Sample tubes, cleaning filling

An absorbance measurement of a sample is obtained as follows. Rinse a clean cuvette or the indexed sample test tube with distilled water and then with several milliliters of sample solution. Half fill the cuvette or the test tube with sample solution, and make certain that the solution is free of bubbles and that the exterior surface of the cuvette or the test tube is wiped clean with a tissue. Then insert the cuvette or the test tube carefully into the sample holder, and close the door. Read the absorbance of that solution directly from the meter. Then remove the cuvette or the test tube from the sample holder, and rinse the cuvette or the test tube with distilled water so that it is ready to receive the next sample. Repeat the above procedure until all absorbance readings at a given wavelength have been obtained. 

The fat is heated to 80 °C in a water bath and a sample tube is fitted for each measuring temperature. The tubes are filled to a height of at least 3 cm and should be clean and dry on the outside. 

Extraction of sediment samples. Prior to extraction, sediment samples were freeze-dried and homogenized. Approximately 10 g of dried sediment were placed in a preextracted thimble, and a small piece of silanized glass wool was placed in the thimble on top of the sample to prevent sediment parts from leaving the thimble. The thimble was placed in a Soxhlet setup and extract for 16 h (overnight) with 200 ml hexane/acetone (3/1 v/v). The extracts were concentrated in the rotation evaporator until approximately 5 ml (/ = 0.05 bar T = 40°C) of extract remained. If the extraet still contained solid particles, the extract was filtered with diatomaceous earth or sodium sulfate. The extract was transferred to a diatomaceous earth- or sodium sulfate-filled funnel and flushed with 10 ml hexane. The eluted extract was evaporated again in the rotary evaporator until approximately 5 ml of extract remained. The extract was transferred to a cleaned glass tube and concentrated until near dryness. The dried extract was finally redissolved in 3 ml hexane. 

Procedure Free the metal from any adhering oil or other impurities by shaving a thin layer. Fill a clean, dry, 1" x 6" Pyrex test tube, about % full with the clean sample and plunge the lower part of the tube in an oil bath at 105°. When the temp of molten sodium... 

Place 100 mg of the substance on a small watch glass, microscope slide, or a piece of clean, dry, glazed paper. Crush the crystals to fine powder with a spatula. Collect the powder with a spatula in the form of a mound and press the open end of the capillary tube into it. Scratch lightly the capillary tube by means of the flat end of a file and tap it on the table in order to force the sample to the bottom. Repeat until the capillary tube has been filled to a height of about 2 mm then proceed to determine the melting point in accordance with directions given on pages 47-48. 

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