G. A. Burrell and I. W. Robertson. 1916. 14 pp., 3 figs. 5 cents.

TECHNICAL PAPER 122. Effects of atmospheres deficient in oxygen on small animals and on men, by G. A. Burrell and G. G. Oberfell. 1915. 12 pp.

5 cents.

TECHNICAL PAPER 134. Explosibility of gases from mine fires, by G. A. Burrell and G. G. Oberfell. 1916. 31 pp., 1 fig. 5 cents.

TECHNICAL PAPER 150.

Limits of complete inflammability of mixtures of mine gases and of industrial gases with air, by G. A. Burrell and A. W. Gauger. 1917. 13 pp., 2 figs. 5 cents.

TECHNICAL PAPER 185. Use of the interferometer in gas, analysis, by F. M. Seibert and W. C. Harpster. 1918. 18 pp., 1 pl., 5 figs. 5 cents.

TECHNICAL PAPER 190. Methane accumulations from interrupted ventilation, by H. I. Smith and R. J. Hamon. 1918. 46 pp., 2 pls., 5 figs. 10 cents. 49530°-26-8