CADY AND MCFARLAND.| Composition of Natural Gas. 231 
hoped that they may be of benefit to other persons in their in- 
vestigations of the subject. 
BIBLIOGRAPHIES. 
Considerable assistance has been obtained from the follow- 
ing bibliographies, which relate at least in part to natural gas 
and petroleum: 
1. Redwood, “Petroleum and its Products,’ second edition, 
London, 1906. Bibliography by W. H. Dalton and L. V. Dal- 
ton. Vol. II, pp. 889-1001. This contains references to 5904 
articles on petroleum, natural gas, asphalt and like subjects, 
and is probably the most complete single bibliography to be ob- 
tained. 
2. Catalogue and Index of Contributions to North Ameri- 
can Geology, 1732-1891, by Philip Creveling Warman. 1898. 
A495 pp. Bull. 127, U.S. Geol. Surv. 
3. Bulletins Nos. 188 and 189, U. S. Geol. Surv. Index and 
Bibliography of North American Geology, Paleontology, Pe- 
trology and Mineralogy for 1892-1900, inclusive, by F. B. 
Weeks, 1901-’02. Especially Bull. 188, pp. 89 and 90. 
4. Bulletin No. 301, U.S. Geol. Surv. Bibliography and In- 
dex of North American Geology, etc., for 1901-’05, inclusive, 
by F. B. Weeks. See “Natural Gas,” p. 491. | 
5. Bibliography of Natural Gas in Ohio. Ohio Geol. Surv., 
Ath series. Bull. 6, pp. 163-165. 
6. List of Books, Papers and References on Rock Oil and 
Gas. U.S. Census Report, 1880, vol. X, p. 281. Penn. Geol. 
Surv., Ann. Rep. for 1886, pt. II, pp. 828-895. 
General Constitution of Natural Gas. 
Analyses of gas from many localities throughout the world 
have shown remarkably small numbers of constituents in 
widely varying proportions. The gas as it issues from the 
ground is always a mixture, often with one constituent in large 
excess of the rest, but still containing more than one gaseous 
substance. An enumeration and brief description of the more 
common constituents may be of use to those readers who are 
less familiar with the chemical nature of gas. 
HYDROCARBONS. 
The chief constituents of most inflammable gases belong to 
the family of hydrocarbons, compounds of hydrogen and car- 
bon. These are all combustible and capable of producing con- 
