SAMPLING AND TESTING HIGHWAY MATERIALS. 61 



The accuracy of the thermometer when delivered to the purchaser shall he such 

 that when tested at full immersion the maximum error shall not exceed the following: 



From 0° to 200° C 0. 5° C. 



From 200° to 300° C 1. 0° C. 



From 300° to 375° C 1. 5° C. 



The sensitiveness of the thermometer shall be such that when cooled to a tempera- 

 ture of 74° €. below the boiling point of water at the barometric pressure at the time 

 of test and plunged into free flow of steam the meniscus shall pass the point 10° C. 

 below the boiling point of water in not more than six seconds. 



(2) The retort shall be supported on a tripod or rings over two sheets of 20-mesh 

 gauze, 6 inches square, as shown in figure 34. It shall be connected to the condenser 

 tube by a tight cork joint. The thermometer shall be inserted through a cork in the 

 tubulature with the bottom of the bulb one-half inch from the surface of the oil in the 

 retort. 



The exact location of the thermometer bulb shall be determined by placing a vertical 

 rule graduated in divisions not exceeding one-sixteenth inch back of the retort when 

 the latter is in position for the test, and sighting the level of the liquid and the point 

 for the bottom of the thermometer bulb. The distance from the bulb of the ther- 

 mometer to the outlet end of the condenser tube shall be not more than 24 nor less 

 than 20 inches. The burner should be protected from drafts by a suitable shield or 

 chimney (see fig. 34). 



(3) Exactly 100 grams of oil shall be weighed into the retort, the apparatus assem- 

 bled, and heat applied. The distillation shall be conducted at the rate of at least one 

 drop and not more than two drops per second, and the distillate collected in weighed 

 receivers. The condenser tube shall be warmed whenever necessary to prevent 

 accumulation of solid distillates. Fractions shall be collected at the following points: 

 210°. 235°, 270°, 315°, and 355° C. The receivers shall be changed as the mercury 

 passes the dividing temperature for each fraction. When the temperature reaches 

 355°, the flame shall be removed from the retort, and any oil which has condensed in 

 the offtake shall be drained in the 355° fraction. 



The residue shall remain in the retort with the cork and the thermometer in position 

 until no vapors are visible; it shall then be weighed. If the residue is to be further 

 tested it shall then be poured directly into the brass collar used in the float test or into 

 a tin box and covered and allowed to cool to air temperature. If the residue becomes 

 so cool that it can not be poured readily from the retort, it shall be reheated by holding 

 the bulb of the retort in hot water or steam, and not by the application of flame. 



For weighing the receivers and fractions, a balance accurate to at least 0.05 grams 

 shall be used. 



During the progress of the distillation the thermometer shall remain in its original 

 position. No correction shall be made for the emergent stem of the thermometer. 



When any measuraole amount of water is present in the distillate it shall be sepa- 

 rated as nearly as possible and reported separately, all results being calculated on a 

 basis of dry oil. When more than 2 per cent of water is present, water-free oil shall 

 be obtained by separately distilling a larger quantity of oil, returning to the oil any 

 oil carried over with the water, and using dried oil for the final distillation. 



