Improvement of Vacuum Distillation BOLESLAW LUDWIK DUNICZ, University, L w ~ w Poland ,
0
BTAIXIXG substances of perfect purity is of the greatest importance in both chemical and physical investigations, When fractionating devices based on the Anschiitz-Thiele apparatus are used for vacuum distillation, the purity of the fractions received is doubtful, because of the necessity of greasing the stopcock through which the distillate passes. Using other devices without this fault, distillation cannot be controlled without interrupting the process, which is inconvenient. This difficulty may be easily avoided by using the fractionating contrivance shown in Figure 1.
FIGURE 3. CONNECTION TUBESWITH GROUND JOINT (3.
P.
Groove Greased part of joint
inner parts of connection tubes with ground joints should also be provided with grooves (Figure 3), as leaking !of grease out of the joint is always undesirable. RECEIVED September 3, 1938.
Direct Titration of Sulfate Erythrosin as Internal Indicator WALTER V. BURG, University of Toledo, Toledo, Ohio
D
URING recent years several suggestions concerning the
use of adsorption indicators for the volumetric determination of sulfate have been advanced. Wellings (6) reported that, in the presence of magnesium or manganous ions, fluorescein can be used as an internal indicator for the direct titration of sulfate with barium hydroxide. His results indicate an average relative error of somewhat less than 0.5 per cent. However, according to Iyer (2), the end point of this titration is not very sharp. Moreover, nitrate ions were found to interfere with the operation of the indicator, a fact that is the more serious since a removal of these ions would render the determination very complicated. Essentially different from Wellings’ method is the one suggested by Roy ( 5 ) ,who mentioned the possibility of using fluorescein as an external indicator for the indirect titration of sulfate with lead nitrate and potassium sulfate. Though, to the author’s knowledge, no data concerning a practical application of this method have been presented, it appears certain that such a determination would be rather timeconsuming. In 1936 Ricci (4)published a study of the direct titration of sulfate with lead nitrate in the presence of eosin as internal indicator, reporting an average relative error of 0.33 per cent in 65 analyses of sodium sulfate solutions. In a discussion of the effect of variations he stated that if the final volume of solution is much above 30 ml. it is difficult to detect the endpoint change, and pointed out that efforts to sharpen the end point by the addition of alcohol did not meet with success. According to Ricci only small percentages of this diluent can be tolerated, while the presence of more alcohol delays the end point so much that the titration becomes impossible.
FIGURE 1. FRACTIONATIKG DEVICE I,. Hole to let in air 8. To vacuum pump
‘ E
FIGURE 2. STOPCOCK G. Groove P. Greased,part of stopoook E. Sealed side of shell
A stopcock is fitted to this contrivance, the simplest form of which is shown in Figure 2. The plug of the stopcock has a groove, and its exterior is sealed a t one side. The plug is greased only in the upper (broader) part of the groove, and the groove prevents dispersion of grease to its narrower part, which in the device described is greased by the distillate. The manipulation of this device (Figure 1) is simple: The three-way stopcock, S, is so arranged that while the distillate is being collected it is evacuated with pump only through tubes 22,but during exchange of the receiving flask i t is evacuated through connections X. The hole, T , of stopcock H i s diagonal, for after exchange of the receiving flask it is possible, by suitably adjusting this stopcock and stopcock 8, to remove air from the new receiver without disturbing the distillation.
I
Erythrosin as Indicator
It was during
st study of the properties of erythrosin (tetraiodofluorescein) that the very low solubility and characteristic violet-red color of its lead salt suggested to the author the possibility of using i t as an internal indicator for the direct titration of sulfate with lead nitrate. However, the conditions under which this indicator works best are very different from those recommended for the eosin method. Preliminary experiments revealed that in the titration of sulfate with lead nitrate the replacement of eosin b y erythrosin
The stopcock may also be applied t o other apparatus, t o avoid contamination usually caused by greasing whole plugsi n stopcocks which join tubes filled with mercury, etc. The 28
