1430
ANALYTICAL CHEMISTRY
rffluent is led ta the tubes-iii the one case t'he solution flow down a glass pendulum (Figure 5); in the other it, drops from a pointed glass rod (Figure 6 ) . The distribution assembly shown in Figure 5 employs the pendulum-type distributor, D , described by Boggs et a2. with modifications to make the tubes less fragile and to make the operation more dependable. The use of the removable insert, E , from which a portion of the lip has been removed provides a relatively large half-circle of glass to catch the pendulum. It is virtually impossible, therefore, for the pendulum to fail to deliver the effluent into the tubes. The insert. tubes are conPtricted a t the level of the t,est t,ube rim, as shown in Figure 5 , before a section of the t,op is cut out, with a glass cutting saw. The purpose of this const,riction or groove is to prevent loss of solution from the test tube. As the pendulum nears the point of disengagement from the top of t,he insert, the solution f l o w down the outside of the insert and, without the constriction, some irould flow o v ~ the r lip of the test tube and he lost. The details of the construction of the distribution assembly are apparent in Figure 5 . The effluent from the chromatograph column, A , flows into cup B. The twoway stopcock diverts the flow either through the eluate bypass, C, into a large receiver or down to the pendulum SUPpended from a glass eyelet on the end of the delivery tube, D. The height of the pendulum is adjusted so that, as the tubes and inserts move past, it remains engaged by the one insert until on release it will hang well over the opening of the next insert. Repeated observations have shonm that there never is loss of liquid during this passage from one receiver to the next. The ot,her distribution assembly, shou-n in detail in Figure 6 and included in the apparatus in Figure 2, is a modification in which the effluent drips from B rod directly into the receiver. This arrangement waE found to be advaritngeous for use with the carbon rolumii! operated with applied pressure, from which the flow of solution was rapid (as much as 4 liters of water or aqueous ethanol in 8 hours) and the amount of a romponent large (up to about 15 grams of D-glucose, for example).
which the solution dripped down close to all the lips. Measurements made on the apparatus in Figures 2 and 6 showed that with care in construction the volume of the fractions could be held to a variation of not over about 2%. For most of the studies for which these fraction collectors have been used, variations of 10% in the volume of fractions did not interfere.
A Modified Nesbitt Absorption Bottle. Carlos F. Ellis, Bureau of Mines, Rifle, Colo., and Harry G. Durham, Julius Hyniati and Co., Rocky Mountain iirsenal, Denver, Colo.
YESBITTbottle is conimonly used in analytical absorption
24 -trains t o remove carbon dioxide for quantitative measure-
ment and it is convenient t o use t,he same charge of reagents for several analyses. The pressure drop around the Kesbitt bottle can increase after several determinations because of caking of the -4scarite reagent; a.nd, in cases where the absorption train is operated under positive pressure, leaks in the system could develop. llemoval of the accumulated caked material from the spent absorption bottle is troublesome and time-consuming. To avoid these difficulties, t8hebottle was modified m shown i i i Figure 1. The gas stream enters the bottle a t the top, and most of the carbon dioxide reacts with the reagent held in the basket of glass tubing. The basket can easily be replaced between determinations; it was made t o fit the walls of the modified bottle rather closely and furt,her assurance of tightness was obtained by means of a seal of a thin narroLv ring of hardened Duco cement on the t,op outer circumference of the basket. As the stopcocks of all Xesbitt bottles ai'e probably not the same size, the diameter of the bottle opening should be measured in order to obtain the correct dimensions for the baeket. The basket repts
Figure 6. Distribution Assembly Used with 32-Inch Turntable ( W C O CEMENT ON
To prevent loss of solution between tubes, a lip is sealed onto the insert tube and made sufficiently long (about 16 mm. in this case) that the edge Tyould extend beyond the nearer edge of the iievt tube. These lips were made conveniently by first cutting a. piece of tubing 14 mm. in diameter in half lengthwise, then making diagonal cuts to obtain the sections t o be sealed onto the inserts as s h o w in Figure 6. The resulting beveled tip and curved shape were very effective in overcoming splashing and loss of droplets which had been experienced with other designs tried. For delivery of the effluent smoothly in small drops a 1)iece of glass rod 2 mm. in diameter was drawn to a point and held on the outlet (8-mm. diameter) of the column with a rubber band permitting adjustment of the height of the tip. The end of the outlet of the column was cut a t an angle to lead the effluent t o the rod. With both distribution assemblies the uniformity of volume collected depends on the duplication of size and position of the inserts as well as on the constancy of rate of flow of the solution from the Chromatographic column. For maximum reproducibility of volume the holes for the test tubes should be evenly spaced. The height of the inserts for the design shown in Figure 5 should be uniform when they are in position in the test tubes. For the type shown in Figure 6 , the distance the lip extends from the insert is the critical factor, although the total height of the insert was held fairly constant in order to bring the tip from
PERFORATED DISK
Figure 1
on a column of Ascarite t o ensure complete absorption of carbon dioxide. This column of Ascarite will last for a considerable time, and the amount of caking will be negligible. By operating with a new basket for each determination, the same pressure drop around the bottle can be expected for all the analyses. It is conceivable that a ground-glass connection between the upper outer circumferenre of the basket and the walls of the modified bottle would be a useful improvement.
