CHAPTER II. DETERMINING CERTAIN CONDITIONS FOR THE TESTS. 



EFFECT OF AIR ON TARS DURING DISTILLATION. 



As already mentioned, it is usually considered good practice in this 

 country to blow air through the tar during distillation. This offers 

 an opportunity for chemical reaction which might have a consider- 

 able effect on the physical and chemical properties of the creosote. 

 It was therefore essential, before work on authentic material was 

 undertaken, that the effect of blowing air through the tar should be 

 known. A tar was distilled without the use of air and also with the 

 use of air under two pressures chosen at random. The pressure of air 

 was kept constant by suitable valves and 

 was recorded in inches of water. A creo- 

 sote thus prepared was carefully analyzed, 

 the values of the index of refraction of 

 the fractions being taken as a guide for 

 changes in chemical and physical proper- 

 ties. Figure 14 shows graphically the 

 change produced in the index of refraction 

 when the same tar was distilled without 

 the use of air, with air under a pressure of 

 7 inches of water, and with the air under 

 a pressure of 14 inches of water. It will 

 be shown later that an increase in index of 

 refraction is accompanied by an increase 

 in specific gravity and a decrease in sul- 

 phonation residue. 



MS 





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Fig. 14. — Effect of using air during the 

 distillation of tar upon tlie index of 

 refraction of the fractions of coal-tar 

 creosote. 



COMPARISON OF COMMERCIAL CREOSOTES WITH 

 LABORATORY CREOSOTES. 



1. Coal-tar creosote from tar dis- 



tilled without air. 



2. Coal-tar creosote from the same 

 tar distilled with air under 7 

 inches of water pressure. 



3. Coal-tar creosote from the same 

 tar using air under 14 inches 

 of water pressure. 



Another point of still greater impor- 

 tance in this investigation was the deter- 

 mination of the differences, if there were 

 any, which existed between creosotes pro- 

 duced from small samples v5 to 10 gallons) of tar in the laboratory 

 and those obtained from the same tar under commercial conditions. 

 Through the courtesy of the Barrett Manufacturing Co., of New York, 

 and the United Gas Improvement Co., of Philadelphia, samples of 

 tar were taken from their stills just before distillation and after 

 thorough mixing. Samples of the creosote were then collected as it 

 came from the still throughout the entire distillation. These samples 

 were used as standard commercial creosotes with which the laboratory 

 creosotes prepared from the same tar were compared. 



The effect of blowing air through the tar being known, it was 

 simply a matter of experiment to ascertain an air pressure that would 



35 . 



