A Rapid Sorting Device for Microfossils
GORDON YOUNGER CRAIG, J. Hogg · Micropaleontology · 1962
A rapid means of picking and separating species of microfossils by a suction apparatus is described. A rapid sorting device for microfossils G. Y. CRAIG AND J. HOGG Department of Geology University of Edinburgh Scotland This note describes a rapid means of picking and separating different species of microfossils by suction. Almost all methods of picking and classifying microfossils depend on the use of a moistened camel hair brush or a waxed needle. Variations are to be found in the type of classifying tray used, such as the German Ausleseschalen or the circular type described by McGugan (1957) in MICROPALEONTOLOGY. The writers are aware that simple suction tubes have been used from time to time and have devised a picking apparatus consisting of a suction tube leading to a revolving chambered tray where different species can be directly sorted. They believe that the chief advantage of this apparatus lies in its great speed, particularly when a large number of forms have to be separated. In essence the apparatus (text-fig. 1) consists of a heavy metal base on which is mounted a revolving tray, sandwiched between two fixed plates. A tube inserted in a hole in the lowest plate leads to the source of suction. The revolving tray is provided with small holes equally spaced along the periphery and floored with a fine wire screen. When one of these holes lies directly above the point of suction the vacuum extends through the sieve and the overlying flexible tube to the picking head and the desired fossil is sucked into the chosen compartment. Specimens can be sorted into the different compartments by rotating the tray to the appropriate number engraved beside each chamber. The details of the apparatus are shown in text-fig. 2. The picking head (1) is a stainless steel tube with an obliquely cut aperture. The bore diameters found most useful were 20, 30 and 40 thousandths of an inch. The tubes are held in polythene tubing with an internal diameter of 60 thousandths of an inch and about 15 inches long. The polythene is heated and drawn out to provide a tight grip for the smaller needles. The needle can be manipulated as it is, or held in a cork. The other end of the polythene tube fits firmly into a brass collar (2) on the upper plate (3). The upper plate is 1/10 of an inch thick, 3.5 inches in diameter, has a central rod (4), 1 inch long and 0.5 of an inch in diameter, which acts as the axial rod for the revolving tray and fits into a half-moon hole (5) in the basal column where it is secured by a screw (6). A small spring-loaded ball (7), engaging depressions (8) on the underlying tray, centers each hole in the line of suction. The revolving tray (9) is constructed of two brass plates (the upper 3/20 of an inch, the lower 1/10 of an inch thick and both 4 inches in diameter) identically bored along the periphery with 18 holes 1/5 of an inch in diameter, along the same circumference as the holes in the overlying steel plate. The holes in the upper brass plate are fully countersunk, to facilitate examination of the picked fossils. A 200-mesh wire screen (10) is inserted between the brass plates, and the three units are soldered together. This compound tray rotates on the rod projecting from the upper steel plate. The lower steel plate (11), 1/10 of an inch thick and 3.5 inches in diameter, is soldered to the base. A countersunk hole (12) is drilled directly below the hole in the upper steel plate. A nozzle (13) is inserted and soldered in the base of the hole in the lower steel plate and a suction tube attached. The base is turned from cast iron, the column being bored out and fitted with a half round rod (5) to receive the axial rod (4), which is clamped in position by a screw (6). A rubber pad is attached to the base to prevent sliding. In operation, the sample is thinly spread on a scanning tray and an appropriate needle size selected (it is better to work with a needle that is too large than one that is too small). The vacuum from a small electric vacuum pump (a water vacuum pump is not adequate) is adjusted so that only that fossil in direct contact with the needle-head is sucked up. Even the most delicate foraminifera such as Hantkenina or Nodosaria do not appear to suffer damage from the journey through the tube to the sieve-bottomed tray. The precaution was taken, however, of decreasing the air velocity at the sieve by increasing the diameter of the suction system at that point. The sample can either be picked over for a particular fossil or for different groups up to a total micropaleontology, vol. 8, no. 1, pp. 107-108, january, 1962 107 This content downloaded from 40.77.167.71 on Sun, 20 Nov 2016 05:16:33 UTC All use subject to http://about.jstor.org/terms