102 BULLETIlSr 1036, U. S. DEPARTMENT OF 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 

 solidify 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. 



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 theu' 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. Neither test apparently can be relied upon to differentiate 

 water-gas tar products from coal-tar products. 



