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. 
1M 
/ 
X 
i 
ul.6t 
S 
/ 
i 
3 
4 
■■/ L 
e 
^ 
=~^ 
1.57 
Fig. 14.— Effect of using air during the 
distillation of tar upon the index of 
refraction of the fractions of coal-tar 
creosote. 
COMPARISON OF COMMERCIAL CREOSOTES WITH 
LABORATORY CREOSOTES. 
Coal-tar creosote from tar dis- 
tilled without air. 
Coal-tar creosote from the same 
tar distilled with air under 7 
inches of water pressure. 
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 (5 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 
