102 BEXLETIX 1036, U. S. DEPAETMEXT OE AGRICULTURE. 
the naphthalene fraction. It may, however, be used by some of the 
manufacturers under the name of the limpid-point test. It gives 
some idea of the naphthalene content, especially that which will 
sohdify in cooling. 
The Forest Service described (50) a test for solids which included 
naphthalene and anthracene solids. A test somewhat similar (54) 
was afterwards adopted by the American Railway Engineering Asso- 
ciation. So far as the author is aware neither of these tests is now 
used to any great extent. 
VISCOSITY TEST. 
am 
The viscosity test has been proposed chiefly in connection with tar 
mixtures (25) . It consists of a determination of the viscosity by the 
use of an Engler viscosimeter. This gives but little information as 
to the amount of tar present. Probably an estimate of the tar con- 
tent fully as accurate may be made by one familiar with analyses of 
creosote by noticing the character and percentage of residue above 
a certain fixed point, as, for instance, 320° C. The latter procedure 
is applicable to water-gas tar, but the former is not. This test has 
now been dropped from specifications. It is believed, however, in 
the light of the relationship that exists between the penetration of 
oils and their absolute viscosity, that it would be a very desirable 
test to make for this purpose alone. 
INDEX OF REFRACTION TEST. 
A description of the apparatus used and the method of making the 
index of refraction test is given on page — . 
SULPHONATION TEST. 
A description of the sulphonation test and directions for making it 
are given on page — . 
DIMETHYL-SULPHATE TEST. 
The dimethyl-sulphate test was designed chiefly for use in light 
creosotes and as sheep dips. Chapin (55) claims that it gives more 
satisfactory results than the sulphonation test which it replaces. At 
the Forest Products Laboratory, however, with creosotes such as are 
used by wood preservers, the sulphonation tests have given the better 
results. Xeither test apparently can be relied upon to differentiate 
water-gas tar products from coal-tar products. 
