SOLUTIONS OF SALTS IN ETHYL ALCOHOL AND WATER. 81 



pure alcohol. They were similar in shape to those employed in earlier 

 work, but were nearly twice as large, having a volume capacity 

 somewhat over 20 c.c., and the capillary was of 0.5 mm. bore. By 

 using one of these as a tare against the other, effects caused by 

 changes in atmospheric conditions were avoided. It may be said here 

 also that in all weighings the load was weighed on each end of the 

 balance beam, and that the final weight represented the mean value of 

 the two. For all other specific-gravity determinations smaller pyc- 

 nometers with capacities of about 10 c.c., were employed, and were 

 weighed directly, as in the previous case, on each end of the beam. 



Corrections were always applied to the apparent weights of the con- 

 tents of the pycnometers in order to reduce them to the vacuum 

 standard. For this purpose a record was kept of the height of the 

 barometer and the temperature of the balance-room at the time of 

 weighing. The buoyancy correction was afterwards determined by 

 means of table 22, page 37 of Circular No. 19 of the Bureau of Standards. 

 The capacities of the pycnometers were found in the usual manner, 

 with the addition of the corrections just mentioned, at 15, 25, and 

 35 C. Moreover, the pycnometers were reset and reweighed twice at 

 each temperature, in order to be sure that the capacities were correct. 



MIXED SOLVENTS. 



The mixed solvents were made up in percentages by weight of alcohol 

 and water. These percentages were found from the density tables on 

 pages 6 and 7 of Circular No. 19 of the Bureau of Standards. The 

 making of the mixtures of alcohol and water on a weight basis was by a 

 volume method, according to the following formula : 



md'(p-x) 



xd 



=y 



m being the number of cubic centimeters of alcohol of density d'; p, 

 the absolute percentage of alcohol ; x, the desired percentage of alcohol 

 to be obtained; d, the density of the water used; y, the number of 

 cubic centimeters of water of density d to give the required percentage 

 of alcohol. The formula in practice was simplified by taking 100 c.c. 

 of the alcohol and calculating a table, using several temperatures as 

 ordinarily met with in the laboratory (each degree from 20 to 25). 

 The above formula is derived in the following manner: 

 Let k = the absolute weight of the alcohol taken; then k = md'p', 

 where p' is the fraction of alcohol in the absolute alcohol taken. 



k 

 "- (100 x) = weight of water to be added to make x per cent alcohol; 



JO 



whence 



-(100-rr) = md'(l -p' 



