32 BULLETIN 314, TJ. S. DEPARTMENT OF AGRICULTURE. 



Public Roads and Rural Engineering indicate that the difficulty may 

 be overcome by placing a small piece of platinum gauze over the 

 sample and about midway of the crucible. The gauze should be so 

 cut or bent as to touch the sides of the crucible at all points, and is of 

 course weighed in place in the crucible before and after ignition. 



USE OF DETERMINATION FOE FIXED CARBON. 



This determination is made on all bituminous products with the 

 exception of tars, upon which reliable results can not be obtained, 

 owing to the error introduced by the presence of considerable quan- 

 tities of free carbon. 



DETERMINATION OF PARAFFIN SCALE. 



EQUIPMENT. 



1 one-half pint iron retort. (Fig. 16.) 



1 piece iron tubing, 30 inches long. 



2 100 cubic centimeter Erlenmeyer flasks. 



1 500 cubic centimeter (16 oz.) flask, with side neck for filtering under pressure. 



1 freezing apparatus. (Fig. 17.) 



1 6-inch test tube, f-inch diameter. 



1 analytical balance, capacity 100 grams, sensitive to 0.1 milligram. 



1 rough balance, capacity 1 kilogram, sensitive to 0.1 gram. 



1 wash bottle. 



1 pint tin cup, seamless. 



1 vacuum pump and connections. 



1 glass crystallizing dish, 50 millimeters in diameter; 



1 steam bath. 



1 desiccator with calcium chloride. 



1 4-inch steel spatula. 



1 Bunsen burner with rubber tubing. 



2 iron stands with retort clamp, and 1 ring. 



Fifty grams of the material under examination should be weighed 

 into the tared iron retort and distilled as rapidly as possible to dry 

 coke. The distillation should be complete in not over 25 minutes. 

 The distillate is caught in a 100-cubic centimeter Erlenmeyer flask, 

 the weight of which has been previously ascertained. During the 

 early stages of distillation a cold, damp towel wrapped around the 

 stem of the retort will serve to condense the distillate. After high 

 temperatures have been reached, this towel may be removed. When 

 the distillation is completed the distillate is allowed to cool to room 

 temperature and is then weighed in the flask. This weight minus 

 that of the flask gives the weight of the total distillate. 



The apparatus for freezing out and separating the paraffin scale is 

 shown in figure 17. It consists of a bell jar a about 16 centimeters 

 high and 14 centimeters in diameter, surrounded by a felt or cotton 



