ANALYTICAL CHEMISTRY
620
melting-point apparatus, on which is placed :I square aluminum block with insert holes of various sizes and a thermometer. Borosilicate glass tubes fit snugly into the holes; coarse sinteredglass plates are sealed into the male ends of the joints. Such joints are commonly used in column chromatography. The heator for this sublimator is manufactured by H. 0. Post. 6822 60th 1to:ul. r\laspeth, S . 1‘. PROCEDURE
The most essential part of this fraction cuttor consisted of a piece of 3-mm. glass rod, A , 30 mm. in length. h e end of this rod \vas thickened to 4 mm. and ground int,o a piece of constricted i-mni. glass tubing a t point H . The other end of the rod JVRP also thickened to 4 mm. and suspended a t point C by two indentations of the 7-mm. t’ube just below point C. Rod .4 should have 2 to 3 mm. clearance a t point R when the system is under vacuum. The 7-mm. tube was sealed int,o a T 24/40 male 24/40 female joint a t point D. The joint and connected to a rontrolled by means of :t two-way
At the stmt of a sublimation t,he aluininum I)lo(ali is fir brought up to the desired temperature by means of a tran former (Variac). The tube containing t’he cmde suhlini:md t,hen evacuated through the sintered-glass plate in the m:tlr joint and inserted into the hot aluminum block. The length of the tube is so adjusted that the, sintered-g area. The first, fraction of subhmate imm ing just outside the heating hloclc. After sublimation has ceased at the initial tempernture. the preswre is released and the malt, joint is replaced by a clean one of the snme type for the nest frartion. The sintered-glass plate preventq pure suhlim:tte from falling back during this operation.
ronnectetl t o the t \v The position and size of the glass rod :incl 1)oints of cwnstruction :it H and c‘ are not ciritical. To c u t :I fraction, a small amount of air or nitrogen \viis l)leil iiito thc system a t stopcock F. The air pushed the sm:tll glass rod tightly agninst the ground-glass surface a t B and thus sealed off ttic still. S o c1i:inge in the pressure in the still \vas noted for :tt least 2 niinutes. .Uter the receiver was changed, stopcock E \v:w c~loscd.stopcock I.’ turned to evacuate the receiver, and stopc.ork E ngain turned into thr system w h m t h e glass y o t i .$ n.:ts
Whcn fractionating materials at vei’y low pr(wur(’s. it ni:i>. I)[, advisable to use a joint without the sintciwl-gl:tss plate. I n such cases the sublimntor may be operated iil :I Iioi~izontnlposition, thus preventing sublimate from falling buc~lc. I n the apparatus described amounts of :I feiv milligi,:tms U I I t,o 1 gram of ma.teiia1 I I I I V C l ) ~ , nfr:iction:rtc~tlnithout difficulty.
“Outrigger” Flask for Color Accentuation. 1log:~crI
