GO 



BULLETIN 940, U. S. DEPARTMENT OF AGRICULTURE. 



(c) Shield. — An asbestos shield of the form and approximate dimensions shown in 

 figure 33 shall be used to protect the retort from air currents and to prevent radiation. 

 This may be covered 'with galvanized iron, as such an arrangement is more convenient 

 and more permanent. 



(d) Receivers. — Erlenmeyer flasks of 50 to 100 c. c. capacity are the most convenient 

 form. 



(e) Thermometer. — The thermometer shall conform to the following requirements. 

 The thermometer shall be made of thermometric glass of a quality equivalent to 



suitable grades of Jena or Corning make. It shall be thoroughly annealed. It shall 

 be filled above the mercury with inert gas which will not act chemically on or contami- 

 nate the mercury. The pressure of the gas shall be sufficient to prevent separation of 



-Thermometer 



Shield 



Retort- 



Condenser 





Fig. 34. — Assembled apparatus for distillation test. 



the mercury column at all temperatures of the scale. There shall be a reservoir above 

 the final graduation large enough so that the pressure will not become excessive at the 

 highest temperature. The thermometer shall be finished at the top with a small glass 

 ring or button suitable for attaching a tag. Each thermometer shall have for identi- 

 fication the maker's name, a serial number, and the letters "A. S. T. M. distillation.'' 

 The thermometer shall be graduated from 0° to 400° C. at intervals of 1° C. Every 

 fifth graduation shall be longer than the intermediate ones, and every tenth gradua- 

 tion beginning at zero shall be numbered. The graduation marks and numbers shall 

 be clear-cut and distinct. 



The thermometer shall conform to the following dimensions: 



Mm. 



Total length, maximum 385 



Diameter of stem (permissible variation, 0.5 mm. ) 7 



Diameter of bulb, minimum (shall not exceed diameter of stem) 5 



Length of bulb (permissible variation, 2.5 mm.) 12. 5 



Distance, 0° to bottom of bulb < permissible variation, 5 mm.) 30 



Distance, to 400° (permissible variation, 10 mm.) 295 



