CHAPTER II.— SPECIFICATIONS NOW IN FORCE BY VARIOUS ASSOCIA- 
TIONS. 
During the last few years a concerted effort has been made in this 
country by various societies interested in wood preservation to adopt 
uniform specifications for wood-preserving oils. Such specifications 
have been adopted or have been proposed by several societies. In 
addition to these, other specifications are still in force which do not 
require all the latest tests. It is believed, however, that enough 
of the more modern specifications are given in Table 36 to answer 
most purposes; but, for the sake of simplification, only those are in- 
cluded which apply to different types of oil. No claim is made for the 
superiority of any of these oils. They differ only in boiling points. 
Although it has been generally believed that the higher-boiling oils 
are the most permanent, it has been shown that oils lighter than those 
of specification No. 3, if used in a proper manner, have outlasted the 
mechanical life of ties and poles. For land work, therefore, it seems 
to be largely a matter of personal opinion as to which of these oils is 
the best. It must be remembered that these specifications are for 
materials of known origin and are in addition to the requirement that 
the creosote shall be a coal-tar product. However, the tests given in 
these specifications do not guarantee a pure coal-tar product. Cer- 
tain selected materials which are not derived from coal tar may pass 
all the tests; but the tests, if rigidly enforced, considerably reduce 
the amount of such materials. At the same time, certain pure coal- 
tar products are eliminated. The specification is intended to insure 
the type of oil which has proved of benefit. Until other materials 
have proved to be of value, or until our knowledge of the mechanism 
of protection by creosote has been enlarged, it is deemed advisable to 
exclude such materials from the best grade of oil, even though they 
are coal-tar products. 
COAL-TAR SOLUTIONS. 
As already stated, tar solutions can not be considered so good pre- 
servatives as pure coal-tar creosotes. They have not been in use 
sufficiently long for their worth to be conclusively proved. It seems 
reasonable, however, to expect that a mixture of coal tar and coal-tar 
creosote will eventually be obtained that will preserve wood up to 
the limit of its mechanical life. Just what proportion of creosote and 
tar such a mixture will contain is problematical. Table 37 gives the 
specifications for tar solutions now in force. 
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