24 



BULLETIN 314, U. S. DEPARTMENT OP AGRICULTURE. 



When solid matter deposits upon the sides of the condenser, it niay be 

 melted by syphoning hot water through the condenser, and collected in 

 the fraction to which it belongs. The last fraction is collected up to 

 300° C, after which the flask and graduates are cooled to room tempera- 

 ture, and their contents determined by volume and weight. The 

 volume of pitch remaining in the retort is found by deducting the 

 total volume of the distillates from the original 100 cubic centi- 

 meters taken. Note should be made of the approximate volume of 

 solids which precipitate from the distillates upon cooling to 25° C. 



The results obtained are calculated in percentages by volumes and 

 weights to tenths of 1 per cent and reported as follows: 



Distillate. 



1. Water or ammoniacal liquor 



2. First light oils to 110° C 



3. Second light oils 110° C to 170° C 



4. Heavy oils 170° C to 270° C 



5. Heavy oils 270° C. to 300° C 



6. Pitch residue 



Per cent, 

 by volume. 



Per cent, 

 by weight. 



The above is applicable only to tars which contain no water. In 

 distilling crude tars or tars which are contaminated with water, it is 

 necessary to dehydrate them before submitting them to the regular 

 distillation. A cylindrical copper still with circular burner, as 

 shown in figure 13, is convenient for this purpose. Two hundred and 

 fifty cubic centimeters of the tar to be dehydrated is weighed in the 

 retort and the apparatus is set up as shown. A low flame is applied 

 to the upper part of the retort and the heating slowly and carefully 

 continued until the volume of water hi the separatory funnel shows 

 no further increase. The volume of water collected is noted and 

 calculated. The water is then drained from the separatory funnel 

 and the supernatant layer of oil is run into and thoroughly mixed 

 with the contents of the retort, which should first be cooled below 

 100° C. A 100 cubic centimeter sample of the dehydrated tar is 

 then submitted to the regular distillation test as above described 



USE OF THE DISTILLATION TEST. 



The distillation test is made upon tars and tar products but seldom 

 upon other materials unless the presence of tar is suspected, or where 

 a determination of water is required. In making the water deter- 

 mination on viscous or semisolid bituminous materials, it is usually 

 advisable to render the samples fluid by the addition of kerosene or 

 benzol before attempting the distillation. 



