this invention consists of two elongate containers concentrically mounted one within the other and sealably joined at their bases by valve means to form two chambers , an inner chamber and an outer annular chamber whose volumes have a discrete proportional relationship one to the other . storage means are connected below valve means to receive proportional fractions of input liquid volumes from one chamber . referring first to top view of fig1 and side view of fig3 cover 3 is in open position exposing funnel like urine inlet 5 of outer chamber 7 . urine stream 25 is shown pouring into outer chamber 7 . cover 3 is attached to tube 4 the lower end of which is tapered and fits sealably in the tapered seat of valve body 24 so that tube 4 rotates between two functional valve positions as cover is rotated 180 degrees between open and closed positions . in the open position depicted in fig1 , 5 , liquid level 22 inside tube 4 will be equal to liquid level 21 in surrounding chamber 7 , because they communicate through hole 8 in valve body 24 and hole 19 in base of tube 4 . fluid communication is indicated by dotted line . the apparatus is so constructed that at every liquid level , cross sectional area 1 inside tube 4 is a constant fraction of cross sectional area 2 inside outer chamber 7 . the result is that the volume of liquid contained within tube 4 is a constant fraction of the total liquid introduced . when cover 3 is rotated to the closed position of top view fig2 and side view fig4 tube 4 is rotated through 180 degrees and the liquid trapped within tube 4 runs down through hole 19 and hole 12 which are now aligned to form first outlet means connecting tube 4 to storage container 16 . hole 23 vents the tube . the aliquot of liquid drains through this first outlet means ( dotted line ) into storage container 16 , which is generally large enough to contain all the aliquots normally expected in the collection period . preservative is also stored in container 16 which fastens to molded valve body 24 by fastening means such as screw thread 17 . groove 20 in tapered base of tube 4 now connects hole 8 and hole 13 to form second outlet means connecting outer chamber 7 to waste , allowing the remainder of the specimen ( dotted line ) to drain out tube 14 to waste . tube 14 is fastened to base of chamber 7 by fastening means 15 . in another embodiment , not shown , tube 14 may enter a temporary waste chamber to hold residue for later emptying . projection 26 of valve body 24 engages hole in base of chamber 7 preventing chamber 7 from rotating relative to valve body . valve body 24 is molded of a resilient lubricous material such as polyolefin . it snaps into base 11 of chamber 7 by inserting taper 9 . slot 10 causes valve body to lock and seal in place . distension 18 at terminus of tube 4 causes taper to pull tightly and lock in place . in operation , each voided specimen is treated alike . the cover is swung open so that the urine inlet is exposed . patient voids in the opening . after voiding , user holds the device vertically over the toilet and closes the cover . this maneuver drains the aliquot through first outlet means into storage and the residue through second outlet means to waste . at the same time , the storage container is closed . detents may indicate open and closed positions . in hospital an attendant may perform these duties after collection in another container . the result for a 1 / 20 aliquot collector might be : 1 ml . of preservative instead of 20 ml . ; 0 . 9 liter container in the refrigerator instead of a 10 liter container ; no larger volume graduates of urine to handle in the laboratory ; less embarassment to the outpatient at work ; and greater probability of a correct sample for analysis . in many cases the entire aliquot will be extracted for analysis so that no urine volume measurements would be required in the laboratory , and the result would simply be multiplied by twenty to yield total excretion . inasmuch as the present invention is subject to many variations , modifications and changes in detail , it is intended that all matter described above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense .