1.4 BULLETIN" 607, U. S. DEPARTMENT OF AGRICULTURE. 



servative. Two series of tests were made with the temperature and 

 pressure of the preservative constant and the time of treatment 

 varied to obtain the same absorption with the mixture as was obtained 

 with the creosote unmixed with tar. Another series of tests was run, 

 in which the pressure of the preservative was varied but the tempera- 

 ture and the time of treatment kept constant, and a comparison made 

 of the pressures required to obtain the same absorption with various 

 tar mixtures as was obtained with creosote unmixed with tar. A 

 further series of tests was made in which the time of treatment, 

 pressure of the preservative, and absorption were constant, but the 

 temperature was varied. For comparison a test was made of the 

 absorptions and penetrations obtained using the same time of treat- 

 ment, temperature, and pressure of preservative for both the creosote 

 unmixed with tar and for the tar mixtures. 



The system of matching the penetrance specimens used in the 

 experiments described on pages 4 to 20 was the same as that described 

 on page 2, except that in one test four specimens were used and in 

 other tests three specimens were used instead of two, as in the 

 previous experiments. All of the blocks used in the impregnation 

 tests were cut from the same stick and are, therefore, considered 

 matched with each other. 



PENETRANCE TESTS WITH COAL-TAR CREOSOTE NO. 6 AND BY-PRODUCT COKE-OVEN 



TAR NO. 4. 



Time of treatment, temperature of preservative, and pressure con- 

 stant. — (Table 15 and fig. 7.) 



The first series of tests was made to study the relative absorptions 

 and penetrations obtained with the creosote unmixed with tar; with 

 mixtures of 80 per cent creosote and 20 per cent tar; and with 66 § 

 per cent creosote and 33 J per cent tar. The pressure, the time of 

 treatment, and the temperature of the preservative were the same 

 for every preservative. These tests were made for comparison with 

 those on the same mixtures where the pressure, time, etc., were 

 varied. Details of the treatment are given in Table 15. 



The average absorption and the average longitudinal penetration 

 obtained with the 80 per cent creosote and 20 per cent tar mixture 

 were each about 73 per cent of that obtained with the creosote. In 

 the case of the 66§ per cent creosote and 33 J per cent tar mixture 

 the absorption was about 66 per cent and the average longitudinal 

 penetration about 69 per cent of that secured with creosote. 



